Roofing
Roof deck substrate types and what they mean for the roof
The structural surface the roof attaches to, deck by deck: steel, structural concrete, lightweight insulating concrete, gypsum, wood, and wood fiber, and how each one drives fastening, fire, and wind uplift.
Direct answer
A roof deck is the structural surface the roof system attaches to, and the deck type decides how you fasten, the assembly fire rating, and the wind uplift path. The common ones are steel, structural concrete, lightweight insulating concrete, gypsum, wood or plywood, and cementitious wood fiber. The manufacturer listing, FM approval, and adopted code control the assembly.
Key takeaways
- The roof deck type decides fastening method, assembly fire rating, and the wind uplift path, so confirm it before bidding.
- The six common decks are steel, structural concrete, lightweight insulating concrete, gypsum, wood or plywood, and cementitious wood fiber.
- The concrete 28-day mark is a strength milestone, not dryness; install a low-perm vapor retarder, on the order of under 0.01 perm, over a new slab.
- Steel fastens with screws into the top flute, not the valley; lower gauge means thicker steel, and pullout more than doubles from 26 to 18 gauge.
- Gypsum, lightweight concrete, and wood fiber are nailable only with auger or base-sheet fasteners, often pre-drilled; field-test pullout per ANSI/SPRI FX-1.
The roof deck, and why it decides everything above it
A roof deck is the structural surface the roof system sits on and fastens to. It is the floor of the roof, the layer that spans the joists or beams and carries the insulation, the membrane, the foot traffic, the snow, and the wind load down into the building frame. Everything above it depends on what it is made of.
The deck is the first decision on a roof, not a detail you sort out later. The deck type decides how you attach the assembly, whether you can screw it, nail it, or have to glue it. It sets the fire rating of the whole assembly, because a combustible wood deck and a noncombustible steel deck are not the same listing. It is the last anchor in the wind uplift path, the thing the fasteners or the adhesive actually grab. And it decides whether a given roof system is even allowed, because a manufacturer approval and an FM listing are written for specific deck types.
Get the deck wrong in the estimate and the whole job is priced wrong. The attachment guide for single-ply covers the methods that ride on top of the deck. This guide is about the deck underneath them, because the method you can use is set by what you are fastening into.
How do you read the deck before you bid?
Read the deck before you price the roof, because the deck drives the fastener, the adhesive, and the method, and those drive the cost. A mechanically attached system on 22 gauge steel is one number. The same roof on a gypsum deck that needs auger fasteners and pre-drilling is another number entirely. Bid the second job at the first job's price and you eat the difference.
On a re-roof, the deck is often hidden under the existing roof, so you confirm it from the original drawings, a core cut, or a small test opening before you commit a price. On new construction, the structural drawings name the deck and its gauge or thickness. Either way, you want the deck type, the gauge or thickness, the spacing of the supports, and the condition.
The questions that change the bid: Can I fasten into this, or do I have to adhere? What is the pullout going to be, and does the wind design need more fasteners than the deck will hold? Is the deck wet, deteriorated, or new enough to still be giving off moisture? Answer those before the number goes out, not after the crew is on the roof.
What is the most common commercial roof deck?
Steel is the most common low-slope commercial roof deck. It is cold-formed corrugated sheet, rolled into ribs that run the length of the panel and give it stiffness across the joists. The ribs, the flutes, are why a thin sheet can span six feet and carry a roof. You see it on warehouses, big-box retail, schools, and most tilt-up and steel-frame buildings.
Two numbers matter: the gauge and the rib profile. Gauge is the thickness, and a lower gauge number is thicker steel. 22 gauge is the common roofing deck, with 20 and 18 gauge on heavier or higher-uplift jobs. The rib profile, most commonly the wide-rib Type B with narrow-rib and intermediate profiles also in use, sets where the deck is solid enough to take a fastener, because you fasten into the top flute, the flat of the rib, not the open valley.
Fastening is screws and plates driven through the insulation into the top flute. The fastener has to hit the steel, so the layout follows the rib spacing, and a fastener that misses the flute and lands in the valley holds nothing. The gauge controls the pullout. Thinner steel strips out and lets the screw back out under uplift cycling, and pullout climbs steeply as the steel gets thicker, more than doubling between thin 26 gauge and 18 gauge. The attachment and wind guide covers how that pullout sets the fastener pattern.
