Spray polyurethane foam (SPF) roof field guide for commercial crews

What an SPF roof is, and where it fits

A spray polyurethane foam roof is a two-component plastic foam sprayed onto the roof as a liquid that expands and cures in place into a hard, closed-cell surface, which is then covered with an elastomeric coating. The foam is the insulation and the waterproofing body. The coating is the weather and ultraviolet protection. Neither half is the roof on its own. Together they are a monolithic surface with no seams, no laps, and no fasteners through the membrane.

The thing that sells SPF on a commercial building is recover. The foam bonds to the existing roof, so on the right substrate you spray over the old metal, built-up, or single-ply roof instead of tearing it off, which keeps the building dry through the work and keeps a landfill from filling with the old roof. The foam follows every shape it lands on, rises up walls and around curbs as its own flashing, and adds real insulation while it does it. Closed-cell roofing foam runs about 6 to 7 R per inch, so the insulation is a selling point on its own, not a side effect.

Where it goes wrong is the half people forget. The foam is not a finished roof. Leave it bare in the sun and it darkens, gets chalky and friable, and erodes from the top down. The coating is what stops that, and the coating wears, so the roof has to be recoated on a cycle to stay a roof. An SPF roof is a renewable system, but only if somebody renews it. That obligation is the part that gets dropped, and it is where most SPF roofs that failed actually failed.

Does a spray foam roof need a coating?

Yes. A spray foam roof needs a coating, and it is not optional. The foam handles insulation, slope, and the monolithic waterproofing body, but polyurethane foam has no resistance to ultraviolet light. Left exposed, the surface discolors within weeks, the top skin turns friable, and the foam erodes at a rate on the order of a sixteenth of an inch a year depending on climate. The coating, or a layer of mineral aggregate, is what protects the foam from the sun and the weather. This is confirmed across SPF industry guidance, not a maybe.

Think of the system as two specs that have to both be met. The foam is specified by density and total thickness, commonly closed-cell roofing foam at 2.5 to 3 lb per cubic foot built to a thickness that delivers the insulation and the slope. The coating is specified by chemistry and dry mils over the foam, commonly silicone or acrylic or polyurethane at a published dry film thickness with granules broadcast into the top. The coating side of this overlaps the companion guide on roof coating mil thickness and yield, which carries the wet-to-dry math and the coverage in detail.

The blunt version: a foam roof with no coating is a countdown, not a roof. The foam can be installed perfectly, on-ratio, full thickness, with a smooth surface, and it will still be gone in a few years if it is never coated. Whoever owns the building owns the coating, the same way they own changing the oil. The roof lasts as long as the coating is maintained and not one season longer.

The chemistry: A-side, B-side, and the rise

SPF is made on the roof from two liquids that react when they meet. The A-side is the isocyanate. The B-side is a polyol resin blend that carries the catalysts, the blowing agent, and the flame retardants. They are pumped separately, heated, and combined only at the spray gun, where they mix, react, and foam within seconds. Roofing foam is mixed at a 1:1 ratio by volume, and holding that ratio is the whole game, because off-ratio foam does not cure to its rated properties.

Roofing SPF is closed-cell foam, which is what gives it its strength, its low water absorption, and its high insulation value. As the two parts react they release a gas that blows the cells and the foam rises off the substrate, expanding many times its liquid volume and setting up in seconds. Closed-cell roofing foam cures to a density around 2.5 to 3 lb per cubic foot, far denser and harder than the open-cell foam used inside walls. ASTM C1029 is the material specification for spray-applied rigid cellular polyurethane insulation, and roofing typically uses its Type III foam, with Type IV where higher compressive strength is called for.

Density is not a detail. The 2.5 to 3 lb foam carries the compressive strength to take foot traffic and the closed-cell content to keep water out, with closed-cell SPF held to a maximum water absorption around 5 percent under the material standard. Spray a lighter, lower-density foam to save material and you get a softer roof that crushes underfoot, soaks up water, and does not hold up. The density is a spec, confirmed by core samples at closeout, not a target you eyeball off the gun.

