Q. We are thinking of putting on a steel roof and wondering if we must remove the shingles or put strapping on before the roofing is applied. Any help would be welcome. The present roof is in good condition with no leaks.
A. It depends on what type of steel roof you plan on installing. If you are considering a standing-seam steel roof, you need to install it on a smooth surface. Otherwise, the unevenness of the shingles will be telegraphed through the metal over time. However, if you are contemplating a screw-on metal roof, strapping is sufficient.
Keep in mind that with any metal roof, you need a water-repellent material underneath, as there will be frosting and condensation forming under the metal. Your present shingles will provide that. Because the strapping will get wet from melting frost and condensation, you would be wise to use pressure-treated wood or to coat plain wood with a wood preservative.
Another consideration is the added weight the metal will put on the rafters. If your roof is steep, this is unlikely to be a problem as the snow is likely to slide right off. But with a lower-pitch roof, or one with protrusions such a skylights, chimneys, plumbing vents, etc., snow may not slide off. It is wise to consult with an experienced contractor or structural engineer to make sure you will not be overloading the rafters.