Carpet and padding (cushion) is a very common finish floor that can be installed directly over Warmboard.
We recommend a carpet assembly with a low R-value (2.0-2.5) so the system can use the same water temperatures beneath all finish flooring types. Higher values may require creating a two temperature system.
The R-values listed below are approximate based on carpet thickness. Check with the manufacturer to obtain accurate values.
While many brands of carpet padding are available in the marketplace, we DO NOT recommend Prime Urethane, Bonded Urethane or Sunburst products due to their high R-values.
Applying carpet to Warmboard is accomplished in exactly the same manner as any carpet installation on any conventional subfloor. Carpet tack strips are nailed directly to the Warmboard panels while taking care to avoid driving a tack strip nail into the visible tubes. Where there are grooves that are not used, fill the empty grooves using thin set or equivalent. Another option is to cut pieces of pex tub- ing from the scrap pile and nail them into the empty grooves. This will provide an even surface for the carpet pad.
In general, all radiant systems work best with a slab foam rubber carpet pad (sfrp) and Warmboard is no exception. We highly recommend use of such a pad with Warmboard. Apart from having excellent heat transfer characteristics, SFRP is a superior cushion for your carpet. Typically 1/4” SFRP feels better than a 3/8” rebond pad and a 3/8” feels better than 1/2” rebond pad.