Foundation cracks can have many causes
SO here’s a question for you, courtesy of dozens of emails: Dear Mike, I’ve got a crack in my foundation — is it a problem?
Yes, absolutely. And, not necessarily. There are different types of cracks, as well as different types of foundations. And, depending on where the crack is, it may or may not be a big deal.
I’m going to say it up front: If you’ve noticed a crack in your basement floor or wall, you should call in a foundation specialist for an opinion. You aren’t qualified to assess if it’s serious, and I can’t see it from here. It may be a new crack, or it’s got bigger so you’ve just seen it for the first time. Neither of those is good news.
A lot of people are afraid of calling in specialists because they think it will cost more, or because they think there will be an upsell on the services required. But this is not something you should let slide, because the crack won’t fix itself.
In this case, what I don’t know can’t hurt me is 100 per cent wrong (like it usually is). With a foundation crack, your house’s structure could be compromised, and that is serious. Here’s some things I do know:
Small cracks can indicate big problems.
Small cracks can let insects, vermin and water in.
Small cracks can grow bigger, and the bigger the crack, the more expensive the repair.
Different cracks indicate different possible problems with your foundation, and they give clues to what the cause might be. Bulging and bowing walls, step cracks in blocks or bricks, vertical cracks, horizontal cracks, in walls, in floors — they all mean something. So what causes foundation cracks? The most common cracks are caused by concrete shrinkage. Concrete is made with water, cement and aggregate — it will shrink as it cures and dries. It is affected by temperature, both cold and hot. If its curing is interrupted by a drop in temperature — let’s say an intense cold freeze happens on the night your basement walls were poured — that will affect the final product. Or, if your basement pad was poured in intense heat and sun, it will dry too quickly. That will cause cracking.
Cracks caused by concrete shrinking aren’t usually a problem — at least not one that’s structural. But they can still allow water or insects to get into your home, so they need to be dealt with.
Another reason might be settlement; your house is settling into the soil. That’s not so good and it might be caused by a few reasons. For example, if your house’s footings aren’t adequate or are damaged, there might be settlement, which can cause cracks.
This settlement might be caused by something beyond your control. For example, if the soil around your home is saturated with water, or if your area has had a drought for a long time, you may find problems develop with your foundation. In the first case, the groundwater rises and exerts pressure against your house’s foundation walls and floor. In the case of extended dry periods, the soil actually shrinks as the water evaporates out and that can allow your foundation to settle. That settling may cause a part of your home to sink.
Concrete has a lot of compressive strength but not much tensile strength, so it’s prone to cracking if there is lateral pressure pushing against a wall. That’s why we add rebar or fibre to concrete in some situations to improve its tensile strength.
So where is that pressure coming from? There is a lot of pressure in the soil. It’s from the water that’s held in the soil around your home, and in the water table. The amount of this water will change, depending on seasonal rain and drought, especially on clay soil.
Think about your house as a boat, except instead of floating in water, it’s sort of floating in the soil that surrounds the basement. That soil is fluid; it’s in motion, and it’s shifting and exerting pressure at all times on your foundation.
Some wet soils can be almost 40 per cent water. So, think about extremely dry conditions, when that soil will shrink, and how that can affect your home. In times when there is too much rainfall over a prolonged period of time, what’s that water pressure going to do? And, in winter when that water freezes, it will expand, putting more pressure against the wall of your foundation. That can cause a crack.
There are lots of other reasons for cracks in foundations, some as simple as backfilling around a house during construction. That can lead to cracking, either by equipment hitting the wall or dumping the load against the improperly supported wall.
Not all cracks should be taken lightly. A horizontal crack is one I’d pay attention to. Typically they indicate your wall’s structural integrity has been undermined.
Horizontal cracking higher up on the wall is usually from frost damage and the freeze-thaw cycle; water from your downspouts or sump pump saturates the area, it freezes and exerts pressure on the basement wall. Or it might be from vehicle damage or improper backfill.
Cracking further down the wall is more likely to be caused by the pressure of the earth itself. This is especially true on hillsides and in areas with wet, heavy soil. The force on your basement wall exerted by the soil is far greater at the bottom of the wall than at the surface. It might start as a crack but it will continue to press inward and push the wall in, causing severe structural damage. It might even cause your basement wall to collapse inward.
When it comes to basement cracks, don’t be an ostrich and stick your head in the ground. If you’ve got a foundation crack, check it out. Call in a structural engineer or foundation specialist for an opinion.
— Postmedia News
Mike Holmes inspects a crack in the basement. A crack in the foundation may be serious, or not.