Kneewalls, those short walls under sloped ceilings, are common in story-and-a-half homes and in bonus rooms above garages. Although kneewalls can help turn attics into living space, they often present insulation challenges. There are two ways to insulate triangular attics behind kneewalls. The traditional approach is to insulate the kneewall and the attic floor behind the kneewall. This method can be made to work, but the necessary air-sealing details are demanding and fussy. A better approach is to insulate the roof slope above the attic. This brings the triangular attic into the home’s conditioned space, and is therefore the only method to use if the attic includes ducts or plumbing pipes.
Read the entire article here: Two Ways to Insulate Attic Kneewalls