In our previous blogs about house foundations, we mentioned that the soil type in which a foundation lies directly impacts the foundation’s condition over the years. Unfortunately, Alberta didn’t win the soil lottery because expansive clay soil, also known as shrink-swell soil, is abundant across the province, including Calgary.
Expansive soil changes a lot in volume; it swells when it’s wet and shrinks and hardens when it’s dry. This swelling and shrinking pattern translates into pressure and release, which can damage foundations over time, forming cracks in walls and floors, ranging from hairline, cosmetic ones to major structural damage.
The good news is that expansive clay soils don’t have to catch you off guard. With some basic knowledge and a proactive approach, you can reduce the risks of owning a rental property in this tricky type of soil and protect the value of your investment. Keep reading to get all the details you need to know about this soil type and how it can wreak havoc on your property.
Why Expansive Soils Are a Serious Problem for Foundations
We already mentioned expansive soil poses a threat to any building’s integrity; its unpredictable nature needs a detailed breakdown so landlords in Alberta have a wider perspective of how it behaves during the year:
- When expansive soil takes in water, it gains a significant force (sometimes over 30,000 pounds per square foot) that pushes laterally against foundation walls, especially in basements where soil is in direct contact with the structure. Over time, constant pushing can make the walls crack, bow inward, or shift out of their alignment. Even the most solid, well-built foundations can struggle under this expansion pattern.
- In the dry months, the same soil that can expand up to 20% of its volume with water contracts and pulls away from the foundation. This shrinkage creates gaps beneath and around the structure, reducing the support the foundation relies on for stability, and resulting in parts of the home settling unevenly, sloped floors, widening cracks, and misaligned doors and windows.
- Alberta’s weather causes big changes in soil moisture throughout the year. While the spring snowmelt saturates the soil, summers are historically dry, and the freeze-thaw cycles are constantly altering soil volume. This means that most Albertan house foundations can be under constant pressure of expansion and contraction.
Let’s look at how expansive soil movement manifests in house foundations and the house itself, and how it evolves in case there’s no maintenance work:
The First Signs of Expansive Soil Foundation Damage
- At first, damage from expansive soil manifests as small vertical or diagonal cracks in the basement walls. And if those cracks are left unattended, they’ll widen or multiply due to repeated soil pressure, creating entry points for water that is a threat on its own, and you can learn more about water damage here.
- On the exterior, clay soil can separate from the foundation walls when it shrinks, creating empty spaces along the perimeter of the home. These gaps are most noticeable around the near areas of the home, such as the corners or downspouts, and they’re a clear sign that the soil is not providing enough support and can create a path for water to reach the foundation. This increases the risk of leaks, water damage, and more soil instability when the ground re-expands.
- Rigid materials like bricks tend to show stress quickly when the structure alters beneath them. The lines often start small, but they can evolve and widen until showing a stair-step shape, as the stress goes through the mortar joints first. As for more flexible materials like the siding ones (vinyl, wood, or composite), they can manifest foundation movement by buckling, rippling, or detaching at seams and corners.
You may notice gaps forming, fasteners loosening, or sections that no longer sit neatly against the wall. This not only will affect the property’s exterior appeal, but can also expose the building envelope to weather and pests.
Indoor Signs of Expansive Soil Foundation Damage
- If there are signs of foundation damage in the interior, it often indicates a severe issue. The pressure can make the walls curve inward, and in the most advanced cases, they can look visibly lean, warped or feel unstable. Structural shifts can also cause:
- Drywall cracks
- Gaps and lines between the connection points between surfaces, such as baseboards, door trims and crown moldings.
- Rigid flooring materials like tiles are very sensitive to foundation movement. The stress is transferred to the tiles, causing them to crack, lift, or loosen. Grout lines may also crumble or separate, allowing moisture to seep underneath and worsen the issue over time.
- The home’s entire structure may look uneven, as it’s common that one part of the building sinks to one side due to the ongoing movement and pressure beneath.
- Sticking and misaligned doors and windows, with diagonal cracks around the frames, are some of the first places severe foundation movement shows up, and tenants often notice these ones first when they notice they can’t close them like usual. That’s because even small shifts in the structure can throw off the precise alignment these openings rely on.
How to Keep Expansive Clay Soils’ Damage Away From Your Rental
Even though changing the soil under your property is not an option, mitigating expansive soil’s impact on your property’s foundation is possible with prevention centred on reducing extreme moisture swings around the foundation and catching early signs of movement before they escalate.
Moisture Control & Drainage Management
Keeping moisture levels as stable as possible helps minimize the problematic swelling-shrinking movement. During dry periods, lightly watering the soil around the foundation can prevent excessive shrinkage, while in wet seasons, proper yard drainage ensures the soil doesn’t become oversaturated. That’s why routine tasks like soil grading around the home, gutters and downspouts and complementary drainage systems maintenance must be at the top of your maintenance list to protect the foundation.
Your goal is to ensure the soil doesn’t go to any of the extremes, as both cause stress to the foundation walls. The key is finding a balance of steady and moderate moisture rather than dramatic fluctuations.
Landscaping Considerations
Landscaping, often associated with curb appeal, is fundamental to controlling the moisture behaviour around the foundation. The balance approach applies here as well, as landscaping with expansive clay soil’s goal is to avoid the drastic wet–dry swings and keep conditions as consistent as possible. Here are a few things to consider:
- Plant large trees and shrubs away from the foundation: Trees and dense shrubs pull a lot of water from the soil, and if they’re planted too close to a home, they create localized dry areas that cause the clay to shrink and pull away from the foundation. This can be especially problematic when one side of the property has more vegetation than the other, leading to uneven moisture levels and differential soil movement.
- Avoid planting fast-growing or very thirsty plants. These aren’t good for Alberta’s climate because they pull water from the soil quickly and unevenly. Their large roots can also reach under the foundation, causing the soil to shrink even more.
- Use appropriate grading and mulch to regulate moisture. Bare soil dries out quickly, especially during the summer; that’s why mulching around the foundation helps the soil keep its moisture by slowing evaporation. Combining mulch with proper grading supports a more stable moisture environment on the soil around the foundation, mitigating the soil’s expansive behaviour effects.
Routine Inspections and Crack Monitoring
The most important step is to make seasonal inspections in the spring and the fall. Spring is ideal for catching issues caused by snowmelt and excess moisture, while fall allows you to prepare the foundation for the cold and catch problems before freezing conditions.
One of the most important things during these inspections is to watch how cracks change over time. Not every crack is a problem, but it’s smart to track them with photos and measurements. This way, you can see if there’s ongoing movement or if it’s time to call a professional.
We have a detailed inspection checklist for foundations that you can check out here.
Expansive Clay Soils Damage Isn’t Inevitable
Expansive soils can cause a lot of issues, and even though in Alberta it’s difficult to avoid properties built over them, this doesn’t mean your investment is doomed. As always, landlords need to take a proactive attitude to catch the warning signs through consistent inspections and maintenance tasks focused on how expansive soils behave to keep them stable. Applying the insights we discussed in this blog, you’re protecting your long-term investment and avoiding very expensive surprises down the road.
