An overlay buys a cheaper roof by spending the only look at your deck.
Steep-slope · single-family and small multifamily
A roof-over leaves the existing covering in place and installs a new one on top of it. It is faster, it costs less, and on some roofs it is the right call. What it never does is show anyone the sheathing.
Can I just put a second layer of shingles on my roof?
Sometimes. Where the adopted code allows a second layer, the deck is sound, the existing shingles lie flat, and the manufacturer permits it, a roof-over is cheaper and faster. What you give up is the tear-off — the only moment anyone sees the sheathing, re-nails it, or lays ice barrier on the deck. Anything wrong up there stays hidden until the next tear-off.
The short versionSection link
Six facts that decide most roof-over conversations. The last two are the ones that arrive late.
- What it is called
- A roof recoverRoof-over, overlay, and second layer are the same thing. Adopted codes and the trades call it a recover, and that is the word to use at a permit counter.
- What it removes from the job
- The tear-offARMA, which speaks for the shingle manufacturers, puts it plainly: “The benefits of replacement include having the opportunity to inspect the roof deck, repair any damage, and improve deck attachment to the underlying structure.”
- The usual limit on layers
- Two coverings, in most placesARMA: “most do not allow more than two roof coverings on a building.” Whether that is the rule where your building stands is set by the edition your jurisdiction adopted and the amendments it made to it.
- The manufacturer question people skip
- Most laminated shingles are not an approved baseARMA: “most manufacturers do not recommend installing new shingles over existing laminated shingles.” NIST records laminated — architectural — products as having grown to over half the US shingle market, so this rules out a great many houses before code is even consulted.
- What it adds to the building
- About 280 lb per roofing squareNIST’s survey of ICC evaluation reports gives roughly 14 kg/m², or 280 lb per 100 sq ft, as the average for laminated asphalt shingles. It is a survey average across manufacturers, not a product figure, and published products sit on both sides of it — Owens Corning publishes 360 lb per square for one of its laminated shingles, while other published laminated products come in lighter. Use the weight on your own product’s data sheet, and whether your framing carries it is a question for a design professional, not for this page.
- What it does to the next job
- Two layers to remove instead of oneThe disposal quantity at the next replacement roughly doubles, and the deck inspection is deferred rather than cancelled.
This page says tear off. Here is when that advice is wrong.Section link
The position taken here is that the deck inspection is usually worth more than the saving. That is a judgement about odds, not a rule, and several of the conditions that overturn it come from the same sources this page relies on.
Best when
- There is exactly one existing covering, it lies flat, and the deck is in good condition. ARMA’s own conclusion in that case is that “replacement may not be necessary,” and it notes the existing layer then serves as a secondary backup roof under the new one.
- The permit office has confirmed that a recover is permitted at that address, under the edition actually adopted there, and has said what it wants to see.
- The shingle being installed is one whose printed instructions permit application over the existing covering — and the existing covering is not a laminated shingle, which most manufacturers do not approve as a base.
- The deck condition is known from evidence rather than assumed: a documented prior tear-off, a recent attic-side inspection by someone equipped to do it, or a contractor’s written report naming what was found and where.
- The roof is a garage, porch, or outbuilding where a concealed deck problem has a small consequence and the framing is simple and visible from below.
- The existing eave assembly already includes an adhered ice barrier. ARMA notes that removing a previously installed ice-dam protection membrane “may be challenging during a roof replacement” — a genuine argument on the recover side, and one nobody mentions.
Think twice if
- Nobody has established how many coverings are actually up there. Two is the common limit; the count is settled by permit records, a documented prior job, or a contractor lifting shingles at several points — not by looking at the roof edge from the driveway.
- The existing covering is an architectural or laminated shingle — the category NIST records as having grown from a minority of the US shingle market to over half of it. Most manufacturers do not approve it as a base for a new roof.
- You want an ice barrier at the eaves. NRCA is explicit that an ice-dam protection membrane “should be installed directly on a roof deck, which dictates the removal of an existing roof system.”
- You are paying for an impact rating. ARMA states that “impact resistance ratings for asphalt shingles may be affected when new shingles are installed over existing shingles.”
- The product you have been quoted forbids it. Owens Corning’s own installation guide states that the existing roof must be removed before installing its Duration STORM shingle, and says of another product that it may not be feasible to apply it over an existing shingle roof at all.
- The house predates 1990 and the existing covering, felts, or mastics may contain asbestos. That is a reason to plan the work properly, not a reason to bury it.
- The deck is board or plank sheathing. ARMA’s removal triggers include gaps greater than a quarter inch between deck boards, and you cannot see those without taking the covering off.
- The roof leaks now and nobody has found out why. An overlay on an undiagnosed leak buys a thicker roof with the same leak inside it.
What changes the answer
- The adopted code edition where the building stands, and the amendments that jurisdiction made to it. There is no national answer to this and no answer this page can give.
- Which shingle is actually going on, and what its printed instructions say about an existing covering as a base.
- Whether anyone has evidence about the deck, or only an opinion about it.
- The ownership horizon. A recover moves cost forward and defers a discovery; whoever owns the building at the next replacement pays for both.
- Why the roof is being redone. Appearance and end-of-service-life are different problems from active water entry.
- Whether the job is already opening the roof for something else — solar, a dormer, a skylight, new venting — in which case part of the tear-off is already being paid for.
The tear-off is the inspection. That is the whole trade.Section link
Everything else about a roof-over — the weight, the appearance, the flashings, the ratings — is a secondary argument. The primary one is that removing the covering is the only occasion on which anybody sees the surface the roof is nailed to.
- The deck. The sheathing that every fastener in the roof lands in, and the plane the covering is only a wearing surface over. DOE’s Building America Solution Center sets out the scope of a roof replacement on an existing house in three steps: “Remove all existing roofing (shingles and underlayment)”; “Replace any damaged wood sheathing”; and “Inspect the roof deck attachment fasteners and re-nail as required to meet current requirements for nail type, size, and spacing.” Steps two and three are only available while step one has just happened.
- Delaminated or punky sheathing. Plywood whose plies have separated, or oriented strand board that has been wet long enough to swell and lose strength. ARMA lists a deck inspection revealing “rotted or warped wood” among the conditions under which the existing shingles will likely need to come off. NRCA is blunter about why it matters: it does not recommend a recover over a damaged or deteriorated deck “because a degraded deck’s fastener holding and load capacities can be reduced significantly.” A roof is held on by what its nails are gripping.
- A gap between deck boards. On older houses the deck is planks rather than panels, and they shrink. ARMA names “large gaps (greater than ¼ inch) between the deck boards” as a removal trigger, and suggests going further: “for best roof performance, consider re-decking ‘board’ (wood plank) roof decks with a layer of code compliant sheathing before installing new shingles.” A fastener over a gap is a fastener in nothing.
