Performance

This Research Report will look specifically at the sill plate requirements according to the 2009, 2012, and 2015 International Residential Code (IRC) and International Building Code (IBC) and clarify if a sill plate is required in the following conditions:

  • Flat truss bottom chord bearing on ICF wall.
  • Flat truss top chord bearing on ICF wall.
  • Roof truss bearing on ICF wall.

This research report will focus on manufacturer or trade association deflection requirements for a number of floor topping/covering related products where deflection requirements may impact serviceability.

Lumber Design Values

No matter the species, component manufacturers (CMs) purchase and rely on the accuracy and reliability of many different lumber design properties, including: bending (Fb); shear parallel to grain (Fv), compression perpendicular to grain (Fc^), compression parallel to grain (Fc), tension parallel to grain (Ft), and modulus of elasticity (E and Emin).

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. 

In a small scale multi-family residential project, I'd like to use a wood truss floor-ceiling assembly to achieve a one hour separation between units. I'd like to directly attach the drywall to the underside of the trusses & use the truss space for ducts & lighting (the floor above will be lightweight concrete on plywood sub-floor). UL assemblies do not seem to address the duct/light penetrations in such an assembly. Can I achieve a one-hour rating in such an assembly and how are penetrations addressed? Can the ducts in the truss space serve both units above and below?

I was working on a job that had trusses that span more than 78 ft. with a 9/12 pitch. We had the #5 truss being installed when the #4 truss gave way. The trusses that were being installed are a two part system. The bottom set is what you would call hip trusses. The trusses contained 2x6 bottom chords, 2x8 top chords and rafters, and 2x4 webs. The roof sheathing was to be 3/4 in. plywood, 15 lb. felt paper and roof shingles. The ceiling was to be 5/8 in. drywall. The #4 truss sheared about 1 in. off the wall.

As an engineer, I have noticed truss designers in some high wind states routinely using “Main Wind-Force Resisting Systems” wind pressure coefficients as opposed to “Components and Cladding” coefficients to design for wind uplift. A roof truss is not a main wind-force resisting system and would have to have a tributary area of more than 1000 sq. ft. before qualifying for the lower Primary Frame coefficients. In my experience this practice is routine.

We keep having problems with dry wall joints raising on the vaulted bottom chords in the track homes that we are building. The joints run from front to back of the house and the trusses bear on the side walls. The trusses are mostly 2-point bearing (a few in the front and back of the building are tri-bearing). The trusses span 40 ft. and have a 4/12 pitch with a tile roof. Is it common to have dry wall problems as the trusses deflect? How long should the roof be loaded before hanging sheetrock? Should the heel of the truss be allowed to slide out on the top plate?

My framers are always complaining that the “trusses are bad.” I am looking for tolerance information that not only addresses the allowable variance in length and height, but also allowable variation in the top chord with regard to straightness (i.e. how straight should a pull string line from the top and bottom of top chord be?). Also, if trusses are set on a perfectly level wall, what variation is allowed from truss to truss (i.e. if I put a 10 ft. straight edge perpendicular to the trusses, how much can they vary in height, not just at peak or bottom but all along the top chord)?

We would like to know if there is a problem with using wood floor trusses with masonry bearing walls without a ledger. Our local supplier has told me that encasing the wood truss in the masonry wall could be detrimental to the truss due to moisture. What, if any, suggestions do you have for this condition? If a bottom chord bearing is used, do the trusses need fire cuts? The two-story building contains masonry bearing walls with wood trusses on the second floor and wood trusses at the roof.