How do I Insulate That Attic Closet Area?
As with most home improvement projects, there are two ways to properly insulate an attic storage space like this. These areas are calling knee walls, because the walls of about 1/3 of their normal height. I am going to concentrate on the option that keeps this storage space warm since most people us e this space for storage.
This is an area where using spray foam insulation can really make a big energy difference. Because this area doesn't need to look pretty, it is beneficial to spray insulation over the roof rafters as well. This eliminates any thermal transfer through the roof making this as efficient as it could possibly be. The insulation depth should be a 5 inches with closed cell foam and cavities filled with open cell foam. If the rafter depth is only 2x6 width, only closed cell spray foam should be used. Please note the any vents or ventilation chutes should be removed prior to insulating with foam.
The Edge of the Floor
Most of these attic will have a finished floor. It is very important that you make sure that you insulate all the way down over the top plate of the wall. If you do not do this properly, you could create an air and moisture issue. When this is done properly, the energy savings are usually around 20%.
There is no need to insulate this area as it is now conditioned space. If you were to have this be otherwise, you would use the same method used on the attic rafters with spray foam insulation.
This is a job that should be performed by a professional because of the unique knowledge of this type of space needed to properly insulate and air seal a knee wall attic. These projects are usually around $1,000 per knee wall attic space.