- A deck fastener that missed the framing. The nail in the drawing is driven through the deck in the middle of a bay; its point comes out into air rather than into a rafter. Deck attachment is invisible from above under any covering and unreliable to judge from below. Deck re-nailing is one of the few genuinely high-value upgrades that exists only during a tear-off, which is exactly why BASC lists it as a step of the replacement rather than an option.
- The ice-barrier zone. A self-adhered ice barrier sticks to the deck. NRCA states the consequence directly: an ice-dam protection membrane “should be installed directly on a roof deck, which dictates the removal of an existing roof system.” In panel B that surface is occupied by the old covering, so the barrier has nowhere to go. If your roof has a history of edge leakage in winter, this single line usually settles the decision. See ice dams.
- The old covering, now a substrate. In a recover the existing shingles stop being a covering and become the surface the new roof is laid on and fastened through. That is a different job for a material that was never made for it, and it is why manufacturer instructions have a separate, shorter paragraph about it.
- The fastener that has to get further. Every nail now crosses two coverings and two underlayments before it reaches wood. NRCA: “Because of the extra layer(s), longer fasteners are needed to achieve proper penetration and embedment into a roof deck…NRCA recommends fasteners extend through the underside of plywood or other acceptable wood panel decks and penetrate at least 3/4 of an inch into wood plank or board decks.” Owens Corning’s reroofing paragraph is one line long on the subject and says only “ensure proper size and length of fasteners.” A short nail on a two-layer roof is a blow-off waiting for a wind event.
Looking at the underside does not settle it
The most common substitute for a tear-off is an inspection from the attic side, carried out by someone equipped and trained to work in that space. That is worth having, and it is not equivalent. NRCA recommends examining the underside of a deck for stains, rust, mould, and degradation, and then adds the sentence that matters: “observations of a deck’s underside may not reflect the extent of degradation that may exist on the top surface of the roof deck.”
Water arrives from above. Sheathing rots downward from the wet face, and the wet face is the one under the shingles. An attic inspection catches the advanced cases and misses the ones that are still only expensive.
What the new roof is actually attached to
A covering resists wind by being fastened to something that does not move. On a recover, part of that load path runs through a roof somebody else installed and nobody has evaluated. NRCA states the risk in its list of conditions that force a replacement: a new roof system installed over an existing one “should be adequately secured to an existing roof deck. If this cannot be achieved, the re-cover roof system relies on the wind-uplift properties of the existing roof system, which may not meet current building code wind-resistance requirements.”
That is the honest technical statement of what a second layer is: not a doubled roof, but a new roof whose attachment is partly inherited.
Where the layer limit actually comes from, and why it is not the same everywhereSection link
Adopted reroofing provisions share a recognisable shape wherever this page was able to read them: replacement means removal down to the deck, recover is permitted on four stated conditions, and it is barred on three others. What each jurisdiction then does with that shape is where the answer stops being general.
| Jurisdiction | What the adopted text does with a second or third covering | Edition and date on the record |
|---|---|---|
| City of Seattle | Follows the familiar structure. Roof replacement “shall include the removal of existing layers of roof coverings down to the roof deck,” with one exception for an adhered ice barrier membrane, which may remain and be covered with an additional layer of ice barrier. A recover “shall not be permitted” where the existing roof is water soaked or deteriorated so that it is not an adequate base, where the 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.” | 2021 Seattle Residential Code, § R908. The 2021 editions of the Seattle construction codes went into effect on 15 November 2024. |
| City of Chicago | Same three bars, with the third one made conditional rather than absolute: a recover is not allowed where the existing roof has two or more applications of any type of covering “unless approved based on a condition report…that establishes the capacity of the roof structure to support additional weight.” A third layer is reachable in Chicago — through an engineering submission, not through a conversation. | Municipal Code of Chicago, Title 14R, § 14R-3-306; section amended by City Council on 9 October 2024, read at supplement 2026 S-73. |
| City of Bellevue, Nebraska | Adopts the 2021 model residential code and then removes the option entirely: it deletes “Section R908.3.1, Roof recover, in its entirety” and amends the prohibition section to read, in full, “A roof recover shall not be permitted.” It also adds a local provision requiring a permit for any reroofing beyond one roofing square, and requiring the whole roof to be brought up to current code. | Bellevue City Code § 8-18.6, amendments to the International Residential Code, 2021 edition; the section’s history records Ord. 4033 passed 4 May 2021. |
| City of McKinney, Texas | Not a layer rule, but the reason a layer rule you read somewhere may be the wrong text. McKinney’s own summary of the 2024 model residential code lists § R908.3 Roof Replacement as modified, so that self-adhering underlayment may be left on when reroofing if it meets certain requirements and the decking is in good condition. The reroofing section is not static between editions. | 2024 International Codes, in effect in McKinney from 1 October 2025. |
Read this table one item at a time
City of Seattle
- What the adopted text does with a second or third covering
- Follows the familiar structure. Roof replacement “shall include the removal of existing layers of roof coverings down to the roof deck,” with one exception for an adhered ice barrier membrane, which may remain and be covered with an additional layer of ice barrier. A recover “shall not be permitted” where the existing roof is water soaked or deteriorated so that it is not an adequate base, where the 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.”
- Edition and date on the record
- 2021 Seattle Residential Code, § R908. The 2021 editions of the Seattle construction codes went into effect on 15 November 2024.
City of Chicago
- What the adopted text does with a second or third covering
- Same three bars, with the third one made conditional rather than absolute: a recover is not allowed where the existing roof has two or more applications of any type of covering “unless approved based on a condition report…that establishes the capacity of the roof structure to support additional weight.” A third layer is reachable in Chicago — through an engineering submission, not through a conversation.
- Edition and date on the record
- Municipal Code of Chicago, Title 14R, § 14R-3-306; section amended by City Council on 9 October 2024, read at supplement 2026 S-73.
City of Bellevue, Nebraska
- What the adopted text does with a second or third covering
- Adopts the 2021 model residential code and then removes the option entirely: it deletes “Section R908.3.1, Roof recover, in its entirety” and amends the prohibition section to read, in full, “A roof recover shall not be permitted.” It also adds a local provision requiring a permit for any reroofing beyond one roofing square, and requiring the whole roof to be brought up to current code.
- Edition and date on the record
- Bellevue City Code § 8-18.6, amendments to the International Residential Code, 2021 edition; the section’s history records Ord. 4033 passed 4 May 2021.
City of McKinney, Texas
- What the adopted text does with a second or third covering
- Not a layer rule, but the reason a layer rule you read somewhere may be the wrong text. McKinney’s own summary of the 2024 model residential code lists § R908.3 Roof Replacement as modified, so that self-adhering underlayment may be left on when reroofing if it meets certain requirements and the decking is in good condition. The reroofing section is not static between editions.
- Edition and date on the record
- 2024 International Codes, in effect in McKinney from 1 October 2025.
