Fiberrock over Roth Panals on existing slab

Michael Pastrone

I am an HO getting ready to install radiant on my 600sf existing basement slab. I am curious what folks think of my plan, and I have a few questions.

I selected 3/4" Roth Panals for several reasons, including preserving as much of the limited 91" ceiling hieght, needing some insulation, and a simple install. The basement is dry.

The build up is as follows:
- Tapcon screw 1x4" plywood around perimeter for carpet tack strips
- carpet glue Roth Panals (R=4.5) directly to the slab (no vapor barrier)
- staple 1/4" USG Fiberock (R=0.3) to the panal for thermal mass
- flooring: rubber pad and nylon plush carpet (total R=1.4)

The carpet is needed as this is my home theatre.

One question is do I even need a thermal mass, and is there a better choice than Fiberock. Durock/Wonderboard seems too brittle and difficult to work with.

While the Roth folks have been somewhat helpful, I have had to create this build up design myself.