Quality Control

SBCA’s latest testing promises value for all CM

How SBCA is improving the way CMs measure and manage QC

In the SBCA booth at BCMC 2018, SBCA staff member Joe Schauer displayed how the SBCA Quality Control (QC) Committee’s initiative is a giant step forward in the area of component manufacturing QC.

Quality control (QC) is often thought of as an effort to catch mistakes made by production. However, many times problems and solutions extend beyond just the manufacturing process. 

Testing is underway to determine the effects of weather exposure and time on trusses.

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).

As the owner for a building designed to have metal plate wood trusses, what documentation should I receive to be assured that the manufactured wood trusses delivered to the site have indeed been manufactured at a licensed and registered wood truss manufacturer under the required written quality control procedures?

When webs are cut is it alright that sometimes the grade mark is removed? From a liability standpoint, what is the rule with grade marks and web members?

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)?

The grading rules usually permit some percentage of visually graded lumber to be below grade – I believe it is 5%. ANSI/TPI 1 requires that all lumber used in trusses be of the grade specified by the truss design. A strict interpretation of ANSI/TPI 1 would require that the fabricator cull the 5% that is off grade. What are your thoughts on this?