These four are adopted law in their own jurisdictions and nowhere else. Model code text published by a standards body is MODEL text: it has no jurisdiction and no effective date of its own, and it becomes enforceable only where a government adopts it, on that government’s effective date, usually with amendments. Confirm the edition, the amendments, the effective date and the permit requirements at your address with your authority having jurisdiction before treating any of this as the rule for your roof.
What the pattern tells you even when the details do not
Two of the four records above quote their recover conditions in full — Seattle and Chicago — and three things hold in both. An existing roof or covering that is water soaked, or deteriorated to the point that it is not an adequate base, bars a recover. So does an existing covering of slate, clay, cement or asbestos-cement tile. And the number of existing coverings matters, because weight and fastener reach both accumulate. Neither code says why; the reasoning on the rest of this page is ARMA’s and NRCA’s, not the code’s.
What does not hold is the number itself, or whether it can be waived, or whether the option exists at all. That is not a gap in this page — it is the actual structure of building regulation in the United States, where there is no nationwide code for site-built construction and the adopted edition is a local fact.
What the saving is made of, and where it comes backSection link
An overlay is cheaper for a specific and honest reason: several line items stop existing. It is worth seeing which ones, because each of them is doing something, and because the largest of them reappears on the next invoice at roughly double the quantity.
Three things leave the job. The tear-off labour goes, because nobody removes anything. The disposal goes with it — ARMA puts this plainly among the arguments for a recover, that leaving the existing layer “will also save the cost and inconvenience of removing and recycling or disposing of the old shingles.” And the deck allowance often goes, not because the deck is fine, but because nobody is going to look at it. The first two are genuine savings. The third is a deferral wearing a saving’s clothes.
This site publishes no dollar figure for either scope, because it holds no dataset that separates residential recover pricing from tear-off pricing by scope, geography and date. What can be stated without inventing anything is the physical quantity, which is what the labour and the landfill are actually charged against. Here is that arithmetic on one worked example.
| Line | The arithmetic | The quantity | What it actually means |
|---|---|---|---|
| Weight added by the new covering | 24 sq × 280 lb/sq | 6,720 lb — about 3.4 short tons | Roughly 2.8 lb per square foot of roof surface, added permanently to the dead load, with nothing removed to offset it. |
| The same line with a heavier product | 24 sq × 360 lb/sq | 8,640 lb — about 4.3 short tons | About 3.6 lb/sq ft. Owens Corning publishes 360 lb per square for one of its laminated shingles and writes, of that product, that “it may not be feasible to apply the product over an existing shingle roof.” Product weight is not a detail. |
| Removed from this job | 24 sq of existing covering left in place | About 6,720 lb not torn off or hauled now | This is the saving, and it is real: the tear-off labour and the disposal for one full covering simply do not happen. |
| Carried forward to the next replacement | 24 sq × 2 layers × 280 lb/sq | 13,440 lb — about 6.7 short tons to remove | Roughly double the tear-off and disposal quantity of a single-layer roof, at whatever labour and landfill cost applies in that year. Where the adopted limit is two coverings, that removal is not optional. |
| Deck work | Not quantifiable from any published figure | Deferred, not avoided | If the deck needs attention, a recover does not cancel that cost; it postpones it and lets the condition continue under two coverings. NRCA notes that a degraded deck’s fastener holding and load capacities “can be reduced significantly.” |
Read this table one item at a time
Weight added by the new covering
- The arithmetic
- 24 sq × 280 lb/sq
- The quantity
- 6,720 lb — about 3.4 short tons
- What it actually means
- Roughly 2.8 lb per square foot of roof surface, added permanently to the dead load, with nothing removed to offset it.
The same line with a heavier product
- The arithmetic
- 24 sq × 360 lb/sq
- The quantity
- 8,640 lb — about 4.3 short tons
- What it actually means
- About 3.6 lb/sq ft. Owens Corning publishes 360 lb per square for one of its laminated shingles and writes, of that product, that “it may not be feasible to apply the product over an existing shingle roof.” Product weight is not a detail.
Removed from this job
- The arithmetic
- 24 sq of existing covering left in place
- The quantity
- About 6,720 lb not torn off or hauled now
- What it actually means
- This is the saving, and it is real: the tear-off labour and the disposal for one full covering simply do not happen.
Carried forward to the next replacement
- The arithmetic
- 24 sq × 2 layers × 280 lb/sq
- The quantity
- 13,440 lb — about 6.7 short tons to remove
- What it actually means
- Roughly double the tear-off and disposal quantity of a single-layer roof, at whatever labour and landfill cost applies in that year. Where the adopted limit is two coverings, that removal is not optional.
Deck work
- The arithmetic
- Not quantifiable from any published figure
- The quantity
- Deferred, not avoided
- What it actually means
- If the deck needs attention, a recover does not cancel that cost; it postpones it and lets the condition continue under two coverings. NRCA notes that a degraded deck’s fastener holding and load capacities “can be reduced significantly.”
Assumptions, stated so they can be argued with: 24 roofing squares of roof surface, not floor area; one existing covering; both layers costed at the same unit weight, which overstates the existing layer if it is a three-tab shingle and understates it if it is a heavy laminated one; no allowance for underlayment, fasteners, or accumulated debris; and no dollar value of any kind. Substitute your own roof area and the published weight from your product’s data sheet. Whether the framing carries the result is a structural question for a licensed design professional.
The line item that is hardest to see
The deferral is the part that does not appear in either proposal. A tear-off converts an unknown into a known and prices it now, usually through a deck allowance with a unit price. A recover leaves the unknown as an unknown, and unknowns about wet wood do not stay the same size. That is the whole argument, and it is a probability argument rather than a certainty: on a roof where the deck really is sound, the recover was the better trade and the saving was free.
It also does not stay with you. A second covering is a fact about the building that shows up in the next inspection report and in the next contractor’s bid, and it removes an option from whoever owns the roof at its next replacement. What you are obliged to disclose is a matter of state law and of the contract in front of you, and is outside what this page can tell you.
Four compromises that do not appear on either proposalSection link
These are not reasons never to recover. They are the things that are quietly different afterwards, and each of them is easier to accept before the work than to discover after it.
1. Appearance, permanently
The new covering takes the shape of the old one. Both manufacturer instruction sets quoted on this page spend their reroofing paragraph on exactly this: nail down or cut away loose, curled and lifted shingles; the surface “must be smooth before shingles are installed”; install bevelled wood feathering strips if necessary. GAF puts the reason in one sentence — “since any irregularities may show through the new shingles, be sure the underlying shingles provide a smooth surface.”
The preparation is real work, and a bid that assumes the old roof is already flat has not costed it. What shows through afterwards is not a defect anyone will fix; it is the roof you now have, visible in raking light for the rest of its life.
