Find a crack in your foundation? Probably no big deal, right? Think again. According to Popular Mechanics, any crack wider than 1/16 of an inch poses a serious problem, even if it’s no bigger than a hairline. It deserves professional foundation crack repair.

Especially problematic are cracks that emit moisture, widen or increase in length, or if its faces rub and grind against each other with the push and pull of temperature changes and humidity.

“All of these indicate foundation movement and that’s not good,” writes Popular Mechanics’ Roy Berendsohn.

The good news? “… in most cases only large cracks indicate structural trouble. You’ll need to contact a structural engineer or foundation repair company if the crack wraps around a corner, reaches from the basement floor to the top of the foundation wall, or runs horizontally and the wall below it leans into the basement. All of these problems indicate that the soil supporting the foundation is moving (horizontally or vertically) and taking the foundation with it.”

Why You Should Do It Right with a Professional

But crack repair in a foundation is very tough to fix. Our advice? Don’t risk a DIY on this job. Call a professional and make sure it’s done right.