Tackling crawl space insulation, ventilation

Hey there, time traveller!
This article was published 14/09/2008 (6201 days ago), so information in it may no longer be current.

111Do I really have to cover the panels to provide a thermal barrier? There is no source of flame or direct heat in that area and for me to haul pieces of drywall through a two-foot-square opening to the crawl space is a difficult task. They would have to be cut into small pieces to get into that area plus I would have to build a stud wall on top of the Styrofoam to accommodate the drywall.

Can I apply a layer of Reflectix foil insulation over the insulation? It comes in easy to handle rolls and I am assuming that it will provide a minimal thermal barrier.

–Dave Magrel, e-mail

QUESTION — I live in a three-level split house that has a crawl space under the main living area. The crawl space has a concrete floor and the foundation walls are uninsulated.

Consequently, the hardwood floors on the main floor are very cool and uncomfortable in the winter. We would like to insulate the foundation walls in the crawl space. There are two vents on one of the foundation walls in the crawl space. A previous owner put some insulation over the vents from the inside, so they are not open.

Is it necessary to have these vents in the foundation? From what I’ve read on the Internet, much of the talk of venting a foundation is for crawl spaces with dirt floors which are more prone to excess moisture than a concrete slab floor. The crawl space is heated in winter and cooled in summer via a pipe from our forced-air heating/cooling ductwork.

What I was thinking of doing is having a contractor insulate the crawl space walls with closed-cell polyurethane foam insulation, which would provide insulation as well as an air/vapour barrier. If the vents are permanently closed over, can I expect moisture problems? What’s the best thing to do?

Also, does insulation in a crawl space have to be covered will a fire-retardant layer such as drywall?

–Eric Poppleton, e-mail

ANSWER — While these two inquiries are not identical, they both relate to insulation of a crawl space from the interior. For that reason, I thought they would be ideal to answer together and address both the insulation and ventilation issues.

The first thing to address is your question about ventilation of the crawl space. While you are quite correct that this is much more important in crawl spaces with dirt floors, having functioning vents in any crawl space will be an advantage. Passive ventilation of any crawl space in the warm months will help improve airflow and reduce the possibility of condensation and moisture build-up. Any confined space, like your crawl space, may be subject to extra moisture issues due to limited air circulation and opening these vents in the non-heating seasons will help in this regard. A simple way to accomplish this would be to make removable, insulated covers out of rigid foam insulation, for installation in the cold months.

I am impressed that both of you have decided to use different types of foam insulation, which is much more preferable for use in crawl spaces than the traditional wood stud and Fiberglas method. This will prevent air leakage to the cool concrete behind the insulation and moisture damage to the wood framing. Covering either type of insulation may not be critical, but will be much more possible with the rigid foam. I would not be in a hurry to use a product like that reflective material. The products I have seen have air-filled plastic bubbles inside a very thin layer of aluminum foil covering, which may not provide much more of a fire barrier than the uncovered insulation.

The same reason that blown-in polyurethane is a better alternative than the rigid foam panels makes it much tougher to cover with drywall or other fire-retardant materials. The blown-in foam conforms much better to the foundation walls and fills small gaps and areas between the floor joists that may be difficult to accomplish with the sheets of Styrofoam. Because of that, sheathing this uneven surface will be difficult.

Alternatively, installation of drywall over rigid foam may be done more easily by simply gluing the drywall to the insulation and supporting it in place until the adhesive cures. You do not have to install a complete wood frame wall over the foam sheathing, but you could install wood strapping over the insulation in a few areas for additional support.

The final thing to address is the need for the sheathing over the insulation, altogether. The main reason for this fire-retardant barrier is to provide a means of preventing toxic fumes emanating from the insulation during a fire. The sheathing will prevent fire from easily and quickly burning the plastic foam insulation, but will not eliminate the possibility. However, this may delay the release of toxic smoke long enough to allow occupants to escape to safety. While I believe precautions for fire safety in homes is paramount, covering this insulation should not be the highest priority.

I constantly see many other exposed plastic products piled up in basements and crawl spaces, so covering the foam insulation may not be essential as long as other fire-prevention items are properly addressed. Operational smoke and carbon monoxide detectors, fire extinguishers and properly installed and maintained fireplaces and wood stoves are much more critical. I would much prefer to see that these items are in place, as well as removal of excess basement storage and a plan for escape during fire, rather than properly covered insulation.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the President of the Canadian Association of Home & Property Inspectors – Manitoba (www.cahpi.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 or check out his website at www.trainedeye.ca.

trainedeye@iname.com