Recover is cheaper right up to the moment the assembly is wet.
Low-slope commercial and industrial roofs · existing buildings
A recover buys a new membrane. It does not buy a new roof, and it does not buy back the information you gave up by leaving the old one in place.
Should we recover this roof or tear it off?
Recover installs a new roof over the old one. It costs less, moves faster and disturbs tenants less — and it is the wrong answer whenever the existing assembly holds moisture, the deck is compromised, or a second covering is already up there. A moisture survey verified by core cuts decides it. Without that survey, you are spending capital on a guess.
The short versionSection link
The code text quoted on this page is model text — language the International Code Council publishes and a state or local government may adopt, amend, delay, or decline. It is not the law at your address. Ohio, to take one real example, incorporates Chapter 15 of the 2021 International Building Code by reference, effective 1 March 2024 — an edition older than the newest the ICC has published. Confirm the adopted code, its edition, its amendments and its effective date with your authority having jurisdiction before treating anything here as a requirement.
- What recover is
- A new covering installed over the existing one, without removing itDistinct from a roof replacement, which the model code requires to include the removal of all existing layers of roof covering down to the roof deck — 2018 IBC §1511.3, as quoted by the City of Philadelphia.
- The three model-code hard stops
- Water soaked · slate, clay, cement or asbestos-cement tile · two or more existing applications2021 IEBC §705.2.1.1. Where any one applies, recover is not permitted — and no budget, schedule, or manufacturer approval changes that.
- What decides the moisture question
- A survey whose anomalies are verified by core cuts, not the survey aloneInfrared, nuclear and impedance instruments all produce relative readings. Professional Roofing puts it plainly: infrared imagers do not see moisture, they see temperature differences.
- Where the model code stops defining
- It does not define “water soaked”The provision quoted here does not define the term, and forensic engineers writing in the Journal of the NAFE record that the 2018 IBC and previous editions did not either. Your design professional and your AHJ fill that gap with evidence.
- Structural trigger
- A design gravity-load increase of more than 5 percent2021 IEBC §1103.1 sets that threshold for additions; the alteration provisions carry a parallel one. Five percent of what is a question for a structural engineer with this building's drawings, not for a table.
- Warranty consequence
- Recover terms come with their own caps and conditionsOne manufacturer's published recover guide-spec caps the warranty at up to 15 or 20 years over its own aged membrane and up to 10 or 15 years over another maker's, the longer terms conditioned on a field assessment. Product-specific, and 2013 — this page has not established what any other manufacturer offers today, so get the current document.
- Energy-code consequence
- A tear-off can trigger an insulation upgrade. A recover generally does not.2018 IECC §C503.3.1, as quoted by the City of Philadelphia, applies to roof replacements where the assembly is part of the thermal envelope and the insulation is entirely above the deck. Whether it bites, and how, is an AHJ reading. That cuts both ways: recover avoids the cost and forgoes the upgrade.
- What recover permanently costs you
- The next tear-off is now a two-layer tear-offAnd a leak below a recover has two membranes and an unreadable interstitial layer between the entry point and the stain.
Where recover is genuinely the right call, and where this page's own advice failsSection link
The position here is that a recover is a legitimate, sometimes excellent capital decision on a dry roof over a sound deck, and an expensive mistake on any other roof. There are real cases where that framing is too simple.
Best when
- The moisture survey came back clean, the verifying cores agree with it, and the cores are documented with photographs and gravimetric results.
- There is exactly one existing covering, confirmed by cores in every roof section rather than by the previous contractor's recollection.
- The deck is sound, and a fastener pull-out test in the worst area still meets the new system's required withdrawal resistance.
- The building has to keep operating — a data centre, a cold store, a hospital wing, a tenant with open stock under the deck — and the shortest possible period of exposed deck is worth real money.
- The existing assembly already carries enough insulation that the energy-code upgrade a tear-off would trigger has little left to give.
- The roof is a candidate for genuine service-life extension rather than deferral, and the assessment says so in writing.
- The building is pre-1990 and the existing felts, mastics or flashing cements may contain asbestos, so a tear-off becomes a regulated abatement project before it becomes a roofing project.
Think twice if
- The moisture survey is elevated in isolated areas only. Cutting out and replacing those areas and recovering the rest is legitimate — but it is a different scope, priced differently, and it needs the wet areas mapped before bid, not discovered during it.
- You are being sold a coating or a restoration as though it were a recover. Restoration over a wet assembly has the same defect and a shorter horizon.
- The drawings for the building cannot be found. The 5 percent load threshold is meaningless without a design gravity load to take 5 percent of, and reconstructing one is engineering work with a fee attached.
- The roof drains badly today. Adding thickness over a roof that already ponds moves the drain sumps further from the surface and can make the drainage worse, not better.
- The existing membrane is a type the new system's manufacturer will not adhere to. One published recover guide-spec excludes PVC as an existing substrate outright and requires like-over-like colour to avoid condensation and heat-ageing problems.
- You are recovering to defer a capital request rather than to extend a service life. That is a financing decision wearing a roofing decision's clothes, and it should be argued on its own terms.
- The building is going to be sold or the tenant is leaving inside the recover's warranty term. A shorter warranty on a buried problem is a disclosure item, and it will be found in diligence.
What changes the answer
- How many coverings are actually up there — which cores answer and memory does not.
- How much of the assembly is wet, and whether it is contiguous or scattered. Contiguous saturation and scattered saturation lead to different scopes.
- Deck type and condition. Steel, concrete, gypsum, cementitious wood fibre and lightweight insulating concrete all fail differently and hold fasteners differently.
- Which code edition your jurisdiction has adopted, and what it amended. Some jurisdictions permit a third layer with a licensed engineer's verification of the framing; the model text prohibits it outright.
- Whether the roof carries mechanical equipment, screen walls, solar, or a future solar plan — all of which change both the load question and the sequencing question.
- Whether the building is occupied during the work, and what is directly under the deck.
- What the manufacturer will actually warrant, in writing, on this substrate, at this attachment, in this wind zone.
- Your ownership horizon. A twelve-year hold and a forty-year hold do not buy the same roof.
Recover does not remove a problem. It removes your access to it.Section link
A recover is not a lighter version of a tear-off. It is a different transaction: you buy a new watertight surface and you keep everything underneath, including whatever put the last roof out of service.
A low-slope commercial roof is a stack, not a surface. Deck, vapour control where the climate calls for it, insulation, a cover board, and a membrane, all fastened or adhered to each other and ultimately to the structure. A recover adds a new stack on top of the old one. A tear-off removes the old stack down to the deck and builds a new one.
The model code draws that line sharply. Philadelphia’s Department of Licenses and Inspections, explaining its own interpretation to its own staff, quotes the provision directly: “Roof replacement shall include the removal of all existing layers of roof coverings down to the roof deck.” Its bulletin then states the distinction in one sentence: “Changing the roof covering of an existing roof assembly which involves the removal of existing roof coverings is considered a roof replacement. Alternatively, installing a new roof covering above an existing roof membrane is a roof recover.”
1 · Water gets in at a detail, not across a field
Membranes rarely fail everywhere at once. A lap opens, a termination lets go, a pipe support wears through, a curb flashing splits. Water enters at that point and then travels laterally inside the insulation, which is why the wet area on a survey is almost never centred on the hole that made it.
