Zone 6 foundation insulation
Zone 6 Foundation Insulation
1 75 foot long ranch log home built in 1984 in southern Vermont (zone 6).
2 1/3 of foundation is a basement garage.
3 2/3 is unvented crawl space of 3-7 feet high with a “Clean Space” basement system with drains and sump pump.
4 Historical volumes of mountain water runoff have been mitigated with many hand dug drains 10’-20’ away from house. After one year through snowmelt, no water detected in sump pump basin leading me to believe that the surrounding soil is quite dry.
5 Now I have to insulate walls and am worried about moisture drive into sill plate (no capillary break).
Proposed Insulation Assembly:
1 3” XPS seems to be too much vapor resistance and would cause a drive upwards into sill plate. One possible saving grace might be the ability for the exterior of the concrete (above grade) 1-5’ around the perimeter to release moisture.
2 Would it be smart instead to limit the XPS to 1 1/2” to control the dew point and cover with Rigid Rockwool for the rest of the assembly allowing a higher perm rating?
3 This assembly would be duplicated in the garage with the addition of furring strips to support sheetrock.
I have read every post you have had regarding this subject and understand the stated assembly of #1 matches your recommendation. Am I overthinking vapor permeability and sill plate problems?
In one article Martin mentioned the possibility of a dimple mat behind the insulation. Could you expand on that assembly because I cannot find any additional information?
Thank you for all the information. Quite helpful and fascinating.
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