2. Flashings, at the places roofs actually leak
Flashing causes more leaks than field material does, and a recover is the scope least likely to renew it. NRCA is direct about why: cladding — metal or vinyl siding, vertical panels, stucco, EIFS — “frequently cannot be easily removed and reinstalled and can conceal the conditions of step flashings and aprons,” and it suggests those be replaced when a new roof system is installed. On a recover they are typically left where they are, now with an extra layer of covering lapping over a flange that was sized for one.
Penetrations are the same story in miniature. A pipe boot, a valley, or a counterflashing that lands on a thicker, softer, less regular surface is harder to seat well, and where it fails it is under two roofs rather than one.
3. Ventilation and the assembly you did not intend to change
A recover changes the roof assembly, so it changes the building science. ARMA states that the reroofing process “should include an evaluation to determine that the existing attic ventilation is adequate,” and NRCA lists vapour retarders and ventilation among its replacement triggers: sometimes the only way to fix a condensation problem is to take the roof off, because the control layer belongs on the deck.
The heat argument sits here too, and it deserves an honest statement rather than a number. ARMA’s technical bulletin on applying shingles over insulation and radiant barriers — a different assembly from a second layer of shingles, so this is the mechanism and not a finding about roof-overs — states that “heat build-up, a typical result of inadequate ventilation, may accelerate weathering and reduce the anticipated life of the asphalt shingles.” DOE’s guide observes that shingles absorbing less heat “tend to last longer” and are “less likely to be damaged by prolonged heat.” A measured comparison of one-layer and two-layer shingle placement exists in the literature — NRCA’s library indexes it — but this page could not obtain the paper, and so it publishes no figure for how much hotter a two-layer roof runs or what that costs in service life. The mechanism is documented. The magnitude, here, is not.
4. The ratings you thought you were buying
Fire class is a property of a tested assembly, not of a shingle, and a two-layer assembly is not the one that was tested. Impact resistance is explicitly in question: ARMA states that impact ratings “may be affected when new shingles are installed over existing shingles.” And wind resistance depends on an attachment that now runs partly through somebody else’s roof.
None of that means a recovered roof performs badly. It means the numbers on the wrapper describe a condition that no longer exactly applies, and that if a rating is the reason for the product choice, the scope has to be chosen to match it. See the asphalt shingle guide for what those ratings do and do not establish.
A tear-off is not free of downside eitherSection link
Recommending the tear-off in most cases is only honest if the costs of that recommendation are on the page too. Three of them are real, and one of them is a hazard.
It exposes the building. A tear-off opens the deck to weather for at least part of a day, and on a multi-day job for longer. That is a scheduling and sequencing risk that a recover simply does not carry, and it is the reason competent crews stage the work by plane and watch the forecast rather than the calendar.
It can destroy something worth keeping. ARMA notes that removing a previously installed ice-dam protection membrane “may be challenging during a roof replacement.” Adopted reroofing text recognises the same problem from the other direction: Seattle’s replacement provision carries an explicit exception allowing an adhered ice barrier to stay and be covered with an additional layer. If the eaves already have a barrier that is doing its job, that is a genuine argument for restraint.
It can trigger scope a recover does not. This is jurisdictional and it is not always small. Chicago, for example, attaches requirements to roof replacement — at low-slope roof edges adjoining shafts and enclosed courts, and at skylights and other openings in the roof plane — that a recover does not trigger. Whether anything comparable applies at your address is a question for the permit office, and it belongs in the conversation before a scope is chosen.
What a defensible decision looks like, in order
- Establish how many coverings exist, and from what evidence.
- Confirm with the permit office what the adopted edition at that address permits, and what it wants to see.
- Read the printed instructions for the covering actually being installed, and find the reroofing paragraph.
- Establish what is known about the deck, and what is only assumed.
- Price both scopes itemised, so the saving is a list of line items rather than a number.
- Decide with the ownership horizon in view, and write the deck allowance into the contract either way.
What changes this on a real houseSection link
- Structural weight
A recover adds permanent dead load and removes none. ARMA’s second guideline for a recover is to “make sure the structure beneath the roof deck has sufficient capacity to bear the weight of another layer of shingles,” and its third is to “ensure the roof deck remains structurally sound and allows for adequate fastener retention.” Owens Corning writes the same caution into a product page for one of its heavier shingles: because it is 360 lb per square, “it must be determined if the roof frame can support workers and the weight of the shingles,” and “it may not be feasible to apply the product over an existing shingle roof.”
Whether a particular roof structure carries a second covering is a structural determination for this building, made by a licensed design professional against the loads required where it stands. No weight table, including the one on this page, answers it.- Code and jurisdiction
There is no nationwide building code for site-built construction in the United States. Layer limits, the conditions that bar a recover, and what a permit requires are set by whichever model code your state or local government adopted, as that government amended it, on that government’s own effective date. The jurisdiction table earlier on this page shows three real jurisdictions answering the layer question three different ways, and a fourth that shows the reroofing section itself changing between model editions. They are not all working from the same text: Seattle and Bellevue amend the model residential code and Chicago administers its own construction code system. Model provisions are labelled MODEL on this site precisely because they are not law anywhere until a government says so.
Confirm the adopted edition, its amendments, its effective date, and what a permit actually requires with your authority having jurisdiction. Note also that the NRCA article relied on here dates from 2004 and its statements about model codes are historical.- Moisture and ventilation
A recover is a change to the assembly, and the assembly is where condensation problems live. ARMA is direct that “this reroofing process should include an evaluation to determine that the existing attic ventilation is adequate.” NRCA lists vapour retarders and ventilation among its replacement triggers: it may be necessary to remove an existing roof system to install a vapour retarder where there are condensation problems, where one was needed and never installed, or where a change of use has raised interior moisture.
This page publishes no ventilation ratio and no required net free area. Those depend on the adopted edition, local amendments, climate zone, and whether the assembly is vented at all. Vented attics and correctly designed unvented assemblies are both legitimate — see the ventilation guide.- Fire
A second layer changes what is under the covering, and what is under the covering is part of what was tested. Adopted reroofing text carries a specific instance of this. Both jurisdictions whose text is quoted in that table — § R908.4 of the 2021 Seattle Residential Code, in effect there since 15 November 2024, and § 306.4 of Chicago’s Title 14R, as amended 9 October 2024 — require that where a new covering over wood shingles or shakes creates a combustible concealed space, the entire existing surface be covered with gypsum board, mineral fibre, glass fibre or other approved materials, securely fastened in place. Whether anything similar applies at your address depends on the edition and amendments adopted where the building stands, and is a question for the permit office. Even a manufacturer’s ordinary reroofing note treats the classification as conditional — GAF’s instruction for going over wood shingles ends “install #30 underlayment to maintain Class A rating.”
