Our 1987 Cape Cod house is built on a concrete slab. We have lived here for 3 years. When we moved in, there were hairline cracks that ran out from the top corners of interior door frames and some window frames.

A year ago, we noticed these cracks were getting significantly larger. The door frames did not appear level and doors would no longer close. The first floor was also lower in the center of the house.

We had several people try to tell us what was happening. There seemed to be a void under our house, but the cause was never determined.

We had to do something, so we hired a company to pump high-density foam underneath our foundation. It worked perfectly! The cracks in the walls closed up and all of our doorways looked level again.

That was 4 months ago and now the cracks are returning and the doors won't shut again. We are noticing cracks getting bigger or appearing in new places.

We suspect that the house is continuing to sink. Could there be something that we're missing? Is there any way to figure out for certain what is going on underneath our foundation?