Renovation & Design

Culprit behind damp basement carpet will determine care


There are multiple potential reasons for damp basement floors, and multiple potential fixes. First, you need to figure out the source cause — interior moisture or exterior leakage.

Question: Let me describe the issue and ask, under which circumstance should I lay carpet again? In our carpeted basement bedroom, I always wore footwear. On one occasion, I was barefoot and found the carpet underfoot to be damp. Two years ago, I took the carpet out, but I left a little section of underlayment in the middle of the room to see if it would become damp.

I’ve checked the room several times for water after rain or snow melts and nada.

I’m wondering why the carpet got wet? Could it be condensation through the basement cement floor? Should I take sections of the north wall of the bedroom apart, around the window, and check for wetness and mould?

The bedroom window is not an egress window and it’s old. I’m thinking of replacing the window, grading better around the window and putting mould- and mildew-proof carpet back in. Do window-well covers work? Should I put a cover over the window well?

— Thanks, Sheri O.

Answer: Wet basement carpets may be a function of the location, situated on a cool concrete floor slab, but is most often from moisture intrusion from outside. Locating the point of leakage may require opening up the inside walls, but exterior grading, water management and window upgrades should be the first items to address.

Water in basements is probably the No. 1 complaint of homeowners. The causes can be categorized under two main areas: interior moisture or exterior leakage. The simplest cause of wet flooring is often the easiest to resolve. Leakage or condensation from the plumbing or heating systems is common and may go undetected until something gets wet. Checking the area above the wet carpet, or other areas nearby where the heating equipment, plumbing drains or supply pipes are located may yield a quick answer. If there is no issue with these mechanical systems, then looking outside the home should be the next phase of investigation.

The first suspect for leakage into a basement is damaged eavestroughs and downspouts, and/or poor grading around the home. In the majority of homes I see with wet basements, the point of leakage is near a downspout termination. If your downspouts are dumping directly beside the foundation wall, or are damaged and leaking directly onto the walls, this is what needs to be addressed. Simple replacement of a downspout with an open seam, or repairs to a loose or missing extension pipe, may channel the problematic moisture sufficiently far from the house. If those are still in good shape, check to see if the soil is eroded and sloping toward the foundation. Even with good water management from the eavestrough runoff, precipitation can pool against the foundation if the grading is poor. Building up the soil to provide a slope away from the foundation walls may be the second-simplest item to address.

If both of these issues are found to be in satisfactory condition, the remaining culprit is the basement window. Older windows, especially wooden basement ones, are notorious for leakage. They rarely have drip flashings and water can often pool along the bottom or leak through rotten frames, sashes or the window buck. Replacing an older, damaged window with a new PVC or fibreglass unit, both of which are highly moisture resistant, may stop leakage during a heavy rain or snow melt. Installation of window-well covers may help prevent excessive snow from accumulating against the window, or filling window wells, but are otherwise not much help against serious water ingress.

If none of these common issues appear to be the cause, then partial removal of wall coverings may be the logical next step. Starting below or around the basement window, removing the wall coverings, air/vapour barrier and insulation should reveal the condition of the concrete foundation wall behind. If you seen visible vertical cracks, especially with white, powdery efflorescence around, then that is likely what is leaking. Also, if you see small rusty holes with water stains below, then deteriorated form ties will be the cause of the seepage. Both of these may require localized exterior excavation and foundation repairs, but are otherwise normal in an older home.

If there are any larger diagonal, or especially horizontal, cracks, then a more extensive exterior foundation repair is warranted. These are signs that there is movement of the home or foundation walls and should be addressed not only to stop the seepage, but to prevent further structural issues from developing.

If your problematic wall is opened and no obvious "smoking gun" is found, condensation from the cool basement floor slab may be the final suspect. This should be minimized by complete removal of any carpet and underpad and improved heat and air circulation in the room. Once that is upgraded, installation of a thin subfloor with corrugated plastic on the underside, followed by moisture-resistant floor covering, should prevent further issues from occurring.

Determining whether your wet basement carpeting is from inside or outside the home should be the primary focus of your efforts, but an outside source is normally the case. Improvements to grading, eavestrough water management and certainly replacement of the rotten window should provide relief, unless there is damage to the foundation itself. If the water persists even after those issues are all addressed, removal of wall coverings and further evaluation by a foundation contractor may be warranted.

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


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