I work for a Vermont company that specializes in restoring and preserving timber-frame structures, so after reading the table of contents blurb for Gary Morrison’s article “Strengthening an Old Roof” in your December issue — which read “New LVL framing straightens and stiffens an underbuilt timber frame” — I enthusiastically turned to the article itself. But my enthusiasm turned to dismay when I saw that the author had cut the purlins and chopped out the “waste” on either side of the rafters.
In any historic timber-framed structure — and especially one dating back nearly 300 years — the joints are among its most important features. Arbitrarily cutting original framing members destroys the historic fabric that makes the buildings so special.
After sharing the article with a co-worker, he and I quickly figured out a way to straighten the roof without disturbing the original framing: by adding supplementary 2-by lumber rafters between the original timber rafters, with their upper edges below the faces of the purlins. Pairs of tapered shims could then be placed between the purlins and new rafters as needed to transfer the load. This would also cost much less than the LVL approach that was actually used.