preservative treatment on wood trusses

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Author Message Robin E. Snyder Senior Member Username: robin Post Number: 272 Registered: 08-2004 Posted on Monday, September 14, 2009 - 12:46 pm:    is it typically required? This particular project is in CA. If you require it, what product do you spec? Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 209 Registered: 10-2007 Posted on Monday, September 14, 2009 - 01:34 pm:    What type of treatment? Fire or termite? Floor or roof trusses? Are they exposed to the weather or high humidity? What type of wood trusses? Short of writing a book I would need more to understand what is driving this question? In most cases wood trusses are not made of treated wood but there are some conditions where it may be appropriate. The type of treatment can impact the corrosion on the fasteners used to connect the trusses and in the case of fire treatment the design values for the wood. Robin E. Snyder Senior Member Username: robin Post Number: 273 Registered: 08-2004 Posted on Monday, September 14, 2009 - 02:50 pm:    sorry - roof trusses. Simple, standard wood framed 2-story apartment complex, low budget. Termite (Boron or similar) treatment Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 210 Registered: 10-2007 Posted on Monday, September 14, 2009 - 03:13 pm:    Typically there is no reason to treat roof trusses. It makes no sense to require treatment of roof trusses for termites unless you treat the lumber below. In Hawaii they have a real problem with termites and require all framing lumber to be treated. This may also be appropriate in some coastal regions. I would not treat them. I seem to recall that there is some poorly worded code language someplace that might imply the need to treat these members but I cannot recall where it is. Suggest that you find out what is driving this issue. Borate is advantagious since it appears to have minimum potential to cause corrosion. The fasteners used with some treatment processes may need to be galvanized or stainless steel. One problem is the metal plates used for the plated trusses may not be availible in stainless steel. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 212 Registered: 10-2007 Posted on Monday, September 14, 2009 - 05:13 pm:    Relevant IBC code provisions are Sections 2303.18, 2303.2, and 2304.11. Section 2304.11.6 was poorly worded to imply all floor framing be treated without requiring wall framing be so treated. George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 484 Registered: 11-2004 Posted on Monday, September 14, 2009 - 05:20 pm:    Mark- Aren't there reductions in structural capacity that need to be taken when treated wood is used in areas subjected to heat, such as attics in certain climates? I seem to remember this as a reason to avoid treating trusses (in a time before truss plate corrosion issue was a factor) George A. Everding AIA CSI CCS CCCA Cannon Design - St. Louis, MO Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 213 Registered: 10-2007 Posted on Monday, September 14, 2009 - 05:59 pm:    There was a problem in the early 90's with fire retardant-treated plywood that degraded when it got hot. It is my understanding that the current treatments used for plywood have mitigated this problem. Similarly I would not expect this degradation using current treatment processes. Fire retardant lumber has lower allowable stresses irregardless of temperature. You need to get information from treater on the stress reductions using their process. Thus unless you specify the treater you run the possibility that the reductions for the treatment process will be larger than assumed in the design. I am not aware of special stress reductions for preservative-treated wood. All lumber should be designed for lower allowable stresses when the in-service temperature exceeds 100 degrees F. If it is over 150 degrees for any significant time you might want to question whether wood is the right material.