How to insulate a crawl space?

14 years ago

This is a bit off topic, but 1/2 my kitchen is over a crawl space. The floor is always cold. We have been advised to insulate the crawl space. My "how-to" book recommends insulating the walls of the crawl space, but others have recommended insulating the ceiling of the crawl space (i.e. under the kitchen floor). If we do the ceiling of the crawl space, how should it be done? Can I just do it like walls with the paper backing facing the floor of the crawlspace or should there not be a paper backing? I'm sure there are some rules of this to help with moisture and such....

Help please.

Thanks,

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Comments (5)

marcy96
14 years ago
I don't have any answers for you, but I have the same problem with the floor in my kitchen. I was going to add radiant heat, but it was too expensive. I also thought about putting insulation under the floor. Very interested in any advice others have.
meg_ma
14 years ago
Our GC insulated the ceiling of the crawlspace with Certainteed Certaspray closed cell insulation (see the link). The insulation qualifies for the tax credit so that helped with the cost.

Here is a link that might be useful: Spray Foam insulation
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Nice article worthy, thanks for that... I love this part... "DonÃ¢ÂÂt vent dryers or other appliances into the crawl" Who would do that? Every load of washing machine water direct into your crawlspace. Sheesh. For closed conditioned crawl spaces the recommendations were... Ã¢ÂÂ¢Insulate the perimeter walls to the level suggested for above-grade walls in your climate. Ã¢ÂÂ¢Exterior perimeter wall insulation is a good option to consider, especially in new construction. It eliminates the problems of moisture management associated with interior wall insulation and provides the possible benefits of additional thermal mass within the structure. The downside is you have to protect the insulation from termites and the above- grade portion of the insulation from deterioration caused by weather exposure. Ã¢ÂÂ¢When insulating a crawl from the interior, you should protect rim joists from condensation with foam insulation. Ã¢ÂÂ¢Use water-resistant insulating materials, such as rigid-foam board or spray foam properly protected to meet fire ratings. Avoid using air-permeable insulation, such as fiberglass batts or spray-on cellulose. Ã¢ÂÂ¢Power venting a sealed crawl space to the exterior can reduce the movement of air from the crawl space into the house. This can improve IAQ, but at the added cost of operating and maintaining the exhaust fan. I just might do that. i.e. insulate the walls and rim joists cuz our floors over the crawl space zone of the house are really cold in the winter. The issue there is "properly protected". Per the fire ratings, XPS sheets are to be covered w drywall or finished. Obviously a crawlspace you're not going to finish in drywall like you would a full height basement. So they don't really address what to do there -- cant leave it exposed but you're not gonna frame and finish... Thoughts?
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I had nearly the same problem in a room addition (although the crawlspace was bigger, it was still completely inaccessible). I did elect to pull out the floor, install insulation, seal the edges, and re-lay the floor over a new sub floor. It really didn't cost that much (my handy man did it, we ran some new wiring for new electric and cable outlets while we were at it), it was done in 2 days, and made a huge difference in the comfort of the room. I didn't do it as well as I could have--at the time didn't think of adding insulation to the walls of the crawlspace too, or wrapping the ducts with insulation. If you are willing to add a layer to the floor, with all the changes you'd have to make to trim, doorways etc, plus expense of new floor surface (and I don't think you could get much insulation value that way either) it sounds like you don't mind sacrificing the original wood floor. So why not pull it up? The only other option I can think of would be blown-in insulation, but you couldn't use cellulose, and I do think although I am not sure, that even with fiberglass the space would still have to be protected from moisture. Insulating foam might be an option if there is more than one point of access to allow even coverage of the underside of the floor. I'd be interested to hear what you decide & how it turns out. Our older houses present many challenges.
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There are several problems I read here. Although it wouldn't hurt to insulate the ceiling under the room, I don't think that is your problem. You mention you did not see a return. It may have one but doesn't sound like it to me since you mention you keep the door to the room closed and the temp. drops drastically. If you are not taking air out of the room, you won't be letting conditioned air in. The size of the room also causes me to suspect there should be 2 supplies and 2 returns (without knowing the size of your existing system). You mention this room is an addition. I suspect the supply, return, heating, cooling systems were designed for the original sq. footage and was not upgraded with the addition. That doesn't mean things can't be done to improve what you have now. For us to really give you much in the way of more precise helpful information, we're really going to need much more information in return. We can steer you in a direction but you will need to have a qualified tech. to come in and do load calculations and make a true assessment of what really needs to be done. Just sitting here reading what you have mentioned, I can only guess (from experience) that you need some rework done. I may be wrong...maybe the original design was to allow for this addition. A Tech doing a site survey can surely better determine that.
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needsometips08
14 years ago
I happen to have the NKBA book "Residential Construction" right here - am reading through it.

Pg 67 addresses this. It says, "Kitchen and bath floors above crawl spaces should contain insulation to stem heat loss and a vapor barrier to keep moisture out. Insulation can go either between the floor joists or at the foundation wall. Insulating the floor itself allows the crawl space to be continuously ventilated (required by some local codes) but is harder to do. Also, any water pipes and heating ducts that run under or within the floor must be wrapped."

We have an over-5-foot crawl space under our entire house and it's insulated just under the floor with the 6" batting type. Our vapor barrier (or at least what I *think* is our vapor barrier - we may have another one in the floor itself as talked about below) is huge sheaths of thick black plastic taped together with heavy duty tape - and the vapor barrier is sitting on the ground. We have not experienced the floor being cold at all - we have linoleum, wood, and carpet, and none are cold, even in the coldest weather.

The paragraph goes on to say, "On the other hand, the foundation can be easily insulated on the inside or outside face. However, any vents in the wall must be closeable during the cold season. The location of the insulation also affects where the vapor-control barrier goes. If the floor joist cavities are insulated, the barrier should go between the insulation and room above, usually between the floor joists and subfloor. The best vapor barrier is a sheet of polyethylene at least 4 mils thick. The foil or Kraft paper facing on batt and blanket insulation is not a reliable vapor barrier. If you choose to insulate the foundations walls rather than the floor, the vapor barrier should go next to the inside face of the wall and extend completely over the soil below the crawl space.

Another way to insulate the foundation is to apply rigid foam to the outside of the crawl space, but this is more easily done on new construction. An existing foundation will have to first be excavated down to the footing."

HTH
billandterry
14 years ago
you can do it a couple of ways: 1. If you are using kraft faced paper...the paper should be warm in the winter side in. 2.There is a product called closed cell foam that is also resists moisture and mold. 3. You could use a blown in insulation that it has some fire retartent properties along with mold resistant.

Is your crawl vented or unvented that will also factor in re: the insulation and pipe wrap to use.
mlo1
14 years ago
Our cellulose insulators attatched tyvec (cap sheeting) to the bottom of the floor joist and filled the joist cavities with cellolose.

How to insulate a crawl space?

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marcy96

meg_ma

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