How To Install Corrugated Metal Roofing Over Shingles. Attach your metal sheets to the framing. The second way is to install 1×4 purlins over the shingles.
The second way to install a metal roof over a shingle roof is with the use of purlins or battens. The purlins are screwed or nailed down to the roof deck, depending on how the metal roofing manufacturer has testing for their roofing panels, and then the metal is installed to the purlins. By removing the old roof before the new roof’s installation, you are able to give the underlayment a thorough inspection to ensure there are no damages that could cause leaks or other issues with your new roof.
This framework has three big advantages.
Step by step metal roof installation. The purlins give the installer a flat surface to install the metal roofing. In simple terms, if the asphalt shingles are not used to support the metal roof, then you can install a metal roof over the asphalt shingles. A layer of underlayment installed on top of the existing shingles will help keep the granules of the old shingles from rubbing against the back of the metal and causing possible corrosion.