Insulation in crawl space keeps house warm, dry

Hey there, time traveller!
This article was published 06/10/2002 (8399 days ago), so information in it may no longer be current.

Question — Your articles are very interesting and informative. Keep up the good work. I am not sure if I have a problem or not, but would like your advice before the weather changes back to winter.

I recently purchased a 780-square-foot house built in 1957. The house is in excellent shape, well insulated, and has updated well-fitting entry doors and triple-pane windows. There is no basement, and it is built on a concrete foundation perimeter wall that is about 12 inches thick. The crawl space is about 24 inches from ground level to the bottom of the floor joists.

The foundation wall has two screened-in window-style openings for access and venting, one on the north side and the other on the south side. In the crawl space are the metal ducts from the down-flow gas furnace that are not covered with insulation and they are positioned to reach six warm air outlets within the house. Also, in the crawl space are the hot and cold water pipes and drain pipes that run from the utility room to the kitchen and washroom.

The crawl space has no insulation on the foundation interior walls or between the floor joists. The former owner told me that he did not cover the two window vents during the winter and that the water pipes never froze, which seems odd to me. I will list my questions as follows.

1) Should I close off those two vents during the winter months?

2) Should I insulate the interior foundation walls? If so, what type of insulation would you suggest?

3) Should I insulate between the floor joists?

4) Should I leave the duct work uninsulated, so as to keep the crawl space warm enough in order to keep the water & drain pipes from freezing?

–Don Montgomery, e-mail

Answer — The question of how to properly insulate and vent crawl spaces is my most popular question next to last week’s on how to reduce excess condensation on windows. An excellent reference guide on this and other insulation techniques is available through Natural Resources Canada, Office of Energy Efficiency (OEE) and is entitled Keeping the Heat In. This and other energy publications can be viewed on the OEE Web site at http://oee.nrcan.gc.ca with information on how to order.

I will attempt to answer all of Mr. Montgomery’s questions, starting with a definitive yes to Question 1.

He is not alone in thinking that the former owner’s admission that he did not cover the crawl space vents in the winter is odd. I am very surprised that he never had a problem with frozen plumbing pipes or frost and condensation on the floor of the home. At best, he wasted a large amount of energy heating the area around the foundation walls and vents.

Proper ventilation for the warm months is very important for reducing the moisture built up in most crawl spaces, but these vents should be covered for the winter. Installing properly insulated and weatherstripped covers for these vents is not difficult and significantly reduce heat loss from this area and will eliminate the chance of water pipes freezing. This should be done in conjunction with proper insulation of the foundation walls.

The answers to questions 2 and 3 can be answered together, because a properly insulated foundation wall (grade beam) will eliminate the need for any insulation in between the floor joists. This, along with the new vent covers, will make the crawl space warmer in the winter and make the entire floor of the home more comfortable to walk on. This may be done most easily with rigid foam insulation installed against the inside of the concrete grade beam, but may also be done with fibreglass batts. If fibreglass is used, short walls will have to be framed inside the existing foundation to hold the batts and support the polyethylene air-vapour barrier stapled on the warm side of the insulation. This vapour barrier should be caulked to the underside of the floor sheathing and to the poly on the crawl space floor. If no poly is currently on the dirt floor it should be installed, as continuously as possible, and caulked at all joints, protrusions and overlaps.

There may be enough heat radiating out from the uninsulated ducts to keep the crawl space above freezing, but likely not enough to keep the uninsulated floor of the home warm. Additional ducts, opening into the crawl space, may be required to keep the area to an appropriate temperature in the coldest months. This should be relatively easy to accomplish, since the existing ducts are already present throughout the area.

Ari Marantz is owner/inspector of Trained Eye Home Inspection Ltd. and is the P. R. Rep. for the Canadian Association of Home Inspectors- Manitoba (www.cahi.mb.ca). Questions can be e-mailed or sent to: Ask The Inspector, P. O. Box 69021, #110-2025 Corydon Ave., Winnipeg, MB. R3P 2G9. Ari can be reached at (204) 291-5358.

trainedeye@iname.com