WATCH THE SLOPE: Make sure water flows away from foundation
MIKE HOLMES
Province
The simplest thing you can do to keep water out of your basement is to control it at the surface. Surface water, like rain or melting snow, or water from irrigation, is pretty easy to control, compared to water below grade. There’s not much you can do about underground streams, or the water table in your area and the resulting hydrostatic pressure on your foundation. But there’s a lot you can do on the surface.
Most of the problems homeowners have with wet basements can be prevented if people corrected the grade around their home. Make sure that surface water doesn’t become groundwater and add to the pressure that’s already down there.
The first step is to make sure that surface water drains away from your house. Ideally, you want the soil level right next to your foundation to slope away. Since water flows downhill, surface water, like rain and snowmelt, will flow away from your basement walls. If the soil around your home has either a flat or a negative grade, surface water will naturally flow toward your home or pool around the foundation. This leads to trouble.
I’m going to hope your home is built right, and that the top of the foundation is at least six inches above the soil. That’s minimum. But, the higher the better. Also, the soil level needs to fall away — on all sides — in a slope away from your house. Bad grading can result in water pooling next to the foundation which can lead to wet basements.
When a house is built, there’s always an excavation for the basement and foundation. That is eventually backfilled of course, but the soil right around the basement’s exterior walls is never as firmly compacted as undisturbed soil. It’s more porous and will always contain more air — which will allow water from rain or melted snow or irrigation from plantings — to collect and seep down to your foundation level.
That’s one reason I don’t like plants around a house’s foundation. It’s not because I don’t like plants, but the irrigation into disturbed soil brings and retains too much moisture near basement walls.
When that backfill soil does eventually settle, after many years, there’s a depression right around your home that will fill up like a bathtub with surface water. And, most homeowners by then will have landscaped the area and won’t even notice that the soil several feet out from their house is lower than further out into the yard.
If you don’t re-grade that soil, the water will continue to pool and gather in the lower spots and eventually make its way down to your footings.
An easy fix is to make sure the downspout from your eavestroughs comes down, and expels water as far away from house as possible — at least two meters (six or eight feet). If you don’t make sure the downspouts expel water far enough away from your foundation — beyond the area of backfilled, uncompacted soil — you are pouring water down to your footings.
In older houses, the downspouts were often connected to the main stack and the sanitary line. Now they are tied into a storm line in the street. In older homes it’s a good idea to disconnect the downspouts and have them empty above the surface.
After a number of years, it’s likely the weeping tile has shifted or broken, or is full of tree roots, and every time rain comes down those downspouts it has nowhere to go but up against your foundation, putting lateral hydrostatic pressure against those walls which could one day crack the foundation. Or it could cause a sewage backup into your home, which you definitely do not want.
You may find you need to direct water away beyond the end of the downspout, or from a low-lying area next to your house. The best fix is to put in a French drain, which is basically a shallow trench filled with gravel that will carry excess groundwater away from your house.
It’s not supposed to happen, but over time homeowners do landscaping projects, and renovations, and little by little they can significantly alter natural surface drainage patterns until they create big problems for people next door. Be aware of how your plans might affect surface water drainage.
For more information on home renovations go to makeitright.ca