Exterior insulation with rigid foam board

Adding foam board against the sheathing and underneath the siding is being done routinely today by high-end contractors, but it is still not common practice. While it does not add any thermal mass to a structure, it will increase a wall’s R-value and the technique is one of many things that should be considered when a new home is planned.

Considerations for adding foam board insulation to an existing structure can be found here.