Crawlspace - Foam Board Need

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Reelsix

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I have a 1950s home with a 600 sq ft crawlspace next to a finished basement. Furnace/AC is located in the crawlspace. It has a dirt floor and cinder block walls. I live in a warmer climate (ATL).

I have received several quotes on encapsulation and the most agreeable is suggesting the option of having R5 Foam board installed along with poly vapor barrier that will go 1' up the walls. The four other quotes I received did not include this step. Walls in the space are no more than 4' high.

Vents will be sealed and will have a 70L dehumidifier installed in the space.

Company suggested the board is not 100% needed so I am thinking of skipping this addition. Is this the right move? House does have humidity issues but i am hoping encapsulation with dehumidifier added will solve.
 

nealtw

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You will need fresh fire air for the furnace or it will suck moist air from the house. Does the dehumidifier not pump air out too?
 

Reelsix

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Yes, they would install a fresh air combustion vent to the furnace.
 

nealtw

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I am never sold on the idea but when you have the furnace down there the ambient heat will warm the floor.
I think the poly should go all the way up and be sealed to the sill on top of the wall and the foam should be from the top down to below the frost depth in your area. And the rim joust should be insulated and sealed .
Moisture wicks up in concrete and it will go to the crawlspace if it is warm in there.
 
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