How much insulation does an SPF roof add?

Closed-cell spray foam roofing adds roughly 6 to 7 R per inch, which is among the highest insulation value per inch of any roof material. At about R-6.5 per inch, a 2 inch foam roof adds around R-13 and a 3 inch roof adds close to R-20, before you account for the rest of the assembly. That is real insulation built into the waterproofing layer, which is the part owners and energy engineers care about.

The insulation is also why SPF makes sense as a recover on an under-insulated building. The existing roof might have almost no thermal value, and the foam adds it without a separate insulation board, fasteners, or a vapor layer, because the closed-cell foam is its own insulation and its own air seal in one pass. On an energy retrofit, the foam thickness gets sized to the R-value target the code or the owner wants, then checked against the slope the foam also has to build.

Hold the claim honestly. The 6 to 7 per inch is the foam's value at install, and like any insulation it is the assembly R-value the energy code cares about, so the total depends on the foam thickness and the rest of the deck. The number to carry is the per-inch figure, then multiply by the installed thickness and confirm the assembly against the adopted energy code. The coating adds reflectivity and a cool-roof benefit, but the R-value lives in the foam.

Substrate and prep: what the foam has to bond to

SPF goes over metal, built-up, concrete, and many existing roofs, and the foam's strength is that it bonds chemically to the substrate across the whole surface instead of being mechanically fastened. That bond is also the whole risk. The foam adheres to what it touches, so it adheres to dirt, oil, rust, and moisture just as readily as it bonds to a clean deck, except those bonds fail. The prep is where an SPF roof is won or lost.

Clean, dry, and sound is the rule, in that order. The substrate gets cleaned of dirt, oils, loose coatings, and biological growth, commonly by power washing, then it has to dry completely before any foam goes down. Metal roofs need rust addressed and loose fasteners reset, because foam over active rust lifts as the rust keeps working. Many substrates need a primer for the foam or the coating to bond, and the way you settle whether you need one is an adhesion test, not an assumption. Concrete and existing membranes each have their own primer and compatibility questions, so confirm the system against the foam manufacturer for that substrate.

Moisture is the quiet killer on a recover. Trapped water under the existing roof, or a wet substrate at spray time, gets sealed in under a monolithic foam layer that water cannot escape, and it blisters, debonds, and rots from underneath months later when you are long gone. On a built-up recover the assembly gets checked for moisture, and saturated insulation gets cut out and replaced before the foam goes on. Spray foam over a wet roof and you have not recovered it. You have buried the problem and signed your name to it.

Can you spray foam over an existing roof?

Yes, recovering an existing roof without a tear-off is the main reason SPF gets specified. The foam bonds directly to a clean, dry, sound existing roof, so on metal, built-up, and many single-ply roofs you spray over the old roof instead of removing it. That keeps the building watertight through the work, cuts the disposal cost and the landfill load, and adds insulation the old roof never had. On a metal roof the foam bonds across the whole panel and fills the seams and around the fasteners that were leaking, turning a panelized roof into a monolithic one.

The catch is the same as any recover. The existing roof has to be a substrate worth bonding to. A metal roof gets power washed and the rust and fasteners dealt with. A built-up roof gets checked for trapped moisture, with wet insulation cut out, because you cannot spray a watertight skin over saturated felts and expect it to last. Some existing surfaces, like loose gravel, ballast, or a failed coating, have to be removed or the foam bonds to the loose layer instead of the roof. The structure also has to carry the added load and the live load of the crew and the rig.

There is also a code question on recover. Most codes limit a building to two roof coverings, so a building already on its second roof may need a tear-off before SPF regardless of how good a recover would be. Confirm the number of existing layers and the structural capacity before you bid the recover, because the cheap, fast no-tear-off job is only cheap and fast if the building actually qualifies for it.

