Rim joists are unsealed and leaking air
Why it happens here
Most Ben Lomond homes were built before air-sealing was standard practice. The rim joist sits at the top of the foundation and is almost always open to the outside, which lets cold air pour in behind the insulation. In a windy mountain climate, that leak makes the whole house feel drafty.
Our approach
We seal every rim joist and band board with closed-cell spray foam before we add any other insulation. It is the single highest-return fix in a Ben Lomond home, and it takes less than a day for most houses.