Why does the edge of my roof look like a health food snack?
When OSB sheathing gets wet it acts like a sponge. And while I am picking on OSB because it is worse, this kind of damage can also happen to plywood–it just takes longer.
On my planet, it has been required for a very long time that there be edge metal along the edge of the roof. It is now part of the building code on this planet as well–and that is awesome. It is all too common for roofers to not extend the roofing materials far enough past the edge of the roof sheathing.
One such metal flashing is called a “D” flashing (no clue why) and it looks like the following picture.
Granted, if you hang the roofing materials far enough over the edge of the sheathing, water will not likely wrap around to the wood. However this can represent a problem with cleaning the gutters and the overhanging shingles fold and break and are subject to mechanical damage from cleaning etc.
Another solution would be to use one of the many types of gutter covers which would act as a flashing to protect the wood edge.
Somehow this edge needs to be protected or it will end up looking like a health food snack sooner or later. Repairs will often require replacement of at least the bottom 12” of the roof sheathing all along the edge of the roof and is typically done in the context of the roof replacement–sometimes sooner if damage is severe enough.
By Charles Buell, Real Estate Inspections in Seattle
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