2 · The insulation holds the water, and keeps holding it
Board insulation between a membrane above and a deck below has almost nowhere to dry to. The forensic engineers Chad T. Williams and Drew Jamison, writing in the Journal of the National Academy of Forensic Engineers, set out why that matters on four separate fronts: water degrades the assembly materials, it can affect the underlying structure, “entrapped water can increase the weight of the roof assembly,” and it creates conditions for bacterial or fungal growth that can reach the air inside the building. They add that all of these “can have a cascading effect over the life of the system.”
3 · The deck under the wet area is the part nobody sees
A steel deck under saturated insulation corrodes from the top down. A cementitious wood-fibre or gypsum deck softens. Either way, the property that matters for a reroof is not appearance but fastener withdrawal resistance — whether the deck will still hold the screws that hold the new roof on in a wind event. That is a tested value, not a judgement call, and the test happens through a hole.
4 · A recover is fastened to the same deck
This is the point most often missed in the sales conversation. The new assembly does not float. Whether it is mechanically fastened or adhered, its wind resistance ultimately depends on the attachment of everything below it. One manufacturer’s published recover guide-spec states the caution outright: “Ensure adequate attachment of the existing roofing system (membrane and insulation) in order to not jeopardize the wind uplift performance of the newly installed membrane.” A new membrane over a poorly attached old one is a new membrane with an old wind problem.
5 · The wet zone is now unreachable and unreadable
After the recover, the saturated block is between two membranes. Infrared can no longer see it, because the new insulation above it is doing exactly the job insulation does — flattening the surface temperature differences the survey depends on. Impedance and nuclear instruments are reading through more assembly than they were calibrated against. And a leak that appears three years later has to be traced through two membranes and an interstitial layer nobody has a record of.
That is the sentence worth remembering about this decision. A recover over a wet roof does not just build on a bad substrate. It destroys the evidence that would have told you it was bad.
6 · A tear-off is the only option that shows you the deck
This is the tear-off’s real advantage and its real risk in the same breath: it converts unknowns into line items, and it does so after the contract is signed. Deck repair discovered under a tear-off is a change order. Deck repair not discovered under a recover is a liability with no line number.
7 · A tear-off can trigger an insulation upgrade
Where the roof is part of the building thermal envelope and the insulation sits entirely above the deck, the commercial energy code applies its new-construction insulation requirements to a roof replacement. Philadelphia’s bulletin quotes the provision and then interprets it narrowly for its own jurisdiction — the requirement bites where the existing above-deck insulation is removed or damaged and must be replaced, and the department will accept certain physical constraints, such as parapet heights and equipment curbs, as making a thicker assembly technically infeasible. That is one authority’s published reading, not a national rule, and it is exactly the kind of thing to ask your own AHJ before you price either option.
The conditions under which recover is simply not availableSection link
Most recover-or-tear-off conversations start with budget. They should start here, because these are the conditions no budget changes. The first table is the adopted code. The second is everything the code cannot decide for you.
| Disqualifying condition | What the model text actually says | What settles it on a real roof | Who decides |
|---|---|---|---|
| The existing roof or covering is water soaked | Recover is not permitted “where the existing roof or roof covering is water soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.” | A moisture survey whose anomalies are opened and confirmed by cores, with gravimetric results. The provision does not define “water soaked”, so the evidence has to. | The authority having jurisdiction, on the design professional’s documented findings. |
| There are already two or more coverings | Recover is not permitted “where the existing roof has two or more applications of any type of roof covering.” | Core cuts in every roof section, plus permit records and prior warranty documents. Not the previous contractor’s recollection. | The AHJ — although some jurisdictions have amended this to permit a third layer where a professional engineer verifies the framing. |
| The covering is slate, clay, cement or asbestos-cement tile | Recover is not permitted “where the existing roof covering is slate, clay, cement or asbestos-cement tile.” | Visual identification confirmed by sample. On a pre-1990 building, asbestos-cement also puts the tear-off inside the federal Asbestos NESHAP inspection requirement. | The AHJ for the code question; a licensed asbestos inspector for the material question. |
Read this table one item at a time
The existing roof or covering is water soaked
- What the model text actually says
- Recover is not permitted “where the existing roof or roof covering is water soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.”
- What settles it on a real roof
- A moisture survey whose anomalies are opened and confirmed by cores, with gravimetric results. The provision does not define “water soaked”, so the evidence has to.
- Who decides
- The authority having jurisdiction, on the design professional’s documented findings.
There are already two or more coverings
- What the model text actually says
- Recover is not permitted “where the existing roof has two or more applications of any type of roof covering.”
- What settles it on a real roof
- Core cuts in every roof section, plus permit records and prior warranty documents. Not the previous contractor’s recollection.
- Who decides
- The AHJ — although some jurisdictions have amended this to permit a third layer where a professional engineer verifies the framing.
The covering is slate, clay, cement or asbestos-cement tile
- What the model text actually says
- Recover is not permitted “where the existing roof covering is slate, clay, cement or asbestos-cement tile.”
- What settles it on a real roof
- Visual identification confirmed by sample. On a pre-1990 building, asbestos-cement also puts the tear-off inside the federal Asbestos NESHAP inspection requirement.
- Who decides
- The AHJ for the code question; a licensed asbestos inspector for the material question.
These are model provisions published by the International Code Council. They have no jurisdiction and no effective date of their own. Your adopted code may differ in wording, in numbering, and in substance — Ohio, for example, incorporates Chapter 15 of the 2021 IBC by reference with a rule effective 1 March 2024. Confirm with your AHJ before treating any line above as a requirement.
| Condition | Why it can disqualify a recover | What produces the answer | Who owns it |
|---|---|---|---|
| Added dead load exceeds what the frame carries | The model existing building code sets a 5 percent threshold on increases in design dead, live or snow load — snow drift included — above which an existing gravity load-carrying element must be replaced or altered. The section quoted on this page is the additions provision; NRCA and STRUCTURE both report a parallel threshold in the alteration provisions that govern a reroof. | A structural evaluation against the original drawings, or a field investigation that substitutes for them, plus an itemised weight take-off of the proposed recover. | A licensed structural engineer, confirmed with the AHJ. |
| The deck will not hold a fastener | The recover is fastened or adhered to a stack that ends at the same deck. Corroded steel and softened cementitious decks lose withdrawal resistance long before they look bad. | Fastener pull-out testing at mapped locations, compared against the design value the new system requires in field, perimeter and corner zones. | The design professional and the system manufacturer. |
| The existing system is inadequately attached | Wind uplift resistance is a property of the whole assembly. Loose laps, protruding fasteners and delaminated adhered areas underneath become the new roof’s weak point. | A physical inspection of the existing attachment and repair of every defect found — one manufacturer makes this an explicit precondition of its recover system. | The contractor, verified by the manufacturer’s field representative. |
| The roof does not drain | The model code's definition of positive roof drainage requires that loading deflections of the deck have been accounted for and that additional slope has been provided to drain the surface within 48 hours of precipitation. Adding thickness above a roof that ponds moves the field further from the drains and can make it worse. | A drainage assessment and, where a fix is needed, a tapered design — which is a different scope from either a recover or a straight tear-off. | A design professional. |
| The manufacturer will not warrant it | Substrate type, membrane compatibility, colour, attachment and the results of a field assessment are all warranty conditions. One published guide-spec excludes PVC as an existing substrate outright. | Written pre-approval from the manufacturer for this substrate, this attachment and this wind zone — obtained before the option is priced, not after. | The manufacturer, in writing. |
| The insulation is wet in places but not everywhere | This does not disqualify a recover, but it changes the scope: the wet areas have to be cut out and replaced first, and that is a quantity that has to be mapped before bid or it becomes a dispute during construction. | A moisture map stating elevated area as a percentage of each roof section, with a unit rate for wet-material removal in the proposal. | The assessing professional, priced by the contractor as a unit rate. |
Read this table one item at a time
Added dead load exceeds what the frame carries
- Why it can disqualify a recover
- The model existing building code sets a 5 percent threshold on increases in design dead, live or snow load — snow drift included — above which an existing gravity load-carrying element must be replaced or altered. The section quoted on this page is the additions provision; NRCA and STRUCTURE both report a parallel threshold in the alteration provisions that govern a reroof.
