Dear James: I need an extra bedroom for my kids. It will be built on a slab and utilize floor radiant heating. I would like to install hardwood flooring over it. Is this OK over a heated slab? — Carrie K.
Dear Carrie: Building a room addition on a concrete slab is the least expensive construction method and a good choice for your new bedroom. Your children will be pleasantly surprised at how comfortable the radiant heated floor will be during cold winter nights. You can install hardwood flooring over it.
The radiant floor heat is ideal for a bedroom because it is totally silent. Also, for children, who often have allergies, the stillness of the air reduces airborne allergens and minimizes indoor humidity level changes. This is also good for hardwood flooring.
When installing hardwood flooring over a radiant-heated slab, you should follow certain guidelines for a long-lasting, attractive floor. The floor does not get extremely hot, but even small changes in the temperature of the hardwood can affect it.
Hardwood flooring, even though it is finished with urethane, is a hygroscopic material because it is porous. This means that it will expand and shrink as it absorbs and releases moisture. An additional problem is when it swells and then later releases the moisture (during drier winter air), it sometimes warps and curls as it shrinks.
To avoid these potential problems, it is extremely important to make sure the concrete slab is fully cured before progressing with the installation of the flooring. Although concrete technically sets and does not dry to get hard, it still gives off moisture for many days. Leaving the windows open in the room during construction will hasten the drying.
On simple method to test the dryness of a concrete slab is to tape two-foot square pieces of plastic film to several locations on the slab. After a day or two, check the pieces of film. If you find no moisture under them, the slab is probably dry enough to proceed with the installation of the hardwood floor.
A vapor barrier should be installed over the slab to block any residual moisture from getting through to the flooring which will be installed on it. On top of this vapor barrier, install plywood underlayment to which the hardwood flooring will be nailed.
When you get to this point, have the hardwood delivered and placed in the new room with the heat set to a normal temperature. Give the hardwood about a week to stabilize its moisture content with that of the heated room. Make sure to unwrap it so the room air can flow around it.
Select narrow hardwood pieces. Widths in the two-inch range are ideal. If you install wider pieces, each one will shrink and grow more throughout the seasons and there are fewer gaps between them to absorb these size changes.
Certain types of hardwood have more size stability than others. American Cherry and red and white oak are some of the more stable species. Finish the hardwood flooring with several coats of high-quality floor urethane.
Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com. To find out more about James Dulley and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.