A.The problem was probably caused by using green rough-sawn lumber. Rough-sawn lumber is rarely dried. It will shrink during the first year or two, leaving nail heads sticking up from the surface of the boards. If the nails were not fully driven below the surface, this will be enough to cause a problem. The boards may also have cupped somewhat as they dried from the inside, pulling some of the nails, then flattened out as the outside dried with time, leaving the nail heads sticking up.

As far as repair is concerned, the nails can be driven down with a small punch, and the resulting hole in the shingle sealed with roofing cement. An alternative is to sandwich the top shingle between two putty knives — one slipped beneath the shingle and over the nail head and a second one on top of the shingle — and strike the top knife with a...

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