I'm converting a 2 car garage into an "in-law" space. I've got a couple of questions for the pros.
1 - I plan to use 2x6 "sleepers" to raise the floor hight. Thsi will provide space to run the GFA ducts and insulate. Should I put a moisture barrier under the 2x6s?

2 - The previous owner had converted part of the area using the existing concrete floor. If I raise the floor by 6+" my resulting cieling height in that room will be only 7.5 feet. Is that code legal?

Thanks!!!!

Check to see if your garage floor is sloped, the majority are...you may need 2x8's and taper them to level the floor and also provide room for duct and insulation. A vapor barrier would be good unless you plan to glue your PT to the floor or float them. Check with your local building codes in reference to the height...may or may not be an issue.

Minimum ceiling height for Habitable Space in the ICC code is 7'-6". Habitable Spaces are spaces in which people live, eat or sleep. Other spaces can be 7+-0", such as bathrooms, corridirs, closets, etc. Perhaps by running ducts in loeer-ceiling spaces, you can minimize the ducts in the floor, and increase the ceiling height a couple of inches.

If there is any hint of dampness in the garage, by all means place a vapor retarder over the slab before placing the sleepers. :ap all joints 6 inches, and tape them, and run the vapor retarder up the wall a bit and tape it there also.

I am also thinking of converting our garage into a bedroom/bathroom.

When you say sleeper 2x6, do you simply mean 2x6's that will sit directly on the cement floor(or on a vapor barrier on the cement floor).

My garage floor is cracked and not anywhere near level. I'm afraid if I build a floor that sits on the slab, it will move over time.

What is the recommended way to avoid this problem?

Thanks.

You only build it once, but you live in it for a LONG TIME! The BEST way to proceed is to remove the garage floor slab, place a proper vapor retarder, and pour a new level slab with welded wire mesh in it. Then everything else will be clean and simple.

Often, garage foundations are built with no foundation beneath the garage doors. You may also wish to investigate this, and construct a proper foundation there also, before doing anything else.