I’m remodeling a 950 square foot 1940’s cape cod house with an unfinished basement that we plan to insulate in the future. The house is in Southeast Alaska, Climate Zone 7.

The cedar shingle siding is in good shape and the shallow eaves, typical to a cape house, are driving me to look at insulating from the interior instead of replacing the siding, extending all the eaves, and adding exterior insulation. We are doing the majority of the work ourselves and have a limited budget for the remodel. 

I’m looking for the most economical and efficient way to insulate from the interior that won’t cause damage to the existing stud walls. One of my concerns is that the thickness of the existing layers of siding, sheathing, and felt paper will prevent moisture from drying to the exterior and if I use rigid insulation or spray foam on the interior that would prevent any moisture from drying on the interior. I have been reading great articles on GBA and building science corporation about addressing moisture with new construction and deep energy retrofits but most of those case studies involve residing and adding exterior insulation with rainscreens etc. 

Option 01

• Cedar Shingles
• Existing fiberboard (1/4”)
• Existing felt paper 
• Original plywood siding 
• Existing horizontal sheathing 
• Existing 2×4 stud wall 
• Mineral Wool Batt Insulation 
• 2×2 horizontal furring strips 
• 1.5″ rigid insulation horizontal between furring strips
• GWB, painted 

Option 02

• Cedar Shingles
• Existing fiberboard (1/4”)
• Existing felt paper 
• Original plywood siding 
• Existing horizontal sheathing 
• Existing 2×4 stud wall 
• ¾” spacer (existing)
• New 2×4 stud wall
• New 7.5” Mineral wool insulation
• Vapor retarder
• GWB, painted

Option 03

• Cedar Shingles
• Existing fiberboard (1/4”)
• Existing felt paper 
• Original plywood siding 
• Existing horizontal sheathing 
• Existing 2×4 stud wall 
• Closed cell spray foam
• GWB, painted