Laying Steel Roofing over Shingles the Right Way
Steel roofing offers many benefits over slate tiles or asphalt shingles. Metal roofing is resistant to fire, rot, and termites. Manufacturers provide 30-year warranties on metal roofing products. Installing steel roofing over existing roofing materials is fairly simple. Use furring strips to build a slat board on the roof, then mount the steel sheets to the slat board. Some consideration for vent stacks and chimneys is required during the design process. Installing a steel roof will cost approximately $60 per square foot.
Step 1 – Work Safely
Choose a day with calm weather to work on the roof. Metal roofing is very slippery when wet. Brace your extension ladder correctly when climbing onto the roof. In some cases, you can lean the metal sheets against the roof surface on the ground and lift them up from the roof while working. This is preferable to carrying large stacks of sheets up a ladder.
Step 2 – Measure Roof
Measure the surface area of the roof to predict your material needs. Add a 2 to 4 inch overhang when buying metal sheeting for the roof plane. You need enough boards to run lengthwise across the roof every 2 feet from top to bottom. You need edging and trim for the perimeter of all roof surfaces and the top ridge. You will also need preformed closures or flashing to close the roof surface around vent stacks or chimneys. Obtain several boxes of 3-inch wood screws, ¼-inch wood screws, and 1-1/4 inch roofing nails. Decide whether to use V-crimp or R-panel roofing. V-crimp does not require lap screws to install.
Step 3 – Install Slat Board
The furring strips are 1x4 pine boards. Secure them to the roof with wood screws at every 4 to 6 inches. Install the slat board as described above.
Step 4 – Install Edging
Bend the metal edging to your needs if necessary and fasten it to the roof with nails at every 4 to 6 inches.
Step 5 – Install Metal Sheets
Begin laying the metal sheets from the bottom to the top of the roof. Overlap the rises and dips if using corrugated sheets, or lay flat sheeting with a slight vertical overlap. Screw the metal sheets into the slat board with a wood screw every 2 feet along the edges. Screw the first sheet in the center as well as the edges. Use tin shears to cut gaps for pipes and exhaust vents.
Step 6 – Install Trim
Cut v-shaped notches into metal sheets and bend them to fit trim pieces to the ridge line and eave. Close the bottom of the metal roof.
Step 7 - Install Closures
Seal around gaps that were left for vents and chimneys with preformed closures or metal flashing. Secure these in place with roofing cement and screws.