Background:

• I’m planning to finish out a portion of my detached garage to use as a home office.
• The garage is on a slab and the office will occupy roughly 25% of the total slab. The remainder of the garage will not be finished, heated or cooled.
• I intend to heat the office with electric baseboard heat and cool it with a in-wall AC unit and ceiling fan.
• I intend to insulate the walls with R-13 and the ceiling with R-30 and to put up a vapor barrier behind the sheetrock on the walls and ceilings. The exterior walls will be wrapped with Tyvek and re-sided (I’m adding new windows and a door).
• I’ve tested the slab and am very sure that there is no vapor barrier below it (I see significant condensation if I spread a sheet of plastic over the slab and leave it for a day).
• The slab to rafter distance is 8 foot, 3 inches.
• I intend to finish the floor with ceramic tile.

Question:

• Are there any materials or techniques that will let me build up the office floor (up to 3 inches), add a vapor barrier to keep the office floor dry and insulate the office floor from the rest of the garage (to prevent my baseboard heat from heating the other 3/4 of the garage slab and to keep my toes warm)?

The simple answer that I’ve come up with was to frame in the office,  lay out 6mil plastic to create a “basin”, lay out reinforcement mesh, and pour a new 3 inch thick slab on top of the garage slab in the office area. However, this doesn’t address the insulation goal.

One final goal is to be cautious about creating an environment for mold to thrive in or around the office area.

Thanks, Jeff