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Foundation Cracks


robert1966
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I have two questions:

At what point are foundation cracks severe enough to note as severe?

A crack is severe when it's the result of continuing movement or when its presence makes the foundation unstable. In my area, which is quite hilly, severe cracks are always the result of soil movement -- either from water movement or from landslides. Small, slow-moving slides are actually very common around here and some very fancy neighborhoods are built on and around them. In your area, with all it's slab-on-grade foundations, I'd suspect that expansive clay would be a big concern. I can't determine whether a crack is severe or not without first looking at the terrain.

Some home inspection books have diagrams of typical "bad" cracks. I think those diagrams are a bunch of crap. You've got to look at each foundation separately and consider t's surrounding environment before you can tell anything meaningful about a crack.

What method do you use to inspect home foundations? Any special tools or measurement devices such as water levels or zip levels?

I just use my eyes. If something's leaning, I'll use a plumb bob to document the exact amount of lean. If something's cracked, I'll use a ruler to document the size of the crack. But if something's out of level, I don't measure that. It takes too long and the benefit isn't worth the time invested.

- Jim Katen, Oregon

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  • 1 month later...

Cracks in any material are due to movement of some sort. Concrete and masonry (brick, block, stone) can crack from very very small movement (especially masonry)......and also from "normal" shrinkage, which occurs as excess water in the mix (concrete and mortar) evaporates.

In general.........horizontal cracks (which are indicative of excess lateral pressure pushing inward) in block or brick walls should always be noted as a defect...........with further action to be taken.

Most often (but not always), horizontal cracks occur along with inward movement (vertical curvature or "bowing") of the wall. Such movement can most easily be observed by holding a 4-foot carpenter level (plumb) against the wall. With one end of the level on the floor slab, you will see a gap between wall and level if the wall has been pushed inward. You will usually see this at top of wall also with end of level pushed up against bottom edge of a floor joist. You might also see the wall tilted inward (instead of bowing inward).

Horizontal cracks are caused by excessive tension stress on inside face of wall (at mortar joints which are notoriously weak in tension) due to bending of the wall in the vertical direction (between floor slab and first floor; though adequate lateral bracing from first floor can be problematic!)

Near ends of wall (at corner)........lateral pressure causes "step" cracking instead of just horizontal cracking..........as the wall tries to bend both vertically and horizontally.

Vertical cracks are (in general) due to vertical settlement or "normal" shrinkage.........though some vertical cracks (such as those formed as part of "step" cracking) can be caused by lateral pressure.

Unless a vertical crack is relatively wide (say, more than thickness of a quarter or nickel), it is likely that settlement (or shrinkage) has stabilized. However, an inspector should note all obvious cracks.

Downward settlement of a foundation must cause downward movement of the entire house......unless a gap develops between top of foundation wall and the house elements above (which can happen). Such downward movement usually causes house floors to slope. Therefore, if the house floors are not sloping in the vicinity of the suspected foundation settlement problem.........there really can not be all that much of a settlement problem.

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