For homeowners and property buyers commissioning a re-roof

The deck is the one part of a roof nobody can price in advance. Price the uncertainty instead.

Steep-slope · single-family and small multifamily

Sheathing condition is genuinely unknown until the covering is off. That is not a contractor's excuse, it is the physical order of the work. What a contract has to settle is not whether there will be a surprise, but who pays for it, at what rate, and on what evidence.

30-second answer

How should deck replacement be handled in a roofing contract?

Nobody can see the deck under a covering, so every roofing contract carries hidden quantity risk. Handle it with a written allowance that states three things: the unit, the price per unit, and the quantity already included in the base price. Two bids only become comparable when all three are present. Everything else — evidence, approval, credit for unused quantity — follows from those.

Safety first

Do not climb up to check a deck finding, and do not go into an attic under an open roof

Verifying a deck finding means standing on a partly stripped roof beside an open hole, at the exact moment the surface is least predictable. OSHA describes falls as the leading cause of death for workers engaged in residential construction and requires conventional fall protection above six feet for the people who do this for a living. You are not covered by their fall protection plan, and nothing you could see up there changes what happens next.

Ask for photographs instead. Everything this page tells you to check can be checked from a phone screen, a written change order, and a conversation on the ground.

If the house predates 1990, old shingles, felts, and mastics coming off the deck may contain asbestos. EPA’s position is that the only way to be sure whether a material contains asbestos is to have it tested by a qualified laboratory, and that sampling should be done by a properly trained and accredited asbestos professional. Do not handle or sort the tear-off debris.

If anyone on site says the roof structure is unsafe, that rafters or trusses are broken, or that a plane is sagging, that is not an allowance question. Keep people out of the rooms underneath, stop the covering work, and get a licensed contractor or a structural engineer to look before anything else is agreed.

Learning paths and saved lessons

At a glance

The short version, in numbersSection link

Five facts do most of the work on this page. Three are about wood, two are about paperwork.

What a real deck allowance names: A unit, a unit price, and a quantity includedAll three. Miss any one and two bids stop being comparable — which is the whole reason the clause exists.
The unit the trade prices by: One 4 ft × 8 ft sheet — 32 sq ftA trade convention, not a standard. NIST Voluntary Product Standard PS 2-18 sets no commodity sheet size; it names 1,220 × 2,440 mm (48 × 96 in.) as a minimum test panel. The 4 × 8 sheet is simply what is ordered, carried up, and billed.
When the quantity becomes knowable: After the covering is off, not beforeManufacturer instructions put deck inspection after removal. TAMKO: “Before re-covering a roof be certain to inspect the roof decks.”
What visible rot already means: Most of the strength is goneUSDA Forest Products Laboratory: by the time weight loss from decay reaches 10%, most strength losses may be expected to exceed 50% — and at losses of 10% or less, decay is detectable only microscopically.
What decay needs to happen at all: Wood above about 30% moisture contentFPL: serious decay occurs only above the fibre saturation point, and wood kept air dry will not decay. Rot maps where the water was; it does not spread evenly across a roof.

Tradeoffs

This page's advice — a unit price and an included quantity, in writing — and where that advice is wrongSection link

The position here is that the deck allowance is the highest-value paragraph in a residential roofing contract, and that insisting on it costs nothing. There are real situations where it is the wrong tool.

Best when

The job is an asphalt shingle tear-off over a plywood or OSB deck, where the sheet is the natural unit and the trade already prices that way.
You are comparing two or more written proposals and need to know which is actually cheaper rather than which has the smaller headline.
The house has a leak history, an ice-dam history, a chimney, skylights, or a valley discharging onto a lower plane — all places where localised decay is genuinely likely.
Nobody can get into the attic to look at the underside of the deck, because the attic is finished, the ceiling is cathedral, or there is no access hatch.
The contractor has already said, honestly, that they do not know what is under there. That is the correct answer, and a written allowance is what you do with it.

Think twice if

The deck is 1x board sheathing or skip sheathing. The likely outcome is not patching but over-sheathing the whole plane — a scope item to price up front, not an allowance to draw against. Malarkey's installation instructions strongly recommend installing sheathing where wood board decking is the existing substrate.
The unit price is set high enough to be a profit centre. A per-sheet price several times the cost of a sheet plus the labour to fit it rewards finding sheets, and you have written that incentive yourself.
The included quantity is large and carries no credit for what is not used. An allowance with no credit-back clause is not an allowance; it is a price increase with an optimistic name.
The roof is already known to be in trouble — an active large leak, a visibly sagging plane, water stains across a whole ceiling. At that point the deck is a scope question needing an assessment, not a contingency line.
The work is insurance-funded. Whether decking sits in the carrier's scope, and what a supplement for it requires, is governed by the policy and the claim, and it may not track the contract you signed.
Your jurisdiction prescribes what a home improvement contract and a change order must contain. A statutory form outranks any template, including a good one.
The plan is a roof-over rather than a tear-off. Then the deck is never inspected at all, which is a different decision with different consequences.

What changes the answer

Deck type: plywood, OSB, 1x boards, skip sheathing, or a mixture where an addition meets the original house.
Framing spacing, which sets how small a piece can physically be cut and still bear at both ends.
Whether an accessible attic exists, because the underside of a deck can be looked at before anyone signs anything.
The building's leak, ice-dam, and ventilation history, including whether a bathroom fan or dryer has been discharging into the attic.
Whether the covering is being torn off or recovered.
Local labour and sheathing prices at the time of the work, which is why a unit price carries a date.
The adopted code edition, and whether the authority having jurisdiction inspects the exposed deck before underlayment.
State home improvement contract law, which in some places dictates the form of a change order and when it must be signed.
How much of the price has already been paid when the discovery is made.

The mechanism

Why the number cannot be known, and why the unit is a sheetSection link

Two separate facts collide here. Decay is invisible under a covering, and a sheathing panel cannot be cut anywhere you like. Together they explain almost every deck argument on almost every job.

Looking down at part of a stripped roof plane. Seven numbered points, keyed to the list below. Every dimension is drawn at 40 pixels per foot, so the three areas — the decay, the piece cut out, and the sheet billed — can be compared directly. Schematic, not a construction detail.Original diagram, Understanding Roofing.

