I was asked to look at some structural changes inside a detached, three-car garage recently. One-third of the garage is converted to finished, usable space. Facing the garage, the finished section is on the far right. On the far left, noticable separation is occuring between the facia boards and brick. There is also a visible sinking of surrounding sidewalk and minor off-setting of the concrete drive and garage foundation. A distinctive void can be seen directly underneath the sidewalk and one must suspect there is some substantial loss of soil beneath the structure. Inside the finished area, sheetrock taping at the ceiling is beginning to separate and a few other, minor aethetic changes are popping up. I am not a professional; I was asked for my opinion.

Surveying the structure, I determined a few things: First, the garage was constructed around 1985. During most of the years since construction, the foundation did not present much in the way of shifting, etc. The structure is built on a heavy clay soil and drainage is not assisted with guttering. Inside the structure, on the left side, the owner has stacked a significant amount of lumber near the further-most end of the slab. There are other items in the general proximity of the lumber such as desks, power tools, etc.

The owner suggested ants or rodents may have removed enough of the soil to cause the problems. I countered the owner's suggestion, stating the more probably cause is the static amount of weight administered to the structure's slab at one specific area, rather than more evenly distributed throughout a larger area. The owner argues a car would probably weigh more and it's, after all, a garage.

I would appreciate any contributions to this post which might help me determine a likely cause of this problem. Is it fair to suspect the added, static weight of lumber and other items, coupled with the effect such weight has on hydrostatic pressure be a more likely cause than what the owner suggests - insects removing soil? Is my suspicion unfounded because, as the owner states, an automobile's weight is substantial too?

My thoughts include the addition of piers along the affected portion of the structure and moving the lumber from the area.

Please help.

Thank you.

If ever a situation demanded thorough on-site evaluation by a qualified design professional, this is it. No matter how careful your description, one can never be certain one has all the information necessary to begin drawing conclusions. On-site examination is the only way to be sure that everything is being taken into account.

I will point out that a car may weigh 3,000 pounds and its weight is carried at four points of anout 750 pounds each, depending on the weight distribution of the car. The lumber, on the other hand, produces a uniformly distributed load over part of the floor, but we have no way to know how much

Consult a structural engineer. It's better than guessing.