Roof Insulation Requirements

“Requiring More These Days”

Roof insulation needs vary depending on what part of the country you live in. The image of the United States represents zoned areas for the required R value needed in your roof / attic space. I do not recommend sprayed insulation in the roof/attic space as it will condense, causing water issues. For the purpose of this article, we are staying with rigid, fiberglass, and cellulose insulation. The code book is a bit more detailed than I am here as well, but, as promised, we keep things simple and practical. The industry is also all over the board. Marketing always minimizes the competitor’s product! In general, here are the facts:

The energy code likes when we use rigid insulation on the outside of our shell. This means they give us a break if we put rigid above our roof joists and under our roofing membrane. There are lots of options on the market for rigid insulation, but on average

1” = R-5.5.

Rigid insulation breaks down over time, so it might start out higher.

Zones 4, 5, 6, and 7 need an R value of at least R-30.

Zones 1, 2, and 3 need an R value of at least R-25.

If we choose to blow insulation onto drywall or other supportive product inside our roof trusses, we can get: Cellulose – 1” = R-3.5, Fiberglass – 1” = R-2.5.

If we choose rolled fiberglass insulation, we can get: 1” = R-3.8 or 5.5”= R-21.

Zones 5, 6, and 7 need an R value of at least R-49.

Zones 1, 2, 3, and 4 need an R value of at least R-38.

* All vapor barriers must be on the heated side of the ceiling if used.