Green Building Elements: Warmboard

September 19, 2007

Radiant heating is a popular option in green buildings. Many green buildings feature it because it is a more efficient, and more comfortable, method of heating. If a building doesn’t require air conditioning, it may be possible to eliminate ductwork altogether, or at least use a much smaller system that is sized for air conditioning. And even in buildings where air handling is still necessary, the systems that push the air around can be run less frequently because they are needed only to provide fresh air, and don’t need to take care of the heating as well. Radiant heating systems don’t cause the air to be dried out in the same manner that heated forced-air systems tend to do. Most of all, radiant heating is comfortable because it is warmest at floor level and slightly cooler at higher levels, matching the human desire for warmth for the feet, and less for the head.

A recent blog post by Jetson Green about the National Solar Decathalon reminded me of an intriguing product that can be used for in-floor radiant heat systems. Warmboard is a specialty subflooring for use in radiant-heated buildings that doesn’t require a concrete slab to embed the radiant tubing. This makes it especially useful for multi-story buildings where a concrete slab floor may be less desirable. Warmboard is much lighter than a corresponding concrete slab, meaning that less structural material is needed to support the floor. It also does not need curing time, unlike a concrete slab, which is another factor that makes it appealing for use with modular and pre-fab construction.

Warmboard is a plywood material that is slightly thicker than typical subflooring plywood. It has regular channels cut into it that the radiant heating system tubing can be laid into. On top of this, an aluminum plate is formed to the surface, providing a transfer surface to uniformly distribute the heat from the tubing across the floor.

Warmboard can be used in place of regular subflooring plywood (although some of the pictures Jetson Green posted showed warmboard being installed on top of regular plywood subflooring, which is both redundant and costly). Almost any kind of flooring can be installed over Warmboard. Hardwood flooring and tile can be set directly over the warmboard. However, carpet, which is not as good a choice to use with a radiant floor heating system, requires a 3/8" underlayment.

Solar heating systems that use collectors to heat water are the most efficient solar energy systems available. Combining solar energy capture with a radiant heating system is an easy way of taking best advantage of the strengths of both systems. A system can be easily designed to take advantage of solar heating on sunny days, with backup heating from an alternative source to heat water to provide supplemental heat or for days when the sun is not as bright. The quick assembly ability and the good integration of radiant heating systems is why Warmboard is popular among the Solar Decathalon teams.

There are some drawbacks to using Warmboard. It is an expensive product, and owners may balk at the perceived cost. However, using Warmboard subflooring makes the installation of the tubing much quicker and easier, as opposed to doing the installation from the underside. In a crawl space, it’s exceptionally awkward, and working overhead is tiring work. Installing the tubing in a Warmboard is much quicker than installing it under the subfloor, and labor costs for tubing installation should be lower. The Warmboard also incorporates an aluminum plate, so a separate reflector plate or reflective insulation is not needed, and both the cost of the material itself and the cost of installation can be saved by using Warmboard, as well.

Warmboard is also configured for a regular 4′ x 8′ sheet of flooring. If you are working with a regular design so that you only need full size pieces, then Warmboard can be an economical choice. It can be worked with much the same as a standard plywood subfloor and can be cut in the field (though a carbide blade is required in order to cut the integrated aluminum plate).

Although the company says that their material can be used in remodeling projects, in most cases I think that would be unfeasible. Laying Warmboard on top of an existing floor will add nearly 2" to the floor thickness with the Warmboard itself (1-1/8" thick) as well as the hardwood or other finished floor covering (3/4" or more). That also would mean doors would have to be cut down or replaced, and other elements would be similarly affected. But for a moderate sized new construction, Warmboard can be a good product to use to help make a comfortable, radiant-heated building.

Image source: Warmboard

Tip of the hat to Jetson Green