- What produces the answer
- A structural evaluation against the original drawings, or a field investigation that substitutes for them, plus an itemised weight take-off of the proposed recover.
- Who owns it
- A licensed structural engineer, confirmed with the AHJ.
The deck will not hold a fastener
- Why it can disqualify a recover
- The recover is fastened or adhered to a stack that ends at the same deck. Corroded steel and softened cementitious decks lose withdrawal resistance long before they look bad.
- What produces the answer
- Fastener pull-out testing at mapped locations, compared against the design value the new system requires in field, perimeter and corner zones.
- Who owns it
- The design professional and the system manufacturer.
The existing system is inadequately attached
- Why it can disqualify a recover
- Wind uplift resistance is a property of the whole assembly. Loose laps, protruding fasteners and delaminated adhered areas underneath become the new roof’s weak point.
- What produces the answer
- A physical inspection of the existing attachment and repair of every defect found — one manufacturer makes this an explicit precondition of its recover system.
- Who owns it
- The contractor, verified by the manufacturer’s field representative.
The roof does not drain
- Why it can disqualify a recover
- The model code's definition of positive roof drainage requires that loading deflections of the deck have been accounted for and that additional slope has been provided to drain the surface within 48 hours of precipitation. Adding thickness above a roof that ponds moves the field further from the drains and can make it worse.
- What produces the answer
- A drainage assessment and, where a fix is needed, a tapered design — which is a different scope from either a recover or a straight tear-off.
- Who owns it
- A design professional.
The manufacturer will not warrant it
- Why it can disqualify a recover
- Substrate type, membrane compatibility, colour, attachment and the results of a field assessment are all warranty conditions. One published guide-spec excludes PVC as an existing substrate outright.
- What produces the answer
- Written pre-approval from the manufacturer for this substrate, this attachment and this wind zone — obtained before the option is priced, not after.
- Who owns it
- The manufacturer, in writing.
The insulation is wet in places but not everywhere
- Why it can disqualify a recover
- This does not disqualify a recover, but it changes the scope: the wet areas have to be cut out and replaced first, and that is a quantity that has to be mapped before bid or it becomes a dispute during construction.
- What produces the answer
- A moisture map stating elevated area as a percentage of each roof section, with a unit rate for wet-material removal in the proposal.
- Who owns it
- The assessing professional, priced by the contractor as a unit rate.
Every row above is a place where a page can tell you what question to ask and cannot tell you the answer. If a proposal answers any of them with a reassurance rather than a document, that is the finding.
The moisture survey is not part of the decision. It comes before it.Section link
Every instrument used to find water in a roof produces a relative reading. Each of the governing practices says so, and each requires the reading to be confirmed by opening the roof. A survey that stopped before that step has not produced a finding.
The method detail — how infrared, nuclear, impedance and core cuts each work, what conditions each requires, and how each fails — belongs to the roof condition assessment page. What matters here is the logic that connects a survey to this decision, and it is short.
Writing in Professional Roofing, the NRCA’s magazine, moisture-survey practitioner Michael T. Williams sets out the chain. “Infrared imagers do not see moisture; they see temperature differences.” Under ASTM C1153, the practice governing infrared roof surveys, “verification of infrared data must be carried out by one of the following invasive test methods: cores (cutting out small sections of the roof) or a combination of cores and moisture meter probes.” Under ANSI/SPRI/IIBEC NT-1, the nuclear field readings are only relative and are to be quantified by gravimetric analysis of cores. Under ASTM D7954, the impedance practice, “cores taken shall be retained for gravimetric analysis for the verification stage.”
Three different instruments, three different governing documents, one common requirement: open the roof and weigh what comes out. A core cut is what turns an anomaly into a fact.
The errors run in both directions
The expensive failure is not only the missed wet area. Williams is equally direct about the other one: false positives and inaccurate readings lead to “unnecessarily removing roofing materials, a costly mistake for building owners, roofing contractors and insurance companies.” An unverified survey can sell you a tear-off you did not need just as easily as it can sell you a recover you should not have.
That symmetry is why the verification step is worth paying for. It is the cheapest line item in this entire decision and it is the one that determines every other line item.
How much wet is too much?
There is no code answer, and the honest position is that there is no general answer either. The model code’s test is qualitative: is the existing roof adequate as a base for additional roofing? A widely repeated industry rule of thumb, published in trade press in 2013 and attributed there to a named roofing contractor, puts the line at roughly 30 to 40 percent of the roof area wet. That is one practitioner’s working heuristic, not a standard and not a requirement, and it is reproduced here so you recognise it when someone quotes it at you as though it were either.
The number that actually governs is the one on your roof plan, stated per roof section, with cores behind it. Scattered saturation in three isolated places on an otherwise dry roof is a selective-replacement scope. Contiguous saturation across a quarter of a section is usually a tear-off of that section. The decision is made per section, which is why the survey has to be reported that way.
What a recover actually weighs, and what the water already up there weighsSection link
Added dead load is the point at which this stops being a roofing decision and becomes an engineering one. The arithmetic below is deliberately simple, and every input is a published number you can check.
The model existing building code sets a numeric trigger for this. Section [BS]1103.1 of the 2021 IEBC — the additions provision — requires that any existing gravity load-carrying structural element for which an addition and its related alterations cause an increase in design dead, live or snow load, including snow drift effects, of more than 5 percent be replaced or altered as needed to carry the loads required for new structures. A reroof is an alteration rather than an addition, and both NRCA and STRUCTURE magazine report that the alteration provisions of the same code carry the same 5 percent threshold under a different section number. STRUCTURE, summarising the 2018 edition for structural engineers, reports that the alterations section carries an additional exception for roofing, allowing a second layer of roof covering weighing 3 pounds per square foot or less over an existing roof.
