Hardwood Floors Oct/Nov 2019

AT THE SITE

Minimizing Moisture Migration through the Structure In many climate zones, building codes dictate construction methods related to placement and type of insulation and moisture control systems installed below the living space, such as in crawlspaces. Whether vapor barriers are placed below the slab, over the bare earth in a crawlspace, or on the underside of the floor joists, these products are designed to stop moisture from finding its way into the structure. The type of insulation systems, and use of vapor control systems vary throughout many parts of the country. With new construction, the ultimate objective of the builder is to control the temperature and moisture gradient from a conditioned space to unconditioned space.

moisture control system as a part of their overall flooring project. Interior Humidity and the Average Moisture Content of Wood Humidity is important because wood products exchange water molecules from the surrounding air based upon the amount of moisture in the air. To understand why temperature and humidity affect wood, it is important to respect the relationship between temperature and humidity. Heating the air will increase its ability to hold moisture; therefore, the relative humidity decreases, whereas cooling the air will decrease its ability to hold moisture; therefore, the relative humidity increases. Humidification and/or dehumidification systems are often necessary before, during, and after installation to maintain an environment appropriate for the flooring specified. Wood, like humans, likes consistency when it comes to the temperature and humidity to which it is exposed. Fortunately, both wood and humans like to live in similar environments. Wood dried for interior usage generally is stable in a controlled environment maintained between 60-80°F at a relative humidity between 30-50%.

the interior air. Heating the air will increase its ability to hold moisture; therefore, the interior relative humidity decreases. Warm air also has higher pressure and is more buoyant than cooler air. Air moves from regions of high air pressure to regions of the home with lower air pressure. As the temperature warms, air pressure increases (e.g., truck tire pressure in the summer versus the winter). Vapor diffusion is the movement of moisture (in the vapor state) from an area of higher vapor pressure concentration to an area of lower vapor pressure concentration. The loss of warm air within the home creates a negative pressure inside the home. In lower levels of the building, low- pressure cool air rushes in to replace the rising air in an attempt to maintain pressure balance within the structure. This is known as the stack effect .

We are seeing promising changes to some of the building codes that are requiring vapor control systems to be installed where continuous moisture is a concern. When installing a wood floor in a remodel situation, the homeowner and flooring professional should both be aware of any existing situation that could have the potential to affect the long-termperformance of the wood floor. Inmany cases, it may be necessary to ask the owner to consider installation of a

Humans generally are most comfortable in a controlled

environment maintained about the same conditions. The following chart

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