If your looking for ways to improve the energy efficiency of your home, you might turn to the area of your unfinished basement ceiling where the joists meet the sill plate (at the top of the wall) and the rim joist (or band board) at the edge of the house.
It’s in this area that most of the air infiltration into a basement takes place, and an area where you can make a significant improvement in the energy efficiency of your home.
Insulating Basement Joists at the Rim Is Important
The reason insulating in this area is important is because much of the heat loss in a home is due to convection – the loss of heat that is carried away by drafts whipping through the basement.
Since wood joists make imperfect joins, they are highly prone to air leaks. The area where the joists meet the rim will have literally thousands of gaps.
Ways to Insulate the Band Board
There are a number of basement insulation options to consider for this job. We chose open and closed cell spray foam for our own home. We believe spray foam is the #1 way to insulate this area and will yield the best results. Unfortunately, spray foam is expensive and generally requires a contractor for the installation. There are DIY kits available but the cost is nearly as high as hiring pro help.
Here’s a few suggestions for insulating this key area of your home:
Fiberglass: The easiest method is to obtain kraft-faced fiberglass batting (the pink stuff) and stuff it tightly in between the joists. We recommend going with an R-30 insulation as opposed to traditional R-13 wall insulation, since you’ll usually have the extra space and you want to maximize the seal. StuccoHouse just added fiberglass in their home and we’re sure it will pay dividends. You can visit that post for some great pictures of this job which only takes a few hours. You can also add to the fiberglass installation with the following:
- Great Stuff Foam: If you want to sure up the seal, before adding fiberglass you can pick up a few cans of Great Stuff spray foam and spray it into the corners and butt joints on the rim joist, sill plate, and flooring above. Use the small straw that comes with to get into small cavities.
- Caulk: As an alternative to Great Stuff, caulk can be used to seal the gaps. Great stuff has the advantage of finding and entering small cavities as it expands, but caulk is also a viable option. After caulking, install fiberglass.
Wet Cellulose: Wet cellulose (like NuWool) is an option only if you’re doing all the walls in the basement. We like closed cell foam better for this option since it provides its own vapor barrier which you’ll need to prevent moisture from condensating on the block/concrete wall, but wet cellulose can work.
Spray Foam: The picture in the upper right of this article shows spray foam installed between the joists. Like Great Stuff, spray foam expands to fill the available space, creating an extremely tight seal. You can watch our video on spray foam for a complete rundown on the material.
Energy Savings & Tax Credits for Insulation
Each home is different, and the energy savings will vary. If you have no insulation in the joists today, you could be wasting more than 15% of the energy in your own. Leaks cost money… a lot of money. Stop them, and you get instant savings.
As a bonus, the U.S. Government will chip in if you tackle this job in the next 12 months. In 2009, and now extended through 2010, there are energy tax credits for insulation that will provide you as much as a 30% back for doing this job.
What do you think? Have you insulated your basement?