Spray Foam Insulation

2012 to 2017 Consumer Choice Award Winner for Insulation Contractor

The Best Way to Insulate Cathederal Ceilings


In this application the spray foam is applied directly to the underside of the roof. Because of the foams high per inch R-value as well as being an air barrier at 1 inch and a vapor barrier at 2 inches this method is also very popular in half story retrofits because of the 2x4 cathedral ceiling rafters.



Cathedral ceilings can add an element of charm and grandeur to any home, but it is important to use the proper building techniques to manage moisture and energy performance issues. Condensation in the insulated cavity space can lead to wood rot and mold, which can compromise the durability of the roof, the efficiency of the home, and health of the homeowners.

The bulk of moisture moving into any insulated cavity is driven primarily by air. The best Practice for building insulated cathedral ceilings is to create an airtight roof assembly.

By using spray foam insulation, air movement through the insulated space is stopped, so venting is not needed (unless still required by code). The sealing nature of spray foam insulation works to make the ceiling cavity airtight. This will help keep moisture-laden air from entering and condensing within the insulation or forming on the underside of the roof sheathing, and it's important for improving homeowner comfort and energy efficiency.

The traditional practice of insulating the underside of the roof has raised much debate in the building industry because 'standard' roofing and design techniques call for the cathedral ceiling to be ventilated in order to reduce moisture problems and heat build-up in the hot summer months.

As mentioned before there are 3 reasons for vents. Venting is to accommodate fibrous insulation like fiberglass, and why do those insulations need vents? Because they can only slow Heat Transfer.

Let me paint a picture for you. In the Summer the sun beats down on your roof and heats the space in your cathedral ceiling up to 60-70 degrees Celsius. That heat radiates through your ceiling and heats the cool conditioned living space below. In the winter the Heat Transfer is reversed, heat from the house is forced out instead of in. Heat will always move from hot to cold never from cold to hot.

What We Accomplished

1. We're stopping radiation and conduction right at the source, the roof line.
2. We've stopped condensation because we created a complete air/moisture barrier.
3. Since we sprayed right on the roofline every area on the house side of the foam is conditioned space be it a cathedral ceiling or a conditioned attic, the heat required to adversely affect the shingles can never again be achieved.