· by Michael Blair, Nashville's Foundation Repair
Most people notice a foundation crack once, worry about it, and then have no idea months later whether it has changed. That is the real difficulty. Houses on expansive clay move a little with the seasons, so a crack that opens in late summer and closes after the winter rains may be doing nothing more than breathing. A crack that grows a little more every year is a different matter. The only way to tell them apart is a record, and late September, when the soil has dried to its lowest point, is the best time to start one.
Why one look is not enough
Clay soil shrinks as it dries and swells as it wets, and the house rides on it. Through a dry Tennessee summer the soil under the perimeter pulls back, particularly on the sunny sides and near thirsty trees, and cracks in brick, block and drywall open slightly. Through the winter and spring rains the soil takes up water again and many of those cracks close most of the way.
A crack that cycles like that is telling you about moisture, and the answer is usually water management around the house. A crack that opens in summer and does not close again, or that comes back wider each year, is telling you the structure is moving in one direction. Both can look identical on the day you first see them.
What to record, and how
The goal is measurements you can repeat exactly. Pick each crack worth watching, inside and out, and give it a name in a notebook or a note on your phone. Then set up the same few checks for each one, and write the date on everything.
Plastic crack monitors, sometimes called tell-tales, are inexpensive and made for this. They glue across a crack with one half on each side and show movement against a printed grid, both opening and sliding. On drywall, pencil marks at each end of the crack with the date beside them show whether it grows in length.
- Pencil the ends of each crack and date the marks
- Fix a crack monitor across the widest point, or photograph it beside a ruler from the same spot
- Note which doors and windows stick or will not latch, and on which side
- Check a long level on floors that seem to slope, and mark where the bubble sits
- Write down the weather: a dry month, a wet week, a hard freeze
Reading the record in spring
Check every crack monthly, or after any unusually wet or dry stretch, and compare in March or April against the September baseline. If the cracks have narrowed and the stuck doors have freed themselves, the movement is seasonal. That points to the soil moisture cycle, and to gutters, downspout extensions and grade as the first fixes.
If a crack has grown past its pencil mark, or the monitor shows it wider in spring than it was at the driest point of fall, the house is moving beyond the seasonal swing. Sliding or offset movement, where one side of the crack has shifted past the other, is also worth an assessment even if the width has barely changed. A dated record like this is exactly what a structural engineer or a foundation inspection wants to see.
When not to wait for spring
A monitoring year only makes sense for cracks that are behaving like cracks. Some conditions need someone looking at them now: a basement or block wall with a horizontal crack and a visible lean, water coming through a crack, a door that suddenly will not close when it closed fine last week, or brick pulling away from a window frame.
When we inspect, the first question is usually whether anyone has been watching the crack, and a homeowner with six months of dated marks saves a great deal of guesswork. The record is useful at sale too. A buyer’s inspector who finds a patched crack will ask what it has done since, and a notebook answers that better than anyone’s memory.