Face the facts. Trusses are large and bulky. They take up a lot of space and often cannot be stored inside. They have a shelf life. What are the factors that need to be considered? Are there ways to extend the shelf life of trusses? Are any of the methods currently used counterproductive?
In the photo [See PDF or View in Full Issue], the owner of these trusses is attempting to protect his investment. Based on site observations, it looks like site preparation might have taken longer than estimated. The trusses are covered with tarps to protect them. Unfortunately, the method utilized has created an acceleration of damage. While the tarp sheds the rain, the trusses are sitting directly on the ground. From the tarp leaks and the moisture collected by the tarp, the environment under the tarp is ripe with moisture. This cycle of moisture is causing the connectors to back out. Mold is everywhere. The wood is decaying. In this situation, the owner would have been better off not covering the trusses at all. At least the trusses could dry.
What should contractors and fabricators do? These are some considerations.
- The cycle of wetting then drying causes the most damage. An excellent book on the subject is R. Bruce Hoadley’s Understanding Wood.
- Trusses should be built just in time if possible.
- If you attempt to mitigate weather damage by providing cover, make sure it is ventilated.
- Trusses should be stored off the ground and asphalt to prevent migration of moisture permeating from the ground.
- Dunnage should be spaced frequently, at least at panel points, to provide an even surface as to not distort the trusses.
- Store trusses standing up vertically as they would be installed, supporting them at their designed bearings (rather than flat). This prevents moisture from ponding on the face of the lumber around the connector joint.
- As a more expensive option but excellent long-term storage, top marine boat wrap conforms precisely to truss packages. It’s installed using propane-fueled heat guns and entirely covers and seals the trusses inside a dry package.
In summary, the best method is to build just in time. When this cannot be accomplished and long-term storage is necessary, provide ventilated cover with dunnage. For long-term storage, consider using boat wrap. It can be expensive, but it greatly extends the shelf life of trusses. Unless you take these protective and preventative steps, you’ll be facing trusses that may require mold remediation or even replacement. Be sure to protect your investment by properly protecting your trusses!
An ANSI/TPI 1 3rd Party Quality Assurance Authorized Agent covering the Southeastern United States, Glenn Traylor is an independent consultant with almost four decades of experience in the structural building components industry. Glenn serves as a trainer-evaluator-auditor covering sales, design, PM, QA, customer service, and production elements of the truss industry. He also provides project management specifically pertaining to structural building components, including on-site inspections and ANSI/TPI 1 compliance assessments. Glenn provides new plant and retrofit designs, equipment evaluations, ROI, capacity analysis, and CPM analysis.