Lumber

This presentation provides an overview of fire-rated assemblies that include wood trusses. Topics covered include assembly testing, Harmathy’s rules, and an examination of fire performance in the field. 

How do you avoid floor performance problems?

I am currently working on a project where a wood truss system was loaded with a heavy spring snow. I do not believe the load was beyond the truss's design capacity, but how do you know? Is there safety built into wood trusses? If the trusses were loaded beyond their design capacity, it would not have been for a long duration.

What is the life expectancy of wood that was used in an attic truss? Does fire retardant change the life expectancy?

Where can I find tolerances and measurements of green and dry lumber?

In RC 2601, is RC-1 Channel used?

Is it possible to construct an assembly for ceiling between first and second floors using 2x with few layers of gypsum to obtain a 3-hour fire rating?

Some questions have been raised regarding the levels of mold in the lumber used in one of our truss projects. The issue of indoor air quality is up and coming. Do you have any information regarding standard allowable values? And how can we test for these contaminants?

I have been told that the high temperatures and low humidity present in attics can cause deterioration of wood, leading to truss failure. Is this true? If so, what length of time are we looking at and can we see the deterioration in the wood by visual inspection?

We recently received bids on a school project, which referenced UL P523. This assembly used light-gauge steel trusses. We noted on the drawing that we could accept an alternate design using wood trusses in lieu of light-gauge steel framing, if the alternate design could meet the fire ratings.