The framing sets the grid. Rafters or trusses at 24 inches on centre are, in APA’s words, “widely recognized as the most economical construction for residential roofs.” Everything above them is laid out to suit that spacing.
One sheet is 4 ft × 8 ft — 32 square feet. It goes down with its long dimension across the supports, and APA’s roof sheathing recommendations assume panels “continuous over two or more spans.” That is the unit ordered, the unit carried up a ladder, and the unit a deck allowance is priced by.
The panel’s short ends land on rafter centrelines. This is the constraint that decides how small a repair can be. A new piece needs something under both ends to bear on and to nail into.
An eighth of an inch of gap. APA recommends 1/8 in spacing at all panel end and edge joints unless the panel manufacturer indicates otherwise. It is a small detail, and it is one of the details that tells you whether a replacement sheet was fitted by someone who does this properly.
The decayed area is about four square feet. Around a leaking pipe penetration, which is where localised decay usually is. Four square feet of actually rotten wood.
The smallest piece that can come out is 16 square feet. Cut back to the rafter centrelines either side of the decay, full panel height, because a horizontal cut across the middle of a panel leaves a new edge with no framing under it. So four square feet of rot becomes a sixteen-square-foot hole.
The long edges have nothing under them. Where a panel edge runs between rafters and the support spacing exceeds the maximum unsupported edge for that panel, APA’s tables call for edge support: blocking, tongue-and-groove edges, or panel edge clips. On a patch this is the part most often skipped, and it shows up years later as a wave in the roof surface along the joint.

Add the last two together and you have the ordinary reason a contractor bills a whole sheet for a small patch: they cut a sixteen-square-foot hole, and the piece that came up the ladder is thirty-two square feet. Whether the offcut gets used depends on the job — on a roof with several patches it often does, and on a roof with one it usually does not, which is exactly why the counting rule belongs in the contract rather than in an argument afterwards. What the geometry settles is narrower and more useful: arguing about the size of a stain misses the point, because the number that decides the price is how many sheets are in play, and that is the number an allowance is written about.

Why the deck is invisible until it is not

Wood does not rot for interesting reasons. The USDA Forest Products Laboratory states the condition plainly: “Serious decay occurs only when the moisture content of the wood is above the fiber saturation point (average 30%).” And the converse: “wood will not decay if it is kept air dry, and decay already present from prior infection will not progress.”

A roof covering is what keeps the roof deck air dry. It is also, inconveniently, what hides it. The deck’s condition is therefore a direct record of where water has been getting past the covering — and the covering has to come off before anyone can read it. Manufacturer instructions are explicit about the sequence. TAMKO tells installers “before re-covering a roof be certain to inspect the roof decks.” The Department of Energy’s Building America Solution Center gives the same order for a re-roof: remove all existing roof covering and flashings, remove debris, clean the deck, then inspect and replace damaged sheathing.

This is the part that reads as an excuse and is not one. Nothing in routine residential practice reads sheathing condition reliably through an intact covering — which is why the installer’s own instructions put deck inspection after tear-off rather than before it. The consequence is worth stating carefully, because it is easy to get backwards. A quantity carried in the price as an allowance is not a claim to know what is up there; it is a priced contingency, and asking for one is the recommendation of this whole page. What nobody can honestly offer in advance is a final deck quantity presented as a measured fact.

The five things a deck allowance clause has to say

An allowance is a sum carried in a contract for work whose quantity is not yet known. Most residential roofing contracts have one. Most of them are written badly. A usable one answers five questions:

What is the unit? A full 4 ft × 8 ft sheet is the normal answer. If the contract says “per square foot” and the crew bills by the sheet, you have two different contracts. State how a partial piece counts.
What is the unit price? A number in dollars, for that unit, including the labour to cut out, fit, fasten, and dispose of the old piece — or explicitly excluding disposal, if that is how it is priced.
How many units are already in the contract price? This is the field that is almost always missing, and it is the field that makes two bids comparable. “Decking replaced at $95 per sheet” carries an unstated assumption of zero.
What happens to unused quantity? If eight sheets are included and four are used, is the difference credited, and at what rate? Without this clause an included quantity is a floor under the price rather than an allowance.
How is quantity above the included number approved? In writing, before the work, with the price effect stated. That is not only good practice — it is what a statutory change order looks like in the states that legislate the form.

California’s home improvement contract statute shows how seriously some jurisdictions take that last point. Business and Professions Code section 7159 requires that “a home improvement contract and any changes to the contract shall be in writing and signed by the parties to the contract prior to the commencement of work,” and that a change order “describe the scope of the extra work or change, the cost to be added or subtracted from the contract, and the effect the order will have on the schedule of progress payments.” That is California law as amended by SB 517, effective 1 January 2026. It is not the law where you live unless you live there, and it is not legal advice. It is a model of what a good clause contains.

Before anyone signs

What can actually be known in advance, and what cannotSection link

The premise of this page is that the quantity is unknowable. That is true of the number. It is not true of the risk, and the difference is worth money.

Knowable before the contract

The underside of the deck, where an attic exists and is accessible. A long-running leak leaves a stain, and chronic attic moisture leaves mould and darkened sheathing across a plane. A contractor or inspector who never asked to look has left free information on the table. You should not go up there yourself.
The building’s leak history. Every previous stain on a ceiling marks a place the deck above it was wet. Write the list down before the first contractor visits and hand it to all of them, so the bids are priced against the same information.
The likely deck type. Panel decks — plywood or OSB — are the norm on later twentieth-century and newer houses; board sheathing is what older ones tend to have, and skip sheathing turns up under old wood shakes and some tile. Age is a hint rather than a rule, and no date settles it: a look from the attic does, and so does the tear-off.
The geometry that concentrates water. Valleys, chimneys, skylights, sidewalls, and low-slope porch roofs are where decay will be if it is anywhere.
Whether the roof has been recovered before. A second covering changes both the tear-off price and the odds on the deck. It is sometimes visible at a rake edge from the ground with a zoom lens, but a glance does not settle it — the eave is exactly where a second layer is often trimmed back and invisible, so the count comes from permit records, a documented prior job, or a contractor lifting shingles at several points. Read what a second layer does for why.

