A case of mistaken crawl-space odours

Hey there, time traveller!
This article was published 30/08/2014 (4150 days ago), so information in it may no longer be current.

Question — I came across one of your 2013 articles in the Winnipeg Free Press about possible asbestos contamination resulting from attic insulation. This led me to wondering about my basement crawl space. We have lived in our 1914 North End home for 16 years. Early on, I removed most of the Rockwool batt insulation from a crawl space ceiling. This is the floor of our dining room, which I prefer to be heated from below rather than insulated against warmth. I re-insulated with fibreglass batts, this time on the floor of the crawl space and also Icynene spray-foam insulation on the exterior walls.

However, it still smells bad, with an acrid kind of smell, which makes me wonder if the few Rockwool batts I did not remove could contain asbestos. Of course, the smell could be something else too. There is only one small window between the crawl space and the rest of the basement.

From my description, do you think our basement air could be contaminated with asbestos?

Thank you for your help, Thomas Steur.

Answer — Improvements or renovations that improve health or safety in our homes are always a primary concern, but care must be taken not to make improper assumptions about a building product. I am glad you have enquired about the older insulation in your home and the possible asbestos content, but your question about the crawl-space odour is troublesome. I hope I can set you straight on both these items, and minimize your concerns at the same time.

The first issue to address is the older Rockwool material that you removed from the floor above your crawl space. I am assuming that you got the name of this product, because in batt form it was often manufactured with a paper backing with that moniker emblazoned on the surface. This paper was likely stapled or nailed to the underside of the joists, which helped secure it and prevent it from falling into the crawl space. In most of the research I have done over the years, I have not come across anything other than anecdotal information that this mineral-fibre wool contains asbestos. Unless you have discovered some concrete evidence to the contrary, you are mistaken in your assumption that this material is hazardous. You are correct in having removed it from the floor joists to improve comfort in the room above, but not because there was any health or safety risk.

While this incorrect assumption is simply an honest mistake, the next one you have made is way off the mark. Thinking that asbestos has a distinct odour, which can help identify its presence, is ridiculous. There are many types of building products that have contained asbestos over the years, but none of these have any type of smell that is caused by its presence. To suggest, in any way, that the “acrid” smell in your crawl space has anything to do with a product containing asbestos is absurd. I hope that this point is strongly reinforced for all the readers, so others will not have the same misconceptions about this hazardous material. The only way to positively identify the presence of asbestos in a building material, physical space or air sample is to subject it to laboratory testing. This may include examination under a microscope, or other physical or chemical analysis, but will required professional testing.

To help you get rid of the odour in your crawl space, you will have to finish the job you started. I commend you on your use of blown-in foam insulation around the perimeter of the crawl space, but Icynene may still require a proper air/vapour barrier over top. This could be accomplished by spray painting the inner surface of the foam with special paint, but is more easily done with polyethylene. The reason that 6Mil poly is preferable is that it will need to be installed elsewhere in the crawl space, as well. The bad smell is most likely cause by the fibreglass batts you have installed over the dirt floor in the crawl space. These will absorb large amounts of moisture from the soil, trapping the moisture beneath. This will prevent easy drying, but will allow enough damp air to pass through to stink up the air above. Removal and discarding the insulation will help dry out the soil, which can later be covered with poly. This layer of plastic sheathing will help keep the moisture in the soil from permeating the crawl space. Extending this membrane up the walls, over the spray foam, will complete the air seal.

Identifying the source of odours in homes can be tricky, but not when it comes to crawl spaces. These areas are below grade, contain exposed soil and have a tendency to be damp. Using the proper insulation and air/vapour barriers in the right locations will help prevent the dampness from causing things to smell. The fibreglass batts on the floor are not providing any real thermal protection, especially if they are wet. That is the wrong location for the insulation, so getting rid of them will solve the biggest part of the problem. Completing the air/vapour barrier installation is the final piece of the puzzle.

Among the many misconceptions homeowners have about their dwellings, health and safety related issues are the most concerning. While the majority of these fall into the category of disregarding potentially dangerous situations, improperly labelling an issue as hazardous can be just as wrong. The odour in your crawl space is definitely not due to any asbestos related building materials, which never was an issue, but due to improperly installed insulation.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the President of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com