The recover case is strongest on the large, low-slope flat roof on a warehouse, a distribution center, or a data center. The monolithic surface has no seams to fail across acres of roof, the foam adds insulation that cuts cooling load on a building running hot inside, and the spraying happens over the existing roof while the building stays in operation underneath. On a low-slope membrane the same building might use TPO, PVC, or EPDM, and the comparison between single-ply and SPF is the kind of selection decision covered in the companion guide on choosing a low-slope membrane. The case for SPF on the big roof is usually recover plus insulation plus no seams, weighed against the recoat the owner has to commit to, and on a mission-critical building you stage the work to keep the deck covered and manage overspray hard near the intakes and equipment.

What is the weather window for spraying foam?

The weather window is the set of conditions the foam needs to bond and cure, and it is tight enough that it drives the schedule. Spray outside it and the foam either does not bond to the substrate or does not cure to its rated properties, and you do not always find out until later. The controlling limits are substrate temperature, ambient temperature, the dew point margin, humidity, and wind. The foam manufacturer sets the exact numbers, and the manufacturer governs over any rule of thumb.

The dew point is the one applicators skip and regret. The substrate has to be dry and commonly at least 5 degrees F above the dew point before and during the spray, because a substrate at or below the dew point has a film of condensation on it you cannot see, and the foam bonds to that water instead of to the roof, then debonds. Check surface temperature and dew point with a meter, first thing in the morning and late in the day when the roof is coolest. Substrate temperature commonly needs to be above about 50 degrees F, with the ambient inside the product's range, often roughly 40 to 90 degrees F, and humidity below about 85 percent.

Wind is the other hard limit, for two reasons. Wind disrupts the spray pattern so the foam mixes and lands unevenly, and wind carries overspray off the roof onto everything downwind. Common practice keeps application below roughly 12 to 15 mph without a windscreen, higher with one, but the overspray exposure makes a still day worth waiting for. In the northern half of the country this window closes the job to roughly the warmer months, so an SPF schedule plans around the weather, not the calendar.

The rig: proportioner, heated hose, and the gun

SPF is sprayed off a proportioner, the machine that meters the A-side and B-side, holds them at temperature and pressure, and pushes them through the hose to the gun. The proportioner is what enforces the 1:1 ratio, commonly held within about plus or minus 5 percent by volume, and an off-ratio machine makes off-spec foam no matter how good the applicator is. The drums, the supply pumps, the heaters, the hose, and the gun are one system, and the system has to be dialed in before the first pass.

The chemicals are heated to spray, commonly into the range around 115 to 130 degrees F, and pumped at high pressure, often roughly 800 to 1500 psi, so they atomize and mix completely at the gun. The hose is heated for its whole length to hold that temperature out to the gun, and roofing hose runs can reach a few hundred feet to reach across a large roof. Lose hose heat or drop pressure and the mix goes off, the foam comes out wrong, and the surface shows it.

The gun mixes the two streams at the tip and is cleaned and maintained constantly, because the reaction starts the instant the parts meet and the gun fouls if it is neglected. The applicator reads the foam coming off the gun the way a welder reads a puddle: color, rise, and surface texture tell you whether the ratio and the temperature are right in real time. A good SPF crew is a machine operator and a sprayer working the same rig, and the daily ratio and temperature checks are part of the job, logged, not assumed.

Applying the foam: passes, lifts, and slope

The foam is built up in passes, called lifts, not laid down in one thick layer. The proper application rate is commonly a minimum of about 1/2 inch and a maximum of about 1 inch per lift, with the total foam thickness built up across multiple passes to the design thickness, commonly a minimum around 1 to 1.5 inches and thicker where slope or insulation demand. Each lift has to set before the next goes on. Spray it too thick in one pass and the foam scorches in the middle, traps heat, and cures with voids and a poor bond between layers.

The applicator builds the roof as the passes go down. Because the foam follows the gun, you can build positive slope and drainage into the surface, fill low spots, taper to drains, and run crickets behind curbs, all in foam, without separate tapered insulation. The foam also rises up every wall, curb, pipe, and penetration as its own flashing, which is the monolithic, self-flashing detail that makes SPF watertight at the transitions where other roofs leak. There is no separate flashing membrane to lap and seal, because the foam wraps the penetration in one continuous skin.