Not knowable until the covering is off

The condition of the top surface, which is where water sat and where plywood delaminates first.
Whether fastener holes have enlarged enough that the deck no longer retains nails — the criterion the manufacturer instructions actually set.
Swollen or crumbling OSB panel edges, which sit at the joints and are invisible from below.
Anything at all where there is no attic: cathedral ceilings, finished attic rooms, dormer cheeks, and porch or addition roofs framed tight to the ceiling below.
The sheet count. Even a contractor who has seen a stained area from the attic cannot tell you how far it runs on the top side.

So the honest brief to a contractor is not “tell me what the deck is like.” It is: here is everything known about where this roof has leaked; look at the attic; then tell me your unit price and how many sheets you have carried. That question can be answered truthfully before work starts. The other one cannot.

Reading a finding

Genuine deck replacement against opportunistic quantitySection link

Rotten sheathing is real and it has to come out. The way to tell a real finding from a padded one is not to argue about whether wood rots — it is to ask what mechanism produced this particular pattern, and whether the photographs show it.

Six deck findings, the mechanism that produces each, the evidence a fair finding comes with, and what a weak justification looks like. Patterns and evidence standards, not a diagnosis of any roof.
What is reported	The mechanism that produces it	What the photographs should show	What a weak justification looks like
A cluster of sheets around a chimney, skylight, or pipe	Water past a failed flashing, running down the deck under the covering for years.	Staining continuous with the penetration, and the failed flashing itself in the same frame or an adjacent one.	Scattered sheets with no water path between them, and no flashing photographed at all.
A band along the eave, the first two to four feet	Meltwater backing up behind an ice dam, or a gutter overflowing back under the first course, over repeated winters.	A band of staining running parallel to the eave, roughly constant in width, with deteriorated eave underlayment in the same photographs.	Eave decay claimed on a roof in a climate with no freeze history, no gutter problem, and no valley discharging above it.
A band following a valley	Concentrated flow down the valley with failed or undersized valley metal beneath it.	A band that follows the valley line and narrows as it climbs, with the valley metal visible.	The valley named as the cause, but the decay photographed out in the middle of the field.
Every sheet on one whole plane	Sustained wetting from below — a bathroom fan or dryer discharging into the attic, chronic condensation, or a leak that ran for a decade.	Uniform darkening and mould across the underside of the plane, plus the moisture source identified by name.	“The whole thing was soft,” with no photographs, no named source, and no explanation of why one plane and not the others.
Stained sheets that still hold a fastener	Old staining from a leak that was fixed. The wood dried, and dry wood does not keep decaying.	The test applied on camera: does the sheet still hold a fastener. Discoloration alone is not the criterion.	Sheets replaced for appearance, under a covering that will hide them completely, billed at the allowance rate.
The entire deck, because it is board or skip sheathing	Not damage at all. The house was built with 1x boards or spaced boards, and the new covering wants a continuous panel deck.	The existing boards, in place, with their spacing visible — and a separate written price for over-sheathing the plane.	A whole-house re-deck drawn from an allowance that was sized for a handful of sheets.

Read this table one item at a time

A cluster of sheets around a chimney, skylight, or pipe

The mechanism that produces it: Water past a failed flashing, running down the deck under the covering for years.
What the photographs should show: Staining continuous with the penetration, and the failed flashing itself in the same frame or an adjacent one.
What a weak justification looks like: Scattered sheets with no water path between them, and no flashing photographed at all.

A band along the eave, the first two to four feet

The mechanism that produces it: Meltwater backing up behind an ice dam, or a gutter overflowing back under the first course, over repeated winters.
What the photographs should show: A band of staining running parallel to the eave, roughly constant in width, with deteriorated eave underlayment in the same photographs.
What a weak justification looks like: Eave decay claimed on a roof in a climate with no freeze history, no gutter problem, and no valley discharging above it.

A band following a valley

The mechanism that produces it: Concentrated flow down the valley with failed or undersized valley metal beneath it.
What the photographs should show: A band that follows the valley line and narrows as it climbs, with the valley metal visible.
What a weak justification looks like: The valley named as the cause, but the decay photographed out in the middle of the field.

Every sheet on one whole plane

The mechanism that produces it: Sustained wetting from below — a bathroom fan or dryer discharging into the attic, chronic condensation, or a leak that ran for a decade.
What the photographs should show: Uniform darkening and mould across the underside of the plane, plus the moisture source identified by name.
What a weak justification looks like: “The whole thing was soft,” with no photographs, no named source, and no explanation of why one plane and not the others.

Stained sheets that still hold a fastener

The mechanism that produces it: Old staining from a leak that was fixed. The wood dried, and dry wood does not keep decaying.
What the photographs should show: The test applied on camera: does the sheet still hold a fastener. Discoloration alone is not the criterion.
What a weak justification looks like: Sheets replaced for appearance, under a covering that will hide them completely, billed at the allowance rate.

The entire deck, because it is board or skip sheathing

The mechanism that produces it: Not damage at all. The house was built with 1x boards or spaced boards, and the new covering wants a continuous panel deck.
What the photographs should show: The existing boards, in place, with their spacing visible — and a separate written price for over-sheathing the plane.
What a weak justification looks like: A whole-house re-deck drawn from an allowance that was sized for a handful of sheets.

This table describes evidence standards, not a diagnosis. It cannot tell you whether a particular finding on a particular roof is genuine; it can tell you what a genuine one is normally accompanied by, and what to ask for when it is not.

Be fair about the direction this cuts. A padded finding and a concealed one are both real failures, nobody publishes a defensible count of either, and this page will not pretend to know which is commoner. What can be said is that concealment carries the larger consequence: rot is common in older housing, tear-off is when it appears, and a crew that covers over punky decking to avoid an awkward phone call has done something much worse than overcharging: they have nailed a new roof to a substrate that cannot hold it, on a covering whose own installation instructions say the deck must be capable of receiving and retaining fasteners.

