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Renovation & Design

Maintaining slope away from foundation is essential

Question: I was reading an old article of yours and have a quick question. We are looking at putting river rock between my house and my neighbour’s house by the sidewalk. Prior to that, we are looking at adding some topsoil to make sure the grading is sloped away from the foundation. Should the topsoil go right up flush with the top of the sidewalk so that water drains on top of the sidewalk, as opposed to against the sidewalk? I realize the river rocks would be three inches or so above whatever height the topsoil goes to.

My main concern is that the grading is OK and water is diverted from the foundation as fast as possible, although with only six feet between the houses, I don’t think we get that much water there to begin with.

Many thanks in advance for your advice and recommendation.

— Regards, Emidio Almeida

Answer: Materials used for regrading and landscaping around a home can vary, but most are acceptable as long as a good slope away from the foundation is maintained. Using topsoil may not be the best, as it can easily wash away, but will be acceptable if you cover it properly with something to prevent erosion.

One of the more common items that I address in almost all pre-purchase inspections is proper grading around a home. Maintaining a good slope away from the foundation is extremely important to prevent moisture intrusion, even if there are no structural issues. Proper grade will go a long way to ensure rainwater and snowmelt runoff is properly channelled away from the home and does not over-saturate the soil directly adjacent to the home. If that soil is saturated and cannot easily drain, water may enter the foundation through small openings, or force its way into the porous concrete by hydrostatic pressure.

Having a sidewalk near the foundation of a home is almost unavoidable, but care should be taken not to install or pour it directly up against a concrete foundation. Too many times I see this done, which will ultimately lead to grading issues. If the soil shrinks, seen during recent dry weather, the sidewalk will settle. Often, it settles toward the foundation, funnelling any precipitation directly toward the unprotected concrete foundation.

So, how do we avoid this issue? By ensuring there is a large enough space between the sidewalk and the foundation.

By leaving a large space between the sidewalk and the foundation wall, easy access for regrading can be achieved. The space will certainly drop, over time, as the soil erodes and shrinks. Building it back up again may be no more complicated than adding more soil. Even if the sidewalk settles or slopes, it may be possible to raise or level it by jacking it from the openings at the sides. If it is directly against the house, that option would not be viable.

From your description, you have exactly the right idea for the proposed sidewalk. Installing it equidistantly between both structures should be the best option. That way you can build up the soil on both sides, creating a swale to channel away water. Using topsoil to create the slope is all right, but it would be better to use more solid fill material that would not erode as easily. Topsoil can be quite fine and may wash away rather than hold solidly in position.

If you can get some of the local clay soil that is often dug up to pour foundations, it would be a better choice. It may seem odd to suggest using this material, but it does pack well when wet and will only absorb so much water. When saturated, it will help shed excess precipitation down to the bottom of the swale.

As far as the height of the fill and the stone, it may be very difficult to prevent the river stone from falling all over the sidewalk if you build the soil to the top. That may create a tripping hazard, as well as added maintenance. You may be better off to raise the sidewalk, slightly above the fill. That way, you can raise the grade to the top with the stone layer without having the stones spill all over the walkway. In that scenario, you may wish to leave the soil layer a few inches below the sidewalk, to improve drainage.

If you install the sidewalk on a compacted layer or stone or sand, and raise it above the bottom of the swale, it may also be more stable. In that scenario, water running down the sloped soil will drain to a small swale on either side, before draining away. That will help prevent the sidewalk from becoming wet and slippery during precipitation and prevent movement due to pooling water. It will also leave space for the decorative river stone, which should not impede water flow due to the gaps between the stones.

The final piece of the puzzle is to ensure you install a proper membrane between the sloped soil and the stone.

The best material is normally known as landscape fabric, which is a woven synthetic cloth.

The beauty of this product is that the small gaps between the weaves allow water to penetrate, but are small enough to prevent weeds from growing through.

The fabric also prevents sunlight from shining through to the soil, further preventing unwanted vegetation growth.

It’s up to you to choose the material for improving the grading between your houses prior to sidewalk installation, as long as you do the job well. Providing enough slope and covering the soil with a proper landscape fabric before completion of the work will be the key to a long-lasting and well-draining job.

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

trainedeye@iname.com

Ari Marantz
August 10

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