Weyerhaeuser EWP and OSB Exposed to Moisture During Construction Delays

Weyerhaeuser’s Trus Joist® engineered wood products (EWP) and oriented strand board (OSB) panels are intended to be used in dry-use service applications only1.  Like other wood framing members, these products will tolerate moisture exposure under typical construction conditions including rain exposure. However, moisture due to conditions such as extended construction delays, improper storage, flooding, or building envelope failure can create significant product and safety issues. 

Weyerhaeuser recommends that builders protect all EWP and OSB products before and during construction.  For uninstalled product, refer to the Product Transportation, Handling and Storage Technical Resource Sheet for proper handling and storage.  For cases where products have been installed but the structure is not yet “dried in”, Weyerhaeuser recommends that the project’s design professional be consulted for appropriate methods to protect the wood products.  The design professional may consider staging or sequencing construction to limit weather exposure.  Some methods to protect the installed wood products include:

  • Preventing standing water from remaining on the products
  • Covering/tarping the installed products to limit moisture exposure but still allow air movement around the product
  • Not storing construction materials on wood framing unless the products are braced, shored, and supported to prevent deflection.


Because each exposure scenario is unique and it is difficult to develop a universal rule to capture all situations, it is the responsibility of the project’s design professional or a qualified consultant (often a forensic engineer hired by the project manager) to determine the suitability of all wood products in question due to prolonged exposure.  The project design professional or consultant has specific job knowledge regarding the demand on the affected wood products to be able to assess the overall performance of the framing members.  Some considerations for the design professional or consultant to keep in mind are summarized in Moisture Effects on Weyerhaeuser Engineered Wood Products and Oriented Strand Board.

In the event that construction conditions and exposures result in mold growth, the products can be cleaned in accordance with EPA recommendations and should be inspected to ensure decay has not occurred.  See www.epa.gov/mold for information on cleaning of mold.  Additional information regarding mold can be found in Frequently Asked Questions About Mold.

Be aware that the EWP and OSB product warranties do not apply to damage resulting from prolonged exposure.  When in doubt, Weyerhaeuser recommends replacing weathered products.


Contact Wood Products Technical Support at (888) 453-8358 or TechSupport@weyerhaeuser.com with any questions.

1 - Parallam Plus® is specifically manufactured for exterior, exposed applications.  This product is available in most East USA markets.