Expert: Ted Barnhill (Principal, Design45 LLC) - 10/27/2007

Question
My buddy wants his old detached garage torn down and a 2 car garage built in its place.  He also would like a bonus room above the garage for friend get togethers etc.  I was just wondering would a slab be efficient enough to carry the extra weight with the beefed up trusses, flooring and 2 dormers with windows.  The current garage is on a slab which needs to be torn up regardless.

Answer
Mike,

The reason his current slab needs to be replaced is probably that it was built without adequate footings, and it heaved and cracked over time.

I would strongly recommend putting in footings to frost.  This will ensure that the structure has a long life, without any uneven settling that will result in cracks in the flooring, walls, and ceiling.

You may want to look into frost-protected shallow foundations (http://oikos.com/esb/43/foundations.html), an increasingly-common technique that could save some money in your friend's application.

Good luck,

Ted