Be careful what that number is. It is reported here rather than quoted from primary code text, so it has to be checked against your adopted code before it is used at all. And on the reported reading it is an exemption threshold, not a weight limit: a lighter second layer escapes the evaluation requirement, while a heavier one simply means the structural evaluation is owed. Exceeding it does not make a recover unlawful and staying under it does not make a recover safe. It is useful here only as a yardstick — a figure small enough that a routine modern recover reaches it quickly, which is the point of the table below.
| Component | Published weight | Source of the number | Running total |
|---|---|---|---|
| 1/2 in. glass-mat gypsum cover board | 2.00 lb/ft² | Georgia-Pacific DensDeck Prime submittal sheet, nominal weight | 2.00 lb/ft² |
| 60-mil TPO membrane | 0.31 lb/ft² | Duro-Last Duro-TECH TPO 60-mil product data sheet, October 2024 | 2.31 lb/ft² |
| Adhesive, fasteners, plates, edge metal | Not published as an area weight | Varies by attachment pattern and wind zone; obtain from the specified system | More than 2.31 lb/ft² |
| New polyiso insulation, any thickness | Not published on the data sheets read for this page | Obtain the manufacturer’s figure for the specified board and thickness | More again |
Read this table one item at a time
1/2 in. glass-mat gypsum cover board
- Published weight
- 2.00 lb/ft²
- Source of the number
- Georgia-Pacific DensDeck Prime submittal sheet, nominal weight
- Running total
- 2.00 lb/ft²
60-mil TPO membrane
- Published weight
- 0.31 lb/ft²
- Source of the number
- Duro-Last Duro-TECH TPO 60-mil product data sheet, October 2024
- Running total
- 2.31 lb/ft²
Adhesive, fasteners, plates, edge metal
- Published weight
- Not published as an area weight
- Source of the number
- Varies by attachment pattern and wind zone; obtain from the specified system
- Running total
- More than 2.31 lb/ft²
New polyiso insulation, any thickness
- Published weight
- Not published on the data sheets read for this page
- Source of the number
- Obtain the manufacturer’s figure for the specified board and thickness
- Running total
- More again
Two components — a cover board and a membrane, before a single inch of insulation, a drop of adhesive or a fastener — already reach about 77 percent of the reported 3 lb/ft² figure above. Substituting a 1/4 in. board at 1.2 lb/ft² brings the same pair to 1.51 lb/ft². That substitution is a design decision with hail, foot-traffic and fire-listing consequences, which is exactly why it belongs to a design professional rather than to a value-engineering conversation — and neither number tells you whether this frame carries this assembly.
Now weigh the water you were going to bury
Water weighs 62.424 pounds per cubic foot. That is the only input the next table needs, and the U.S. Geological Survey publishes it. The left column is not the moisture content of the insulation — it is the depth of free water that the same amount of water would occupy if you poured it out flat, which is the easiest way to make an abstract percentage into a load.
| Water in the assembly, as an equivalent free depth | Added dead load | For comparison |
|---|---|---|
| 1/8 inch | 0.65 lb/ft² | About twice the weight of the entire new 60-mil membrane |
| 1/4 inch | 1.30 lb/ft² | About four times the new membrane, and more than half the new cover board and membrane together |
| 1/2 inch | 2.60 lb/ft² | More than the new cover board and membrane put together |
| 1 inch | 5.20 lb/ft² | More than twice the whole recover, and it is already on the structure |
Read this table one item at a time
1/8 inch
- Added dead load
- 0.65 lb/ft²
- For comparison
- About twice the weight of the entire new 60-mil membrane
1/4 inch
- Added dead load
- 1.30 lb/ft²
- For comparison
- About four times the new membrane, and more than half the new cover board and membrane together
1/2 inch
- Added dead load
- 2.60 lb/ft²
- For comparison
- More than the new cover board and membrane put together
1 inch
- Added dead load
- 5.20 lb/ft²
- For comparison
- More than twice the whole recover, and it is already on the structure
The load in this table is not added by the recover — it is there now. What a recover does is guarantee it stays, remove the drying path, and put a second assembly on top of it. That is why the forensic-engineering literature lists increased assembly weight among the reasons entrapped moisture is a repairability limitation, alongside material degradation, effects on the underlying structure, and biological growth.
Five percent of what?
This is where the arithmetic stops and the engineering starts. The threshold is 5 percent of the design gravity load on the element in question — a number that lives in the structural drawings for the building, and that has to be reconstructed by investigation where the drawings are gone. Snow load, snow drift against a parapet or a taller adjacent structure, mechanical units, and any water that does not drain all sit in the same calculation, and they interact.
No website can do this for a building, and this one does not try. A dead load determination is a licensed structural engineer’s work, confirmed with the authority having jurisdiction. What the table above is for is recognising, before you commission anything, that a recover is not obviously under the threshold and a wet roof is not obviously over it — and that both questions have to be asked.
The cost gap is real. It is also not where the risk is.Section link
This page publishes no dollar figures, because no defensible public dataset separates commercial recover pricing from replacement pricing by system, deck, market and building size. What it can do is name every line item that differs, so you can see whether a proposal has priced them.
A recover is cheaper for reasons that are structural to the scope rather than negotiable. It removes an entire demolition trade, an entire disposal stream, and the calendar risk of an open deck. Trade press puts the same point in a practitioner’s words — a design professional quoted in Building Design + Construction in 2013 said overlayment “can be the quickest, least expensive, and easiest solution because it eliminates tear-off costs and reduces replacement time.” That is one practitioner speaking rather than a published dataset, but the mechanism behind it is not controversial: the scope items below exist on one side of the comparison and not the other.
What a tear-off adds that a recover does not
- Removal labour and disposal. An old assembly is tonnage, and tipping fees are a local number. A gravel-surfaced built-up roof is a different disposal problem from a mechanically fastened single-ply.
- Asbestos survey, and possibly abatement. The federal Asbestos NESHAP requires a thorough inspection where a demolition or renovation operation will occur. On a pre-1990 building this is a scheduled, priced activity that precedes mobilisation.
- Deck repair discovered mid-project. Which is a feature, not a defect — it is the cost of learning something true. It belongs in the contract as a unit-rate allowance with a documentation requirement, not as a lump sum.
- Temporary protection and daily tie-ins. Open deck has to be made watertight every night, and the exposure scales with how much area a crew opens in a day.
- An energy-code insulation upgrade, potentially. Where the assembly is part of the thermal envelope and the insulation is entirely above the deck, the commercial energy code applies new-construction requirements to a roof replacement. Whether that bites, and how, is an AHJ question — Philadelphia’s department reads it as applying where the existing above-deck insulation is removed or damaged and must be replaced, and will accept parapet heights, equipment curbs, window sills and door thresholds as constraints that can make a thicker assembly technically infeasible.
What a recover adds later that a tear-off does not
- A shorter, more conditioned warranty. Documented above, product-specific, and worth pricing as a term difference rather than treating as a footnote.
- A closed door on the next cycle. The roof now has two coverings. Under the model provision quoted on this page, a future recover is off the table, so the next capital event is a two-layer tear-off with roughly twice the disposal.
- Diagnostic cost on every future leak. Two membranes, an unreadable interstitial layer, and surveys that no longer resolve what is underneath.
- The forgone energy upgrade. Whatever the tear-off’s insulation requirement would have cost, it would also have bought something on the operating side for the life of the roof.