Pace and overlap matter. The applicator works in passes that overlap so the foam ties together with no cold joints, holds a consistent thickness, and leaves a surface the coating can bond to. Build it thin and even, lift on lift, slope where the water has to go, and the result is a continuous insulating surface drained to the outlets. Rush it, run thick passes, or leave ridges and voids, and you have created the defects the coating then has to live with.

What foam surface texture is acceptable?

The acceptable SPF surface is smooth or what the trade calls orange peel, including a coarse orange peel. That surface is tight enough for the coating to wet out and bond, and it sheds water and stays cleanable. The texture you do not accept is popcorn or anything rougher, because the deeper the texture, the more the foam surface is open and broken, the more coating it drinks to cover, and the more it cracks and lets water and UV reach the foam.

The names track how far the surface degraded from smooth, and applicators sort them: smooth and orange peel are good, coarse orange peel is the edge of acceptable, and verge-of-popcorn, popcorn, and tree-bark are progressively worse and get rejected or cut out. A rough surface is a symptom, usually of spraying too cool, in too much wind, or off-ratio, so the texture also tells you the spray conditions were wrong. Fix the cause, do not just coat over the rough foam.

Texture is what an inspector reads first, because it is visible from across the roof and it predicts coating failure. A popcorn surface needs extra coating to bury the peaks and still cracks at them, so the cheap move of coating a rough roof costs more coating and fails sooner. Where the foam surface is too rough to coat, the answer is to grind or recoat the foam to a sound, smooth-enough surface, not to bridge it with coating and hope. The acceptable texture is in the manufacturer's and SPFA guidance for a reason.

Building slope and drainage in foam

One advantage of SPF that often pays for itself is slope. Because the foam is built up pass on pass, the applicator can add positive slope, taper to the drains, and build crickets and saddles behind curbs and between drains directly in the foam, on a roof that was dead flat and ponding before. Standing water is hard on any roof and on the coating in particular, so draining the roof is part of making it last, not a luxury.

Slope built in foam is still slope built in foam, not a structural fix. If the deck sags or the drains sit high, the foam can correct the surface drainage to a point, but a major slope correction in foam gets thick and expensive fast, and at some point tapered insulation under a membrane or a structural fix is the right answer. The general principle of sloping a low-slope roof to drain, with tapered insulation and crickets, is the same one covered in the companion guides on roof drainage and coating, and it applies here whether the slope is built in foam or in board.

Decide up front what the roof needs. A roof that ponds because of a few low spots is a good candidate for correcting the drainage in foam as part of the recover. A roof that ponds because the whole structure pitches the wrong way is a different and bigger job. Price the slope work for what the roof actually needs, because a coating over a still-ponding roof buys time, not a fix.

The coating over the foam: chemistry, mils, and granules

The coating is the elastomeric layer that protects the foam from UV and weather, commonly silicone, acrylic, or polyurethane, applied to a published dry film thickness over the cured foam. Silicone is the common call where the roof ponds, because it does not break down under standing water. Acrylic is a value option where the roof drains. The coating is specified by dry mils, and SPFA guidance commonly calls for a minimum around 20 mils of silicone over the foam, with as much as 40 mils where the chemistry, the ponding, or the warranty demands it. The wet-to-dry math and the coverage that turns those mils into gallons are in the companion guide on roof coating mil thickness and yield.

Granules are broadcast into the wet top coat while it is still tacky. They add walkability and impact resistance, give the surface UV and weather protection, embed a wear layer so foot traffic and hail do not cut straight to the foam, and they discourage birds from pecking the soft foam. The granules get rolled or broadcast at the manufacturer's rate into the final coat so they key into the coating and stay put. A coated foam roof with granules is the standard finished system, not a coated foam roof alone.

The coating is also the renewable part of the system, which is the whole maintenance model of an SPF roof. The coating wears under sun and weather and gets recoated on a cycle to keep the foam protected, commonly every 10 to 15 years depending on the coating and the mils, with a recoat often applied at a lighter dry film, around a minimum of 10 mils with fresh granules, over a cleaned and prepped existing coating. The dry mils set the warranty term the same way they do on any restoration coating, so confirm the mils and the recoat interval against the coating manufacturer's system.

