Norbord Blog Feature: The Wood Whisperer
When the sun is at a particular angle, you can see the outline of the OSB panels on my roof. This causes a ‘windowpane’ effect. Why is this happening and what can I do to prevent it?
This is a common complaint on residential homes. The effect is most visible when the sun is low, roof framing spaced at 24”o.c. and light weight shingles.
A couple of years back we rounded up the APA rep and we walked some neighborhoods with the builder’s area managers and quality assurance manger.
We were looking for a solution and the APA explained that it wasn’t edge swell because we were seeing a uniform problem (many, if not all, panels showing an outline on the shingles). In the attics he used used a thin feeler gauge from the truss side of the panels to locate fasteners (many where 2″ to 6″ up from the panel edges and there were some shiners—nails that missed the framing member).
He explained the problem as a shadow effect. When sun is low a 2″ roof vent will cast a 16’ shadow. Therefore, when panels are not nailed the required 3/8″ from the edges (nailed 1″ or more from the edge) it creates a lift at the panel edges creating a shadow/outline on to the shingles.
Be sure that your framers are following the right nailing schedule and that the sub-roofing is inspected before shingling. It’s much easier to fix issues before the shingles are installed.