How to Retrofit My Barn's Metal Roof

Run the purlins horizontally on top of the existing metal roofing and directly over the old purlins. Purlins are horizontal boards that provide a nailing base for the metal roofing panels. You can tell where the old purlins are because the screws on the existing roof will fall in horizontal rows over the purlins.

Attach the new purlins with 8d galvanized screws spaced about 8 inches apart. Different types or brands of metal roofing might require different-sized purlins, but a standard purlin is 1-by-4 treated lumber that runs across the roof. Purlin rows are generally 24 to 30 inches apart.

Remove the existing metal roof ridge with a flat bar but leave the purlins in place. Once the ridge is off, install two more purlins on top of the existing ones.

Run the first metal roofing panel from the side of the barn roof least affected by the prevailing wind in your area. For example, if the prevailing wind is from the southeast, install the first piece of metal roofing on the west or northwest edge of the roof.

Align the edge of the new panel parallel to the edge of the old panel. Insert neoprene screws about every 8 inches through the metal and into the purlins beneath. Neoprene screws have little rubber washers beneath the screw heads that form a tight seal on top of the metal roofing. The caveat here is to insert the screws only until the washer is snug against the metal but no farther. If the screws are too tight, the metal can look wavy.

Install the next roofing panel by overlapping the edge of the first panel at the designated corrugation. This also depends upon the type and brand of metal roofing, but on the installation layout that comes with the panels, there should be a diagram that shows the required overlap. Insert a neoprene screw 1/2-inch from the edge of the new panel and every 8 inches thereafter into the purlins.

Continue to install the metal panels until you reach the far side of the barn roof. If the final panel is too wide, cut off the excess with metal shears then install it as you did the previous panels.

Attach a metal roof rake, which is an L-shaped strip of metal, to the edges of the barn roof. The lip of the metal fits over the top of the new roofing, and you will insert two neoprene screws, evenly spaced, through the top of the roof rake into every purlin. Insert additional metal screws along the side of the roof rake and into the side of the barn every 8 inches. This will cover the gap between the new roofing and the old roofing to reduce damage from strong winds.

Install a gutter apron along the bottom edges of the roof. The gutter apron, which is a long angled piece of metal that is 3 to 4 inches wide, slips under the lip of the new metal roofing and on top of the lowest purlin. Insert neoprene screws into the top of the metal roofing every 8 inches to hold the apron in place.

Attach a new metal roof ridge to the top of the barn roof. The new ridge will have a foam or rubber-type strip along the bottom of both edges with a peel-off paper covering. Once you remove the protective paper, place the ridge so it covers the tops of both side panels and insert neoprene screws through the top of every other corrugation peak on the panels below. If the panel corrugations are wider than 12 inches, insert one screw through the top of every corrugation.