Tips for Installing a Metal Roof Over Shingles
Asphalt shingles have a typical lifespan of 8-10 years, sometimes even less depending upon the conditions of the area. Instead of replacing your old shingles, you may want to consider replacing your old roof with a metal roof. These can last well over 100 years with just minimal maintenance. Best of all, they are simple to install over an existing asphalt shingle roof. Use this guide to installing a metal roof over your old shingle roof and get the most out of your new roof investment.
Remove the Old Vents
The first step to installing a new metal roof is to remove the old lead boots that cover the plumbing vents. You’ll also need to remove any galvanized vents and the aluminum/vinyl ridge ventilation.
Install the 1×3’s
Because a metal roof can easily bend and become dented when you walk on it, you’ll need to add a series of 1×3 spacers onto the existing shingle roof. If your roof is stripped down to the bare plywood, you can skip this step.
Using ring shank 8d nails, attach the 1×3’s into the shingles every 4-6 inches. You’ll need to wrap the perimeter of the roof, all of the edges and every valley/ridge with a 1×3. You’ll also need to place 1×3’s on the main span of the roof every 16-24″ inches apart. Be sure to keep the main span 1×3’s evenly spaced apart as these will not only be used as spacers, but they will also be used as deadwood for the screws. For larger ventilation stacks, you may want to consider wrapping a 1×3 box around them for screws.
Trim Pieces
The next step is to install the drip edge trim pieces. This metal needs to be attached using galvanized ring shank roofing nails spaced about 4-6″ apart. You have to start at the bottom eve of the roof and work your way up to the top to get a water tight drip edge trim. Be sure to overlap each of the trim pieces 2″ or more to get a good coverage that won’t leak. For roofs that have a pitch less than a 3/12, you’ll need to overlap every metal piece at least 3″ or more. Add any valley trim as needed.
Panels
Metal roofing panels should be attached beginning with the side that faces the most wind. You’ll need to attach the panels with metal roof screws that have a butyl grommet to prevent leaks. Use the 3-4-5 squaring method to get the panels aligned properly before you finish screwing them down to the old roof. Add the side trim panels, roof peak panels and vent covers to complete the roof.
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