The reason to write the clause is not that contractors are dishonest. It is that an honest finding and a padded one look identical from the driveway, and the only way to keep them apart is to have agreed the rate and the evidence before either party knew what would be found.

The bad moment

Where you stand when the roof is already openSection link

If you are reading this with a stripped roof and a phone call waiting, the paragraph you needed is not in your contract. Here is what is still available to you.

Be clear-eyed about the position. The covering is off, the house is open to weather, a crew is standing on the roof being paid, and some portion of the price is usually already handed over. Every one of those facts pushes toward saying yes to a number you have not checked. That is not a character failing; it is the structure of the situation, and it is exactly why the useful version of this page is the one read before signing.

Four things are still worth doing, in this order.

Ask for photographs before removal, not after. Of each sheet in place, with a landmark in the frame. It costs the crew a few minutes, and it is the only record that will exist. If the sheets are already off, ask for photographs of the exposed framing where they came from — the pattern of the opening is itself evidence.
Get the number and the rate in writing before the work proceeds. A text message with a count and a price, replied to, is a written record. It is not the same as a signed change order, and in some states it is not what the law requires of a contractor, but it is enormously better than a phone call.
Separate the categories. Sheathing is one conversation. Framing damage is a different one that should stop work rather than continue it. Suspected asbestos-containing material is a third that should stop work and get tested. A single number covering all three is a number to slow down on.
Ask what the roof needs today, as against what it needs overall. Drying the building in safely is urgent. Optimising the deck is not. If the quantity is genuinely contested, the immediate question is what has to happen before nightfall, and that is usually a much smaller number.

What this page will not do is tell you what your rights are. Whether you may refuse, what happens to money already paid, what notice is required, what a mechanic’s lien can be filed for and when, and what remedies exist are all questions of state law and of your specific contract. If a genuine dispute is developing, that is a conversation with a lawyer licensed where you live, and it is worth having early rather than after the final invoice.

One structural note for next time, offered as illustration rather than as advice about your situation: some contracts signed at a buyer’s home carry a cancellation window. The federal cooling-off rule at 16 CFR Part 429 covers sales personally solicited away from the seller’s permanent place of business above $25 at the buyer’s residence, requires the seller to furnish notice of a right to cancel “without any Penalty or Obligation, within THREE BUSINESS DAYS,” and carries specific exclusions. Several states set their own, sometimes longer, periods — California’s home improvement statute gives three business days, and five for senior citizens. Whether any of that reaches a given contract is a legal question, not a website question. The point is only that the cheap moment to change your mind is at the beginning, and the expensive one is on an open roof.

Worked example

Two bids, one roof, and the arithmetic that decides which is cheaperSection link

This is the whole argument for insisting on an included quantity, done as arithmetic. The dollar figures are invented inputs chosen to make the structure visible. They are not rates for any market.

Where these two bids cross over: 12 sheetsBelow twelve sheets of replaced decking the lower headline price wins. Above it, the higher one does. Neither proposal tells the reader that.

The same 28-square asphalt re-roof, quoted two ways, priced across a range of deck quantities. Bid A: base $18,600, decking at $95 per sheet, none included. Bid B: base $19,450, eight sheets included, further sheets at $72, unused sheets credited at $72. Illustrative arithmetic — no figure here is a market observation.
Sheets actually replaced	Bid A total	Bid B total	Cheaper, and by how much
0 sheets	$18,600	$18,874	Bid A, by $274
4 sheets	$18,980	$19,162	Bid A, by $182
8 sheets	$19,360	$19,450	Bid A, by $90
12 sheets	$19,740	$19,738	Bid B, by $2
20 sheets	$20,500	$20,314	Bid B, by $186
40 sheets	$22,400	$21,754	Bid B, by $646

Read this table one item at a time

0 sheets

Bid A total: $18,600
Bid B total: $18,874
Cheaper, and by how much: Bid A, by $274

4 sheets

Bid A total: $18,980
Bid B total: $19,162
Cheaper, and by how much: Bid A, by $182

8 sheets

Bid A total: $19,360
Bid B total: $19,450
Cheaper, and by how much: Bid A, by $90

12 sheets

Bid A total: $19,740
Bid B total: $19,738
Cheaper, and by how much: Bid B, by $2

20 sheets

Bid A total: $20,500
Bid B total: $20,314
Cheaper, and by how much: Bid B, by $186

40 sheets

Bid A total: $22,400
Bid B total: $21,754
Cheaper, and by how much: Bid B, by $646

Bid B is computed with its credit clause applied in both directions: $19,450 − (8 × $72) + (n × $72), which reduces to $18,874 + $72n. Bid A is $18,600 + $95n. They are equal at n = 274 ÷ 23 = 11.9 sheets. Strip the credit clause out of Bid B and its price simply never falls below $19,450 — which is the point of asking for the clause.

Units: U.S. dollars, as arithmetic performed on figures a reader takes from their own proposals
Scope included: Two illustrative written proposals for the same 28-square asphalt shingle re-roof, differing only in how the deck allowance is written.
Not included: Everything else in either bid. This page publishes no roofing rate, no per-sheet decking price, and no national average, because no transparent dataset separates deck work from the rest of a roofing job by market and by date.
Geography: None. These are not rates for any state, metro, or market.
Data as of: Not applicable. The dollar inputs are invented for the arithmetic, not observed in any market on any date. The arithmetic itself was checked on 27 August 2026.
Confidence: The arithmetic is exact and reproducible from the two formulas in the footnote. The inputs carry no market basis at all and should be replaced with the numbers on your own two proposals.
Method: How this site builds cost figures — no figure above came from it

Bid A is $850 cheaper on the front page. It is also the bid whose exposure is unbounded and whose per-sheet rate is 32 per cent higher. A reader who chooses on the headline is making a bet on a number neither bid states.

Read the last column downward and the real shape appears: the “cheaper” bid stays cheaper only while the deck turns out to be in decent condition. At a full re-deck — 2,800 square feet of roof surface divided by 32 square feet per sheet, so about 88 sheets — Bid A adds $8,360 to its own base while Bid B adds $5,760 to a base only $850 higher. That is not a small difference on a house, and none of it was visible when the two proposals were laid side by side.