Steel has one more issue: it is a vapor and condensation surface. Warm, moist building air that reaches the cold underside of a steel deck condenses, drips, and rusts the deck and wets the insulation above. On humid-interior buildings, a pool, a kitchen, a paper plant, the air barrier and vapor control over the deck is not optional.
Structural concrete deck
Structural concrete decks are cast-in-place slabs or precast units that span the structure and carry the roof as part of the building frame. They are heavy, strong, and noncombustible, and they take load and uplift better than anything else. You find them on parking structures, hospitals, data centers, and any building where mass, fire rating, or blast and uplift resistance is the point.
Cast-in-place is poured on formwork on site. Precast is plant-cast planks or double-tees set by crane and grouted at the joints. Both are non-nailable. You do not drive a roofing screw into structural concrete and trust it. Attachment is by drill-in anchors set into the slab, or, more commonly on concrete, by adhering the insulation and membrane directly with adhesive, which skips the fastener-pullout question altogether.
The problem with concrete is water, and it is a new-concrete problem. A fresh slab holds a large amount of mix water that has to leave, or be blocked from, the roof above. That gets its own section, because roofing over a wet new slab is one of the more expensive mistakes in the trade.
Can you roof over new concrete?
You can roof over new concrete, but not because the slab is 28 days old. The 28-day figure is a strength milestone from the concrete side, not a dryness number. A slab can hit full design strength and still be wet enough to wreck a roof, and depending on the climate it can take months to dry, longer in a cold or humid one.
The water in a fresh slab does not disappear, it migrates. Without protection it moves up into the roof assembly as vapor, condenses, and goes after the things that fail when they get wet: the facers on the insulation, the cover board, water-based adhesives, and steel fasteners that corrode. The roof looks fine for a season, then the cover board softens and the adhesion lets go.
Waiting for a slab to dry fully is rarely practical on a schedule, so the common move is to install a vapor retarder over the deck instead. Industry guidance, from groups like NRCA, IIBEC, and MRCA, points to a very low-perm vapor retarder, on the order of less than 0.01 perm, which is effectively a vapor barrier that keeps the slab moisture out of the assembly. Confirm the perm rating and the detail against the membrane manufacturer requirement and the project documents, because the warranty rides on it. Skip the vapor retarder over a green slab and you own the failure.
Lightweight insulating concrete (LWIC)
Lightweight insulating concrete, LWIC, is a poured deck made of cement with an aggregate like perlite or vermiculite, or a foamed concrete, placed over a galvanized steel form deck or a slotted form. It gives slope and some insulating value in one pour, which is why it shows up on long-span roofs and re-cover jobs that need to build drainage. It takes fasteners, but only special ones.
LWIC holds water by design, and that is the catch. The same low density that makes it insulate makes it a sponge, and a fresh LWIC deck carries a lot of water that dries slowly. You attach base sheets with expanding or self-locking base-sheet fasteners made for lightweight concrete, set into the deck and allowed to age and grab. The withdrawal value is low compared to steel, often on the order of tens of pounds per fastener after the pour ages, and it depends on the cure, so the fastener has to be the listed one for that system and the value confirmed by test.
Treat LWIC as a wet deck until proven otherwise. The form deck underneath, usually a vented galvanized steel, is there partly to let the deck breathe and dry downward. If that drainage path is blocked or the deck never dries, the water stays in the system and you get the same corrosion and adhesion problems as a wet slab, just slower.
Gypsum deck
Gypsum decks are poured gypsum concrete over formboard and bulb tees, or precast gypsum plank, and they are mostly an older-building deck you meet on re-roofs rather than something you spec new. Gypsum is noncombustible, which is why it was used, and it is light. The trouble is moisture and fastener hold.
Gypsum does not hold a standard roofing fastener well, and it holds one worse when it is wet. Crews have put concrete screws into gypsum and read a decent pullout at first, but the deck is not resilient, so as the roof above moves under wind and thermal cycling the screw works the hole larger and the pullout falls off. The fix is the right fastener: auger-type fasteners made for gypsum and cementitious decks, set in a pre-drilled hole. Pre-drill deeper than the fastener embedment, commonly about a half inch deeper, so the debris that falls back into the hole does not bottom out the fastener.
A wet gypsum deck is a structural question, not just a roofing one. Gypsum that has been soaked loses strength and can deteriorate to where it will not carry the roof or hold any fastener. On a re-roof over gypsum, the deck condition is the first thing you check, because you may be looking at deck replacement, not a recover.