Put those two lists next to each other and the shape of the honest comparison appears. It is not recover-versus-tear-off at today’s price. It is the total cost across the ownership horizon, including the option value you are spending. On a short hold with a dry roof, a recover frequently wins that comparison outright. On a long hold, or on any roof where the survey is ambiguous, it frequently does not.
Disruption is not a soft factor when the building is occupiedSection link
In practice, tenant impact settles more of these decisions than structural analysis does — and unlike most of this page, it is a subject on which this site has mechanisms to describe and no data to publish.
Everything below is a mechanism, stated so you can plan around it. None of it is a measured figure, and this site holds no dataset on noise levels, odour transport, or business interruption from either scope.
- Noise and vibration travel through a steel deck. Fastening is percussive and the deck is the ceiling of the space below. A recover fastens through more material, but a tear-off adds demolition on top of the fastening.
- Tear-off drops debris and dust through deck flutes, around penetrations, and through any opening the demolition creates. Whatever is under that bay needs covering or moving, and that is a tenant negotiation before it is a construction task.
- Adhesive and hot-work fumes find rooftop air intakes. Which units get shut down, when, and who signs off on restarting them belongs in the contract. On a hospital, a school, a laboratory or a food plant it belongs in the contract in writing and with names.
- Open deck is a weather exposure the tenant carries. The largest single disruption cost on a tear-off is usually a storm arriving on an open tie-in, and the risk allocation for that should be explicit rather than assumed.
- Roof access has to be controlled for the duration. Under OSHA’s general-industry rule an employer must protect employees from falls at 4 feet or more above a lower level, with specific duties for work on a low-slope roof keyed to distance from the edge. That obligation touches your own staff and your tenants’ staff as well as the contractor’s.
- Phasing changes the arithmetic. A recover can often be run in larger daily areas because there is no open deck at the end of the day. On a very large single-ply field, that difference is weeks.
None of this makes a recover right on a wet roof. It does mean that where the survey comes back clean and the structure checks out, the disruption argument is a legitimate reason to choose recover — and it should be argued explicitly, in the capital request, rather than smuggled in as “the cheaper option”.
What a defensible decision looks like, in sequenceSection link
Each step produces a document. If a step cannot produce one, that is the finding, and the next step does not start.
- Establish what is up there. Cores in every roof section, photographed against a scale, recording layer type, thickness, condition and the presence of moisture.
- Establish how wet it is. A survey run under its governing practice, with anomalies verified by cores and gravimetric analysis, reported as a percentage of each roof section on a drawing.
- Apply the code. Confirm the adopted code, edition, amendments and effective date with the AHJ, and test the roof against the disqualifying conditions. If any hard stop applies, the decision is made and the rest is scope.
- Establish what the structure carries. A licensed engineer, against drawings or a field investigation, with the itemised weight of the proposed assembly in front of them.
- Test the deck. Fastener pull-out at mapped locations against the design value the new system requires in field, perimeter and corner zones.
- Get the manufacturer’s written position. Term, exclusions, substrate acceptance and any required field assessment — before either option is priced.
- Then price both. With the same scope assumptions, the same allowances, the same tenant-impact provisions, and the same ownership horizon applied to each.
A proposal that arrives before step two is not a proposal. It is a quotation for a scope nobody has established yet, and the mid-project change orders are already written into it.
What changes this on a real buildingSection link
The axes below are the ones that actually move this decision on a real building. A page cannot resolve any of them for you; it can tell you which ones to put in front of a design professional.
- Code and jurisdiction
Reroofing rules live in the adopted building code and, for existing buildings, commonly in the adopted existing building code. Both exist, and which one governs depends on what your jurisdiction adopted and how it amended it. Section numbers move between editions and between the two codes.
Every code sentence on this page is model text. Ohio’s administrative rule incorporating Chapter 15 of the 2021 IBC is a worked example of the gap: a real adopting jurisdiction, a specific effective date, and an edition that is not the newest one published.
Jurisdiction, edition, amendments and effective date are recorded per claim in the source list below. None of it is a determination for your address. Only your authority having jurisdiction can make that.- Moisture and ventilation
Moisture is the precondition, not a consideration among others. The order of operations is survey, then verify, then decide — and a survey that has not been verified by cores has not finished. Method detail, false-positive modes, and what each instrument can and cannot resolve belong to the roof condition assessment page rather than this one.
Elevated readings are a repairability limitation whatever caused them. The model code's prohibition is about the condition of the substrate, not about who is to blame for it.- Structural weight
Added dead load is a structural question with a numeric threshold attached, and neither the number nor the answer can be produced without this building’s drawings and an engineer’s reading of them. Snow drift, mechanical units, a future solar array and any ponded water all sit in the same calculation.
This page publishes no structural-capacity determination and none can be made remotely. Load capacity, snow load and drift are answered by a licensed structural engineer for this building, and confirmed with the AHJ.- Wind
A recover inherits the attachment underneath it. Wind performance is site- and building-specific: basic wind speed, exposure, building height and geometry, pressure zone, enclosure classification, risk category, the attachment pattern, and the tested assembly all enter into it, and perimeter and corner zones are not the field.
A marketing wind rating is not a code determination. A recover assembly's uplift resistance is a property of the whole stack including the old layers, and it is established by design and by a tested assembly, not by the new membrane's data sheet.- Fire
Fire classification applies to a tested assembly — deck, insulation, cover board and covering together — never to a covering in isolation. A recover changes the assembly. One manufacturer’s recover guide-spec is explicit that the “existing code ratings (FM and UL) will remain the same as the existing roofing system” and directs the specifier to consult the local FM or UL representative.
Adding a new membrane over an old one does not upgrade a classification and can change it. The listing that governs is the one for the assembly as built, confirmed with the listing body and the AHJ.- Slope and drainage
The model code’s definition of positive roof drainage has a measurable at the end of it: consideration of the deck’s loading deflections, additional slope provided, and drainage of the roof surface within 48 hours of precipitation. Where that is not happening now, adding thickness above the existing surface rarely fixes it and can bury the drain sumps deeper. Drains, scuppers and edges are part of this scope, not a separate project.
Drainage design, tapered layout and sump detailing are design-professional work. This page does not publish a drainage determination.- Maintenance
Both options land you in a maintenance obligation, and warranty documents commonly make that obligation a condition of coverage. The difference is that after a recover the assembly is harder to diagnose, so the value of a documented inspection cadence and a leak log goes up, not down.
- Access and site conditions
Staging, hoisting, crane picks, laydown area, and the route debris takes off the roof are usually the physical constraints that make one option cheaper on a specific site — a tight urban block with no laydown makes a tear-off disproportionately expensive, and that is a legitimate input to the decision.
What a recover does to the warranty, and what a warranty is notSection link
Warranty terms are the clearest signal manufacturers send about which assemblies they trust. They are also contracts, and this page is not legal advice.
- Recover terms are usually shorter and more conditioned
One manufacturer’s published recover guide-spec sets out the pattern plainly. Recovering over that manufacturer’s own aged single-ply membrane, the warranty runs up to 15 years at one membrane thickness and up to 20 years at a greater thickness. Recovering over another manufacturer’s membrane, the same document caps the term at up to 10 and up to 15 years respectively — and notes that the longer terms require a field assessment by the manufacturer’s representative or a consultant.