Flashing and penetrations: the self-flashing detail

Penetrations and transitions are where most roofs leak, and they are where SPF has its strongest detail. The foam is sprayed up and around every pipe, curb, drain, wall, and projection in the same continuous pass as the field, so the flashing is the same monolithic foam as the roof, with no separate flashing membrane, no metal counterflashing to lap, and no sealant joint to fail. The foam wraps the penetration in one skin, then the coating goes over all of it as one surface.

That self-flashing detail removes the seams and laps that are the usual failure points, but it does not remove the need to detail. The foam has to be built up cleanly at the base of the penetration with positive slope away from it so water sheds and does not pool against the pipe, and the coating and reinforcement have to cover the transition at full mils, because the inside corners and the base of a curb move and work the coating hard. Sharp inside corners get a cove of foam so the coating is not asked to bridge a knife edge.

Where SPF ties into something it cannot bond to, like a wall cap, a metal edge, or a different roof system, that joint gets a real termination detail with the right sealant or flashing, because the monolithic foam ends there and the edge becomes a seam again. The strength of the self-flashing field does not carry to the perimeter and the tie-ins, so those still get the attention any roof's edge needs.

Overspray protection and the liability

Overspray is the single biggest off-roof risk on an SPF job, and it is a real liability, not a nuisance. Atomized foam carried on the wind lands as a fine grit that bonds permanently to whatever it touches: cars, windows, HVAC units, signage, the building next door, and the parking lot. It does not wash off. Overspray claims on cars and adjacent property are a known source of SPF lawsuits, and they are entirely preventable, which is exactly why they are so costly when they happen.

The protection is masking and wind control. Mask and tarp everything downwind that overspray could reach, including rooftop units, skylights, vents, walls, and the perimeter, and shut down or cover air intakes so foam mist is not pulled into the building. On the ground, move or cover vehicles and protect adjacent property, and put up windscreens at the roof edge. The wind limit in the weather window is as much about overspray as it is about the foam quality, and on a marginal day the right call is to wait.

Walk the property before you spray and after. Document what is downwind, what got masked, and the wind conditions, and notify the building owner and neighbors before the work. A cheap morning of masking and a windscreen is nothing against repainting a row of cars, and the crew that treats overspray as a paperwork item finds out the hard way that a judge treats it as damages.

Inspection and QC: cores, mils, and adhesion

Quality control on an SPF roof checks the things that decide whether it lasts: the foam thickness and density, the bond, the coating mils, and the surface texture. The honest check on the foam is a core sample, a plug cut through the foam and measured for total thickness and, in the lab or by density, for the cured density against the spec. Cores get taken on a grid across the roof and patched, because thickness and density drift with the applicator and the conditions, and an average that meets spec can still hide a thin or light area.

The bond gets verified with an adhesion or pull test, commonly a fixture bonded to the cured surface and pulled to confirm the foam is bonded to the substrate and the coating is bonded to the foam, to the strength the manufacturer requires. A roof that reads thin on the cores, light on the density, or weak on the pull test fails the check no matter how good it looks from the ladder. The coating gets its own check, with wet mils read on a grid during application and dry mils confirmed against the spec the warranty is written to.

The texture is read across the whole roof, because a popcorn or tree-bark surface predicts coating failure even where the mils are right. The inspector, often the manufacturer's technical rep on a warranted system, looks at prep and primer, foam thickness and density from the cores, the adhesion, the coating mils, the surface texture, and the details at the penetrations and edges. Keep the daily ratio and temperature logs, the core and pull results, the wet-mil readings, and the photos, because the warranty is a document and the inspection is how the manufacturer confirms the document is true.

How often do you recoat an SPF roof?