Wood plank and plywood or OSB deck
Wood decks come in two forms: solid sawn plank, the old tongue-and-groove or square-edge boards on older buildings, and wood structural panels, plywood or OSB, the standard on steep-slope and on smaller low-slope roofs. Wood is nailable in the true sense. It takes nails and screws directly, which is why steep-slope roofing lives on it.
Thickness sets the hold. A fastener needs enough wood to grab, so codes and manufacturers set a minimum panel thickness, often around 15/32 in for sheathing in higher-wind work, with 5/8 in and 3/4 in used where the load or the spacing calls for it. Confirm the minimum against the adopted code and the panel span rating, because it is driven by the fastener spacing and the support spacing together. Plywood's cross-laminated plies give it good withdrawal resistance, and OSB holds well too when it is dry and the right thickness. In high wind, the move is ring-shank fasteners for more withdrawal.
Wood moves with moisture, so panels are laid with a small gap at the edges, commonly about 1/8 in, to let them expand without buckling. On plank decks, the boards have gaps between them by nature, which is why a separator or a base sheet goes down before a membrane so it is not bridging open joints. The killer on wood is water. A wet or rotted deck loses its fastener hold and its strength, and a soft spot underfoot is a deck you do not roof over until it is replaced.
Cementitious wood fiber (Tectum-type) deck
Cementitious wood fiber deck, often known by the Tectum brand, is a panel of wood fibers bound with portland cement or a similar binder, set on bulb tees or a frame. It gives a finished acoustic ceiling on the underside and a deck on top in one product, which is why it shows up in gyms, schools, and natatoriums. It takes fasteners, but like gypsum and LWIC it needs the right one.
You attach to it with auger-type fasteners made for cementitious and gypsum decks, the same family used on gypsum, set into a properly sized hole. The pullout is modest and it depends on the panel density and condition, so the fastener has to be the listed one and the value confirmed by a pullout test on the actual deck, not assumed from a table.
Because it is a wood-fiber product, it is sensitive to moisture, and the wood content matters to the fire assembly. A natatorium deck that has lived over a chlorinated pool for decades can be soft, corroded at the fasteners, and weak. Inspect it hard before you recover it.
What is a nailable deck?
A nailable deck is one you can secure a roof to with fasteners driven into the deck. A non-nailable deck is one you cannot, so the roof is adhered or set on drill-in anchors instead. The split decides your whole attachment approach before you pick a membrane.
Nailable decks are wood plank, wood structural panels, cementitious wood fiber, gypsum, and lightweight insulating concrete. Of those, only wood takes ordinary nails and screws. Gypsum, cementitious wood fiber, and lightweight concrete are nailable only with special fasteners, auger types or expanding base-sheet fasteners, often in a pre-drilled hole. So nailable does not mean any fastener works. It means the deck accepts a fastener made for it.
Non-nailable decks are steel and structural concrete. Steel is the odd one in the naming, because you absolutely fasten to steel, with self-drilling screws into the flute, but it is often grouped as non-nailable because you cannot drive a nail into it. Structural concrete is the true non-nailable case: you adhere to it or you use drill-in anchors. When in doubt, the deck type and the manufacturer's approved fastener list tell you which world you are in.
Fastener pullout and the deck
The deck is what holds the fasteners on a mechanically attached roof, so the deck sets the pullout, and the pullout sets how many fasteners the wind design needs. The membrane and insulation do not hold themselves down. The fastener transfers the uplift into the deck, and the deck either keeps it or lets it pull out.
Pullout varies enormously by deck. Thicker steel holds far more than thin steel, and the difference is large: pullout climbs steeply, well over double, going from thin 26 gauge up to 18 gauge. Concrete anchors hold a lot. Gypsum, lightweight concrete, and wood fiber hold far less, and their value depends on cure and condition. Because the published numbers are starting points, the reliable way to know what a deck holds is a field pullout test with the actual fastener, by a procedure like the ANSI/SPRI FX-1 test that FM and the manufacturers recognize.
Run the test on the real deck, calculate the pullout the wind design needs, and set the fastener density from that, not from habit. The single-ply attachment and wind guide walks through how the required pullout becomes the fastener pattern in the field, perimeter, and corner zones. The deck is the variable that whole calculation rests on. Get the deck's real pullout wrong and the pattern is wrong everywhere.
How does the deck affect wind uplift?
