We hear a lot about how excess moisture can damage hardwood floors, but too little moisture can be just as problematic, particularly during cold winter months. Dry brittle air can, over time, cause “cracking” or shrinkage that results in gaps between boards. And once the damage is done, repairs can be costly and, depending on a number of factors, warranties may or may not cover the damage.
Prevention is by far the best cure for cracking—and that begins before installation, not after the fact. Here are some factors you should take into consideration.
Even after it is processed into planks, hardwood will respond to its environment by expanding when moisture levels are too high and shrinking when they are too low. When choosing a hardwood flooring species for those who reside in locations where harsh winters are the norm, choose one that is more suited to the natural local environment.
The more dimensionally stable the hardwood, the less likely it is to crack in cold months. Maple is an infamously poor choice for hard-winter climates, and Hickory is also more likely to gap as moisture levels fall. Cherry, Poplar, Cypress, and Mahogany are better choices for arid climes. Width and cut also play a role—the wider the plank, the greater the gap between boards should cracking occur. Narrow boards that are quartersawn are a better choice. Flatsawn boards are twice as unstable as quartersawn.
Maintaining consistent RH (relative humidity) levels year-round is key to avoid cracking. Gaps occur when RH levels plummet. A home or structure with excessive ventilation will let in outdoor air, and cause RH levels to quickly drop. Before installation, run an energy audit to ensure doors, windows, crawl spaces, basements, attics, and lighting fixtures in ceilings aren’t letting air in or out.
When cold sets in and the furnace or heating system gets cranked up, air is going to dry out—you need a baseline to work from, and to determine if adding moisture back in is going to be necessary at peak points. A simplified psychometric chart from the American Society of Heating, Refrigeration and Air-Conditioning Engineers can help you determine the optimal balance between temperature and moisture levels, which may need to be increased with a humidifier or by other means to avoid cracking.
If you’re not handling the install yourself, make sure customers understand the importance of hiring a competent, seasoned contractor. Or, more importantly, make sure the customer understands that a contractor who doesn’t follow NWFA (National Wood Flooring Association) guidelines during installation may void their warranty should problems occur.
If you are doing the installation yourself, make sure the hardwood is delivered early to the jobsite so it can be allowed to acclimate for a few days to typical occupancy levels while temperature and moisture levels are monitored. Also be sure to test the hardwood itself as well as the subfloor to get a baseline to work from.