The lesson is not that Bid B is better. It is that neither bid can be evaluated without the included quantity, and that asking both contractors for it costs one email. The same normalisation problem runs through every other line of a proposal; comparing roofing quotes handles the rest of it.

Three things this example is not

It is not a price for a roof. Nothing here was sourced from a market, and it should not be quoted at anyone.
It is not a claim that per-sheet pricing is universal. Some contractors price deck work by the square foot, some fold a modest quantity into the base with no line item at all, and on a board deck the unit is not a sheet.
It is not a suggestion that the lower unit price is always the better clause. A very low unit price attached to a very large non-refundable included quantity is the same trick pointed the other way.

These figures exist to show a structure, not to price a job. The only price that binds anyone is the one in a signed scope of work for this building — and the point of this page is that the deck line in that scope should be written before anybody climbs a ladder.

Considerations

What changes this on a real buildingSection link

Code and jurisdiction: Whether the exposed deck is inspected by the building department before underlayment goes on, whether a re-roof needs a permit at all, and whether any deck upgrade is triggered are all set by the code your jurisdiction has adopted, as amended locally. There is no nationwide building code for site-built construction. Ask the authority having jurisdiction which edition applies at your address and what a re-roof inspection covers, and get the answer before signing a schedule of payments that assumes a particular sequence.
This page cites no code provision as applicable to you. Model code text is a model provision, not law where you live, and re-roof permitting practice varies between neighbouring towns.
Structural weight: Sheathing is not structure. A rotten sheet is a covering-substrate problem. A cracked or deflected rafter, a sagging ridge, a truss with a broken web, or a plane that dips between framing members is a structural question, and it belongs to a registered design professional and the authority having jurisdiction rather than to a roofing allowance. If a crew reports framing damage, that is the moment work should stop and a different conversation should start.
Nothing on this page is a structural determination. Roof framing capacity for a specific building is established by a qualified design professional who has looked at that building.
Moisture and ventilation: Deck decay is a moisture record. It clusters where water concentrates: under failed flashing, in valleys, at eaves that have ice-dammed, around pipe penetrations, and along the underside of a deck over an attic that has been receiving wet air from below. That last one is worth naming separately: a bathroom fan or dryer discharging into an attic can rot sheathing from underneath with no roof leak at all, and replacing the sheets without fixing the source buys a repeat. Attic ventilation is where that thread continues.
There is no universal ventilation ratio and no universal right answer here. Vented attics and correctly designed unvented assemblies are both legitimate, and which one a building has changes the diagnosis completely.
Access and site conditions: An open deck is a building without a roof. Weather during the exposed period is why a good contract says what happens if the work is stopped by rain: who dries the roof in, with what, and at whose cost. Ask before signing, because that answer is much more expensive to negotiate on a Thursday afternoon with a front coming through. How a replacement actually runs covers the rest of the sequence.
Older buildings and asbestos: If the building predates 1990, old shingles, felts, and mastics may contain asbestos, and tear-off is exactly the operation that disturbs them. Age is not determinative in either direction. EPA says the only way to be sure whether a material contains asbestos is laboratory testing, and that samples should be taken by a properly trained and accredited asbestos professional. A contract for an older building should say what happens if suspect material is encountered — normally, stop and test — rather than leaving it to be decided in the moment.
Insurance-funded work: If the work is being paid for through an insurance claim, the carrier’s scope and your contract are two documents that can disagree about decking. Whether replacement sheathing is covered, whether it requires a supplement, and what evidence a carrier will accept are governed by the policy, the claim, and the law of your state. Do not assume the allowance you negotiated and the settlement you receive describe the same work.
This page makes no representation about any insurance policy, coverage, claim outcome, or contract enforceability. Those questions need a qualified professional in your jurisdiction.

Warranty and repair

What the deck has to do for a warranty to mean anythingSection link

Deck condition is not a side issue for a covering warranty. It is a precondition written into the installation instructions the warranty depends on.

The manufacturer's precondition: TAMKO’s Heritage instructions describe acceptable decks as “plywood, oriented strand board (OSB) or sheathing boards capable of receiving and retaining fasteners,” and require nails long enough to penetrate 3/4 in into the deck, or completely through and at least 1/8 in past it where the deck is thinner than that. Malarkey’s instructions call for a surface “in good shape and solidly sheathed,” minimum 3/8 in exterior-grade plywood, 7/16 in OSB, or nominal 1 in seasoned lumber, and state that “deteriorated or rotted boards should be replaced.” A deck that cannot hold a fastener has failed the only test the covering actually cares about.
Who carries the risk if the deck is wrong: Both manufacturers put the consequence on the installer and the owner rather than on themselves. TAMKO: “TAMKO assumes no responsibility for leaks or defects resulting from improper application, or failure to properly prepare the surface to be roofed over.” Malarkey: failure to use properly conditioned deck materials “can result in deck movement which can damage the roof covering and may void your warranty.” These are product-specific documents. Read the ones for the product going on your roof.
Workmanship coverage and the substrate: A workmanship warranty covers what the installer did. It does not normally promise anything about a substrate they were asked to work over, and a contractor who warned in writing that a deck was marginal and was told to proceed has a strong position. That cuts both ways: it is a reason to take a documented warning seriously, and a reason to want the documentation. How roofing warranties are structured covers the rest.

Repairability

Replaced sheathing becomes invisible the moment the underlayment goes down. There is no way to audit it later, no way to count it from the ground, and no way to prove a number after the fact. The photographs taken on the day are the entire evidentiary record of the most disputed line in the contract, which is why asking for them in advance is not distrust — it is the only mechanism available to either party.

Ask for each replaced sheet photographed in place before removal, with something in the frame that locates it: a chimney, a vent, a valley, the ridge. A picture of rotten wood on the driveway proves that some wood was rotten. It cannot prove where it came from, how much of it there was, or that it came off your house.

One thing genuinely worth buying while the deck is open is deck re-nailing — adding fasteners to sound existing sheathing. It is available only at that moment, it is cheap relative to the access, and it is a separate line item or it does not happen.