That is product-specific data from a 2013 guide-spec, quoted here to show the shape of the tradeoff rather than to state anyone’s current terms. Get the current document for the actual product, in writing, before it is priced.
- The substrate is a warranty condition, not a preference
The same guide-spec excludes PVC as an acceptable existing membrane for that recover system, directs that recovering be like-material so the two membranes expand and contract at similar rates, and warns against covering a black membrane with a white one because the colder white surface increases wintertime condensation, and against covering a white membrane with a darker one because of accelerated heat ageing of the substrate. Each of those is a condition on the warranty as much as a technical recommendation.
- The load verification is assigned to you
That document states it directly: “It is the responsibility of the building owner or his/her designated representative to verify structural load limitation.” A manufacturer’s warranty on a membrane is not a manufacturer’s opinion that your structure carries the assembly.
- NDL is not the same as a material warranty
A no-dollar-limit warranty and a material-only warranty are different products with different exclusions, and neither is a workmanship warranty from the installer. What each covers, what voids it, whether it transfers on sale, and what a claim actually requires are questions for the documents in front of you — the warranty guide covers how to read one.
Repairability
A recovered roof is harder to repair well, for a mechanical reason: a leak has two membranes, two sets of laps, and an interstitial layer between the entry point and the stain. Tracing it usually means opening the new roof, which is a warranty event in itself.
And the recover permanently changes the next decision. The roof that had one covering now has two, which — under the model code quoted here — takes a future recover off the table entirely. The cheaper option today is the option that removes the cheaper option next time.
A warranty is a contract between a reader and whoever wrote it. What it covers, what voids it, whether it transfers, and how it is enforced are set by that document and by the law where the reader lives. Read the actual warranty for the product and the installer in front of you — not a summary of one, including this one.
Questions to ask before a recover is pricedSection link
These are aimed at a contractor, a consultant, or a design professional. A confident answer to every one of them is what a defensible recover recommendation looks like.
How many cores did you take, in which roof sections, and can I see photographs of each one against a scale?
Cores are how the layer count and the substrate condition stop being an assumption. One core on a 90,000 sq ft roof with four distinct sections is not a survey; it is a sample of one.
Which moisture survey method did you use, under which standard, and how did you verify the anomalies?
Each instrument has a governing practice and each of those practices requires invasive verification. An answer that names a method but not a verification step is describing half a survey.
What percentage of the roof area came back elevated, and is it contiguous or scattered?
It changes the scope from recover, to selective replacement plus recover, to full tear-off. It should be a mapped number on a drawing, not an adjective.
Which code edition is adopted here, and what does its reroofing section say about layers and about water-soaked substrates?
The answer should name the jurisdiction, the code, the edition and the effective date. If it names a model code without naming an adopting authority, the person answering has not checked.
What is the added dead load of your proposed recover, in pounds per square foot, itemised by component?
Every component has a published weight on a data sheet. A contractor who cannot itemise it cannot have compared it against a structural threshold.
Who is doing the structural evaluation, and what are they evaluating against?
The right answer names a licensed engineer and a document — the original structural drawings, or a field investigation that substitutes for them. “It will be fine, we do this all the time” is not an evaluation.
What fastener pull-out testing was done, where, and what values did you get?
Withdrawal resistance is what holds the roof on in a wind event and it is the property most degraded by a wet deck. It is measured, and the measurements have locations attached.
What warranty term and what exclusions will the manufacturer actually issue on this recover, on this substrate?
Ask for the manufacturer’s written pre-approval, not the contractor’s expectation of it. Terms over an existing roof are frequently shorter and frequently conditioned on a field assessment.
If we tear off instead, what triggers under the energy code, and what is that worth over the roof's life?
An insulation upgrade is a cost on the tear-off side and a benefit on the operating side. It belongs in the comparison in both places, with the AHJ’s reading of the requirement attached.
Was the building built before 1990, and has an asbestos inspection been done for the tear-off scope?
Old felts, mastics and flashing cements can contain asbestos. The federal Asbestos NESHAP requires a thorough inspection where a demolition or renovation operation will occur, and finding out after mobilisation is the expensive way.
Require these in writing
- A roof plan showing every core location, with the layer stack recorded at each one
- A moisture map with the elevated area stated as a percentage of each roof section
- The standard each survey method was run under, and the verification method used
- Itemised added dead load in pounds per square foot, with the data sheet cited for each component
- The named structural engineer, their scope, and what they are evaluating against
- Fastener pull-out test locations and results, with the required design value stated
- The manufacturer's written pre-approval of the recover, with the warranty term and exclusions
- A named allowance for deck repair, with a unit rate and a documentation requirement before it is drawn on
- Wet-material removal quantities as a unit-rate line, not a lump sum
- The jurisdiction, code, edition and effective date the design is being permitted under
- Tenant-impact provisions: work hours, noise windows, HVAC intake protection, hot-work procedure, and roof access control
- Daily tie-in and temporary watertightness requirements, and who carries the risk of an overnight storm
Misconceptions and failure modesSection link
Common misconceptions
Common belief
A recover is just a cheaper way to get the same roof.
What is actually true
It is a different product. The new membrane is new; everything under it is as old as it was yesterday, and its condition now governs the performance and the warranty of the thing above it. Two roofs at the same price per square foot are not comparable if one of them starts from a deck and the other starts from an unknown.
Common belief
The infrared scan was clean, so the roof is dry.
What is actually true
Infrared measures temperature, not water. Professional Roofing states it directly: “Infrared imagers do not see moisture; they see temperature differences.” A survey performed outside the meteorological conditions its governing practice requires, or one whose anomalies were never opened and confirmed, has produced a picture rather than a finding — and the same article warns that false positives and inaccurate readings lead to “unnecessarily removing roofing materials, a costly mistake for building owners, roofing contractors and insurance companies.” The error runs in both directions.
Common belief
There is only one layer up there — the last contractor said so.
What is actually true
Confirm it with cores in every roof section. Layer count is the single most consequential fact in this decision, because under the model code two or more existing applications remove recover as an option entirely, and it is also the fact most often carried forward from a conversation rather than a document.
Common belief
The code lets you have two layers, so a second one is always fine.
What is actually true
The model provision quoted here says recover is not permitted where the existing roof already has two or more applications. It does not say a second layer is automatically permitted — the water-soaked test, the material test, the structural provisions, and any local amendment all apply as well. And amendments run in both directions: forensic engineers note that some jurisdictions have adopted local amendments permitting a third layer where a professional engineer verifies that the framing can carry it.
Common belief
A recover is lighter than a tear-off, so load is not an issue.
What is actually true
A recover only adds load. A tear-off removes an old assembly and adds a new one, and can end up close to net neutral. The arithmetic below shows how much a routine recover weighs before the insulation is even counted — and how much more a saturated area is already contributing that nobody put on a submittal.
Common belief
Wet insulation is a thermal problem we can live with.
What is actually true
It is a structural, biological and durability problem before it is a thermal one, and it is a code problem before any of those. A water-soaked substrate is one of the three model-code conditions that disqualifies a recover outright.
Common belief
The manufacturer's warranty means the assembly is approved.