An SPF roof is recoated about every 10 to 15 years, depending on the coating chemistry, the dry mils originally applied, and the climate. The recoat is what makes SPF a renewable roof instead of a tear-off-and-replace roof. The coating wears under sun, weather, and traffic, getting thinner over the years, and before it wears through to the foam it gets cleaned, prepped, and recoated, often at a lighter dry film with fresh granules, which resets the protection and extends the roof another cycle. Done on schedule, the foam underneath can last for decades.

This is the owner's obligation, and it is the part that gets dropped. The roof gets installed, the warranty gets filed, and ten years later nobody recoats because nobody told the next facility manager that the roof has a maintenance step. The coating wears through, the foam sees UV, and the renewable roof becomes a failed roof for want of a recoat that costs a fraction of a replacement. The recoat is not optional maintenance any more than the original coating was optional.

Inspect the coating before it fails, not after. A roof inspection looks at the coating thickness, the granule cover, the wear at the traffic paths and the south-facing slopes, and the details, and it catches a coating getting thin while a recoat is still all it needs. Once the foam is exposed and degrading, the fix is no longer a recoat. The renewable model only works if somebody is watching the coating and recoats on the cycle the manufacturer set.

The recoat cycle is also what keeps the warranty alive, so read what the warranty covers before you sell it. The term ties to the coating dry mils the same as any restoration coating, with more mils buying more years, and it commonly assumes the roof gets inspected and recoated on schedule. A warranty that requires recoats and inspections is void the day the owner stops doing them, which is the most common way an SPF warranty quietly lapses. Know whose warranty it is, too: the manufacturer warrants the materials and, on a system warranty, the watertightness when an approved applicator installs to spec and the roof passes the closeout inspection, while the contractor warrants the workmanship.

Set the owner's expectation in writing. The roof comes with a maintenance obligation, the recoat cycle, and an inspection schedule, and the warranty depends on meeting them. The cores, the pull tests, and the mil readings from the install are what release the manufacturer's warranty, so the records you kept are the evidence the system was built to spec. An SPF roof that is inspected and recoated can last decades. An SPF roof that is installed and forgotten is a claim waiting for a denial, because the maintenance the warranty required never happened.

Fire rating, ignition barriers, and the code

SPF is a foam plastic, so the code treats its fire performance carefully, and the requirements come in a few layers. The foam used in roofing commonly has to meet a flame spread index of 75 or less under ASTM E84, which is the surface burning test the building code calls out for SPF. The finished roof covering also has to meet an external fire rating, Class A, B, or C, tested under UL 790, which is the same external fire test, ASTM E108, used for any roof covering. The class required depends on the building and the jurisdiction.

Inside the building, foam plastic generally needs separation from the interior. On a roof over a structural deck the deck itself often provides that separation, but where foam is exposed to an occupied space the code calls for a thermal barrier or, in some assemblies, an ignition barrier, with the thermal barrier verified by a fire test such as ASTM E119. This is a code detail that depends entirely on the assembly and the occupancy, so it gets confirmed against the adopted code for the specific building, not assumed from the roof system alone.

Insurance and wind ratings ride alongside the fire rating. FM Global and UL list SPF roof assemblies for fire and for wind uplift, and a building insured to an FM standard will specify the listed assembly, the foam, the coating, the substrate, and the attachment as a system, because the rating belongs to the assembly, not the foam alone. Confirm the fire class, the assembly listing, and any thermal or ignition barrier requirement against the adopted building code, the insurer, and the project spec before you bid the system.

What to document

The record on an SPF roof is what proves the system was built to spec and the warranty is earned, and it is the difference between a paid claim and a denied one years out. The foam and the coating both cure invisible, the thin spot and the off-ratio batch do not announce themselves, so the daily logs and the core data are the only evidence the roof is what the spec demanded. Capture it by area as you work, not from memory at the end.

Record the area, the foam thickness and the cured density from the cores, the coating chemistry and the dry mils, the adhesion or pull test results, and the surface texture, along with the substrate and prep, the primer used, the daily ratio and temperature checks, the weather, and the granule rate. Carry the actual material used back against the takeoff so the next estimate is calibrated. The table below is the core of the closeout package, the same data the manufacturer's rep checks before releasing the warranty.

