Home>Discussions>INSULATION & HVAC>insulate crawlspace ceiling, walls, or both??
5 posts / 0 new
Last post
insulate crawlspace ceiling, walls, or both??

We moved into our house in CT, built in 1977, about a year ago. The house has a vented crawlspace with a dirt floor that has recently been waterproofed. The crawlspace ceiling has R-19 fiberglass insulation (R-30 is recommended in our region), and there are leaks in the ductwork running through the crawlspace. Our problems are cold floors in winter and high heating and cooling costs.

We are looking into foam insulation for this space but aren't sure if we should do just the ceiling, just the walls, or both? I have read to do the ceiling in a vented space and the walls in an unvented space. Because the crawlspace has been waterproofed, should we permanently seal the vents and just add foam to the walls? We have received a few quotes from insulation contractors and they are suggesting we insulate both, but I'm wondering if that is just because they make more money that way!

Obviously, we want to get the most bang for the buck in this economy, and want to be more energy efficient and more comfortable in our home. Any advice would be greatly appreciated!!

Re: insulate crawlspace ceiling, walls, or both??

If it's in the budget then applying the foam to the underside of the floor as well as the perimeter walls would be a very good way to go .... providing the vents are closed.
Otherwise if the vents remain it's a waste of money and material insulating the perimeter walls.

Depending if you are using the closed cell spray foam .... you could have a 3 inch layer applied to the underside of the floor .... giving approx. R21 and reuse the batt insulation as well ... giving approx R39/40.

2 inch closed cell foam applied to the perimeter walls will give around R14.

Hope this helps.:)

Re: insulate crawlspace ceiling, walls, or both??

this is just my opinion but i'm not a fan at all of unvented crawl spaces. it becomes a place for moisture and mold to collect regardless of the insulation installed. therefore, i would just go with insulationg the floor. i'm sure you'll get a few responses that disagree with me, but that's just my thoughts on the matter

Timothy Miller
Re: insulate crawlspace ceiling, walls, or both??

Howdy, With r19 in the floor cavity your floor are cold... How cold? R22 is what i have read over and over again in solar books and super insulation of homes. With the floor insulated no need to insulate the foundation walls per all the information i have read- about 40 books- too much free time in winter. First i would seal up the duct work why waist your $. Have you considered slippers?
or installing radiant heat.

Re: insulate crawlspace ceiling, walls, or both??

Insulating the perimeter walls of a crawl space is advantageous .... only if the vents are sealed.

By doing this you are raising the temperature of the crawl space .... therefore changing the temperature differential ( delta T ) between the conditioned space ( the living area ) and the crawl space.

The less temperature differential ( delta T ) the less heat loss from the living space.

If the vents remain open then it's a waste of time and materials insulating the perimeter walls.

Since this would expose the floor of the living space to cold moving air this would increase the temperature differential ( delta T ) which increases heat loss from the living space. With the presence of cold moving air more effort is needed to properly insulate the floor.

A high R value insulation placed in the joist bays along with rigid foam covering the underside of the joists ( seams sealed to prevent air movement ) would be an example of keeping the floor comfortable. The rigid foam placed on the underside of the joists will increase the performance of the insulation as well as preventing thermal bridging.

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.