I was called to inspect a splitting wood floor with dry-cupping in Albuquerque, N.M.
Less than two years earlier, in late summer the 9/16-inch engineered hickory had been glued to concrete with thermal mass hydronic heating. The following winter, the floor dry-cupped, and three splitting boards were replaced. The floor flattened during the summer. The following January, the floor had four splitting boards, and the dry-cupping returned. The thinking by the retailer, installer and a third-party independent inspector was that the in-floor heat was the culprit and that the wood flooring itself was not suitable for that application.
In January, the distributor and the inspector separately noted very low RH—between 18–22%—as well as several splitting boards. The distributor took MC readings below 6% and found the floor's surface temperature ranged from 78–84⁰F. Samples of these boards were subsequently tested, revealing a MC of 3%.
By the time of my inspection at the end of March, the visual on the floor had greatly improved, and the MC was 6%, the floor temperature was 72⁰F, the air temperature was 68⁰F and the RH was 26%.
The MC at the time of installation had been recorded at 9%—consistent with a significant seasonal swing in RH and MC.
The house was cooled with a swamp cooler, a common practice in the region. This translates to an average RH up to 60% in the summer and down to 20% in the winter.
How to Fix the Floor
The following corrections were made (and the floor has now been problem-free for years):
- A whole-house humidifier was added for use during the drier times of year. This balanced out the seasonal humidity swings, keeping RH between 30%–50%.
- Damaged boards were replaced.
- Boiler temperatures were adjusted to ensure the floor surface temperature did not exceed the flooring manufacturer's standard of 80⁰F.
In the Future
Seasonal problems in wood flooring are not isolated to structures with in-floor heating systems. Use of in-floor temperature sensors, data loggers to monitor floor conditions and humidification systems will help provide optimum floor performance. A well-designed in-floor heating system should allow for even emission of heat without hot spots or surface temperatures exceeding manufacturers' standards (commonly 80⁰F).