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Re: Roof deflection
I have been seeing (or at least noticing) more and more of this type of deflection in roof lines lately, mostly in newer construction. I have become convinced through research and interviews with contractors and repair type folk that some of the deflection is due to improper installation practices by the installers of the roof sheathing. During my research (I'm too lazy to find the exact source again right now but believe it was the APA) I came across instructions concerning proper installation techniques for roof sheathing using plywood and OSB. It is always recommend that the installer stand on the sheathing directly at the rafter to promote good sheathing to rafter contact as it's being fastened but if the sheathing is a thinner type, it was made quite clear that if the installer stood to either side of the rafter while nailing, the sheathing may sag and create a dip in the surface plane of the roof after being nailed in place. The problem will most likely not be noticeable to the crew on the roof at the time but from a distance or at an oblique angle, particularly as the sun glances across the roof plane after shingling, it is very noticeable. Of course this problem has no structural consequence but the building aesthetics greatly suffer.
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