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.

Ask before you sign

Questions to ask before the contract is signedSection link

Every one of these is answerable in a sentence by a contractor who works this way, and awkward for one who does not. The awkwardness is the information.

What is your unit price per sheet of decking, and how many sheets are already included in the price you have quoted me?
The single most useful question on this page. A good answer is two numbers. An answer that gives only the first has told you the included quantity is zero — which is fine, as long as it is written down and you price the other bids the same way.
If we use fewer sheets than the number included, do I get credited? At what rate?
Without this, an included quantity is a price floor. With it, the allowance behaves the way the word implies. Some contractors quite reasonably price a small included quantity into the base and do not credit it; that is a legitimate position, and you only need to know which one you are buying.
Is the unit a full 4 ft by 8 ft sheet, and how does a partial piece count?
Because a sixteen-square-foot cut out of a thirty-two-square-foot sheet is the normal case, not the exception. If half sheets are billed as whole sheets that may be entirely fair — but it should be the stated rule rather than a surprise on the invoice.
What thickness and product will you use, and does it match what is on the roof now?
A 1/2 in sheet let into a 3/8 in deck leaves a step, and a step telegraphs through the underlayment and the shingles. Matching thickness, or shimming, is part of doing this properly.
Do you re-nail the existing deck while it is open, and is that a separate line?
It is one of the few upgrades available only during a tear-off. A contractor with a considered answer — including “no, and here is why not for this roof” — is telling you they think about the deck as an assembly rather than as a surface.
Before you replace a sheet, will you photograph it in place with something in the frame that shows where it is?
Ask before, not during. A contractor who agrees in advance has made the most disputed line auditable for both of you, and contractors who already work this way are usually glad to be asked, because it protects them from the reverse accusation.
Who approves quantity above the included number, in what form, and before or after the work?
“I’ll text you a photo and you say yes” is a real workflow and can be a fine one — as long as it is agreed in advance and the messages are kept. In some states a written, signed change order before the work is a statutory requirement rather than a preference.
What happens if the deck turns out to be board sheathing or skip sheathing?
That is a substrate change, not a quantity. It should carry its own price and its own conversation rather than being drawn from an allowance sized for a handful of sheets. Any house old enough to have skip sheathing should have this asked before signing.
What happens if you find framing damage rather than sheathing damage?
The right answer involves stopping, not estimating. Structural repair is a different trade, usually a different permit, and sometimes a design professional. A contractor who treats a cracked rafter as an allowance draw is the wrong contractor for that discovery.
If the building predates 1990, what is your procedure if you encounter suspect asbestos-containing material?
You are listening for “we stop and it gets tested,” not for reassurance. Anyone who answers by telling you not to worry about it has answered a different question.

Require these in writing

The word “allowance” never standing alone — always with a unit, a unit price, and a quantity beside it
How a partial piece is counted against the unit
Whether unused included quantity is credited, and at what rate
The product and thickness of the replacement sheathing, and how a thickness mismatch is handled
Whether deck re-nailing is included, and at what fastener spacing
Whether removal and disposal of the old sheathing sits inside or outside the unit price
The approval mechanism for quantity above the included number, in writing, before the work
A photographic documentation requirement, with a rule for identifying location
What happens if board sheathing, skip sheathing, or a mixed deck is found
What happens if framing damage rather than sheathing damage is found
What happens if suspect asbestos-containing material is encountered
Who dries the roof in if weather stops the work while the deck is open, and at whose cost

What goes wrong

What people get wrong, and how deck clauses actually failSection link

The first misconception is the one that produces the argument. The rest decide how badly it goes.

Common misconceptions

Common belief
A competent contractor should have known the deck was bad before starting. This is a bait and switch.
What is actually true
Partly wrong and partly right, and the split matters. Where a house has an accessible attic, the underside of the deck can be looked at before anything is signed, and a long-running leak usually leaves a stain there. A contractor or inspector who never asked to look has skipped a free piece of information. Expecting that look is reasonable, and what a real inspection covers sets the standard.
But the underside view misses a great deal: decay that starts at the top surface under the covering, enlarged fastener holes, delaminated top plies of plywood, swollen OSB edges, and anything at all over a cathedral ceiling, a finished attic, or a low-slope porch with no space above it. The instructions the installer works to put deck inspection after the covering comes off, because that is the only point at which the deck can actually be inspected.
Common belief
If the sheathing looks fine it is fine, and if it looks bad someone is padding the bill.
What is actually true
Neither inference holds, and the Forest Products Laboratory explains why in both directions. On the reassuring side: “Strength losses during early stages of decay can be considerable,” and at weight losses of 10 per cent or less “decay is detectable only microscopically” — a sheet can look acceptable and have lost a great deal. On the suspicious side: “It may be assumed that wood with visually discernible decay has been greatly reduced in all strength values.” If you can see it in a photograph, it is already well past the point of argument.
The test that actually decides it is not appearance. It is whether the deck is, in the manufacturer’s words, capable of receiving and retaining fasteners.
Common belief
Rot on one part of the roof means the whole deck is going.
What is actually true
Decay needs sustained wetting, and it stops when the wood dries. So decay maps water: penetrations, valleys, eaves, chimneys, the plane under a failed flashing. A claim that an entire plane is gone is not automatically wrong — chronic condensation, a bathroom fan discharging into an attic, or a leak that ran for a decade will all do it — but it is a claim that comes with a mechanism attached, and the mechanism should be visible in the photographs alongside the damage.
Common belief
The allowance is money the contractor keeps whether they use it or not.
What is actually true
Only if that is what you signed. An allowance with a credit-back clause returns unused quantity; one without is a floor under the price. Both are legitimate ways to write a contract, and both are used honestly every day. The failure is not the structure — it is signing one while believing you signed the other.
Common belief
The lower bid is the lower price.
What is actually true
Only at a deck quantity neither bid states. The worked example above crosses over at twelve sheets, and nothing on either front page would tell a reader that. A proposal without an included quantity is not cheaper or more expensive than one with it — it is simply not yet comparable.
Common belief
If they find something mid-project I can just refuse, and they will finish anyway.
What is actually true
This page will not tell you what your rights are, because they depend on your contract, your state, and facts nobody here knows. What can be said plainly is that the practical position is bad: the covering is off, the house is open to weather, the crew is on site, part of the price is usually already paid, and the alternative to agreeing is a stopped job on an open roof. That asymmetry is the entire reason this page is about the paragraph written beforehand rather than the argument had afterwards. If a genuine dispute develops, that is a question for a lawyer in your jurisdiction, not for a website.

