Covering an old shingle roof with a metal roof can be easily done if you’re skilled enough to install metal roofing and you’re not afraid of heights. Metal roofing is the perfect cover for asphalt shingles as it lasts for decades and even centuries longer than conventional roofing systems.
1×3 wood strips are used to cover the existing roof and provide a base for the metal roofing. It also serves as an added layer of insulation, reducing your overall heating and cooling bill further. You’ll need to attach the 1×3 pressure treated wood strips with 10d screw/ring shank galvanized nails to the underlying trusses or sub-fascia whenever possible.
Attach the strips around the perimeter of every roof line. That includes gable ends, ridges and hip lines. Ridge lines and hips should have strips on either side, spaced apart 1″ minimum. For peaks and ridges that will get a ridge cap, measure the overall length of each side and transfer that measurement to the roof line, setting a horizontal piece of 1×3 wood strip as a deadwood nailer. Gable to gable sides should be measured to ensure that an equal length is met on each side.
Finish the deadwood by installing horizontal deadwood every 16″ or according to metal roof manufacturer’s specifications. Make sure that you’re hitting the trusses below. You can do this by snapping lines every 24″ on the shingle roof prior to installing the horizontal deadwood.
Once your deadwood is complete, you can begin installing the metal roofing. This is easily done by beginning on the windward side of your roof. Have a helper hold one end of the panel and adjust it until it is square. Screw a waterproof self-tapping grommet screw through the roof into each of the deadwood pieces below.
Work your way across the roof overlapping each piece of metal and screwing through the deadwood. Keep checking measurements are consistent, or you may have to back up and re-install the panels.
Cut out any opening and attach new metal vent boots. Finish off by attaching the ridge and your new metal roof is complete!