How Temperature Changes Affect Concrete
Concrete isn't static. It expands when warm and contracts when cold. Not a lot, but enough to matter over the length of a foundation wall.
The Daily Cycle
Even within a single day, my foundation experiences temperature swings. The part above grade heats up in afternoon sun and cools at night. The buried part stays relatively constant. That difference in expansion between the top and bottom creates stress.
Rick explained it like this: "Imagine a board that's warm on top and cold on bottom. The warm part wants to be bigger. The cold part doesn't. The board bows." Same thing happens to concrete, just less dramatically.
The Seasonal Swing
My basement goes from maybe 55 degrees in winter to 85 degrees in summer. That's a 30-degree swing just in the basement air. The concrete walls might swing even more since the exterior is exposed to weather.
Concrete expands about half an inch per 100 feet for every 50-degree temperature change. My longest wall is about 35 feet. That's almost a quarter inch of seasonal movement. Not huge, but multiply that by 45 years and thousands of cycles, and you start to understand why cracks develop.
Restraint Creates Cracks
My walls want to expand and contract, but they're constrained. The bottom is attached to the footing. The top is attached to the house structure. The corners are attached to adjacent walls. Something has to give, and what gives is the concrete itself. It cracks to relieve the stress.
Most of my vertical cracks are probably thermal in origin. They appeared in the middle sections of walls, away from corners where there's less restraint. Classic thermal cracking pattern.
The Freeze-Thaw Problem Up North
This is the big one for those of us in cold climates. Water and freezing temperatures are a terrible combination for concrete.
Water in Cracks Gets Worse
I have a crack in my basement that started as a hairline. Over five years, it's grown to about 1/8 inch. That growth happened one freeze-thaw cycle at a time.
Water gets into the crack. Winter comes. Water freezes and expands 9%. The crack gets a tiny bit wider. Spring comes. Ice melts. More water gets in because the crack is wider now. Next winter, cycle repeats. Every year, a little worse.
This is why Rick kept telling me to seal my cracks before winter. The freeze-thaw progression is real.
Frost Pressure Against Walls
The soil around my foundation freezes in winter. When it freezes, it expands. That expansion pushes against my basement walls. Not enough to cause immediate damage, but year after year, it adds stress.
My neighbor's house has horizontal cracks that the structural engineer said were from frost pressure combined with hydrostatic pressure from wet springs. The combination of frozen soil pushing and then melting snow saturating the soil was too much for his walls.
Spalling and Surface Damage
The exposed part of my foundation, the part above grade, shows surface damage that the buried part doesn't have. Pitting. Flaking. Areas where the surface has popped off. That's freeze-thaw damage to the concrete itself.
Water gets into the pores of the concrete, freezes, expands, and breaks off the surface layer. It's called spalling. My foundation has some. It's mostly cosmetic, but it tells me the concrete has been fighting winter for 45 years.
What I Saw in Texas
Texas foundations deal with completely different problems. The freeze-thaw cycle barely exists there. But the wet-dry cycle is brutal.
The Expanding and Shrinking Clay
My roommate in Austin had a slab foundation on clay soil. After heavy rains, his doors wouldn't close. After summer drought, they swung freely but the floors sloped differently. The foundation was literally rising and falling with the soil moisture.
I thought this was insane until I understood the numbers. Expansive clay can swell 10% when saturated. On a slab foundation, that's enough to lift the center of the house while the edges stay put. Or vice versa depending on where the moisture is.
The Drought Problem
Texas has droughts. Bad ones. During drought, the clay shrinks dramatically. Foundations settle into the void left behind. Cracks open up. Then rain returns, the soil swells, and... well, the foundation doesn't go back to exactly where it was.
My roommate's house needed mudjacking after a bad drought year. $3,200 to pump material under the slab to fill the voids. Common problem down there.
The Watering Solution
This blew my mind. People in Texas water their foundations during drought. Soaker hoses around the perimeter, running regularly, just to keep the soil moisture somewhat consistent. It sounds nuts until you understand the alternative is foundation damage.
My roommate started doing this after the mudjacking. His foundation has been stable since. Costs him maybe $20 a month in water during dry spells. Cheap insurance.
Regional Foundation Challenges
Talking to people from different parts of the country, I've learned every region has its signature foundation problems.
The Northern Cold Zone
Deep frost lines mean deep foundations. My footings are 4 feet below grade to get below the frost line. Freeze-thaw is constant. Spring snowmelt can create hydrostatic pressure as frozen ground prevents drainage. Winter heating creates temperature differentials through the foundation.
The upside: clay soil is less common here, so the wet-dry expansion problem is minimal.
The Southern Clay Belt
Texas, Oklahoma, Louisiana, parts of Colorado. Expansive clay dominates. Foundations move seasonally. Slab foundations are common, which means the whole house moves with the soil. Pier and beam construction helps but doesn't eliminate the problem.
The upside: minimal freeze-thaw damage. Concrete lasts longer when it's not fighting winter.
Coastal and Humid Areas
My cousin lives near the Gulf coast. High water table. Constant moisture. Her basement walls show efflorescence everywhere from water migrating through. Sump pump runs constantly. Hydrostatic pressure is a year-round problem, not seasonal.
Salt air also causes issues she doesn't see inland. Accelerates concrete deterioration.
The Arid West
Minimal rainfall sounds great for foundations. But when rain does come, it can cause dramatic soil expansion in clay areas. And irrigation concentrated near foundations can create localized moisture problems. The desert doesn't forgive mistakes with water.
What I Do About Climate Effects
I can't change the climate. But I can minimize its impact on my foundation.
Seal Cracks Before Winter
Every fall, I check my cracks and seal any that have opened or developed. Keeping water out of cracks prevents the freeze-thaw progression. An afternoon of work with $50 in materials potentially prevents serious damage.
Manage Drainage Year-Round
Spring snowmelt dumps a lot of water against my foundation. My drainage setup handles it, but I check every spring to make sure nothing is blocked or has settled. Frozen downspouts in winter are a problem too. Water has to go somewhere.
Monitor Seasonally
I check my foundation more carefully in spring and fall. Spring because that's when freeze-thaw damage reveals itself. Fall because that's my last chance to fix things before winter makes them worse.
The cracks that look the same in spring as they did the previous fall? Those are stable. The ones that grew? Those need attention.