Properly installed skirting keeps moisture at bay

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This article was published 27/08/2006 (7050 days ago), so information in it may no longer be current.

Hello Ari;

I hope you can help me with a situation that has perplexed me.

I have purchased a cabin that was built in 1984. They had somewhat insulated in between the floor joists, which in time has fallen down and the squirrels had nested in. So this past summer, I removed the insulation. One weekend recently, with a constant two-day rain, I noticed some damp patches on the plywood floor above where I removed the insulation. One patch is near a wall and a couple of smaller patches towards the middle of the living room. What would be the cause of this and how do I correct it?

I should also let you know that we had put skirting around the cabin this year. We used about two feet of perforated skirting around each corner.

Darrell Richcoon, e-mail

ANSWER — Questions about insulating cottage floors and the crawl spaces beneath them are some of the most common inquiries I get. The best method for this is not a difficult concept, but may be tricky to achieve for many homeowners. When a properly insulated knee-wall or skirting is not done, problems such as your squirrel and moisture issues will often arise. I will try to offer some suggestions for the dampness you are seeing.

Insulating between the joists of the floor of a building that is built above grade, with the underside fully exposed to elements, does little to add warmth or reduce heat loss. Because warm air rises naturally by convection, heat loss through the floor is much less that that of the walls and the attic of the building. Also, without a source of heat in the floor system or below, the floor will always be cold, even if the insulation and vapour barrier is done very well. For this reason, installation of a proper knee-wall or insulated skirting between the bottom of the floor joists and the ground is much superior.

You have stated that you have removed the old insulation from beneath the floor, which is great, and put skirting all around the cabin. I don’t quite know what your perforated skirting is made of, but it sounds to me like you have not bothered to insulate the skirting, which is fine if you are not using the cabin during the heating season. The ventilated skirting is a good idea to prevent moisture buildup in the crawl space. If you wish to insulate the skirting in the future, you could make removable covers for the vented corners to allow ventilation in the summer.

As for the source of the damp floor sheathing, there are several possibilities. Firstly, it may be just a coincidence that you are seeing the moisture on the floor after the insulation removal. The two may have no relationship, but the recent heavy rain has shown a leak somewhere that only occurs when the rain is constant and heavy. These types of leaks are commonly associated with roofing flashings around vents or chimneys, or windows and doors. When the weather is dry, go up on the roof and check these things for leakage with a garden hose. Look around the windows and doors for gaps in caulking or brick mouldings and sills. Check the siding for any new holes or damage due to moisture or pests that might let wind-blown rain enter the walls or floor system. It is possible the squirrels have chewed through some deteriorated wood and left some holes that were previously plugged with insulation.

If you can’t identify the source of the leakage, the obvious place to look is the new skirting. Check the installation to see if any old siding boards or flashings were removed during installation that may have opened a hole for rain to enter. Look at the method of fastening the new skirting for possible leaks along nails or screw holes through the old building floor system. Any of these should be repaired or sealed with caulking or blown-in foam to prevent further leakage.

The final possibility is dependent on the height of the cottage off the ground. If the cabin floor is fairly close to grade in several areas, the new skirting may actually act as a medium to transfer moisture to the floor. This is made possible by the new skirting wicking up moisture from the wet ground, which may soak small spots in the floor sheathing. It is unlikely this would happen unless the skirting is very short or constructed of highly porous material like K. B. board or other similar sheathing. This should be inspected by looking at the back side of this skirting to see if it is damp or has moisture stains. If that is the case, it should be cut back so it is no longer in contact with the ground and a moisture-proof insulation or other material installed to bridge the gap.

The causes of moisture in homes and cottages and leaks are often the most difficult to diagnose. Check out the areas recommended, and if this does not provide a suitable answer, consult a home inspector or reputable general contractor to do a site visit to look for the exact cause.

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.

trainedeye@iname.com