Assistance with dew point calculations to determine basement insulation requirements
I’m looking for help to determine if I need to insulate my basement slab to combat condensation at any time during the year, and the minimum thickness foam board wall insulation I can utilize. I am not set on flooring yet. Deciding between 1) polished concrete, 2) LVP, 3) insulated slab w/ T&G subfloor if required.
Climate Zone 5A, 21 year old poured concrete foundation. 8ft ceilings, 1ft above grade. I don’t know if there is sub slab insulation, but I suspect not. I believe there is a vapor barrier under the slab (no slab moisture issues using tape down plastic test). The space is not heated or cooled aside from duct leakage. I mechanically dehumidify with a high efficiency dehumidifier to sub 50% year round. The air temperature in winter hovers between 66-69F, and in summer 70-72F.
I have been using a laser thermometer to measure slab and foundation temperatures throughout the winter and summer. In winter the temps range from 56-61F (coldest part being the foundation wall right around the window well), and in summer 70-72F.
I’ve been trying to use this calculator http://www.dpcalc.org/index.php to assist, but I’m not sure how to use the information. Is temperature the air temperature, then as long as concrete temp remains below dew point based on the current interior humidity, I will not get condensation? Example, if I put summer air temp 72F, humidity 50%, I get dew point 52F, which is well above the summer concrete temp of 70-72.
I realize that my slab temperatures are probably heavily influenced by the interior air temps because there is no insulation on the interior. But, if I leave the slab uninsulated with a polished floor, or LVP on the bare concrete, the slab temps should remain the same, and I should have no summer condensation issues as long as I continue to mechanical dehumidify, correct?
1) Do I need to insulate the slab if I mechanically dehumidify?
2) Can I get away with 1.5″ polyiso on the walls and prevent condensation?
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