Common mistakes

• Leaving the foam bare or under-coated, so UV chalks and erodes it within a few years.
• Spraying outside the weather window, especially within 5 degrees of the dew point, so the foam bonds to condensation and debonds.
• Letting overspray drift onto cars, units, or adjacent property, which bonds permanently and becomes a claim.
• Applying thin or uneven coating, or coating a popcorn surface, so the coating cracks and the foam sees sun.
• Building no positive slope, so the roof ponds and the coating works harder than it should.
• Recovering over trapped moisture or a wet substrate, sealing in water that blisters and rots the assembly later.
• Spraying lifts too thick, which scorches the foam, traps heat, and leaves voids and a weak interlayer bond.
• Skipping the recoat on its 10 to 15 year cycle, so the coating wears through and the renewable roof fails.
• Treating overspray and dew point as paperwork instead of the two limits that cause most SPF failures and claims.

Field checklist

Standards and references

The documents that govern an SPF roof are the foam and coating manufacturer's published system and the project specification, full stop. They set the foam density and thickness, the substrate-by-substrate prep and primer, the weather window, the coating chemistry and dry mils, the recoat interval, and the warranty, and the closeout inspection runs against them. Everything below is the framework around that controlling document, so confirm the specifics against the actual products.

The Spray Polyurethane Foam Alliance, SPFA, is the industry body that publishes SPF guidelines for design, application, and quality, and its guidance on the foam, the coating mils, the surface texture, and the inspection is the trade reference. ASTM C1029 is the material specification for spray-applied rigid cellular polyurethane insulation, with roofing commonly using Type III foam, and ASTM D2842 covers the closed-cell water absorption limit. The coatings have their own ASTM specifications, including ASTM D6694 for silicone coatings used over SPF and ASTM D6083 for acrylic roof coatings, and ASTM D4414 for the wet film thickness reading. Confirm each designation against the current edition, because designations are revised and withdrawn over the cycles.

Fire and wind ratings come from the code and the listing agencies. ASTM E84 covers the foam's surface flame spread, UL 790 and ASTM E108 cover the roof covering's external fire class, and ASTM E119 covers the thermal barrier test where one is required. FM Global and UL list the assemblies for fire and wind uplift, and the NRCA gives low-slope roofing practice generally. Let the adopted building code, the energy code, the insurer's requirement, and the project spec govern, and never cite a section number you have not confirmed for the edition the jurisdiction adopted.

Units, terms, and conversions

SPF roofing carries terms from two trades, the foam side and the coating side, so the same roof reads differently across a data sheet, a spec, and a takeoff.

Foam density is in pounds per cubic foot, with roofing foam at 2.5 to 3 lb per cubic foot. Foam thickness is in inches, and R-value is per inch, around 6 to 7 for closed-cell. The A-side is the isocyanate and the B-side is the polyol resin, mixed 1:1 by volume. Coating thickness is in mils, where one mil is one thousandth of an inch, about 25.4 microns, and coverage is square feet per gallon or gallons per square, where a square is 100 square feet of roof. SPF stands for spray polyurethane foam, and the finished roof is the foam plus the coating plus the granules as one system.

SPF

Spray polyurethane foam, the closed-cell foam body of the roof, sprayed from two components

A-side / B-side

The isocyanate (A) and polyol resin (B) mixed 1:1 by volume at the gun to make the foam

Closed-cell foam

Foam with sealed cells, giving low water absorption, strength, and about 6 to 7 R per inch

Density (lb/ft3)

Cured foam weight per cubic foot, 2.5 to 3 for roofing foam, confirmed by cores

Elastomeric coating

Silicone, acrylic, or polyurethane top layer applied in dry mils for UV and weather protection

Granules

Mineral granules broadcast into the top coat for walkability, impact, and UV protection

Recoat

Cleaning and re-coating the roof on a roughly 10 to 15 year cycle to renew the protection

Self-flashing

Foam sprayed continuously up and around penetrations as its own monolithic flashing

Related tools

Calculators and readiness checks for this work

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