Does having EIFS siding affect your basement insulation strategy?
I own a home built in 1998 with a barrier type Exterior Insulation and Finishing System (EIFS). It is in Zone 4, near Knoxville, TN, I had the home inspected by an EIFS inspection specialist before purchase. There were no moisture problems discovered; they did a very thorough job. FYI – This house has huge eaves, in most locations 36″, which gives siding some protection. I am now interested in finishing the basement, which after a year carefully watching seems perfectly dry. I have examined my options to insulate, but I am confused and worried about what I should and should not do given the EIFS?
The basement has three sides concrete masonry block walls. Most of the CMU walls are below grade. I don’t believe the CMU walls are insulated below grade. CMU wall that is above grade appears to be covered with 1″ expanded polystyrene EIFS. On the basement interior, the CMU walls are un-insulated. I plan to have professional apply 1.5″ of closed cell spray foam (R10) to CMUs on interior . I will stud out the walls beforehand, setting studs back from wall about 3/4″ to avoid thermal bridging but preserve space.
Most of the rim joist area (22″ high) above the CMU walls is covered with 3/4″ expanded polystyrene EIFS on exterior side. This makes me nervous. Rather than spray foam, I thought I would “cut-and-cobble” 2″ XPS, air sealing perimeter with spray foam. That way I can ultimately get to the OSB to inspect. The remaining rim joist area (about 38ft) is covered by the lower garage wall (2×6) that is filled with fiberglass batts, paper facing inward toward basement. Not sure I need to insulate here? If I do, I will use the same “cut and cobble” technique, but don’t want to cause problems by sandwiching the OSB with a “double” vapor barrier?
The remaining basement side is a “daylight” wall that is a 2×6 stud and currently un-insulated. The OBS sheathing on this wall is again covered with 3/4″ expanded polystyrene EIFS, but most of it is protected from any chance of rainfall wetting by porch roof extension. Where protected, I’m thinking of filling the bays with 2-2″ layers of XPS, sealing perimeter with foam. The parts of the daylight wall that are left have a small eave overhang, so I’m nervous about continuing with 2-2″ layers of XPS. Perhaps just 2″ XPS, perimeter sealing with foam, and then fiberglass with no paper?
I want to make the basement well insulated but don’t want to overinsulate given the circumstances. I worry that my strategy may create problems in rim joist/daylight walls with EIFS?
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