Lumber Grades In Truss Design


In truss manufacturing, can hemlock, fir and spruce be used instead of Douglas Fir/Larch? What grades can be used: Structural Light Framing (Select Structural through #3) only, or Light Framing (Construction through Utility) as well?


Yes, species combinations like Hem-Fir and Spruce-Pine-Fir are used regularly in truss manufacturing as well as Southern Yellow Pine and, as you mention, Doug Fir-Larch. What you use generally depends on the part of the country you’re in and what is in most plentiful supply.

Structural framing grades like Select Structural, No. 1, No. 2, No. 3, MSR and MEL are all used in trusses. It is important to make sure that the proper lumber size, species and grade chosen in the truss design program will be used in production because selecting that information in the truss design software allows the program to pull lumber and plate strength. If the species and grade used is not included in the program’s lumber file, it may mean that the plate manufacturing company does not have data on plate strength values in that particular type of lumber. At that point, contact the plate manufacturer for more information.

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