Crawl space Insulation

Posted by on Dec 30, 2011 in Crawl Space Insulation | 2 comments

Crawl space Insulation

Crawl Space Insulation-

A very common question in the repair process is; what is the right way to insulate my crawl space? This is a complicated issue and does not have a simple answer. What makes matters worse is the amount of readily available wrong and misleading information on the internet.

There are three areas that can be insulated, but not all three should be insulated. The three areas are; floor joists, rim joist and foundation walls.

Floor joist insulation-
The floor joist area, or the crawl space ceiling, is the most commonly insulated area. This area is usually insulated with fiberglass and held in place with metal wire or staples. The fiberglass insulation in nearly half of the homes that have insulation in this area has it installed improperly. This kind of crawl space insulation should be installed with the paper vapor barrier on the heated or conditioned side of the space. This means the paper should be closest to the floor boards and not exposed to the crawl space. Until around 2003 insulating your floor joist was really your only option if you wanted to have any hope of keeping the winter air from entering your home. Today there is a better and more efficient way to make your home more comfortable and energy efficient; this type of crawl space design is called a conditioned crawl space.

Rim Joist Insulation-
The rim joist area is the part of the wood structure under your floor. Like the floor joists, the rim joist’s job is to help hold up the floor and walls of the home. The rim joist goes around the perimeter, or the rim, of the home and its primary job is to support the exterior walls as well as giving the floor joist an adjacent surface to be attached (on half the home). Other names for this area are band joist, sill box and bond. The proper insulation here can one of two options: fiberglass or rigid foam. Of course, spray foam has made an appearance as a crawl space insulation, but there are many more reason not to use spray foam in a crawl space then there are reason to use it. You can read more about crawl space spray foam here. Back to rigid foam and fiberglass. If the crawl space is going to stay an open crawl space then it would be better to insulate this area with rigid foam board. The reason for this is due to the rim joist being on the outside wall, which will cause this area to condensate first in cold weather. The fiberglass insulation will get wet almost immediately and be rendered useless.However, if the space is going to be a conditioned crawl space then I would recommend the fiberglass insulation. The reason for this, your crawl space will be clean and dry. The fiberglass will be in the same exact environment as the exterior walls in your first floor and you get a much higher R-value from fiberglass than you do from rigid foam.

Foundation Wall Insulation-
Insulating the foundation walls of a crawl space is a complete waste of money, IF you have an open crawl space. A crawl space with foundation vents that can be opened and closed is considered an open crawl space. It is considered open because the vents, even while mechanically closed, offer little protection from the elements outside the home. An open crawl space with rigid insulation on the foundation walls is like having the walls of your home insulated and opening the windows. It neutralizes the usefulness of the insulation by having the open vents/windows. More on closing the foundation vents here.

When it comes to installing crawl space insulation, ask yourself- Am I trying to keep something in or am I trying to keep something out. They seem like the same question, but they’re not. For example, with a vapor barrier you are trying to keep something out, the moisture. With insulation, you are trying to keep something in, your conditioned air. Knowing this helps the process to move forward in the right order. With crawl space insulation and a vapor barrier like SilverBack™ properly installed in your crawl space you can now begin to control the environment under your home. Now your crawl space is part of your home and you should protect it from the outside as such. The days of separating your home from the crawl space is over, mostly because it is impossible to do. It is far more reasonable to accomplish a plan to protect your crawl space from the outside than it is to protect your home from the crawl space and the outside.

So the recipe goes like this:
1. Close foundation vents permanently with a cement block and the proper caulk/sealant
2. Install rigid foam insulation on the foundation walls, R5 is 1″ thick and R10 is 2″
3. Install R-19 fiberglass in the rim (band) joist area
4. Install SilverBack™ vapor barrier on the floor and walls
5. Add conditioned air or use a crawl space dehumidifier to control crawl space moisture 
Doing this will eliminate the freezing cold floors, high energy costs and freezing water lines.

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