Your house’s foundation is literally the thing that supports the entire structure, so it’s pretty important.  And so cracks in the foundation can be alarming.  But foundation cracks are fairly common and usually nothing to worry about.  However, some are serious problems and should be repaired.

Let’s keep a few things in mind when we’re talking about foundation cracks.  First there’s often not a definitive answer about how bad a crack is or how urgent a repair might be needed.  Different people can come to reasonable but different conclusions about the severity of a foundation crack.  Second, one of the most important aspects of a foundation crack is whether or not it’s moving and getting bigger, and the only way to know that is to monitor it over several months at a minimum – or maybe monitor it over several years.  A home buyer certainly doesn’t have that kind of time before needing to decide to move forward with the home purchase, so there’s always going to be a little bit of uncertainty when dealing with a foundation crack.  Third, what to do about a crack can depend on what type of soil the house is built on.  Soil with lots of clay will behave differently than sandy soil, and this can affect the decision on the proper course of action.  And fourth, if water is coming through the crack then it should be repaired or sealed to help prevent the water seepage.

Here are some of the more common types of cracks, what they usually mean, and how much of a problem they are.

Horizontal

A horizontal crack is exactly the type of foundation crack that you should worry about.  A horizontal crack is usually caused by pressure from the outside pushing on the wall, and this pressure is likely to continue to push the wall farther and farther in, until it becomes unstable and collapses.  If the wall is bulging at the crack that’s an especially bad sign – a wall that isn’t vertical can’t support as much load.

There are various repair methods to be used with a horizontal foundation crack, and they all seem to work pretty well.  But they’re not cheap.  You can have a structural engineer evaluate a horizontal crack, but this is a time when it might be better to skip that step and move straight on to a foundation repair specialist.

Vertical

A vertical crack is the most common type of foundation crack and the vast majority of the time it’s of very little consequence.  Many vertical cracks occur as the poured concrete foundation shrinks a little bit as it first cures, so they’ll develop within the first months of a home’s life.  A vertical crack can also be caused by settling.  Like any crack, a vertical crack can allow some water seepage and if this is happening then it makes sense to get it professionally sealed.  Also, if you plan to finish off your basement and cover a crack with drywall then I recommend that you get it sealed first regardless of any water seepage, just as a precaution and a little insurance against future water seepage problems.

A vertical crack that’s very wide – about 1/8 inch or so – or that’s displaced so that the wall on one side is leaning in a bit can be a concern because of the evident motion of the wall.  In this case having a structural engineer might be of help (but it might not), and the crack really needs to be monitored over many months to determine if it’s still moving.

If a vertical crack is bigger at the top than at the bottom then the wall has clearly settled and allowed the foundation to shift a little bit.  And if there are two vertical cracks facing each other on opposite sides of the house then probably one side of the house is settling a little bit and the house is tilting along the line between those cracks.  But again, how serious this is depends on how much it’s shifted and if it’s still moving.

Diagonal or stair-step

A diagonal crack in a poured concrete foundation and a stair-step crack in a concrete block foundation are basically the same thing and they’re usually caused by differential settlement.  One part of the foundation is settling more than another part.  This often happens at corners, and cracks like this on both sides of a foundation corner are very common.

Cracks from window or door corners

It’s very common to see foundation cracks that start at the corner of a window or door opening.  These square openings are a stress concentration in the foundation wall and so it’s a natural place for cracks to start, even in the absence of any other problem.  These cracks are almost always of no consequence.

 

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