What is actually true
A material or system warranty covers what its own document says it covers. One published recover guide-spec assigns verification of structural load limitation to the building owner and states that existing FM and UL code ratings remain those of the existing roofing system. The warranty is not a structural opinion and not a listing.
How it actually fails
- Recover over undetected saturation
- The wet area continues to degrade the insulation and corrode the deck under two membranes, with no drying path and no way to survey it. Fastener withdrawal resistance falls quietly until a wind event finds it.What you can see: Usually nothing, for years — which is the problem. Then leaks that cannot be traced, fasteners backing out and telegraphing through the new membrane, and deck deflection visible from inside.
- Wind uplift failure of a new membrane over an under-attached old one
- The recover’s resistance depends on the whole stack. Loose laps, protruding fasteners, and delaminated adhered areas in the existing membrane are load paths that were never repaired.What you can see: Billowing or fluttering of the new membrane in wind, seams lifting at perimeter and corner zones, edge metal working loose.
- Drainage made worse by added thickness
- New insulation raises the field but the drain bowl and the scupper openings stay where they are, so water has further to fall and less slope to get there. Ponding that used to dry now does not.What you can see: Standing water more than 48 hours after rain, dirt rings and vegetation at the low points, and deflection increasing where the water sits.
- Condensation inside a recovered assembly
- A recover can put a second, less permeable membrane above the old one and create a cavity between them with no vapour strategy and no drying direction. Membrane colour changes the surface temperature and therefore the dew-point behaviour, which is why one manufacturer warns against overlaying black with white.What you can see: Interior staining unrelated to rainfall, seasonal rather than event-driven, sometimes worst in the coldest weeks.
- Tear-off caught by weather
- Deck is exposed section by section and has to be made watertight every night. A storm arriving on an open tie-in puts water directly into the building, and the exposure is greatest on the largest, flattest roofs where a day’s work is a large area.What you can see: Interior damage during construction rather than after it; often the single largest disruption cost on a tear-off, and the reason phasing and tie-in details belong in the contract.
- Asbestos discovered after mobilisation
- Pre-1990 felts, mastics and flashing cements are disturbed by a tear-off. The federal Asbestos NESHAP requires a thorough inspection where a demolition or renovation operation will occur, and the inspection has to come first.What you can see: A stopped job, a re-scoped contract, and an abatement contractor on a schedule nobody planned for.
Sources and further readingSection link
Understanding Roofing / Published
Scope and limitations
- It cannot tell you whether your roof can be recovered.
- That is decided by cores and a moisture survey on that roof, by a structural evaluation of that building, by the code your jurisdiction has adopted, and by what the manufacturer will warrant.
- Four separate answers, none of them obtainable remotely.
- It cannot tell you what either option costs.
- There is no defensible public dataset that separates commercial low-slope recover pricing from replacement pricing by system, deck type, market and building size, so this page publishes cost drivers and no dollar figures at all.
- It cannot tell you what your adopted code requires.
- Every code sentence here is model text with no jurisdiction and no effective date of its own.
- Ohio's adoption is included as evidence that adopted editions trail the model, not as a requirement for anywhere — including elsewhere in Ohio.
- It has not verified the reported IEBC exception for a second layer of roof covering weighing 3 pounds per square foot or less in primary code text.
- That figure is reported by STRUCTURE magazine summarising the 2018 IEBC, and it is presented on this page as a reported threshold to check against your adopted code, not as a quotation from it.
- It cannot tell you your building's design gravity load, and therefore cannot apply the 5 percent threshold.
- That number comes from structural drawings or from an engineer's investigation.
- The disruption and tenant-impact section describes mechanisms, not measured data.
- This site holds no dataset on noise levels, odour transport into rooftop air intakes, or business interruption from either scope.
- The manufacturer data quoted here is product-specific and dated.
- The recover warranty terms come from one manufacturer's 2013 guide-spec and the component weights from three current data sheets; none of them describes any other product or any other manufacturer's current position.
- It cannot tell you whether your insurance or an existing warranty responds to any of this.
- Coverage, causation, exclusions and enforceability are set by the documents and by the law where the building is.
2021 International Existing Building Code, Sections [BS]705.2.1 Roof recover and [BS]705.2.1.1 Exceptions (MODEL code text, as published in ICC errata)
International Code Council, republished by the North Carolina Office of Administrative Hearings / 2021 edition; errata posted 22 January 2021 and 6 September 2022
The verbatim model text of the roof-recover provision and its exceptions: that a roof recover shall not be permitted where the existing roof or roof covering is water soaked or has deteriorated to the point that it is not adequate as a base for additional roofing; where the existing roof covering is slate, clay, cement or asbestos-cement tile; or where the existing roof has two or more applications of any type of roof covering. Also Section [BS]1103.1, which requires that any existing gravity load-carrying structural element for which an addition and its related alterations cause an increase in design dead, live or snow load, including snow drift effects, of more than 5 percent be replaced or altered as needed to carry the loads required for new structures.
MODEL code text published by the ICC. It has no jurisdiction and no effective date of its own; it becomes law only where a government adopts it, on that government's own effective date, and adoptions routinely amend it. This document is an errata sheet, so some sentences carry both struck and inserted wording — only the exceptions in 705.2.1.1 and the threshold in 1103.1 are quoted on this page, both of which read cleanly. Section 1103.1 sits in the additions chapter; the alteration provisions carry a parallel threshold under a different number. Confirm the adopted code, edition, amendments and effective date with your authority having jurisdiction.
Ohio Administrative Code Rule 4101:1-15-01 — Roof assemblies and rooftop structures
State of Ohio, Legislative Service Commission / Effective 1 March 2024
That a real adopting jurisdiction incorporates Chapter 15 of the International Building Code, 2021 edition, by reference with modifications, with a rule effective date of 1 March 2024 — evidence that the edition in force in a jurisdiction is not necessarily the newest model edition published.
One state's administrative rule. It incorporates the model chapter by reference rather than reprinting it, so it does not itself state the reroofing section text, and modifications are made elsewhere in the Ohio code. It establishes nothing for any other state, and local Ohio authorities administer it.
Policy Bulletin PB_004 — FAQ: roof covering replacement and the energy code (Rev. 11.2021)
City of Philadelphia, Department of Licenses and Inspections / Revised November 2021
The verbatim distinction between roof replacement and roof recover; the verbatim text of IBC Section 1511.3, that roof replacement shall include the removal of all existing layers of roof coverings down to the roof deck; the verbatim text of IECC Section C503.3.1, that roof replacements shall comply with the listed envelope sections where the existing roof assembly is part of the building thermal envelope and contains insulation entirely above the roof deck; and one authority having jurisdiction's own published interpretation, including the physical constraints it will accept as making a thicker assembly technically infeasible.
One city department's interpretation, written against the 2018 I-codes and expressly stated by the department to be guidance for its own staff that is subject to change without notice and may vary by project. It is not a requirement anywhere else, and Philadelphia's currently adopted editions should be confirmed with the department before relying on it there.
