What causes Hardwood Floors to Cup?

Wood floors cup (edges are higher than the center of the board) when there is a moisture imbalance though the thickness of the wood.  In relation to crawlspaces- wood floors cup because of high relative humidity.

Why does a Hardwood Floor Buckle?

Buckling occurs when the flooring lifts or separates from the sub-floor. For buckling to occur the flooring has to gain moisture, expand, and reach an area (s) that prevents it from moving.

~Cupping and buckling of wood floors is always associated with moisture ~

To understand the cause of wood floors cupping or buckling (when you're sure there is no water damage due to a flood or leak), you must understand the relationship between relative humidity, your wood floor and your crawl space.

During the summer months in the northeast region (year round in other regions) wood sub-floors and floor joists often measure 19-25% moisture content in a VENTED crawl space. In an air conditioned house the wood floor moisture will typically measure 7-10%. The difference between the wood sub-floor and the hardwood flooring shouldn't exceed 4%- however, as little as 1% difference can result in cupping. Greater differences in moisture may lead to buckling.

How moisture develops in a Vented Crawlspace:

Most homeowners believe they have no moisture in their crawlspace- after all,  they have a vapor barrier installed, the crawlspace vents are open and the space looks dry- so why did the wood floors cup and buckle?

Crawl space ventilation was meant to keep a constant supply of fresh air circulating throughout the crawl space environment. It was thought that this would help purge the space of the heavy, damp air that settles in the lower levels of a house. This belief had become so widespread that crawl space vents were written into the International Building Code. As a result, many have crawlspace vents which are counterproductive in keeping your crawl space dry, mold and insect free.

Water surfacing from the damp earth, humidity entering from crawlspace vents, and moisture seeping through porous concrete creates a perfect environment for condensation,  mold and mildew.

As air warms in a home, it rises and leaves through the upper regions of the house, much in the same way that air moves through a chimney. This phenomenon, called the "stack effect," causes the home to suck air up from the crawlspace into the main area of the home. Moisture from the crawl space, mold spores and fecal material from dust mites enter the home.

Installation of a plastic vapor barrier that will not support mold growth or allow humidity from the earth into the crawlspace is recommended. This helps to insulate the crawlspace and discourages insects and vermin..

Winter air fills your crawl space, making the floor above cold. It cools your hot water pipes and heat vents, and in some instances, your furnace and hot water heater- your heating bill increases and the house is drafty and uncomfortable.

Summer air is hot and humid; when it enters the crawl space it instantly cools and drastically increases the relative humidity. When the relative humidity goes over 100 percent, the moisture is released into the crawl space atmosphere leading to condensation on your wood, pipes, mechanicals and other cool surfaces. It also leads to mold, rot and insect infestation. This damp air rises upward into the house (Stack Effect) with mold spores and other contaminants and you spend more on utilities. Over time, the crawlspace insulation gets wet and loses its insulative value, mold begins to grow, moisture drips to the floor and wood begins to rot. Your crawlspace is now the perfect haven for insects such as termites, ants, spiders, centipedes, camelback crickets, cockroaches and rodents.

Molds can not grow when humidity is maintained between 30 and 50 percent. By maintaining humidity levels -wood floors won't cup or buckle, mold and contaminants will not enter the house, and heating/air conditioning bills will be lower. Next Page

~To maintain humidity levels between 30-50%, the crawlspace should be sealed~