Winter does not cause foundation cracks the way most homeowners think. The damage is rarely from a single hard freeze. It is from repeated freeze-thaw cycles working on water that is already in the wall or in the soil right next to it. Connecticut and the Hudson Valley typically see forty to seventy freeze-thaw cycles between November and March, and each one expands water by about 9% inside any crack or void it has already entered.
Here is what to watch for during the cold months and what each pattern usually means.
The four crack types we see most often
Vertical hairline cracks (often harmless)
A single vertical hairline crack, narrower than the thickness of a credit card and not actively leaking, is usually a shrinkage crack from when the concrete originally cured. These do not get worse from freeze-thaw alone unless they are letting water in. Mark the ends with a pencil and check in spring. If they have not lengthened, they are stable.
Horizontal cracks (call us)
A horizontal crack across a poured wall or following a mortar joint in a block wall is rarely cosmetic. It usually indicates lateral pressure from outside soil pushing the wall inward. Freeze-thaw amplifies that pressure when ground water in the saturated soil freezes and expands.
If you are seeing this with any inward bowing, do not wait until spring.
Staircase cracks in block walls (variable)
Staircase cracks follow the mortar joints in a diagonal step pattern. These can be from settlement, lateral pressure, or both. A staircase crack that is also showing daylight or efflorescence at the joints needs assessment now, not in April.
Cove-joint seepage (very common in winter)
The cove joint is where the basement wall meets the basement floor. Seepage here during a January thaw is one of the most common winter calls we get. It is almost always from hydrostatic pressure underneath the slab, not from a structural failure. Interior drainage solves it; epoxy injection does not.
What freeze-thaw actually does to a crack
Water enters a crack during a melt event. Temperature drops below freezing. The water expands by 9% as it freezes, pushing the crack open slightly wider. Temperature rises again, the ice melts, water settles in deeper, and the cycle repeats. By March, a hairline crack from November can be wide enough to fit a coin.
This is why we tell homeowners that the cheapest time to fix a foundation crack is in October, before that first cycle starts. The second-cheapest time is right now, before next winter.
What to check during a January thaw
When the temperature climbs above freezing for a stretch in January or February, walk the basement with a flashlight and look for:
- Active water at the cove joint or in cracks.
- Damp shadows that were not there in November.
- Efflorescence growing along any wall seam.
- A new crack you did not see in the fall walk-through.
Photograph anything new. Send us the photos. We can usually tell from images and a phone call whether it needs immediate attention or whether it is reasonable to wait for warmer weather to schedule the work.