Good afternoon Ari. I read your column religiously and as a new home owner, find your information most valuable.
Recently, the City of Winnipeg located a water leak affecting the water line to my house. After detecting the leak from a routine street check on the water main, they determined that a leak occurred on their side of the water line to my property. They shut my water off and let the water to their line gush out freely on my property, the sidewalk, boulevard and street for a period of 24 hours before their repair crew arrived. When the crew showed up they said, “How long has the water been flooding out like this?”. I informed them it has been 24 hours and they couldn’t believe it. Ever since the water was disconnected and allowed to flood out my part basement, part crawlspace developed an overwhelming odour that can be detected all the way through the house. It is a musty, mildew odour that is disgusting. My family told me that it is probably due to the water pouring out, which was entering into my crawlspace and saturating the earth. I went and bought a dehumidifier and I am emptying out buckets of water. Will the dehumidifier solve this problem? Will I be able to rid the basement of this odour with the dehumidifier? Should I be in touch with the City? What if there is long term damage that I am not aware of at this time?
Any help would be greatly appreciated.
Homes with crawlspaces, particularly part foundations, are much more likely to have moisture related issued due to the exposed soil in the crawlspace. Most part basement homes, like the one I inspected earlier this week, have little protection on the soil from moisture intrusion into the home. I will offer some suggestions to help minimize the smell and prevent a repeat of the mustiness in the future.
For those that are not familiar with part basement homes these typically have a small, central lower basement area with a perimeter concrete retaining wall surrounded by a dirt crawlspace. This lower area was often installed to house the furnace or boiler, hot water tank, and some other mechanical and plumbing fixtures. The lower area resembles many traditional concrete basements, except that the walls do not extend up to the underside of the floor joists and may be only partially load bearing. The outside walls of the home do not sit on these concrete walls, which may only be supported by a series of posts, piers, grade beam or wooden knee-walls. Many of these homes have poor protection from moisture intrusion into the crawlspace due to the wooden perimeter walls or skirting that may extend only a little below grade.
I agree that it is very likely the damp smell is due to excess moisture seepage into your crawlspace from the water main leak. Because of the reason noted above, there was little to stop the water from leaking into the crawlspace soil under your home. What you likely smell is a combination of damp soil, mould, and rot, if you have wood exposed to the damp soil. While the dehumidifier may help take the excess moisture from the air in the basement area, it may not do enough to dry the wet soil in the crawlspace. Unless you can sufficiently dry this soil, you will notice the odours for a long time.
Effectively drying the soil in the crawlspace will depend on several factors. Most part basement crawlspaces that I see have limited or no air-vapour barrier installed over the soil. Often, there is excessive debris, storage, and improperly installed insulation over the soil. The first thing to do is clear the entire area of debris, wood, storage and any loose insulation. Once this is accomplished getting additional ventilation, passive or mechanical, into this small space is critical for drying. Because the weather is now too cold to open any windows or exterior vents in the perimeter of the crawlspace, fans and space heaters may be used to help dry the moisture in the soil. Fans should be used on low speed to minimize blowing dry soil and dust around. Careful use of space heaters will help speed up evaporation of the moisture within the soil.
Drying the soil in this manner will likely elevate the relative humidity in your home, so use of bathroom and kitchen exhaust fans for extended periods of time is recommended. Also, running your furnace fan continuously will help move the damp air through the house, decreasing the drying time. If you experience excessive sweating on your windows while the soil is drying, open your doors or windows a few times a day for brief periods to allow fresh air in and some moist, warm air out.
The good news is that the soil outside your home is now cooling fast, which will likely freeze any excess moisture within the ground and prevent further intrusion into your crawlspace over the winter. This should allow you to dry your basement and crawlspace sufficiently over the next few months and take one critical measure to help prevent reoccurrence of the moisture related smells. Once the soil is fairly dry and the smells abated, you should install a 6 mil polyethylene air-vapour barrier over top of the entire area of exposed soil in the crawlspace. This plastic sheathing should be extended up over any insulation on the perimeter walls and the interior retaining wall. It should also be caulked to the underside of the floor sheathing and any protrusions from the soil. After completed, this air-vapour barrier should trap excessive moisture in the damp soil, preventing dampness in the air in the shallow crawlspace, in the future. Further installation of screened summer vents in the perimeter skirting or knee-walls of the crawlspace will also help air circulation and drying in the warmer months.