Crawl space Crawlspace

Published on September 16th, 2018 | by Henri

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Insulating a crawlspace

Q.  We have a basement under most of the main level of our 1960s split-level home but only a cement crawlspace under the room I’m using as my office—and it’s not insulated and cold!

The entrance to the crawl is about 4 feet off of the basement floor. We have a “door” made of a rigid insulation panel keeping warm air in the basement (and from the crawlspace) and keeping a crawlspace smell out of the basement. I’d like to add insulation to the ceiling of the crawlspace. The room above has wood floors.

Can I use rigid insulation or would fiberglass batting be better? The vents to that room also run through the crawl space – should I also somehow insulate the vents? Thanks for your help!

A.    There are two different approaches to this question.

Since the crawlspace has a concrete floor, and you haven’t mentioned any leakage problem, except for a musty smell, consider insulating the exterior walls of the crawlspace with 2-inch thick XPS applied to clean foundation walls with dabs of polyurethane caulking. Remove the insulated panel between the basement and the crawlspace.

The crawlspace will now become conditioned by warm air from the basement and the radiation from the heat ducts within it. This will solve the problem of insulating the ducts and may eliminate the crawlspace smell.

The other way is to install Roxul mineral batts (no itch and healthier than fiberglass) between the first floor joists, making sure that the batts are in contact with the floor sheathing. In that case, you should insulate the ducts, using special insulation for that very purpose.

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