It’s always best to install trusses immediately upon delivery, but sometimes things don’t go as planned. Follow these tips to store trusses safely and help protect them from damage.
We have a customer looking for some information about trusses left exposed to the weather. Due to project delays, they were not able to install the trusses when they were delivered to the jobsite, and the trusses have been sitting for almost a month. Although there is no visible damage to the plates or lumber, there is a bit of discoloration and some bowing. Will the trusses be safe to use?
According to the Building Component Safety Information Series (BCSI), which is referenced in the International Residential Code and is also defined as “Standard Industry Details” in ANSI/TPI 1 and the International Building Code, trusses may be stored directly on the ground for up to one week. For trusses left exposed for more than a week, BCSI makes the following recommendations:
There is no hard limit for how long trusses can be exposed to the elements, and the duration depends on the temperature, moisture and humidity of the site.
Per ANSI/TPI 1-20071, the contractor should always examine the trusses delivered to the jobsite for: (a) dislodged or missing connectors, (b) cracked, dislodged or broken members, or (c) any other damage that may impair the structural integrity of the truss. Since the trusses in question were left outside for about a month, a thorough inspection of the lumber and the plates is even more important.
Some questions to ask while inspecting the trusses include:
What is the condition of the wood?
Discoloration on the trusses is not a concern because surface mold and mildew do not cause wood to rot or otherwise impact the strength of the trusses, but mold and mildew are symptoms of high moisture. According to the Wood Handbook, wood kept constantly dry does not decay, and even wood continuously submerged in water for long periods of time would decay very slowly. Most wood in use today is kept so dry at all times that it lasts indefinitely.2
Is the lumber warped or bowing?
If damage is discovered that would likely impair the structural integrity of the truss, per ANSI/TPI 1, the contractor shall ensure the truss not be erected3 and contact the truss manufacturer to determine an adequate field repair.4
What is the condition of the plated joints?
Repeated wetting and drying cycles cause expansion and contraction of the lumber, which might push the connector plate teeth out of the lumber. If the metal plates are still firmly embedded in the truss with no gaps between the connector and the lumber greater than 1/32"5 and the connectors are not discolored (as this may be a sign of corrosion) there may be no structural damage. Again, if the contractor discovers anything that would likely impair the structural integrity of the truss, he or she should contact the truss manufacturer to determine if an engineered repair might be necessary.
If the contractor has any uncertainty about using the trusses, the best course of action may be to hire a professional engineer with wood truss experience to inspect the trusses and determine if any damage discovered would likely impair the structural integrity of the truss. SBC
To pose a question for this column, call the SBCA technical department at 608-274-4849 or email email@example.com.
1ANSI/TPI 1-2007 Section 18.104.22.168 Pre-Installation Check
2Wood Handbook: Wood as an Engineering Material, United States Department of Agriculture, Forest Service, General Technical Report FPL-GTR-190, Chapter 3: Physical Properties and Moisture Relations of Wood, Decay Resistance, Page 3-15: www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf
3ANSI/TPI 1-2007 Section 22.214.171.124 Post-Installation Check
4ANSI/TPI 1-2007 Section 126.96.36.199 Truss Damage Responsibilities
5According to ANSI/TPI 1-2007 Table 3.7-1, a tooth embedment gap less than or equal to 1/32" (0.03") is equivalent to 100 percent tooth effectiveness.
SBCA offers a number of resources that discuss the topic and solutions to consider. For more information, visit sbcindustry.com/pubs.
- TTB – Facts Regarding Mold on Wood Structural Building Components*
- TTB – Builder Advisory on Mold*
- BCSI book
- B1 Summary Sheet
*Also available as an online Component Technology Workshop.