How it actually fails

The unpriced allowance: No unit, no unit price, no quantity — just a promise that decking will be replaced “as needed.” Every number in the sentence gets set after the roof is open, which is the one moment the buyer has no leverage.What you can see: Phrases like “as needed,” “if required,” “at cost,” “prevailing rates,” or “market price” anywhere near the word decking.
The included quantity that only goes one way: A generous-sounding included quantity with no credit for what is not used. It reads as protection and functions as a minimum price, and it makes the bid look worse than it is against a competitor who included nothing.What you can see: “Includes up to N sheets” with no sentence anywhere about what happens below N.
The unit that changes between the contract and the invoice: The contract states one unit and the invoice uses another — priced per square foot, billed per sheet, or partial pieces billed as whole ones with no stated rule. Nobody has to be dishonest for this to produce a fight.What you can see: An invoice line whose arithmetic you cannot reproduce from the contract in one step.
Verbal approval on an open roof: A phone call from the roof, a yes, and no record. Weeks later neither party remembers the number the same way, and there is nothing to check it against.What you can see: A quantity that first appears on the final invoice. In jurisdictions that legislate the form of a change order, this can also be a compliance problem for the contractor.
The substrate surprise dressed as an allowance draw: The deck turns out to be 1x boards or spaced boards under an old covering. Over-sheathing an entire plane is a scope change of a different order from replacing a few sheets, and drawing it out of an allowance sized for eight sheets satisfies nobody.What you can see: An older house, a previous wood shake or tile roof, or a covering that has been recovered more than once.
The thickness mismatch: Replacement sheathing of a different thickness let into the existing deck with no shimming. The step telegraphs through the underlayment and the shingles.What you can see: A straight-line ridge or trough along a sheet edge, visible in raking light months after the job is finished.
Documentation that proves nothing: Photographs of removed material on the ground rather than of sheets in place. They document that something was rotten. They cannot document how much, or where, or whose roof it came off.What you can see: A folder of close-ups with no roof, no landmark, and no context in any frame.

Sources and further readingSection link

Understanding Roofing / Published August 27, 2026

Scope and limitations

It cannot tell you what your contract says or what it means.
Contract terms, cancellation rights, change-order formalities, deposit limits, lien rights, and remedies vary by state and by the facts of a project.
Nothing here is legal advice.
It publishes no price for decking, for roofing, or for anything else.
The dollar figures in the worked example are invented inputs chosen to make an arithmetic structure visible.
No transparent dataset separates deck work from the rest of a roofing job by market and by date, so a sourced per-sheet range would be decoration rather than evidence.
It cannot tell you how many sheets your roof will need.
That number does not exist until the covering is off, which is the premise of the whole page.
It cannot tell you whether a particular contractor's finding is honest.
It can tell you what evidence a finding should come with, which is a different and more useful thing.
It makes no code determination.
Whether your jurisdiction inspects an exposed deck, requires a permit for a re-roof, or triggers any deck upgrade is set by the edition adopted where the building is, as amended, and confirmed by the authority having jurisdiction.
It makes no structural determination.
Framing damage, deflection, and load capacity belong to a registered design professional who has looked at the building.
It makes no representation about insurance coverage, claim outcomes, or whether decking will be paid for by any carrier.
The two sets of manufacturer instructions cited below are product-specific documents for two products.
They are not a standard, they do not describe every asphalt shingle, and they are not law.
Read the instructions for the product going on your roof.

