Foundation Cracks on the South Shore: Which Ones Should You Worry About?

Most homeowners on the South Shore eventually find a foundation crack. The good news: most of them are not a problem. The hard part is knowing which ones to worry about.

The crack types you'll see

Vertical hairline cracks are the most common. They appear in poured-concrete foundations within a few years of construction as the concrete cures and the house settles. If the crack is straight up and down and less than 1/8 inch wide, it's almost always cosmetic.

Diagonal cracks running from a corner of a window or door usually mean some minor settling. They're worth sealing to keep water out, but they're not structurally urgent in most cases.

Horizontal cracks are the ones to worry about. They typically mean the wall is being pushed in by hydrostatic pressure from outside, and they often appear about halfway up the wall. If you see a horizontal crack — especially with any visible bowing — get an inspection soon.

Stair-step cracks in brick or block foundations follow the mortar joints in a staircase pattern. They usually indicate settlement, and the wider they are, the more urgent the situation.

What causes them on the South Shore

Three things drive most foundation cracking around here:

• Wet, clay-heavy soils. When the soil around the foundation gets saturated (very common in the spring), it expands and pushes against the foundation walls. Over years, that pressure causes horizontal cracks.
• Ledge under the house. Many older homes around Hanover, Norwell, and the inland parts of Marshfield were built on uneven bedrock ledge. When the soil between the ledge and the foundation settles unevenly, you get diagonal and stair-step cracks.
• Storm exposure. Coastal towns like Scituate and Marshfield see repeated nor'easter wind loading on foundations, plus salt-water-driven concrete spalling that accelerates crack formation in older basements.

What to do

If you've found a crack:

1. Measure it. Use a credit card or a ruler. Anything under 1/8 inch wide is likely cosmetic; anything over 1/4 inch deserves a look.
2. Check for water. Run your hand along the crack after a rainstorm. If it's wet, it needs sealing regardless of width.
3. Photograph and date it. If it gets wider in the next few months, that's a sign of active movement that should be addressed.

If you're unsure whether what you're seeing is serious, get in touch. Most of the time the answer is "it's fine, here's what to keep an eye on" — but the few cases that ARE urgent are better caught early.

Looking for specifics on the repair side? Our foundation crack repair page walks through how each crack type gets treated.