Daylight basement insulation
Peterson_Todd
| Posted in Energy Efficiency and Durability on
I am in the insulation phase of an addition project to my house and ran into a question regarding the daylight basement insulation. The below grade walls are furred out and I have R-5 foam board against the stem wall, leaving me 4” of space to insulate, the above grade walls are plenty large for R-21 batts.
My question is, am I better off putting a continuous run of R-21 from floor to ceiling and having it compressed 1” against the stem wall portion, or am I better off splitting the cavity insulation in the middle using R-15 against the stem wall and R-21 in the above grade portion?
First time post here so any help is appreciated.
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Replies
Todd,
I don't think there is much benefit to having more than the R-15 batts at the concrete portion of the walls.
One dilemma is that the upper double-stud wall is too wide to be completely filled by the R-21 batts, leaving you with an air space on either the exterior or interior of the cavities. Those voids have convective air currents that diminish the effectiveness of the insulation, and can sometimes accumulate moisture. I would either completely fill the stud bays, or move the batts to the outside of the wall on that part.
Thanks for the reply! I understand what you mean, the building inspector said I will have to put the batts on the interior side of the double wall because that is the separation of the “conditioned” space, which is why this question was raised in the first place.
It makes more sense to me to have the above grade batts in the exterior cavity, and the void against the interior wall, but in reality, I’m not sure hence why I am here.
I will say a couple things. I am in Eastern Washington State where the climate is dry in the winter and drier in the summer, and the existing structure (1978) had the batts against the interior wall.
Todd,
If the inspector wants them on the inside, and you don't want to fill both walls, I'd suggest tacking a house-wrap air barrier on the inside face of the exterior studs to limit air movement in the batts.