Fire classification — Class A, B, or C — applies to a tested assembly: deck, underlayment, and covering together. It is not a property of a shingle, and a covering’s listing does not travel automatically to a two-layer assembly nobody tested.- Wind
Wind performance is an attachment question, and a recover changes the attachment on both ends: the fasteners are longer and are driven through a compressible layer, and part of the load path runs through an existing roof of unknown condition. NRCA’s warning that a recover may end up relying on the wind-uplift properties of the existing system is the operative sentence, and it is not a small caveat.
Wind design is site- and building-specific — basic wind speed, exposure, height, geometry, pressure zone, enclosure, and risk category all feed a calculation performed against the standard your jurisdiction has adopted. A marketing mph rating on a shingle wrapper is not a code determination for your roof.- Hail and impact
Impact-rated shingles are the most common reason a homeowner pays more for a covering, and a recover can undo part of what they paid for. ARMA states that “impact resistance ratings for asphalt shingles may be affected when new shingles are installed over existing shingles.” If the reason for choosing a product is an insurance credit or a hail exposure, that sentence belongs in the conversation before the scope is priced. See the hail hazard guide.
A Class 4 rating under UL 2218 is a steel-ball test result for a specific product, not a promise that a roof will not be damaged by hail. Whether a rating earns an insurance credit is decided by the insurer and by state regulation, not by the covering.- Slope and drainage
Everything on this page is about steep-slope, water-shedding roofs — shingles and their relatives. Recover on a low-slope roof is a different decision with a different evidence base: it turns on a moisture survey verified by core cuts, on entrapped water, and on capital timing. If the building is commercial or the roof is a membrane, read recover versus tear-off at commercial scale instead. Do not carry conclusions from one to the other.
What a warranty does with a second layerSection link
Two documents are in play and they fail in different directions: the shingle maker’s, which is conditioned on its own printed instructions, and the installer’s, which is written by someone who never saw the deck.
- The manufacturer warranty is conditioned on the instructions
Owens Corning’s installation guide states the rule as a precautionary note repeated above product after product: “the manufacturer will not be responsible for problems resulting from any deviation from the recommended application instructions.” The instructions are the contract term. If they contain a reroofing paragraph, follow it; if they say the existing roof must be removed, there is no version of a recover that keeps the coverage.
- Some products simply cannot be overlaid
This is not hypothetical. The same guide states, of one impact-rated shingle, that “the existing roof must be removed before installing Duration STORM shingles,” and of a hip-and-ridge product that “the existing roof covering must be removed before installing WeatherGuard HP.” Ask for the printed instructions for the exact product being quoted, and read the reroofing paragraph yourself.
- The workmanship warranty covers work nobody could see
A workmanship warranty is the installer’s promise about their own labour. On a recover, the substrate under that labour was never examined, so a later failure has an easy attribution fight built into it: the installer says the deck was already bad, and nobody has a record that says otherwise. On a tear-off, somebody looked, and what they found should be written down.
- Ratings ride on the assembly, not on the wrapper
Fire class is an assembly property; impact resistance, per ARMA, “may be affected when new shingles are installed over existing shingles.” Neither of those is a warranty term, but both are things a buyer commonly believes they are buying.
Repairability
A two-layer roof is harder to repair well. A repair fastener has to cross both coverings to reach wood, the surface it lands on is softer and thicker at every penetration, and a repairer cannot open a small area to see the deck without opening two roofs. Matching is worse too: the roof under the repair is not the roof anybody has a sample of.
The larger repairability point is about the job after this one. Where the adopted code caps coverings at two, the next reroof is not a choice between recover and tear-off — it is a mandatory removal of two layers. The option you used is the option the next owner does not have.
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 an installerSection link
These are the questions that separate a proposal that has thought about the deck from one that has priced around it. A contractor who answers them well is worth more than one who is cheaper.
How many roof coverings are on this house right now, and how did you establish that?
A good answer names a method: permit records, a documented prior job, or lifting shingles at several points on different planes. A weak answer is a glance at the eave, and the eave is the one place a second layer is often trimmed back and invisible.
Which adopted code edition applies at this address, and has the permit office confirmed that a recover is allowed here?
The answer should name a jurisdiction and an edition, not “code allows two layers.” There is no national rule, and jurisdictions amend the model text in both directions — some ban recover outright, some allow a third layer on conditions.
Show me the printed installation instructions for the shingle you are quoting, and the paragraph that covers application over an existing covering.
Manufacturer instructions are the warranty condition. Some products forbid overlay outright; most manufacturers do not approve an existing laminated shingle as a base at all. This is the single question most likely to change a scope.
If we tear off, what is your unit price for replacing sheathing, how is the quantity measured, and how will you show me what you replaced?
A written allowance and unit price agreed before work starts is the difference between a priced surprise and an argument on a Thursday afternoon. Ask for photographs of what came off.
If we recover, what fastener length are you using, and how far does it penetrate the deck?
NRCA’s guidance is that fasteners extend through the underside of plywood, or at least three quarters of an inch into plank decking. An installer who has not thought about fastener length on a two-layer roof has not thought about wind.
What happens to the step flashing at the walls, the valley metal, and the pipe boots in each scope?
NRCA suggests step flashings and aprons be replaced when a new roof system is installed, and notes that cladding often conceals their condition entirely. Flashing causes more leaks than field material does — see flashing failures.
What happens to the ice barrier at the eaves under each scope?
A self-adhered barrier has to go on the deck. If your jurisdiction requires one, or your roof has a history of winter edge leaks, this question can end the conversation on its own.
The existing shingles are uneven in places. What will you do about that, and what will show through if you do not?
Manufacturer reroofing instructions require the surface to be made smooth — nailing down or cutting away loose, curled, and lifted shingles, and using bevelled wood feathering strips where needed. Irregularities telegraph through a new covering, and that is permanent.
Give me both scopes, itemised, and tell me which line items disappear in the recover version.
This turns a vague saving into a list you can read: tear-off labour, disposal, and sometimes the deck allowance. It also makes the two proposals comparable — see comparing roofing quotes.
Require these in writing
- Which scope is being priced — recover or tear-off — using those words, not “new roof”.
- The number of existing coverings the price assumes, and what happens to the price if a second one is found.
- The exact covering product, and a copy of its application instructions.
- Fastener type and length, and the penetration into the deck it achieves.
- Deck replacement: unit price, measurement method, and how the quantity will be evidenced.
- Which flashings are replaced and which are reused, location by location.
- Underlayment and, where required, ice barrier: product, extent, and where it is adhered.
- Disposal: what is being hauled, and whether the volume assumption changes if a second layer appears.
- Permit responsibility, the inspections expected, and who calls for them.
- What the warranty covers, and the specific effect of the chosen scope on the manufacturer’s coverage.
Misconceptions and failure modesSection link
Common misconceptions
Common belief
Two layers is allowed everywhere. Everyone knows that.
