Question: On the north and west sides of my house I made decorative areas right against the house for planters to sit on, using river rock laid over landscape fabric. Due to our extremely dry spring and summer, the soil has shrunk away from the foundation, creating a gap which some of the river rock fell into. I removed all of the rock which had fallen into the gap, and I now have a gap about four inches wide by six inches deep. I am unsure whether I should leave the gap and hope enough rain falls to swell the soil back to the foundation, or fill it at once with soil.
What would you suggest is the best option? Yours truly,
— Keith Bolland
Answer: Maintaining a moderate level of soil moisture content is often a challenge as the weather changes, and you have highlighted one area of concern. Keeping the soil near your foundation from eroding and shrinking is not only a matter of adding more, but also keeping it well hydrated during warm, dry spells.
As summer has recently arrived, this is an ideal time to discuss your issue with soil shrinkage. Due to the lack of snow this past winter, several previous dry summers and the continuing lack of precipitation, dry soil issues are continuing in our area. I have addressed this issue quite often in the past few years, but it is more noticeable recently to most homeowners as they personally see the low water levels in the local rivers and lakes. Unfortunately, other than a few recent thunderstorms, we are still receiving below-average rainfall, making matters worse.
The main issue with the gap you are seeing between the soil and the top of your foundation is not the cosmetic issue of your new stones, but the potential drying of the soil lower down. Filling in the current gap with new topsoil should not cause any issues in the future, due to the lack of depth of this void.
If further excavation reveals a space continuous for more than a metre downward, then you may not want to fill it in to prevent issues if the rains return. So, if your primary focus is the look of your new planter area, go ahead and spread some fresh topsoil in the crack and cover it with the landscape cloth and stone, but other future maintenance is also warranted.
Even though the newly landscaped area next to your foundation looks like it is a fine bed of river stone, it is still mainly expansive Red River Valley clay beneath. This not-so-wonderful soil is at the higher end of problematic soils, because it not only expands considerably when saturated, it alternatively shrinks markedly when it is too dry. For this reason, you will not only have to fill in the small trench near your house, you will also have to water the area regularly. This will be required to prevent a repeat of the existing conditions, but also to help prevent further drying of the clay soil beneath.
As our weather has become quite dry in recent months and years, it has begun to affect more than the dry timber in our forests, which can lead to dangerous wildfires. The dryness has caused some moderate to major settlement in many homes in southern Manitoba. Numerous homes that have not moved in decades now appear to be sinking once again. This is directly attributable to the lack of moisture in the soil, as the drought continues, causing dryness deeper and deeper below the surface. So, can we replenish the soil moisture that deep down by watering at the surface?
The answer to that questions is up for debate, but I have a somewhat different approach to addressing that issue. As I have been advising my clients for several years, watering the soil at the surface is critical. No amount of watering will likely replenish the lack of moisture in the clay underneath the footings and foundation of your home, but it is still very important. Maintaining moderately saturated soil at the top of the column with prevent further drying of the deep soil. If the top is dry, water vapour will naturally migrate upwards until it evaporates through the surface. If the surface has a reasonable moisture content, it may prevent further excessive drying of the moisture still in the lower soil. That may keep the deeper clay from reaching a critical moisture level, where it shrinks enough to allow your home to settle.
So, how do we know when our soil has a reasonable amount of moisture content, without simply wasting water down the weeping tile?
The answer may be simpler than you think. Look at the vegetation in your yard and at the surface. If the grass, shrubs, flowers and other vegetation are green and healthy, then moisture content may be good. If your vegetation looks dry and dying, or if there are fissures in the topsoil, then it is time to water. At your home, if the river stones start to again sink into a void near the foundation, take out the garden hose and nozzle.
Filling in a small area near the top of the soil outside your foundation is warranted, and should not cause any lasting issues if we return to average or above-normal precipitation.
The key to preventing an early recurrence, and preventing further drying and shrinking of the soil in this area, is regular watering in the dry, hot summer months.
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.