Exterior foam insulation can be used to enhance the energy performance of a wood stud wall system. When a traditional wall system, using 2x studs, is the only place you insulate – 25% of the wall is left un-insulated. Or rather, 25% of a traditional wall is made of wood studs which does not have a very good R-value. If you install a rigid foam over the studs or OSB you create a continuous insulation envelope increasing the overall performance of the wall system.
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