The deck is the end of the wind uplift path, so the roof is only as anchored as the deck and the deck's own attachment to the structure. Wind lifts the membrane, the load goes through the attachment into the fasteners or adhesive, through those into the deck, and from the deck into the joists or beams. Any weak link in that chain is where the roof leaves.
Two deck-related links get missed. First, the deck-to-fastener connection, the pullout already covered, which is what most people think of. Second, the deck-to-structure connection. A steel deck welded or screwed to the joists at too few points can peel off the structure as a unit, with the roof still attached to it, in a high enough wind. The deck attachment to the frame is part of the uplift design, governed on the structural side by the steel deck standards and on the assembly side by FM and the wind code.
This is why the wind uplift rating is an assembly rating, not a membrane rating. ASCE 7 sets the design wind uplift for the building height, exposure, and zone, and FM and the manufacturer listing give a tested assembly that meets it, on a specific deck. Change the deck and you have changed the assembly, so the rating has to be re-confirmed for the deck you actually have.
Fire rating and the deck
The fire rating of a roof is an assembly rating, and the deck is a defining part of it. A combustible deck and a noncombustible deck are different assemblies even with the identical membrane and insulation on top, because the deck is part of what the fire test measured.
Wood and cementitious wood fiber are combustible decks. Steel, structural concrete, and gypsum are noncombustible. That split drives which fire-rated assemblies you can build and what the building code requires for the construction type. A Class A roof assembly over a wood deck is a different tested build-up than a Class A over steel, and the listing names the deck. You do not borrow a steel-deck assembly rating for a wood deck.
The numbers and the allowed assemblies come from the listings, UL and FM, and from the building code requirements for the construction type and use. Cite the listing for the assembly you are actually building, on the deck you actually have, and confirm the code requirement against the adopted edition. A roof that fastens fine and sheds water can still fail a fire inspection if the assembly was built for the wrong deck.
Recover or tear off over an existing deck
On a recover or a re-roof, the deck is the thing you assess before you decide between recovering over the old roof and tearing off to the deck. The new roof attachment and warranty depend on what is underneath, and on a recover you are trusting a deck you cannot fully see.
The questions are the same ones that drive a new bid, asked of an old deck. Is it the deck the drawings say it is, or did someone change it in a past re-roof? Has it corroded, rotted, softened, or stayed wet under the old roof? Will it still hold the fastener the new wind design needs? You answer with core cuts and test openings, with a pullout test where the new roof is mechanically attached, and with a walk that listens for soft spots and deflection.
A recover that adds load to a tired deck is its own problem. The deck was designed for the original roof weight plus the code loads, and a second roof, ponded water, or new rooftop equipment can push a marginal deck past it. Whether you can recover or have to tear off is a topic on its own, but the deck condition is the input that decides it. Recover over a bad deck and you have built a new roof on a failing foundation.
Moisture and deck deterioration
Water is what kills a deck, and the kind of damage depends on the deck. Steel rusts, thins, and loses both strength and fastener pullout, and it rusts fastest where condensation collects on the underside or where a leak has sat. Wood and wood fiber rot and go soft, and a soft deck holds no fastener and may not hold a person. Gypsum and lightweight concrete lose strength and crumble at the fastener when they are soaked. Structural concrete is the most water-tolerant, but trapped moisture still corrodes its reinforcing and the fasteners set in it.
The deck inspection happens at tear-off, when you can finally see it. That is when you find the rusted-through steel over the wet bay, the rotted plank under the old chronic leak, the gypsum that has turned to mush. The mistake is pricing a tear-off as if the deck is sound, then discovering on the open roof that a third of it needs replacement, with no allowance in the number for it.
Plan for deck repair you cannot see. On any tear-off over a deck with a history of leaks, carry an allowance for deck replacement and a way to price it as you uncover it. A moisture survey before the job, infrared, nuclear, or a core program, tells you where the wet insulation and the likely bad deck are before you are committed.
Deck slope and drainage
Some decks are sloped and some are dead flat, and that decides whether your drainage comes from the structure or from tapered insulation on top. A structural slope is built into the frame, the joists or the slab pitched to the drains, so the deck itself runs water. A flat deck holds water unless you build slope above it, usually with tapered insulation.
