Foam attic insulation is the most popular type of insulation being used on new homes for a variety of reasons. I think one of the main reasons is that it is a “new” technique and material which has a certain chic’ appeal to it. It doesn’t hurt that it also completely seals the spaces where it is sprayed helping keep out drafting air and unwanted pests like cockroaches.
There are two common methods of insulating your attic space with foam insulation – spray foam insulation in the attic floor for vented spaces and non-vented spaces. The most common in the U.S. is a highly vented attic spray foam is used where traditional fiberglass batts are between the floor joists. It is not the most effective, but it does insulate the ceiling from seasonal heat or cold. Another area that I have heard about is garage door insulation, but we really don’t recommend spray foam for this type of use.
The non-vented installation is the most effective and is achieved by applying spray foam directly to the underside of the roof between the joists, on the wall ends and soffit areas which effectively seals off the entire attic space. This helps prevent the severe temperature swings that can happen with a vented attic space. Some of the benefits of installing foam insulation this way include:
- Tests show lower energy usage on sealed attic
- Loose insulation and dust are less of a problem
- Sealing the roof is much easier than the ceiling
- Air duct leakage is much less of an issue.
If our heating and cooling units and ducts are located in the attic and/or crawl spaces (most usually are) then their radiant contact with the ducts will cause them to lose up to 10% or more of the hot or cold air flowing through them due to radiant transfer.