Structural problems

There is a widely repeated shorthand that vertical cracks are fine and horizontal cracks are serious. It is a useful prompt, not a diagnosis. This Old House quotes structural engineer Jim Graham: "Horizontal cracks indicate that the soil is exerting enough pressure on the wall to make it bulge inward." Diagonal cracks typically point to uneven settlement, and hairline cracks are usually curing shrinkage. But the same crack can be benign in one house and a symptom of active movement in another, depending on soil, drainage, age and what is above it.

What matters more than the shape is change. General contractor Tom Silva, quoted by This Old House: "Any crack that appears suddenly isn't normal, and any crack that continues to grow in width or length isn't normal." So monitor. Mark each end of the crack with a pencil and the date, measure the width, and photograph it monthly. A crack that hasn't moved in a year is a very different conversation from one that grew a quarter inch over a winter.

Water is the common thread behind a large share of foundation problems. Soil that swells and shrinks, downspouts dumping at the wall, and grading that slopes toward the house all put load where it wasn't designed to go. Before anyone sells you piers, ask whether the drainage has been assessed.

Do not accept a diagnosis over the phone, from a photo, or from a salesperson holding a laser level in your hallway for ten minutes. Ask for elevations across the whole floor plan, and for the reasoning, in writing.

How to choose

Monitor before you spend, if it's safe to

Date-marked pencil lines and monthly photos over 3-6 months tell an engineer whether movement is active. That evidence is genuinely valuable and free.

Treat a visibly bowing or leaning wall as urgent

Bulging, leaning or displaced masonry is a load-path problem, not a cosmetic one. Get a structural engineer out, and keep people out of the space until you have an opinion.

Look for the water source first

Gutters, downspout extensions, grading and a leaking supply or drain line are cheap to check and often part of the cause.

Multiple symptoms at once raise the priority

This Old House flags cracks appearing alongside sticking doors, sloping floors and water intrusion as the combination that warrants an engineer.

Never let one company both diagnose and bid unchallenged

Get the engineer's written scope, then at least three bids against it.