Know which one you have, because a dead-flat deck with no positive drainage is a ponding roof waiting to happen, and ponding is load, leaks, and faster membrane aging. The common low-slope minimum is a 1/4 in per foot slope to drain, which on a flat deck has to be made entirely by the tapered insulation package. That tapered layer is part of the insulation and attachment story, covered in the insulation and cover board guide, but the decision of whether you need it at all comes from the deck.
Watch for deflection on long-span decks. A steel deck or a long joist can sag between supports under load and create low spots that pond even when the design slope looks right on paper. Set drains and crickets to where the water actually goes, not just where the plan put them.
The data-center and large-roof deck
On data centers and large industrial roofs, the deck is almost always steel or structural concrete, and the reason is load and uplift, not roofing preference. These roofs carry heavy and continuous rooftop equipment, big air handlers, chillers, screen walls, and they cover wide spans where the wind uplift forces are large and the consequences of a failure are severe.
Structural concrete shows up where the load, the fire rating, or the uplift demand is highest, and where the building wants the mass. Steel shows up where the span and the speed of construction favor it, usually at a heavier gauge, 20 or 18, with tighter deck-to-structure attachment to take the uplift. Either way the deck on these roofs is engineered for the equipment loads and the wind, and the roofing attachment has to match a deck that was designed first as structure.
The roofing lesson is that on these jobs the deck and its attachment are not yours to assume. The structural engineer set the deck gauge, the span, and the connection to the frame for loads the roofer never sees. Confirm the deck and the design uplift from the structural documents, and match the roof assembly tested rating to them, because on a roof this size the wind load in the corners is where the assembly gets proven or fails.
What to document
Write down what the deck is and what it means for the roof, because the deck is the assumption the whole roof design rests on, and the next person needs to know what you found. On a re-roof especially, the deck you confirmed by core cut is information that does not exist anywhere else.
| Deck type | How you attach | Key issue | Nailable? |
|---|---|---|---|
| Steel | Screws and plates into the top flute | Gauge sets the pullout; condensation rusts it | No (screwed, not nailed) |
| Structural concrete | Adhered, or drill-in anchors | New-slab moisture; needs a vapor retarder | No |
| Lightweight insulating concrete | Base-sheet fasteners made for LWIC | Holds water, dries slowly, low pullout | Yes, special fasteners |
| Gypsum | Auger fasteners in pre-drilled holes | Weak pullout, worse when wet; can deteriorate | Yes, special fasteners |
| Wood plank / plywood / OSB | Nails or screws direct | Thickness sets hold; rots when wet | Yes |
| Cementitious wood fiber | Auger fasteners; test the pullout | Modest pullout; moisture-sensitive | Yes, special fasteners |
Common mistakes
- Using a steel-deck fastener in gypsum, lightweight concrete, or wood fiber instead of the auger or base-sheet fastener those decks need.
- Roofing over a green concrete slab with no vapor retarder because it hit 28 days, then chasing the moisture damage later.
- Driving a nail or screw into a non-nailable deck and trusting it, or fastening into the open valley of a steel deck instead of the top flute.
- Ignoring the deck gauge or the cure and assuming a pullout value instead of testing it on the actual deck.
- Pricing a tear-off as if the deck is sound, with no allowance for the rotted, rusted, or soaked deck you find when the old roof comes off.
- Borrowing a fire-rated or wind-rated assembly listed for one deck and building it on a different deck.
- Recovering over a wet or deteriorated deck, or adding a second roof load to a marginal deck.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The deck lives at the meeting point of the structural standards and the roofing standards, so more than one body governs it. On the structural side, the Steel Deck Institute, SDI, sets the design and the gauges for steel roof deck, currently consolidated in the ANSI/SDI standard for steel deck. The deck attachment to the structure and its load capacity come from there and from the structural engineer.
On the roofing side, FM Global data sheets and approvals tie the deck to the wind uplift assembly, including the fastener pullout and the deck-to-structure requirements, and ASCE 7 sets the design wind uplift the assembly has to meet. NRCA guidance covers the deck types, the nailable and non-nailable split, and the roofing-over-the-deck details. The ANSI/SPRI FX-1 procedure is the field pullout test FM and manufacturers recognize for confirming what a deck actually holds.
For fire, the assembly ratings come from UL and FM listings, and the building code sets what the construction type and use require, by the adopted edition. For new concrete moisture, groups like NRCA, IIBEC, and MRCA have published guidance pointing to a low-perm vapor retarder over the slab. Cite the standard that controls the point you are making, and confirm the gauge, the pullout, the perm rating, and the assembly rating against the manufacturer listing, FM, and the adopted code, because those are the numbers that govern, not the rule of thumb.
