Large buildings with flat roofs typically are roofed with some type of a roll product. Such roofing is relatively easy to apply and inexpensive. The concern with these products centers around the number of seams and lap joints that must be sealed to maintain a watertight roof system.
There is an option for roofing that is seamless — spray polyurethane foam. It’s not as common a type of roof, but spray foam roofing has definite advantages. Read on to learn more about spray foam roofing and how it can benefit your building.
SPRAY FOAM ROOFING BASICS
Spray foam gets its name from the application process. Contractors use a pressurized machine with a hose to spray the foam in liquid form over the surface of the roof. The machine consists of two tanks each with a different component — the products are heated in the tanks and atomized and mixed as they leave the application gun.
The foam coats the surface of the roof and expands, then solidifies. As it does so, it creates a seamless system that seals around the perimeter, so no flashing is required. Contractors can apply foam over the deck sheeting (plywood or OSB) of new construction, or apply it as an overlay over an existing roof system.
After foam application, the new roof system is finished with a protective coating, which protects the foam from the damaging effects of the sun’s ultraviolet (UV) rays. The coating may be an elastomeric acrylic, silicone, or even polyurea, each of which are available in a variety of colors.
ADVANTAGES OF SPRAY POLYURETHANE FOAM
Spray polyurethane foam provides a number of benefits.
It is seamless, with no joints to allow water or air to pass into the building beneath. It can be applied at varying depths to minimize ponding of special value to older buildings that may have areas of structural settling. Since it is spray-applied, it can be applied over unusual roof shapes with ease. It is lightweight (with coating, approximately 0.60 lbs/ft2) so can generally be installed over an existing roof system, thereby eliminating landfill costs.
Foam also aids in soundproofing, minimizing transmission of exterior noise into the building. It provides additional insulation, generally around R-7.0 with light-colored coating. This results in a more comfortable interior temperature and lower utility bills. Properly maintained, a foam roof should last decades.
SPRAY FOAM ROOFING DISADVANTAGES
Polyurethane foam must be coated to protect it from the damaging effects of the sun’s ultraviolet (UV) rays. It can be damaged by hail, birds, and bees. The type of coating applied can minimize the potential of damage by hail and insects, together with application of roof granules over the coating.
Thermal shock is the term used to describe sudden expansion/contraction of a roof system due to abrupt temperature changes. This can result in a roof system opening at seams/lap joints, pulling away from walls, and separating from penetrations. Polyurethane foam is an inert product, which neither expands nor contracts once it is cured.
Imagine a disposable foam cooler. It keeps the contents cool inside, even while exposed to heat on the outside. It doesn’t change shape, it doesn’t crack, and it looks the same. A foam roof responds the same way to heat and the sudden changes of temperature associated with monsoon rains — it doesn’t expand or shrink, so no risk of cracking or seams opening.
Annual roof maintenance is quite simple. A modern-day cowboy can go up on the roof with a caulk gun, utility knife, and good quality elastomeric or urethane sealant and easily address the minor details needed to keep the roof system in good condition between periodic recoats.