Spray foam roofing (sprayed polyurethane foam, or SPF) is a flat roof built on site: two liquid components are mixed at the spray gun, expand into a rigid layer of foam with no seams, which insulates and sheds water, and are then covered with an elastomeric coating that shields the foam from sunlight. It has no seams and follows any shape, but more than almost any other roof it depends on the crew and the weather on the day it is sprayed, and its coating has to be renewed over its life. For a straight answer on whether foam suits your roof, call NEMA Roofing at 866-631-3366.
How a spray foam roof is built
- Preparation. The existing surface is cleaned, loose material and wet areas are removed, and the substrate is dried and primed where the system calls for it.
- Foam. The foam is sprayed in passes to the specified thickness. Extra foam at low spots and around drains builds in slope, which is one of SPF’s practical advantages on a roof that ponds.
- Coating. A liquid coating goes on in more than one coat, usually in contrasting colors. The California Residential Code requires the protective coating within a window of not less than 2 hours and not more than 72 hours after the foam is applied (section R905.13.3).
- Granules or walkway areas are added where the roof will be walked on.
The code sets the same minimum design slope for foam as for membranes, 1/4 inch per foot (R905.13.1), requires the foam to meet ASTM C1029 (Type III or IV) or ASTM D7425 (R905.13.2), and requires wind-resistance testing (R905.13.4). The coating must be one of three types in its table: acrylic (ASTM D6083), moisture-cured polyurethane (ASTM D6947) or silicone (ASTM D6694).
Why the crew and the weather matter so much
A membrane arrives on the roof as a factory-made sheet. Foam is manufactured in the air above your roof, so its quality depends on how it is mixed and sprayed. U.S. Department of Defense roofing criteria (UFC 3-110-03) are blunt about this: SPF roof integrity depends on proper field mixing of the components, the weather at the time of application, the texture of the finished foam surface and full coverage by the coating. They require trained, certified applicators because the foam is hard to spray at an even thickness, and they list its sensitivities:
- Moisture. Foam sprayed on a damp surface or in humid, misty conditions bonds poorly and can blister.
- Wind. The criteria give wind above 12 miles per hour as a limit; overspray also drifts onto cars and neighboring buildings.
- Sunlight. Even brief exposure to ultraviolet light degrades uncoated foam, and the damage keeps progressing until the system fails. That is why the coating goes on as soon as the foam has cured.
In practice, spray days on the coast wait for the morning marine layer to lift and the surface to dry, and a well-run job has someone checking foam thickness and surface texture as it goes. Ask how both are measured and recorded.
What spray foam does well, and where it falls short
| Strengths | Limits |
|---|---|
| No seams: the whole roof is one continuous layer | Quality depends heavily on the applicator and the conditions on the day |
| Adds insulation and roofing in one layer | The coating wears and must be renewed over the roof’s life |
| Can be sprayed thicker at low spots to improve drainage | Uncoated foam breaks down in sunlight; damaged coating must be fixed promptly |
| Follows curved and irregular shapes other systems cannot | Birds and sharp debris can damage the surface where granules are missing |
| Can often go over an existing roof that is dry and sound | Overspray has to be controlled, which limits spraying on windy days |
The federal criteria single out foam as a strong option for a leaking metal roof on a building that also needs insulation, and for curved roofs. Over a dry existing roof, the California Residential Code lists spray foam among the systems allowed as a recover without tearing off the old covering (R908.4), though not over a roof that is water soaked or deteriorated. Your own roof qualifies or not on the evidence of an inspection, not a brochure: recover or replace a flat roof covers that test.
The coating is the part you maintain
On a foam roof, the coating does the weatherproofing and the foam does the insulating and shaping. The federal criteria make two practical points: the base coat should be a clearly different color from the top coat, so that when the base color starts to show through, it is time to recoat; and the cost of recoating is a significant part of what a foam roof costs over its life. Budget for it from the start, and ask any contractor which coating type they propose, how thick, and how you will know when it is due.
The coating is also where California’s energy code comes in. When a low-slope roof is replaced or recovered, the new surface often has to meet the state’s cool-roof values, and for a foam roof that surface is the coating; a rated white coating is the usual answer. The details are in energy efficient flat roofs.
Caring for a spray foam roof
- Look over the roof after the rainy season and after any work on rooftop equipment: coating worn thin, cracks, bare foam, blisters, bird pecking.
- Any exposed foam gets cleaned and recoated quickly, before sunlight starts eating into it.
- Keep drains clear and keep foot traffic on walkway areas.
- Damaged foam is cut out, the hole filled with new foam and the patch coated; a trade maintenance manual (SPFA-127) is the reference the federal criteria point to for these repairs.
Is spray foam right for your building?
Foam makes the most sense on a roof that needs both waterproofing and insulation, on awkward shapes, and on a sound metal or built-up roof that can be covered rather than torn off. It makes less sense where no one will keep an eye on the coating, or where the budget cannot carry periodic recoating. Compare it with the membrane options in the best flat roof material for a house and with the welded PVC roofing system before deciding.
Getting a flat roof assessed by NEMA Roofing
NEMA Roofing holds CSLB license #1083283 for roofing (C-39) and general building (B) work and is bonded and insured. Wherever your building sits in Santa Barbara, Ventura, Los Angeles, Riverside or San Bernardino County, one of our five Google-verified locations (Santa Barbara, Oxnard, Woodland Hills, Tarzana and Downey) puts a NEMA team near you; the Ventura County towns we serve are one example. Start with our flat roofing services, or call 866-631-3366 to have your roof inspected and the options compared.