Wood Handbook — Wood as an Engineering Material, Chapter 14: Biodeterioration of Wood
U.S. Department of Agriculture, Forest Service, Forest Products Laboratory / General Technical Report FPL-GTR-190, chapter by Carol A. Clausen
That serious decay occurs only when wood moisture content is above the fibre saturation point, average 30%; that fully air-dried wood usually has a moisture content not exceeding 20% and that wood kept air dry will not decay, with decay already present from prior infection not progressing; that the early or incipient stages of decay are accompanied by a discoloration which can be difficult to recognise; that strength losses during early stages of decay can be considerable, with toughness losses of 6% to more than 50% at 1% weight loss, and most strength losses expected to exceed 50% by 10% weight loss; that at weight losses of 10% or less decay is detectable only microscopically; and that wood with visually discernible decay may be assumed to have been greatly reduced in all strength values.
A federal research publication, not adopted law and not a roofing document. It describes wood decay generally; it establishes nothing about any particular roof deck, and its strength-loss figures come from laboratory tests on wood specimens rather than from field assessment of sheathing.
Application Instructions for Heritage Architectural Asphalt Shingles
TAMKO Building Products LLC / Rev. 07/31/2024
That the deck must consist of plywood, oriented strand board, or sheathing boards “capable of receiving and retaining fasteners”; minimum 3/8 in plywood and 7/16 in OSB, both APA-rated, and sheathing boards of nominal 1 in minimum thickness not over 6 in nominal width; that the roof deck must be smooth, dry, and free from warped surfaces; that nails must penetrate 3/4 in into the deck, or completely through and at least 1/8 in past it where the deck is thinner; that “before re-covering a roof be certain to inspect the roof decks”; that buckled shingles usually indicate warped decking or protruding nails; and that “TAMKO assumes no responsibility for leaks or defects resulting from improper application, or failure to properly prepare the surface to be roofed over.”
Product-specific manufacturer instructions for one shingle line — tier 6 in this site's source hierarchy. Not a standard, not code, and not applicable to other products. The revision date printed in the document read at this URL was 07/31/2024.
Architectural Laminate Shingle Installation Instructions
Malarkey Roofing Products / Rev. 09/25
That the surface to receive new roofing “should be in good shape and solidly sheathed,” of minimum 3/8 in exterior-grade plywood, 7/16 in OSB, or seasoned lumber nominally 1 in thick, positioned tight and securely nailed to framing; that “deteriorated or rotted boards should be replaced”; that the manufacturer “strongly recommends installing sheathing when wood board decking is the existing substrate,” because leaks and buckling increase when installed directly over board decks; that failure to use properly conditioned deck materials “can result in deck movement which can damage the roof covering and may void your warranty”; and that where old roofing is left in place, code allowance depends in part on the old wood deck being “sound and able to provide good anchorage for nails.”
Product-specific manufacturer instructions for one shingle line — tier 6. The document read carried the revision marking 09/25. It is not a standard and does not describe any other manufacturer's requirements.
Roof Deck Sheathing and Sealing for Sloped Roofs
U.S. Department of Energy, Building America Solution Center (PNNL)
The re-roof sequence in which the existing roof covering and flashings are removed and the deck cleaned before sheathing is inspected and damaged material replaced; that existing roof sheathing and flashing should be inspected and damaged materials replaced; that IBHS recommends roof sheathing of minimum 7/16 in plywood or OSB; and that solid sheathing should be installed over older 1x deck boards.
Best-practice guidance written around the IBHS FORTIFIED Home programme, not adopted law. Its code references are to the 2015 IRC, an edition many jurisdictions have superseded, and its recommendations aim at high-wind resilience rather than at contract structure.
Roof Construction — an excerpt of the Engineered Wood Construction Guide
APA — The Engineered Wood Association / Form No. E30X, revised December 2019
That roof sheathing panels are assumed continuous over two or more spans with the long dimension or strength axis across supports; that 1/8 in spacing is recommended at all panel end and edge joints unless the panel manufacturer indicates otherwise; that where support spacing exceeds the maximum length of an unsupported edge, blocking, tongue-and-groove edges, or panel edge clips are required, with one clip per span placed midway between supports; and that roof trusses spaced 24 inches on centre are widely recognised as the most economical construction for residential roofs.
A trade association funded by wood structural panel manufacturers — tier 4, and not a neutral party on wood panels generally, although the geometric and edge-support recommendations used here are not contested claims. It is recommendation, not code. The copy read was the roof-construction excerpt mirrored by a building-products distributor; the document identifies itself as APA Form No. E30X, revised December 2019, and APA is the publisher.
Voluntary Product Standard PS 2-18: Performance Standard for Wood Structural Panels
National Institute of Standards and Technology, U.S. Department of Commerce / PS 2-18, March 2019
That the standard names a minimum test panel size of 1,220 mm by 2,440 mm (48 in. by 96 in.) — the dimension used on this page for one sheet and for the 32 square feet it covers.
A voluntary product standard, not a building code and not a commodity sizing rule. PS 2-18 does not declare 4 ft by 8 ft to be the standard panel size; it names 1,220 by 2,440 mm as a minimum test panel size within its test methods, and other test specimen sizes appear alongside it. The 4 by 8 sheet is used on this page as the trade's ordering and billing unit, which is a market convention rather than a requirement of the standard, and nothing on this page rests on PS 2-18 beyond the dimension itself.
California Business and Professions Code section 7159 — home improvement contracts
California Legislative Information / Amended by Stats. 2025, Ch. 585, Sec. 1.5 (SB 517), effective 1 January 2026
That in California a home improvement contract and any changes to it must be in writing and signed by the parties before work commences; that extra work and change orders become part of the contract once prepared in writing and signed prior to commencement of the work covered, and must describe the scope of the extra work or change, the cost added or subtracted, and the effect on the schedule of progress payments; that the contract must contain a description of the project and of the significant materials to be used and equipment to be installed; that the down payment may not exceed $1,000 or 10 percent of the contract price, whichever is less; and that the contract carries a three-day right to cancel, extended to five days for senior citizens.
This is California law and nothing more. It does not apply outside California, other states legislate home improvement contracts differently or not at all, and quoting it here is illustration rather than legal advice. The section as read carries the note “(Amended by Stats. 2025, Ch. 585, Sec. 1.5. (SB 517) Effective January 1, 2026.)” — confirm the current text before relying on it.
16 CFR Part 429 — Rule Concerning Cooling-Off Period for Sales Made at Homes or at Certain Other Locations
U.S. Government Publishing Office (Federal Trade Commission rule) / 16 CFR Part 429, Title 16 CFR 2025 annual edition (revised as of 1 January 2025) — the most recent annual edition published; no 2026 edition of Title 16 volume 1 was available on govinfo on the access date
That a federal cooling-off rule exists for sales personally solicited away from the seller's permanent place of business, with a purchase-price threshold of $25 or more at the buyer's residence and $130 or more elsewhere; that it requires the seller to furnish notice of the buyer's right to cancel “without any Penalty or Obligation, within THREE BUSINESS DAYS from the above date”; and that the definition carries specific exclusions.
A federal trade regulation with defined exclusions, including transactions at a seller's fixed place of business and certain maintenance or repair calls. Whether it reaches a particular roofing contract is a legal question about that contract and those facts. Many states also have their own home-solicitation cancellation statutes, sometimes with longer periods. The text was read in the govinfo annual edition of the CFR; ecfr.gov blocked automated retrieval. An annual edition is a snapshot; confirm the current text at eCFR before relying on it.
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 recommends testing suspect materials if they are damaged or if a renovation would disturb them; and that samples should be taken by a properly trained and accredited asbestos professional.
General homeowner guidance. It does not identify asbestos in any specific product and is not a determination about any building. Roofing shingles appear on EPA's list of materials that may contain asbestos; presence is established by testing, not by age.
Fall Protection in Residential Construction — guidance
U.S. Occupational Safety and Health Administration
That falls are the leading cause of death for workers engaged in residential construction, and that workers six feet or more above lower levels must be protected by conventional fall protection — guardrail systems, safety net systems, or personal fall arrest systems.
The page states of itself that it “is not itself a standard or regulation and it creates no new legal obligations.” It addresses employers and workers in residential construction, not homeowners, and it is cited here only to establish the seriousness of the hazard a homeowner would be walking into.

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