A cracking foundation

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Q. My home is on a hillside, and I have no problems with drainage, but I’m seeing cracks along the outside of the concrete on all four sides. Is this possibly caused by the house moving down the hill? I’m concerned that the foundation isn’t made right or held in the ground well enough to keep it from moving, even a little. How can I be sure that it’s going to stay put and not continue cracking? If it does, I may start to get leaks through the walls. What should I do?

A. When houses begin to move on a sloped site, it’s all downhill from there. Houses on hills, or in hills, are common, and aren’t a problem if planned and, more important, built correctly. I rarely see the people on the jobsite of a residential project actually follow the design configuration of the embedded steel rods, according to plan. They proudly show me some deviation of what was calculated and drawn, as if the essence of the idea was just as good.

Foundations on slopes are actually preferred. They promote water movement away from the building and allow for better light, ventilation and escape from fire through bigger openings, such as doors, instead of windows on the low side. But, like all foundations, the ones built on uneven terrain need site-specific engineering design. Your foundation walls may be cracking for one of several reasons, and to find out why, we have to check the building department records to start the investigation with what was once designed to see if that was where the problem began.

As I said, the plans are rarely followed to the letter in the field, so if the plans show details that clearly explain what was supposed to be there, which also rarely happens, then we work backward, recalculating the loads, horizontally as well as vertically, to compare what should have been with what was planned. I look for soil strength information, depth of the configured anchorage, and imagine how the foundation would react in extreme situations. Now, knowing what should have been, to resist extreme rain, snow, wind and ground movement, we compare. I can predict where cracks will occur just from the configuration.

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