Hairline crack or hairline trouble?

Most foundation cracks aren't a structural problem. Concrete shrinks as it cures, settles a little as the house ages, and shows hairline cracks in places that look alarming but aren't.

Here's the test: take a pencil and try to push the tip into the crack. If the tip goes in easily, the crack is wider than 1/16" — that's worth taking seriously. If it doesn't, you almost certainly have a cosmetic crack.

The second thing to check is whether the crack is moving. Mark the end of it with a date in pencil. Come back in three months. If the crack has grown past your mark, the foundation is still settling and the crack should be sealed before water finds its way in.

Vertical cracks are usually shrinkage. Diagonal cracks running from a corner are usually settlement. Horizontal cracks across a wall are the ones that need attention now — they're a sign of pressure pushing the wall in.

If you're not sure what you're looking at, send us a photo. We'll tell you over the phone whether it's worth a visit.