The roof truss is the entire triangle-like structure of a roof, including the upper chord beams for supporting the roofing and the lower chord for attaching the ceiling to, along with any bracing material or gussets in between. This triangular space is generally the crawlspace or attic space in most homes. Insulation is usually installed against the top of the roof line amidst the rafters, or on the bottom next to the ceiling, or both. Many roofs are also required to have ventilation ports installed in the eaves or other areas to ventilate the insulation, so make sure you consult your building codes.

    The most difficult part of the roof to insulate is near the eaves, where the roof begins to overhang away from the house. These areas are sometimes too small and sometimes too long to reach with normal batt or fiberglass insulation. In this case spray foam insulation can work very well, and if you want you can use the same insulation for the rest of the roof as well, but be careful to have a divider that separates the insulation from any crawlspace openings and from air vents that have access to the eaves, since spray foam is often airtight.

Spray Foam Insulation

    Spray PE foam is a chemical-based insulation that is sprayed from tanks as a wet solution. This way, the spray nozzle can be used to reach the tiny spaces or low eaves of a roof. Once you have the foam sprayed it will immediately expand to many times its size and then dry, forming a strong barrier against water, heat and air. This barrier is also useful for plugging any unwanted holes, protecting against pest intrusion and sealing any possible water leaks. It compensates for any lack of end dams along the eaves, which can allow the wind to tear at other types of insulation.

    There are many different types of spray foam insulation, including green-based kinds that are more expensive but are made out of less harmful products like soy rather than the common plastic-based solutions. Timing is an important consideration in spray insulation. If you use spray foam on a new roof, it may not be as effective, because the wood is still fresh and moist; over time it will dry, pulling away from the foam and creating pockets of space around the insulation. To avoid this, install spray insulation a year or two after the roof is built.