We’re in the process of renovating our kitchen including the tear down of the existing wall between our eating area and the garage and converting the garage into a den area.A new garage with a laundry area will be constructed next year against the existing garage (Den).

A natural gas fired zero clearance fireplace is going to be installed at the far end (South) where a new thermal window will be installed replacing the existing garage door. The existing outside wall of the garage will be insulated between the studs with a blown in cellulose and the bricks removed and a 1″ styrene sheeting will be attached. This will become the inside wall of the new garage and outside wall of the den. The existing garage ceiling will be insulated with 10.375 pink insulation with plans to install 2 skylights facing South.

 To continue the kitchen floor level I’m installing 2 x 8 joists across the 11-1/2 foot x 21-1/2 foot garage floor area and laying a floor to the same height.

 I’m looking for the best way to insulate the existing garage concrete floor.

Should I put insulation between the joists and a 6+ mil. plastic sheet on top of the concrete and run round ducting from the existing hot and cold air rectangular ducting into the new room ( holes have been cut to do this) or is it better to lay the plastic on the concrete and lay the pink batts (10.375″ thick) already purchased at a good price last January on top of the plastic and pipe the heat under the joists between the top of the insulation and the bottom of the den floor ?

Any suggestions and comments would be appreciated.

Murr