Basement Insulation Diagram

I noticed a structural flaw in the exterior plan set up in preparation for the installation for the foundation rigid foam insulation. I do agree fully that it is a definite good idea to extend the rigid foam insulation above the foundation covering the framing rim board. This not only acts as a ground water or rain water barrier ( not a water plane). It also creates a more efficient insect and pest barrier as well.

When the exterior wall is pushed out over the rim board 2" to allow the rigid foam insulation to run flush with the exterior wall sheathing. This greatly reduces the exterior structures stability to adequately rest on the floor system platform.

If 2" x 6" exterior wall framing is used ( 1 1/2" x 5 1/2") true dimension, then only 3 1/2" of the exterior wall ends up resting on the edge of the plat form.

This is very important because in states that have mass rain water , snow, and ice. The foundation and structure may move little by little over time potentially causing structural failure. The most adverse affects found are in regard to heavy snow loads mixed with freezing rain water trapped on a roof system.

The resolution to this problem would be to fasten a " band" rim board around the perimeter of the platform 1/2 the width of the rim board. This “band” should be flush with the top of the rim board and decked over to the outside of the band.

The structural downward and lateral load bearing strength would then not become an issue. Thus giving adequate room for the rigid foam insulation to still run half way above the primary rim board protecting the sill plate and foundation joints.

In either case, if this design is incorporated in the industry. It must be noted to the architect / contractor due to the slight increase in structural volume. This of which accumulates probable unforeseen additional costs overall.

I don’t know if this is any help: