Expert: Daniel Humphrey - 12/31/2008

Question
There is space over my 2 car garage which is approximately 20X12, it's all unfinished, rafters and floor joists, I would like to make it into a walk in closet and I have a few questions.  1. The rafters have supports every third one and they are 2x4's.  Can we remove those and add additonal supports up higher in the rafters to increase the head space?  2.  The floor would be a step down, should we build it up to meet the floor height of our bedroom?  3.  When you insulate the floor does it have to have a vapor barrier?  The garage is not heated.  Half of our existing bedroom is over the garage.

Answer
Steven,

1. Without seeing the trusses and supports you propose removing, I cannot advise you on this. Normally, if a support is there, it is obviously needed and its structural role needs to be taken up by some other member if it is removed. I think the supports you mention may be collar ties, and these prevent deflection of the rafters under load, as well as prevent the rafter feet from spreading. The closer to midspan they are placed, the better they prevent rafter deflection, and the lower they are placed, the more effective in preventing spreading. If you remove these, you must find some other way to prevent deflection of the rafters and to complete the structural triangle.

2. It would be best for future use if all the floors on that level are at the same height.

3. A vapor barrier  for a closet is probably not necessary, but a good air seal is. You need to take special care to foam or caulk all joints so that no interior air can migrate to the garage, and no fumes from the garage can get into the closet. You also need to install sheetrock between the garage and any living space for fire protection. This should be on the garage ceiling to protect the floor joists as well.

--Daniel