Ensuring good air quality in garage apartment
We are building a garage with an upstairs apartment in southern Minnesota. Our house is from the 1890’s, so we have lots of experience with drafts, but little experience with a tight, well insulated space. The garage is a simple design (24×24) and the apartment is equally simple (bathroom, and an open living space). We are fully insulating the garage and apartment (3” exterior insulation extending all the way down the footing, 2” sub-slab insulation, 2×6 cavity fill, and r-50 roof). There will also be insulation in the floor, and everything will be fully sealed and detailed to prevent airflow between apartment and the garage. Only penetrations are electrical and water/waste lines, which will also be sealed. At this point, we don’t plan to condition the garage, but would have that option in the future. We’ll use a small ductless ERV in the apartment, and there will be a bathroom and kitchen fan. There is a passive radon system (required for ADU in our town). We could install an exhaust fan in the garage if needed. The question is, is the garage exhaust needed to be sure the garage air isn’t making it into the apartment? Or only if we start conditioning the garage? Would adding a active radon fan help with pressure somehow? Are there other aspects to consider that aren’t on the list above? What have I missed?
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