So, why all the hoopla about environmental conditions and wood flooring? In today’s homes and commercial installations the interior heating and air conditioning units are continually operating. Wood products react to the surrounding environmental conditions. This is the nature of wood as a hygroscopic material. When the environment is dryer than a previous condition, wood flooring will be influenced to shrink. The opposite is also true; wood flooring will be influenced to expand when the conditions are wetter than previous conditions. The beauty of wood flooring is that it is generally protected by a finish that can slow the imposed changes. In addition, most seasonal conditions are variable so extremes are not in place continually and when coupled with the slow reaction, unacceptable results are not common. This is particularly true if customer expectations are properly set for the reality of a wood floor.
What are the requirements for wood flooring?The environmental goal is to create conditions that are normally expected for the geographical area and the site involved. If the area is arid it makes no sense to require restrictive high relative humidity conditions. This creates an extra cost that changes a normally quite stable, dry (relative humidity consistently 20 to 25%) environment. A consumer will likely resist the extra costs for the equipment to maintain such conditions and ultimately choose another floor covering that doesn’t require the added burden. Another caution is when malfunction occurs the moisture drop is much higher than normal environmental swings and the flooring can be adversely affected with associated gapping and cupping.
Environmental conditions for those northern areas with extended heating are also different, particularly during the winter. From the Washington D. C. area across to St. Louis and northward the heating season is significant. During December, January, and February outside temps often average below freezing. Some wood flooring manufacturers/dealers support the recommendation that the relative should be maintained at 35% to 55%, or 40% to 60%, or 30% to 50% for the life of the flooring. In these areas during high heating degree day requirements the related indoor relative humidity can often be from below 10% to 15% RH. Humidification units on heating units would normally struggle to maintain humidity at 30% much less above 30% as suggested by many. At 30% RH and above, on those below-freezing days condensation would likely form on the cold surfaces like windows. After 3 or 4 days any air leak in the building envelope would likely result in some form of condensation if the relative humidity is maintained above 30 to 35%, thereby putting the structure of the home at risk. Another choice the homeowner doesn’t want to make.
What about the humid areas with normally higher relative humidity? The objective is the same so check that near occupied conditions are present. The moisture content of building components again shows what the ongoing environmental conditions have been and what adjustment is needed. In most cases the conditions are wetter than normal and drying by either time, ventilation, or heating is the requirement. These areas can also be problematic when the HVAC systems are not operating during the more pleasant seasons. In these cases, windows are opened letting the humid exterior air into the home. Depending on the length of the pleasant weather, the associated gain in moisture may or may not result in slightly cupped floors. Customer education is critical in these areas in that the cupping is generally not permanent and will flatten with heating and or seasonal air conditioning. Again the upper range of RH recommendations-50%, 55%, or 60%--can be exceeded without causing the flooring to fail.
Of course if site environmental conditions at installation are not anywhere near the normal occupied range, problems will result. The most often situation is with the extra or excessive moisture of the building process. The home was rained on extensively during framing, the basement has standing water, the crawl space is wet and muddy, the slab is too new, the slab has been repeatedly wetted-are all situations that are not normal and require drying before any wood flooring is even delivered to the site. These situations require the use of a moisture meter. Checking wood building components determines if the environment is within limits. If normal moisture content for flooring in the area is 6% winter and 9% summer then subflooring at 15% tells us that the environment has been adverse and conditions are too wet. The 6% to 9% average is 71/2% so when other wood building components check at 111/2% and less the conditions are good for installation. We can even get by if some of the readings are somewhat higher at 12% and 13% as long as there are still the lower readings and the overall condition is drying out. As reported before the wood does not react immediately and with the felt paper over the subfloor it is initially protected while additional drying occurs.
Know your area’s normal environmental conditions; use your moisture meter to check that conditions are near these normal conditions. When situations are on the drier side add spacing to prevent later cupping. And, as always, set proper customer expectations, particularly where the overall humidity range is greater than 20%.