Six Reasons Your Foundation Fails

A foundation rarely fails because of one dramatic event. It moves slowly, because of what is under it, beside it or growing near it. The first signs are small: a crack in a wall or a floor, a door that sticks, a gap around a window. Understanding why foundations fail helps you spot the cause early, while it is still cheap to fix.

This guide explains the six most common causes, how they connect, the warning signs to look for, and what repair involves.

The short answer: most foundation failures come from the soil moving, and water is behind most of that movement. The six causes are clay soil, poorly compacted fill, a sloping lot, erosion and poor drainage, poor construction and thirsty trees. See our foundation repair service for the options.

Where the six causes sit

The picture below shows where each cause sits around a house. Most houses have only one or two of them.

Six reasons your foundation fails

1. Clay soil that swells and shrinks

Many parts of the Greater Toronto Area have clay-rich soil. Clay takes in water and swells, and when it dries it shrinks. Those cycles push a foundation up in wet seasons and let it drop in dry ones, and they rarely do it evenly. That uneven movement is called differential settlement, and it opens cracks in walls and floors. Clay near a house is the first thing to check if cracks open in summer and close in the fall. For how the damage looks, see the types of foundation damage, and our guide to homes on clay or silt soil.

2. Poorly compacted fill

Soil that was dumped and not packed properly settles over the years. Because of this, a foundation built on loose fill, or beside it, can sink slowly. The problem is common on lots that were filled or reclaimed, and on soil next to the foundation that was backfilled after a repair. Gaps or sunken soil beside the wall are warning signs. If you are buying a property, ask about the fill and the soil. See the best soil for grading around a house.

3. A sloping lot

Soil on a slope can slowly creep downhill, and it pushes on any foundation in its path. That is a concern on steep lots and near ravines. Water makes it worse, because it loosens the soil. If your lot slopes, good drainage and a stable grade matter even more. See how to fix a sloping yard.

4. Erosion and poor drainage

Erosion is the simplest cause of settlement. Bad drainage, uncontrolled water flow and bare soil let water wash the ground from under and beside the foundation. Clogged gutters, short downspouts and soil that slopes toward the house all feed it. If it isn’t caught early, erosion can leave a foundation with nothing to rest on, and then the repair is underpinning. See our guides to improving your home’s drainage and how gutters affect waterproofing.

5. Poor construction

Building codes and inspections have made poor construction a less common cause than it was. It still happens, especially in older homes and unpermitted work. A footing that is too shallow or too small, missing drainage or weak concrete can’t carry the house for decades. Cracks that appear within a few years of a new build are a clue. If you are buying, ask for the permit and the inspection records.

6. Thirsty trees

Plants pull moisture from the soil in a process called transpiration. Large trees near a house can dry clay soil in a hot summer, and the soil shrinks, which can let the foundation settle. The effect is greatest with big, thirsty trees close to the wall and in a dry season. If you have large trees nearby, make sure they get enough water in a drought, and plan new planting at a sensible distance. Don’t cut a mature tree without advice, because removing it can make the soil swell.

The thread that links them: water

Look again at the six causes, and water appears in almost every one. Clay moves with moisture, fill settles when it gets wet, slopes creep when they are saturated, and erosion is water. That is why fixing the drainage, and keeping water away from the foundation, protects against most of them. See our guides to exterior waterproofing and weeping tile.

Signs your foundation is failing

• Cracks in walls and floors, especially horizontal, stair-step or growing cracks.
• Doors and windows that stick, or gaps that open around them.
• Floors that slope or feel uneven.
• A wall that bows inward.
• A porch, a chimney or a staircase pulling away from the house.

Our guides to spotting and repairing cracks and the seven signs your basement needs waterproofing explain what each sign means.

Which of the six might be yours?

Tap the clues that match your house in the finder below, and the likely causes light up.

What does this mean for homeowners?

Knowing the causes helps you find the source of a problem. If you live on a slope, learn how stable it is. If you have large trees near the house, make sure they get enough water, and choose new planting carefully. Keep the gutters clear, the downspouts long and the soil sloping away. And if you see a warning sign, mark it with a pencil and a date, photograph it, and have it assessed before it grows.

What does this mean for people planning to build or buy?

• Find out about the soil on the lot, and whether it is clay.
• Ask about any fill, and how well it was compacted.
• Be careful with a lot on a slope or near a ravine.
• Plan drainage and erosion control from the start.
• Check that the work was permitted and inspected, and get an engineer’s opinion when in doubt.
• Ask a landscaper about existing trees, and about planting at a sensible distance.

What repair costs

The cost depends on the cause and the damage. Epoxy injection crack repair typically costs $400 to $800 per crack, and foundation repair typically ranges from $500 to $15,000 or more. Underpinning typically costs $30 to $100 per square foot. Fixing the water around the foundation matters too: interior waterproofing typically costs $69 to $190 per linear foot, and exterior waterproofing $110 to $500. Only a free on-site estimate gives you a number for your house. See our cost guide.

How Aquatech helps

We start with a free on-site inspection, look at the cracks, the soil, the drainage and the structure, and tell you honestly what is causing the movement. Then you get a written, itemized estimate. A lifetime warranty backs every project and transfers to the next owner. Also, if you have a comparable written quote from a licensed Ontario contractor, we will match it.

FAQs about why foundations fail

Worried about your foundation?

Book a free assessment. We will find what is causing the movement, tell you what it needs, and give you a written, itemized estimate. You can also call 647-794-1701 or 866-620-8492.