Renovation & Design

Renovation & Design

Dry soil around home can cause foundation issues

Question: I have heard a lot about watering foundations, given the dry conditions we are experiencing. From what I understand, the main reason for watering is to prevent the house from shifting. The shifting occurs due to dried out soil under the footings, which may cause the footings to drop, resulting in serious damage to the house.

My house is built on 16-inch diameter concrete piles, 25 feet deep. Is it just as crucial to water your foundation if your house was built on poured concrete piles? Can my house still shift if it’s on piles? I have tried finding an answer to this question on the internet but have been unsuccessful. Please help.

Thank you, Robert Fontaine.

Answer: You are correct that watering the soil around the foundation in these drought conditions is more important for homes built on footings, but can also help prevent other issues with your piled foundation, as well. Keeping the soil in your yard minimally saturated by watering may currently be a challenge, but should be done until we return to normal precipitation levels, even in your home built on piles.

The most serious issue that can often happen to a home, from a structural perspective, is for it to sink, or settle, over a short period of time. This will normally only occur if the soil underneath the foundation loses its structural integrity, in one or more areas. In the majority of homes built in our area, which are built on concrete footings, this may be caused by changes to the moisture level in the soil under these footings. If the expansive clay dries out too much, or becomes oversaturated, it will shrink or expand accordingly. In very dry weather, like the recent drought conditions, this can cause the clay soil to become powdery. In that state, it can lose much of its strength, which can allow the heavy foundation and house walls to sink. If that occurs in one area of a home and not others, it will cause some serious cracks and damage.

As I have written recently, and several times in past years, it is very important to keep the soil around the foundation hydrated, to prevent the deeper soil below the foundation from excessively drying out. You have a good understanding of the issue, as it is much less of a concern with a home like yours, which is built on deep concrete piers, commonly called piles. Because the piles go much deeper down in the soil, it is much less likely that the soil beneath those structures will be affected by weather-related soil conditions near the surface. The soil down that deep should be quite stable and always well saturated. However, it is not impossible that some settlement may still occur, because most concrete piers rely partially on friction with the soil surrounding them for support. If that soil dries excessively, it may pull away from the concrete, allowing some settlement due to excessive forces from above.

The above scenario is unlikely with your home, due to the size and depth of the concrete piers, but other issues may arise if the surface soil dries excessively. Initially, a sign of extreme dryness in this area is a gap between the foundation walls and the surrounding soil. This gap may not cause much concern, until it rains. Once significant precipitation returns, it may run down the house walls, easily entering this gap. If the damp-proofing on the foundation is worn out, the walls have moderate cracks, or the form ties have rusted through, seepage is likely. This may appear as a small leak at first, but could become serious leakage over time if the gap is not filled with returning higher soil moisture levels. Even though it may not cause the foundation walls to settle, excessive leakage through the foundation walls will be costly to repair, with major excavation still required.

Another possible side effect of very dry soil outside your foundation may be movement in the basement floor slab. Most foundation walls built on concrete piers have some type of void forms installed under them, to prevent the soil between the piles from moving after the concrete is poured. This cardboard or foam component is normally left in place, even after the basement floor slab concrete is poured. It then will help prevent the soil around the foundation falling into any gaps or voids created under the floor slab, over time. If the clay outside the foundation dries excessively, it may shrink unevenly in some locations, creating isolated gaps. If the same thing occurs underneath the perimeter of the basement floor, it can crack and sink. The void forms may deteriorate or crush over time, creating even more chance of this occurring. While it may not be otherwise structurally significant, a damaged basement floor slab can cause basement partition walls to move. In the worse case scenario, major movement in the soil beneath this concrete slab can cause shifting and damage to the plumbing drains and/or weeping tiles.

Adding moisture to dry soil around a house foundation, by watering with a garden hose or sprinkler, is definitely more important for a home built on footings than one on deep concrete piers. But that area should not be neglected in a piled home, either. Excessive drying of the soil due to lack of moisture can lead to future seepage, and/or basement floor slab movement issues, even in a house like yours. Regular watering is still required as long as the hot, dry summer weather continues.

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
July 24

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