What is actually true
Two is the common answer and it is not the universal one. Bellevue, Nebraska adopts the model residential code and then deletes the recover section entirely, amending the prohibition to read, in full, “a roof recover shall not be permitted.” Chicago keeps the two-covering bar but allows it to be lifted on a condition report establishing the roof structure’s capacity to support additional weight. Same model text, opposite outcomes, both adopted law where they apply.
Common belief
A second layer is a second roof, so it is actually more protection.
What is actually true
Half true, which is why it survives. ARMA does say the existing layer “will provide a secondary backup roof for the new shingles.” But redundancy over a deck nobody has seen is not the same as a sound roof: it does nothing about the sheathing, the deck fasteners, the flashings, the ice barrier, or the ratings, and NRCA warns that the new covering may end up leaning on the wind-uplift performance of the old one.
Common belief
The shingles are worn out but the deck is obviously fine — the roof has never leaked.
What is actually true
A roof can shed water for many years while the deck under it takes on moisture from condensation, from a flashing that wets a small area, or from an ice dam that backs up once a winter. NRCA warns that observations of a deck’s underside “may not reflect the extent of degradation that may exist on the top surface,” and the top surface is the wet one. “It has never leaked into the house” is evidence about the ceiling, not about the sheathing.
Common belief
Tear-off is just contractors selling extra work. The old roof is fine as a base.
What is actually true
Sometimes it is exactly that, and this page says so above: where there is one flat layer and a deck known to be sound, ARMA’s own position is that replacement may not be necessary. But the organisation that speaks for the shingle manufacturers — which has no commercial interest in more tear-off labour — is also the one that lists inspecting the deck, repairing damage, and improving deck attachment as the benefits of replacement. Both sentences are in the same document.
Common belief
Tearing off will damage my deck.
What is actually true
NRCA’s stated experience is the opposite: “for wood decks, removal of the roof covering and associated fasteners typically does not damage or reduce the deck’s structural capacity,” and fasteners left behind can be removed or hammered flush. What a tear-off does is reveal damage, which is a different thing from causing it, and is easy to confuse when the bill arrives.
Common belief
It is my house and my money, so the layer count is between me and my contractor.
What is actually true
It is also a permit matter, an inspection matter, and a fact about the building that the next buyer’s inspector will find and the next contractor will price. Where the adopted limit is two coverings, using the second one converts the following reroof into a compulsory removal of both.
How it actually fails
- Telegraphing
- The new covering follows the shape of the old one. Manufacturer reroofing instructions require the surface to be made smooth first — nailing down or cutting away loose, curled, and lifted shingles, and adding bevelled wood feathering strips where needed — precisely because irregularities show through.What you can see: Ripples, waves, and shadow lines in raking light that follow the old shingle courses rather than the new ones. Visible from the ground, permanent, and not a warranty claim.
- Fasteners that never reach wood
- A nail sized for one layer, driven through two. It grips shingle mat instead of sheathing, which has almost no withdrawal resistance.What you can see: Courses lifting or sliding after a wind event, a scatter of shingles on the lawn from one plane rather than uniformly, and nails found still bedded in the old layer rather than the deck.
- Deck decay that continues out of sight
- A wet or already-degraded deck sealed under a second covering. NRCA notes that a degraded deck’s fastener holding and load capacities can be reduced significantly, and nothing about the recover addresses the cause.What you can see: Sagging between rafters visible from the ground in low sun, springiness underfoot reported by a roofer, and staining or musty odour on the attic side. All of these are late signs.
- Flashings reused and then buried
- Step flashing and aprons at walls are concealed by cladding that cannot easily be removed and reinstalled. NRCA suggests they be replaced with a new roof system; on a recover they are commonly left, now with an extra layer of covering above their flange.What you can see: Interior staining at the top of a wall below a roof-to-wall junction, usually appearing in wind-driven rain rather than in every storm.
- The third-layer trap
- The second covering uses up the allowance. Where the adopted code bars a recover over two or more applications, the next reroof has only one legal scope.What you can see: Discovered on a document rather than on a roof: a permit refusal, a bid that is materially higher than the neighbours’, or an inspection report on a sale.
Sources and further readingSection link
Understanding Roofing / Published
Scope and limitations
- It cannot tell you how many coverings are on your roof.
- That is a fact about your building, established from permit records, a documented prior job, or a contractor lifting shingles at several points.
- It cannot tell you what your jurisdiction permits.
- The four jurisdictions in the table are cited to show that the answers genuinely differ, not because any of them applies where you live.
- Confirm the adopted edition, its amendments, its effective date, and the permit requirements with your authority having jurisdiction.
- It publishes no cost figure and no percentage saving.
- The saving is real and this site holds no defensible dataset that separates residential recover pricing from tear-off pricing by scope, geography, and date.
- Naming a number would be decoration.
- The arithmetic in the economics section is arithmetic, not an estimate.
- It uses one published average weight for laminated asphalt shingles on one assumed roof size; a real roof has a real product with a real published weight, and that is the number to use.
- It cannot tell you whether your framing carries a second covering.
- That is a structural determination for one building, made by a licensed design professional, not by a weight per square.
- It publishes no figure for how much hotter a two-layer roof runs.
- A measured comparison of one- and two-layer shingle placement exists in the building-science literature — NRCA's library indexes an ASHRAE paper by William Rose that lists it among the study variables — but this site could not obtain the paper, so it states the mechanism and no number.
- It publishes no ventilation ratio, no required net free area, and no ice-barrier extent.
- Those depend on the adopted edition, local amendments, climate zone, and assembly type.
- The manufacturer instructions quoted here are product-specific and dated.
- They describe two named products from one manufacturer in a 2015 guide and one 2007 instruction sheet from another.
- They state nothing about any other product and may have been superseded.
- Obtain the current instructions for the exact shingle being installed.
- It cannot tell you what you are obliged to disclose to a buyer, or whether an insurer or a warranty responds to any of this.
- Those are set by the documents in front of you and by the law where the building stands, and this page has not had legal review.
2021 Seattle Residential Code, Chapter 9 — Roof Assemblies, Section R908 Reroofing
City of Seattle, Department of Construction and Inspections / 2021 Seattle Residential Code
The reroofing text as adopted in one jurisdiction: that roof replacement 'shall include the removal of existing layers of roof coverings down to the roof deck', with an exception permitting an adhered ice barrier membrane to remain and be covered with an additional layer; the four conditions under which a roof recover is permitted, including installation per the covering manufacturer's approved instructions and complete separate systems that transmit loads directly to the structure; the three conditions under which 'a roof recover shall not be permitted' — a water-soaked or deteriorated existing roof that is not adequate as a base, an existing covering of slate, clay, cement or asbestos-cement tile, and 'where the existing roof has two or more applications of any type of roof covering'; and R908.4, requiring that where a new covering over wood shingles or shakes creates a combustible concealed space the entire existing surface be covered with gypsum board, mineral fibre, glass fibre or other approved materials securely fastened in place.
