Preventing Moisture-Related Problems in Residential Wood Framing

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Jeanette Fitzgerald

Pressure-treated Wood
Pressure-treated wood was invented over 70 years ago to protect wood components from termites, wood-ingesting insects, and rot. Pressure treating is a process that forces chemical preservatives deep into the wood. The wood is placed into a large holding tank, and then the tank is depressurized to remove all air. After all air has been removed, the tank is filled with the preservative under high pressure, which forces the preservatives deep into the wood. Pressure treatments make wood unappetizing to termites and other wood-ingesting insects. Pressure-treated wood will not rot.

This pressure treatment is written into the building codes to protect a specific piece of the wood frame package, the sill plate. Sill plates are the lowest framing boards in a wood home. They are bolted to the top of the foundation and the house is then erected on top of them.

In the Gulf States, where termites are a large concern, some builders use pressure-treated wood for more of the framing package than the sill plate. Unfortunately, this preventative treatment essentially water logs the wood pieces, making them heavy and hard to work with.

Pressure-treated wood has a lifespan of 20 years under the harshest conditions.

A Comparison of Treatments

Although the job site spray, two-step coating process, and pressure treatment are each geared toward protecting the life of construction lumber, they differ dramatically in important ways. Their impact on both indoor and outdoor environments is different-swinging from non-toxic and LEED® supportive to requiring special disposal procedures. The ease of installation, potential corrosion issues, and the impact that the treatment will have on the structural integrity of the wood are each unique to the wood preservation treatment selected.

EPA Regulations
The Environmental Protection Agency (EPA) is a governmental agency formed to protect human health and the environment. As the watchdog of both people and organisms, it is not surprising that if a product makes claims about its ability to prevent mold or rot fungi, or to deter termites, the product must be registered with the EPA. It is an absolute requirement. The EPA evaluates every registered product to determine if it has enough of any type of chemical in it to be labeled hazardous, polluting, or carcinogenic. If it does, then that product becomes regulated by the EPA Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).

The EPA also has very strict requirements about how companies can promote their product capabilities with regard to mold, rot fungi, and termites. In order to remain compliant with the EPA, mold claims by topical application can only be made about the surface of the product. For instance, the job site spray designed to prevent mold growth can only be marketed as preventing mold growth on the wood, cement, and steel surfaces that have been treated. Also, the two-step coating process can only make mold prevention claims about the surface of the product that has been coated at the factory.

Architects should be wary of companies that are either not registered on the EPA website or attempt to bend around EPA regulations in their promotional materials.

With regard to the wood treatments described earlier, the two-step coating process has been reviewed by the EPA and is not regulated by FIFRA. The wood components treated in the two-step process, coated with a semi-vapor permeable film and DOT, are considered non-hazardous, non-polluting, and non-carcinogenic per the limits of FIFRA.

Wood components treated in the two-step process are considered non-hazardous, non-polluting, and non-carcinogenic per the limits of FIFRA, making them safe to use throughout a home.

The EPA also regulates all wood preservatives, such as the ones employed during the pressure treatment process. Until 2003, the preservative most commonly used in the residential pressure-treated lumber was chromate copper arsenate (CCA). CCA is extremely toxic and contains arsenic, the same chemical used in rat poison. Leading up to 2003, nearly 40 million pounds of arsenic were used to create pressure-treated wood in the United States every year. Finally, the construction industry voluntarily eliminated the presence of CCA treated wood in residential projects, limiting the use of CCA to marine and industrial applications.

The less toxic preservatives amine copper quat (ACQ) and copper azole (CA) provide pressure treatment protection for wood components used for decks, mailboxes, swing sets, and oceanside boardwalks, and are considered safer for human contact. The use of copper as a main element in these preservatives has made pressure-treated wood more expensive that its toxic brother. In an attempt to manage the escalating costs, pressure-treated wood manufacturers have started offering wood options with different levels of pressure treatment protection. The most lightly treated product is meant to be used for decking, then there is wood meant for above-ground construction, ground contact, and permanent wood foundations (PWF). It is important for the construction team to make sure, when using pressure-treated wood, that the level of protection specified, purchased, and delivered matches the intended use of the lumber.

 

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Originally published in Architectural Record.
Originally published in November 2007

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