I've got a question regarding some of the liability issues surrounding lumber grading and I'm hoping somebody can point me in the right direction. If a piece of dimension lumber is properly graded with visual grading rules but ultimately turns out to not have the strength associated with the visual grade, will the manufacturer/grader be liable should the board break and cause damage? Is anybody aware of a reported case involving this scenario?
(Sawing and Drying Forum)
From contributor E:
There should be no liability if it was graded using visual grading rules. The lumber has to be stress tested and certified as to load stress limits. That was the rule when I was grading under SPIB grading rules. Visual grading makes no claims as to structural strength of the lumber.
When building a house or other frame structure, if we do get a weak piece, it is very likely that the adjacent pieces will be stronger and help carry the load (called load sharing) along with the OSB or plywood. So, using visually graded lumber, a structure is tremendously over-designed, strength-wise. Further, the design of a floor using visually graded material is actually based on the deflection limits, which are the governing factor before the strength is. So that gives even more safety, strength-wise.
Of course, some argue that over-design is wasting wood. So, a trend is to test each individual piece of wood and come up with a good estimate of the actual strength and stiffness and then use these values to develop design values for a structure. This lumber is called MSR lumber (machine stress rated). In some countries, they also test the wood and then if they find a weak spot, they cut out the weak wood (like a knot) and glue the remaining pieces together (finger joint) and end up with a strong piece (which is tested again to be sure).
A lawyer will probably tell you that you can be sued for anything, but the key for having to pay is that it must be shown that you were negligent. However, as trials of this sort are very expensive ($300,000 minimum for each side), it is likely that there will be a settlement prior to trial. If you have insurance, your company will handle this aspect, as it is their money.