Units, terms, and conversions
The deck shows up in a few units and a few names across the structural drawings, the roofing submittal, and the fastener catalog, so the same deck can read differently depending on who drew it.
Steel deck thickness is given as gauge, where a lower gauge number is thicker steel, and sometimes as a decimal thickness in inches or as a metric thickness in millimeters. Pullout and uplift are in pounds-force, psf for area loads, or kept in metric as newtons and pascals. Wood and panel thickness is in inches or fractions, often as a span rating. Vapor permeance is in perms, where a lower perm is a tighter vapor retarder. Slope is in inches of rise per foot of run, commonly written as 1/4 in per foot.
- Deck (substrate)
- The structural surface that spans the framing and that the roof system attaches to
- Gauge
- Steel sheet thickness; a lower gauge number is thicker steel and holds more pullout
- Flute / rib
- The corrugation in a steel deck; you fasten into the top flute, not the open valley
- Nailable deck
- A deck that accepts fasteners; some only with special auger or base-sheet fasteners
- Pullout (withdrawal)
- The force needed to pull a fastener out of the deck, set by deck type and condition
- LWIC
- Lightweight insulating concrete, a poured deck over form deck that gives slope and holds water
- Perm
- Unit of vapor permeance; a vapor retarder over concrete is commonly below 0.01 perm
FAQ
What is a roof deck?
A roof deck is the structural surface that spans the framing and carries the roof system above it. It holds the insulation, the membrane, and the loads, and it transfers the wind uplift into the building frame. The deck type, steel, concrete, gypsum, wood, or others, decides how the roof is attached and what assemblies are allowed.
What is the most common commercial roof deck?
Steel is the most common low-slope commercial roof deck. It is cold-formed corrugated sheet, usually 22 gauge, fastened with screws and plates into the top flute. The gauge sets the fastener pullout, and the cold underside can condense moisture, so humid-interior buildings need vapor control over the deck.
Can you roof over new concrete?
You can roof over new concrete, but the 28-day mark is a strength milestone, not a dryness one. A slab can be at full strength and still wet enough to damage the roof. The common solution is a low-perm vapor retarder, often below 0.01 perm, over the slab, confirmed against the manufacturer and the project documents.
What is a nailable deck?
A nailable deck accepts fasteners driven into it; a non-nailable deck does not, so the roof is adhered or anchored. Wood, gypsum, cementitious wood fiber, and lightweight insulating concrete are nailable, though all but wood need special fasteners. Steel and structural concrete are non-nailable, with steel screwed into the flute and concrete adhered or drilled.
Steel deck or concrete deck: which is better for a commercial roof?
Neither is better; they solve different problems. Steel is lighter, faster, and the default on warehouses and steel-frame buildings, fastened with screws into the flute. Structural concrete is heavier, stronger, noncombustible, and better for load, fire, and uplift, but it is adhered and a new slab needs moisture control before roofing.
Why does steel deck gauge matter for fastener pullout?
Gauge is the steel thickness, and a lower gauge number means thicker steel that grips a fastener harder. Pullout climbs steeply with thickness, more than doubling from thin 26 gauge toward 18 gauge. Thin deck strips out and lets screws back out under wind cycling, so the gauge sets how many fasteners the design needs.
Can you nail to a gypsum or lightweight concrete deck?
Not with ordinary nails or screws. Gypsum, lightweight insulating concrete, and cementitious wood fiber are nailable only with fasteners made for them, auger types or expanding base-sheet fasteners, often set in a pre-drilled hole. Their pullout is low and depends on cure and condition, so test it on the actual deck before setting the fastener pattern.
How do I know if a deck is bad before a recover?
You cannot fully know until tear-off, but you reduce the surprise with core cuts, test openings, and a moisture survey, plus a pullout test where the roof is mechanically attached. Look for rust, rot, soft spots, deflection, and trapped moisture. Carry a deck-replacement allowance, because pricing a recover as if the deck is sound loses money.
What deck do you need for a fire-rated roof assembly?
The fire rating is an assembly rating and the deck is part of it. Wood and cementitious wood fiber are combustible; steel, structural concrete, and gypsum are noncombustible. A Class A assembly is listed for a specific deck, so build the one listed for the deck you have. Do not borrow a rating across deck types.
People also ask
Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.