Crawl Space Insulation
If your home has a Crawl Space it is critical to make sure it is properly insulated. In many homes, this area has been neglected. It can be difficult to access, making it impossible for many homeowners to address common problems like missing, deteriorated, and improperly installed Insulation.

To get it right here, you may have to go back to the basics to determine where a particular Crawl Space should be insulated. The question is: do you insulate the Floor above the Crawl Space or the Foundation wall? (You always want to Insulate the Band Sill that is exposed to the outdoors.)

If the Crawl Space is vented the Floor should be Insulated. If not, then the Foundation Wall should be Insulated. Of course, it may not always be quite so simple. Many times you find a Crawl Space that has vents when it should not. Let’s dig further into the fundamentals. In warm climates, a crawl space should be vented so that moisture can escape. In cold climates, a Crawl Space should not be vented because the ventilation brings the cold air into the crawl space and causes cold floors. Who wants to live with cold feet?

In cases where the Crawl Space is under a room addition that is attached to the basement it may be better if the Crawl Space is left open to the basement, bringing it into the thermal boundary. In this case you should consider insulating the Foundation Wall and the Band Sill.

Any Crawl Space should have a Vapor Barrier installed on the ground. This is usually a piece of 6 mil plastic laid out on the ground that overlaps the walls by 8” to 10”.
Foundation/ Band Sill Insulation
Foundation Insulation is often overlooked. Many people have the misperception that the foundation wall has a good R-Value, due to its thickness. The truth is, the concrete or block walls have very little R-Value. Typically a 10” thick foundation wall only has an R-Value of between 1 and 2. This results in poor insulating performance and explains why the basement is so cold in the winter.

To address this issue you need to insulate it properly. Common questions include: Where to insulate and to what R-Value and what materials are right for the job. Lets start with where:

Foundations that a a part of the Thermal Boundary should be insulated from the sill plate to 4’ below grade.

The type of material that is right for the job will vary depending on how the wall is to be finished as well as the budget for the project. If the basement wall is to be left unfinished it should be insulated with foil faced fiberglass board insulation. The foil provides the ignition barrier and has the appropriate R-Value.

If the wall is to be finished you can use Fiberglass Batt Insulation, foil faced fiberglass insulation board or open cell spray foam. Good, better and best, respectively.
Band Sill
Band Sill, which is also known as Sill box, Rim Joist or Band Joist among other things, is the area at the top of the foundation wall where the floor joist meet the rim joist. This is another area often overlooked when it comes to Insulation. Again the question is: what are the correct products to use to properly insulate this area.

Technology has had a great impact on Insulation with the development and advances in Spray Foam. The Band Sill is the one place in most homes where Spray Foam can be utilized. (With the exception of new construction.) Again, a great Thermal Boundary consists of an air tight seal and plenty of Insulation. Spray Foam accomplishes both.

Most homes were built using only Fiberglass Batt to insulate the sill box. This is the wrong approach because it does nothing to cause an airtight seal so the Fiberglass just acts as an air filter. Take a look at your home’s band sill area and see if the fiberglass is dirty or discolored. This is an indication of air flow and tells you that the sill box needs addressing.
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