Adopted law in the City of Seattle and nowhere else. Its section numbers follow the model IRC, but a section number is not evidence that the same words are in force anywhere else, and the model text itself has been republished since. Seattle amends the Washington State Residential Code, which in turn amends the model code; this chapter should not be read as unamended model text.
2021 Seattle Code Adoption — Timeline
City of Seattle, Department of Construction and Inspections
The effective date recorded for the code above: 'The 2021 editions of the Seattle construction codes went into effect on November 15, 2024.'
A department web page recording one city's adoption date. It says nothing about any other jurisdiction, and a later amendment cycle can supersede it; confirm the current edition with the department.
Municipal Code of Chicago, Title 14R Building Rehabilitation Code, § 14R-3-306 Reroofing
City of Chicago, published by American Legal Publishing / Section amended by Chicago City Council 9 October 2024; read at supplement 2026 S-73
That a second large jurisdiction reaches a different answer from the same structure of text: § 306.3 requires roof replacement to remove all existing layers down to the deck; § 306.3.1 permits a recover on four conditions; and its exception bars a recover where 'the existing roof has two or more applications of any type of roof covering unless approved based on a condition report complying with Section 104 of the Chicago Minimum Requirements for Existing Buildings that establishes the capacity of the roof structure to support additional weight.' Also § 306.4, requiring that where a new covering over wood shingle or shake roofs creates a combustible concealed space the entire existing surface be covered with gypsum board, mineral fiber, glass fiber or other approved materials securely fastened in place; and that roof replacement in Chicago triggers compliance work at low-slope roof edges adjoining shafts and enclosed courts (§ 306.7) and at skylights and other openings (§ 306.8), which a recover does not.
American Legal Publishing is the city's code publisher, and its own notice states that the posted documents may not reflect the most current legislation and that the official printed copy should be consulted before any action is taken. This is Chicago law only, and Chicago administers its own construction code system rather than adopting a model code unchanged.
Bellevue City Code § 8-18.6 — Amendments and changes to the International Residential Code, 2021 edition
City of Bellevue, Nebraska, published by American Legal Publishing / Amendments to the IRC 2021 edition; the section's history line records Ord. 4033 passed 4 May 2021
That an adopting jurisdiction can remove the recover option altogether: subsection (MM) deletes 'Section R908.3.1, Roof recover, in its entirety', and subsection (NN) amends 'Section R908.3.1.1, Roof recover not allowed' to read, in full, 'A roof recover shall not be permitted.' Subsection (OO) adds a local Section R908.7 requiring a permit for any reroofing exceeding one roofing square and requiring the entire roof to be brought up to current code.
One municipality's amendments, published by the city's code publisher, whose notice states the posted code may not reflect the most current legislation. It binds nobody outside Bellevue, Nebraska, and the ordinance history should be confirmed with the city before it is relied on there.
Significant Changes in the 2024 International Residential Code
City of McKinney, Texas / For 2024 I-Codes effective in McKinney 1 October 2025
That reroofing text moves between model editions and that adopted editions differ by jurisdiction and year: this city's own summary states that the 2024 International Codes go into effect there on 1 October 2025, and lists 'R908.3 — Roof Replacement (Modification)' among the significant changes, described as 'self-adhering underlayment may be left on when reroofing, if the underlayment meets certain requirements and the decking is in good condition; new underlayment can be placed over it.'
A city handout summarising a model edition for permit applicants. It is a summary, not code text, and it is not a complete account of the 2024 changes. This page therefore states that R908.3 was modified in the 2024 edition and does not quote or renumber any 2024 provision it has not read in full.
Asphalt Shingle Reroofing: Replacement vs. Recover
Asphalt Roofing Manufacturers Association / 22 February 2024
The definitions of reroofing, roof replacement and roof recover; that 'most' building codes 'do not allow more than two roof coverings on a building'; that 'there is no easy, universal answer if only one roof is in place'; that 'the benefits of replacement include having the opportunity to inspect the roof deck, repair any damage, and improve deck attachment to the underlying structure'; that 'most manufacturers do not recommend installing new shingles over existing laminated shingles'; the three recover guidelines — confirm local codes permit an additional layer, confirm the structure beneath the deck has capacity to bear the weight, and ensure the deck remains structurally sound and allows adequate fastener retention; that where one flat layer sits on a deck in good condition 'replacement may not be necessary' and the existing layer 'will provide a secondary backup roof' while saving the cost and inconvenience of removal and disposal; the removal triggers — two existing layers, sagging across ridge or truss lines calling for inspection by a licensed structural engineer, a deck inspection revealing rotted or warped wood or gaps greater than a quarter inch between deck boards, and shingles too uneven and distorted to be flattened; the recommendation to consider re-decking board decks with code-compliant sheathing; that reroofing should include an evaluation of existing attic ventilation; that removal of a previously installed ice-dam protection membrane 'may be challenging during a roof replacement'; and that 'impact resistance ratings for asphalt shingles may be affected when new shingles are installed over existing shingles.'
A trade association funded by the manufacturers of one product category, so it is not a neutral source on asphalt shingles generally. Its statements here are cited because most of them run against that interest — they name conditions that force removal and limits on what a recover preserves. It is not code text, and its own disclaimer states that nothing in it revokes or changes the requirements of individual manufacturers or of the building officials with jurisdiction.
Technical Bulletin — Application of Asphalt Shingles to Decks Installed over Insulation or Radiant Barriers
Asphalt Roofing Manufacturers Association, Steep Slope Committee
The mechanism behind the heat argument, in the association's own words: 'Heat build-up, a typical result of inadequate ventilation, may accelerate weathering and reduce the anticipated life of the asphalt shingles.' Also that applying shingles to a non-rigid surface risks damage and inadequate fastener holding, and that fire classification 'may be adversely affected' when shingles are applied directly over insulation.
This bulletin is about shingles over insulation and radiant barriers, not about shingles over an existing shingle layer. It is cited on this page only for the general statement that heat build-up shortens shingle life. It quantifies nothing, and this page therefore publishes no figure for how much hotter a two-layer roof runs.
Steep-slope reroofing considerations
Tom Bollnow and Joan P. Crowe, AIA, Professional Roofing (National Roofing Contractors Association) / 1 August 2004
NRCA's definitions of re-cover, replacement and reroofing; its 'replacement triggers', including building code requirements, roof deck condition, ice-dam protection and vapour retarders or ventilation; that NRCA 'does not recommend installing a re-cover roof system over a damaged or deteriorated roof deck because a degraded deck's fastener holding and load capacities can be reduced significantly'; that 'observations of a deck's underside may not reflect the extent of degradation that may exist on the top surface of the roof deck'; that an ice-dam protection membrane 'should be installed directly on a roof deck, which dictates the removal of an existing roof system'; that where a recover cannot be adequately secured to the deck it 'relies on the wind-uplift properties of the existing roof system, which may not meet current building code wind-resistance requirements'; that because of the extra layers longer fasteners are needed, extending through the underside of plywood or penetrating at least three quarters of an inch into plank decks; that wall cladding frequently cannot be easily removed and can conceal the condition of step flashings and aprons, and that NRCA suggests step flashings and aprons be replaced when a new roof system is installed; that existing wood shake roofs should not be covered with asphalt laminated shingles; that some roofing materials may contain asbestos and that diagnosis, removal and disposal are regulated; and that 'for wood decks, removal of the roof covering and associated fasteners typically does not damage or reduce the deck's structural capacity.'
