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I have a slab on grade, no insulation that I want to insulate and include a vapor barrier in zone 5B. What is the best way?

This is for a summer cabin and I would like to reduce the humidity in the cabin and also reduce air conditioning costs.

Asked by Joseph LeBeau
Posted Sep 3, 2014 4:46 PM ET


2 Answers

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If you are talking about a summer cabin that won't be heated in the winter, there is no need to insulate your concrete slab. Because the concrete slab is in contact with the earth, it will stay cool in the summer, lowering your cooling costs.

To reduce your indoor humidity levels, you will need to operate an air conditioner or a dehumidifier.

To lower your cooling costs, keep your windows shaded with proper roof overhangs, exterior awnings, or porches; specify low-solar-gain glazing; and include adequate attic insulation.

Answered by Martin Holladay, GBA Advisor
Posted Sep 4, 2014 5:27 AM ET


Air sealing the cabin will be an important first step to being able to manage the humidity, as well as grading the exterior to drain away from the house, and installing gutters (or extending roof overhangs to at least 2' on all sides) to keep water away from the slab and walls.

It's probably going to be worth insulating the attic/roof to minimize direct gains from the roof, but we need to know a bit more about how it's constructed (rafter depth, vented attic with a ceiling below vs. a cathedralized ceiling, etc.), and maybe the walls too. The type of siding/sheathing/decking matters too.

Answered by Dana Dorsett
Posted Sep 4, 2014 10:47 AM ET

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