Q: Can metal roofing be applied directly over old shingles?
A: Yes. Definitely. If the existing shingles are not badly curled and are reasonably sound, it’s okay to install metal roofing on top. Anchoring 1×6 strapping across the roof first, then fastening the metal roof to these strips is the easiest and best approach. Anchor the strips with rust resistant deck screws long enough to extend at least 1 1/2″ into the underlying rafters or trusses. If the old roof frame is wavy and uneven, you may need to install shims or wedges underneath the strips of wood, to level things up. Metal roofing is an attractive, long-lasting option, but the first thing to go bad will be the appearance of the finish. Definitely check out the finish warranty before you buy.
Metal Alternative . . .
All this said, I prefer asphalt shingle roofs over metal for several reasons. The big attraction with metal roofs is long life, but today’s best asphalt shingle roofs carry a 50 year warranty. In some cases shingles are even warranted for life. Asphalt looks better to my eye, and snow and ice doesn’t go avalanching down the roof slope, either. To learn more about best the details behind the best 50-year asphalt roofs, check out “Asphalt Roof Best Practices” below.