We are thinking about buying a house that has a wet basement. It’s a private sale and the owners have already told us that the basement floor gets wet and water comes in around a big rock outcrop that forms part of the basement foundation wall. Do you think there are ways to change this situation or at least control it, or will we always be dealing with a wet basement forever?

Without seeing the particular site conditions affecting this basement, it is difficult to pinpoint the possible sources of water coming into this basement. But I can give some generic suggestions and reasons for the wet basement you describe.

There are two categories of water that affect basements: ground and surface water. For instance, if water is “pushing” through the basement concrete slab, it is probably because of hydrostatic pressure. In other words, ground water under pressure comes through the floor because this basement presents less resistance than the rock fissures and soil below the concrete slab. In other words, because the concrete slab is less resistant to this pressure, the ground water rises through the slab into the basement. This type of ground water penetration is much more difficult to control and eliminate than surface water.

If there is any hope in eliminating this water from a basement, you must start by providing the ground water with a path of travel that is less resistant than the concrete slab it is pushing through. This is easier said than done because it involves understanding where the water source is and then devising a way to tap into it and drain it away before it gets under the concrete slab. There are several ways to address ground water control. Which method you choose is determined by particular site conditions. One generic approach is to dig a trench uphill of the basement and install a “french drain” that intercepts the ground water before it gets to the basement. But, there is no guarantee this will work. Ground water has a mind of its own and is not easy to predict or anticipate. Often, it will bypass an interceptor and continue to plague a homeowner. There are several other more site specific solutions that may be worth investigating. 

The water you describe that is seeping in around the boulder is probably related to poor control of surface water. This type of water is much easier to capture than ground water. Here are some easy and relatively inexpensive ways to control surface water. Start by installing gutters and downspouts on all the eaves of the house. You don’t want to dump thousands of litres of roof water beside your basement walls, so also install 8 or 10 foot leaders on the ends of the downspouts to carry this roof water away from the foundation walls.

Also, look at the way the ground slopes around your foundation walls. If there are negative slopes pushing water toward the foundation, these slopes will also contribute to surface water entry around the boulder. Of course re-sloping negative grades can be expensive and difficult to achieve, often requiring retaining walls and extensive yard work.  So, start with the gutters, downspouts and leaders.

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This article was written by Steven Cannon, a Registered Building Official and partner in Lynch Building Inspection Services Ltd. of Nelson, British Columbia. It originally appeared in The Nelson Express.

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