Factors to Consider in Developing Conceptual Scopes of Repair for Common Low-Slope Roofing Assemblies
Chad T. Williams, PE, DFE and Drew Jamison, Journal of the National Academy of Forensic Engineers / December 2023
That coring typically means drilling a two-inch cylindrical core to the deck or opening a rectangular section, and that composition, dimensions, condition and the presence of moisture should be documented; that the 2018 IBC and previous editions do not provide a specific definition of water soaked; that entrapped water degrades assembly materials, can affect the underlying structure, increases the weight of the roof assembly and creates conditions for bacterial or fungal growth, with a cascading effect over the life of the system; that the presence of moisture from any cause is a repairability limitation; that two or more coverings is a repairability limitation; that some jurisdictions have adopted local amendments permitting a third layer subject to a professional engineer verifying the framing; and the model code's definition of positive roof drainage as drainage of the roof surface within 48 hours of precipitation.
A peer-reviewed forensic engineering paper written for expert witnesses developing scopes of repair. Its code quotations are to the 2018 IBC and 2018 IEBC, and section numbers and wording move between editions. It is not adopted code anywhere, and it does not evaluate the economics of either option.
Surveying roof moisture
Michael T. Williams, Professional Roofing (National Roofing Contractors Association) / December/January 2025–26
That infrared imagers do not see moisture, they see temperature differences; that verification of infrared data must be carried out by cores, or a combination of cores and moisture meter probes; that under ANSI/SPRI/IIBEC NT-1 nuclear field readings are only relative and are to be quantified by gravimetric analysis of core samples; that ASTM D7954 requires cores taken to be retained for gravimetric analysis at the verification stage; that pin moisture meters have no roofing-specific standard and sample only a tiny area; and that false positives and inaccurate readings lead to unnecessarily removing roofing materials, a costly mistake for building owners, roofing contractors and insurance companies.
A trade-press technical article by a moisture-survey practitioner. It is not a standard, and the standards it describes should be read directly before a survey is specified. It does not address the recover decision itself.
Reroofing by the book
Mark S. Graham, Professional Roofing (National Roofing Contractors Association) / 1 February 2019
NRCA's own summary of the reroofing provisions: that recover is prohibited where the existing roof is water-soaked or deteriorated so that it is not adequate as a substrate, where the covering is slate, asbestos-cement, or concrete or clay tile, or where two or more layers are already present; that the existing building code requires evaluation of any gravity load-carrying element where an alteration increases dead, live or snow loads by more than 5 percent; and that the commercial energy code applies minimum insulation requirements to roof replacements where insulation is entirely above the deck.
Trade guidance written against the 2018 I-codes and directed at roofing professionals. It is not adopted code, and its section numbers are for that edition and that compliance path.
The Basics of the 5% Rule
Kirk Wagner, S.E., STRUCTURE magazine
The verbatim 2018 IEBC wording of the gravity-load provision, quoted by the article from Section 502.4 in the additions chapter, and the report that the alterations section — Section 503.3 — echoes the same threshold and includes an additional exception for roofing which allows a second layer of roof covering weighing 3 pounds per square foot or less to be applied over an existing roof.
A structural-engineering magazine article summarising the 2018 IEBC for practitioners. The 3-pounds-per-square-foot exception is reported here rather than quoted from primary code text, and it was not verified against an adopted code during the writing of this page. On the article's own account it is an exception to the evaluation requirement rather than a cap on how much weight may be added, so it is neither a permission nor a limit. Treat it as a threshold to check, not as a requirement.
GUIDE-SPEC: Retrofitting Aged Single-Ply with a FleeceBACK Adhered Roofing System
Carlisle SynTec (Carlisle Construction Materials) / May 2013
Product-specific recover requirements and consequences: that recover warranty terms run up to 15 or 20 years over that manufacturer's own aged membrane and up to 10 or 15 years over another manufacturer's, with the longer terms requiring a field assessment; that existing FM and UL code ratings remain the same as the existing roofing system; that it is the responsibility of the building owner or designated representative to verify structural load limitation; that a core cut may be taken to verify the composition of the existing system; that recovering should be like-material and that black membranes should not be overlaid with white because of condensation, nor white with darker because of accelerated heat ageing; that PVC is not an approved existing membrane for this system; that crushed or damaged insulation is to be cut out and replaced; and the caution to ensure adequate attachment of the existing system so as not to jeopardise the wind uplift performance of the newly installed membrane.
Manufacturer instructions for one product line, dated 2013, and read on a distributor-hosted copy rather than on the manufacturer's own site. It describes no other product and states no other manufacturer's position, and it may have been superseded. Obtain the current document from the manufacturer before relying on any term in it.
DensDeck Prime Roof Board submittal sheet
Georgia-Pacific Gypsum
The published nominal weight of one common gypsum cover board: 1.2 lb/ft² at 1/4 in. and 2.0 lb/ft² at 1/2 in., used in the added-dead-load worked example on this page.
Product-specific manufacturer data for one cover board. Other cover boards — high-density polyiso, cementitious, wood-fibre — weigh materially different amounts, and the document itself states that the information may change without notice.
Duro-TECH TPO 60-mil Membrane product data sheet
Duro-Last (Holcim Solutions and Products US) / Created 14 October 2024
The published weight of one 60-mil TPO membrane, 0.31 lb/ft², at a nominal total thickness of 60 mil, tested to ASTM D6878 — used in the added-dead-load worked example on this page.
Product-specific manufacturer data for one membrane. Other membranes and other thicknesses weigh different amounts, and adhesives, fasteners and plates are additional.
Water Density — Water Science School
U.S. Geological Survey
That water weighs 62.424 pounds per cubic foot at 39.2 °F, the constant behind the entrapped-water weight table on this page.
A physical constant. It says nothing about how much water any particular roof assembly holds, which is measured on that roof by gravimetric analysis of cores.
29 CFR 1910.28 — Duty to have fall protection and falling object protection
U.S. Occupational Safety and Health Administration
That in general industry an employer must protect employees on walking-working surfaces with an unprotected side or edge that is 4 feet or more above a lower level, and that work on a low-slope roof carries specific duties keyed to distance from the roof edge, including within 6 feet, between 6 and 15 feet, and 15 feet or more.
An occupational-safety standard directed at employers and their employees. It is a reason for an owner or facilities manager to send a properly equipped contractor rather than a procedure for anyone to follow personally, and construction work on a roof is governed by a separate set of standards.
Asbestos NESHAP
U.S. Environmental Protection Agency
That the Asbestos NESHAP at 40 CFR Part 61, Subpart M requires a thorough inspection where a demolition or renovation operation will occur, and requires notification of the appropriate delegated authority.
A federal regulation summarised on an EPA page. It does not identify which specific roofing products contain asbestos, and states and localities administer delegated programmes with their own additional requirements. Whether a particular tear-off triggers it is determined by the inspection, not by this page.
Roof renovation tips: making the choice between overlayment and tear-off
Building Design + Construction / 19 September 2013
Triangulation only: that a widely repeated industry rule of thumb holds that a tear-off is in order where more than 30 to 40 percent of the existing roof is wet — attributed in the article to a named roofing contractor — and a second named practitioner's statement that overlayment can be the quickest, least expensive and easiest solution because it eliminates tear-off costs and reduces replacement time.
Trade press from 2013 quoting individual practitioners. The 30-to-40-percent figure is one contractor's rule of thumb; it is not a code provision, a standard, or a published finding, and this page presents it as such. It is cited to show what the industry says, not to establish a threshold.