Trade guidance written for roofing professionals in 2004 and summarising a manual edition since superseded. Its statements about what model building codes allow are twenty-two years old and are not cited on this page as current code. Its technical reasoning about decks, fasteners, flashings and uplift is why it is cited; its code statements are not.
Asphalt Shingle Roofs — Retrofit guidance for existing homes
U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory)
The scope this guide states for a roof replacement on an existing home: 'Remove all existing roofing (shingles and underlayment)'; 'Replace any damaged wood sheathing'; and 'Inspect the roof deck attachment fasteners and re-nail as required to meet current requirements for nail type, size, and spacing.' Also that 'when reroofing, the existing roof structure should be strong enough to support the additional load of the shingles' and to 'ensure the surface of the roof is flat; sagging roofs could indicate structural problems'; and that lighter-coloured asphalt shingles 'tend to last longer as they absorb less heat than darker shingles and are less likely to be damaged by prolonged heat.'
Federal technical guidance, not adopted law anywhere. Its retrofit guidance describes replacement and does not evaluate a recover as an option, so it cannot be read as a prohibition. Several of its code references are to the 2018 IRC, which has been superseded in many jurisdictions.
Generic Asphalt Shingles — Product Selection and Description (BEES)
U.S. National Institute of Standards and Technology, Building and Fire Research Laboratory
The weight used in the arithmetic on this page: that a roofing square is 9.29 m² or 100 ft², and that a typical laminated asphalt shingle covering has 'an average weight of about 14 kg/m2 (280 lb/square)', with the constituent table totalling the same 14 kg/m². The document states this figure is based on a survey of product information in ICC evaluation reports on laminated asphalt shingles from various manufacturers. Also the market statement quoted on this page: that the asphalt shingle market has changed 'from primarily 3-tab shingles to now over 56 % of the market consisting of laminated/multi-layered products.'
A life-cycle-assessment product description, not a product data sheet. It carries no publication date on its face and its most recent internal reference is to a 2005 article, so its market-share sentence is historical. It is a survey average across manufacturers; a specific shingle has a specific published weight, and published products sit on both sides of the average — this site's roofing squares page records one laminated product at 211 to 225 lb per square, and the Owens Corning guide cited below records another at 360.
Owens Corning Roofer's Guide to Roof Installation
Owens Corning Roofing and Asphalt / © 2015 Owens Corning
Product-specific manufacturer instructions: the precautionary note above each product that 'the manufacturer will not be responsible for problems resulting from any deviation from the recommended application instructions'; that for one laminated shingle published at 360 average weight per square 'it must be determined if the roof frame can support workers and the weight of the shingles' and 'it may not be feasible to apply the product over an existing shingle roof'; that 'the existing roof must be removed before installing Duration STORM shingles'; that 'the existing roof covering must be removed before installing WeatherGuard HP'; and the reroofing paragraph requiring that loose, curled or lifted shingles be nailed down or cut away, that the surface 'must be smooth before shingles are installed', that bevelled wood feathering strips be installed if necessary, and to 'ensure proper size and length of fasteners.'
Manufacturer instructions for one manufacturer's product line, dated 2015 and read on the manufacturer's own asset host. It describes no other manufacturer's position and may have been superseded. Obtain the current printed instructions for the exact product being installed before relying on any sentence in it.
Timberline Shingles — Application Instructions
GAF (published as GAF-Elk Corporation) / Information sheet updated 2007; © 2007 GAF-Elk Corporation
A second manufacturer's reroofing paragraph, to show these instructions are not idiosyncratic: that where old asphalt shingles remain in place, loose, curled or lifted shingles are nailed down or cut away and replaced; that 'since any irregularities may show through the new shingles, be sure the underlying shingles provide a smooth surface'; that 'fasteners must be long enough to penetrate the wood deck at least 3/4" (19mm) or just through plywood'; and that where shingles are applied over wood shingles, '#30 underlayment' is installed 'to maintain Class A rating.'
A 2007 instruction sheet for a product line that has since been replaced, and the copy read was a training-library mirror rather than the manufacturer's own site, which blocks automated retrieval. It is cited only for the general shape of a manufacturer reroofing paragraph and is not current instruction for any product on sale today.
How do I know if I have asbestos in my home (floor tile, ceiling tile, shingles, siding, etc.)?
U.S. Environmental Protection Agency
That 'the only way to be sure whether a material contains asbestos is to have it tested by a qualified laboratory'; that EPA 'only recommends testing suspect materials if they are damaged (fraying, crumbling) or if you are planning a renovation that would disturb the suspect material'; and that 'samples should be taken by a properly trained and accredited asbestos professional (inspector).'
Consumer guidance from a federal agency. It does not identify which specific roofing products contain asbestos, it sets no age threshold, and it is not the regulation that governs a renovation or demolition; states and localities administer delegated programmes with additional requirements.
Fall Protection in Residential Construction — OSHA guidance document
U.S. Occupational Safety and Health Administration
That 'falls are the leading cause of death for workers engaged in residential construction', and that under 29 CFR 1926.501(b)(13) workers engaged in residential construction six feet or more above lower levels must be protected by conventional fall protection or another allowed measure.
An occupational-safety guidance document addressed to employers and their trained employees, and OSHA states it 'is not itself a standard or regulation' and 'creates no new legal obligations'. It is cited here as a reason for an untrained reader to stay on the ground, not as a procedure for anyone to follow personally.
Measured summer values of sheathing and shingle temperatures for residential attics and cathedral ceilings — library record and abstract
National Roofing Contractors Association, indexing William Rose, ASHRAE (Performance of Exterior Envelopes of Whole Buildings VIII), December 2001 / December 2001
Only this: that a measured, multi-summer thermocouple study of a Midwest test facility included 'one- and two-layer shingle placement' among its variables alongside dark and white shingles, vented and unvented construction, and measurement location, and reported the percentage by which each test case ran hotter or colder than a base case.
This is a bibliographic record and abstract, not the paper. The abstract reports no values, and NRCA's library directs users to obtain publications from the publisher. This page therefore names the mechanism and states that a measured comparison exists, and publishes no temperature figure and no service-life effect from it. Anyone relying on the heat argument should read the paper itself.