Spraying in Lifts on a Dry Substrate
Foam is built in layers, called lifts, each sprayed thin enough to cure evenly and stacked until the total thickness gives the insulation value and slope the roof needs. The substrate has to be clean, dry and sound, so the crew sweeps, power-washes where a gravel surface demands it, and replaces any wet board before the rig is switched on. A slow, controlled pass leaves a lightly textured surface that sheds water and takes coating evenly, while a rushed pass leaves hollows that hold water against the foam.
Weather decides when the work happens. Foam cannot be sprayed in wind, on a wet surface, or in a fog, and Santa Ana days in the foothills are the worst of the three, since a gust carries overspray onto parked cars and neighboring glass. We watch the forecast and tape off or screen everything below the roofline, then spray in the dry months, when Pasadena sees almost no rain and the heat helps the foam cure. With no tear-off, tenants on an occupied building hear a rig for a day or two, not a month of demolition.
Terminations, Counterflashing and Sheet Metal
Because foam is sprayed, it flows into every corner without a seam, and that is exactly why the sheet metal around it deserves attention. At a parapet the foam is carried up the wall and stopped under a counterflashing set into a reglet, with a sealant joint tooled where the metal meets the masonry so water cannot slip behind it. We hand-form copings, edge metal and scupper boxes to fit the foam thickness, since a thicker roof needs taller metal.
The brick-facade buildings of Old Pasadena are a good example of why this matters. Where a parapet cap was cut for a thin roof, it cannot take an extra few inches of foam without rework. We rework those terminations so the roof edge still sheds water away from the brick, and we replace the failing edge metal and coping before the foam goes down, not after. Equipment curbs and supports get raised the same way, so flashing clears the new surface.
Class A Assemblies and the Cool Roof Value
Fire rating belongs to the whole assembly, not to the foam by itself, so a Class A result depends on the foam, the coating and the substrate being a tested combination. After the Eaton Fire in January 2025, with Santa Ana gusts forecast at 60 to 80 miles an hour, owners in the Arroyo Seco and upper Hastings Ranch, where Pasadena's mapped fire zones sit, have reason to ask about this directly. In those mapped fire hazard zones, state rules call for a Class A covering on a new roof or when more than half of an existing one is replaced, and we match the foam system to a listed assembly before quoting.
Heat is the other side of the same decision. The cool roof numbers for a low-slope commercial roof under the 2025 code are an aged reflectance of 0.63 and an emittance of 0.75, with an SRI of 75 accepted instead, and they bind a new roof as well as any alteration touching over half of it or 2,000 square feet, whichever is less. A white acrylic or silicone topcoat is what gives a foam roof that value, and it also helps a building through a 100 degree October heat advisory.
Recoating, Walk Traffic and Slow Wear
A foam roof needs regular coating maintenance, and replacement is still appropriate when the foam or substrate has deteriorated beyond repair. Every few years we inspect the whole surface, clean it, repair dents and pecked spots, and add a fresh coat so the foam is never exposed. Done on schedule, the work is small. Skipped, it ends in a tear-off that could have been avoided.
Foot traffic is the thing owners forget. A roof that carries lab exhaust fans or the cooling plant for an office building gets walked far more than a warehouse roof, and foam does not like boots. We set walkway pads along the routes technicians use and leave wide clearance around serviced equipment. When heat and UV damage has already started, the coating and the cracked spots are repaired before they become a replacement.
Commercial Roofing Questions
Is sprayed foam a good choice over my existing built-up roof?
It can be, when the old roof is dry and sound enough to hold the foam. Foam bonds to a clean gravel or smooth built-up surface and adds insulation without a tear-off, which is attractive for a tenant-occupied building. The test is moisture and attachment, so we survey and cut cores before we recommend it, and we say plainly if the old roof needs to come off. A recover over the existing roof only works on a dry base.
How does foam compare with a single-ply membrane on a hospital or lab building?
Foam gives a continuous, joint-free surface and handles odd shapes and many penetrations well, which suits rooftops crowded with ducts and exhaust stacks, as on a hospital or lab building. A single-ply sheet goes down faster on big open roofs and has more predictable foot-traffic wear.
Why does foam need a coating at all?
Ultraviolet light breaks down bare polyurethane quickly, and the foam itself is not waterproof against standing water for long. The coating, whether silicone, acrylic or a granule-surfaced urethane, is what protects it and what gives the roof its reflectivity. Choosing the coating is as important as choosing the foam, which is why we plan the two together.
Can foam be applied in the middle of a Pasadena winter?
Only on the dry days. February is the wettest month here at about four inches of rain, and foam will not cure properly on a damp deck or in a drizzle. We usually schedule foam in the long dry stretch from late spring through fall, and we keep a patch kit and temporary dry-in on hand for any leaks that cannot wait for the weather.
