There is an art and a science to metal roof installation. Here is a step-by-step guide on how to install metal roofing, such as metal soffit panels. This tutorial is about how to install metal roofing over plywood, but toward the end, it also touches upon metal roofing installation on shingles.
1. Apply Underlayment
The underlayment is the first layer over the plywood. The essential thing here is to keep the underlayment flat and wrinkle-free.
Start by carefully unrolling the underlayment across the roof surface, overlapping layers by six to eight inches. As you unroll the underlayment, remove the bottom half of the adhesive backing.
Once you have rolled out the underlayment, cut it flush. Then, remove the remaining adhesive from underneath.
2. Cut and Bend Trim Ends
Before installing the trim, cut and bend the ends and wrap them around the corners.
Use aviation snips to make a series of one-inch cuts and create tabs at each bend. Then, using a hand seamer, fold the tabs to meet a wall or a corner (or close a trim gap).
Note that each trim — eave trim, gable trim, sidewall flashing trim, or mono-pitch ridge cap — requires unique cuts and bends depending on its shape.
3. Fasten the Eave Trim
Install the eave trim close to the fascia, and fasten it onto the underlayment using one-inch roofing nails.
If you live in a colder climate, install the eave trim over the underlayment to protect the roof against water damage. In warm and dry climates, install the eave before the underlayment.
4. Splice and Overlap Trims
Next, you want to splice the trim ends where they meet. To do that, cut the bottom hem of the underlapping end at an angle. Install the underlapping trim and apply sealant on top.
Then, pry open the overlapping trim’s bottom hem and slide it over the hem of the underlapping trim.
5. Snap a 90-Degree Reference Line
A square reference line 90 degrees to the eave is essential for evenly installing metal roofing panels (and other exterior building materials).
One way to create a square reference line is to make a mark along the eave three feet from the corner. Measure four feet toward the ridge from the mark and make a second mark. Then, measure five feet from the original corner, and mark the intersection with the second mark. Finally, draw a line from the first mark through the meeting point of the second and third marks.
6. Set the Panels
Place inside foam closure strips along the eave at around one inch from the edge, then attach them to the panels using butyl tape.
Next, run a bead of sealant on top of the closure strip, and place the panel so it hangs by an inch beyond the eave. Make sure any measurement from the panel to the square reference line is identical at the top and bottom.
7. Fasten the Panels
Fastening the panels correctly is one of the most important steps in metal roof installation.
Begin at the eave by placing screws on each rib and lining them up to go through the closure strip. Space each row of screws by up to 24 inches, ensuring there is one screw at each rib on the overlapping side.
Start fastening each panel at the bottom and then across. Fasten panels in rows, working your way toward the ridge. Make sure to drive screws flat — crooked screws will not seal.
8. Overlap Panels and Cover the Rake Edge
Overlap the last rib on each panel. The overlapping edge has a shorter rib leg that does not contact the roof surface when laying flat. The underlapping rib has a drainage channel.
Once you have fastened all panels, attach the gable trim. Bend the end to meet the eave corner, then apply butyl tape between the trim underside and the flat part of the panels. Press the trim and drive screws over the butyl tape, spacing them at 12 inches.
9. Secure the Ridge Cap
Use butyl tape to stick a line of outside closure strips four inches from the peak’s top. Then, apply sealant on the foam closure, and fit the ridge cap on the peak. Fasten the cap by driving two-inch screws through every rib.
How To Install Metal Roofing Over Shingles
Installing metal panels over existing shingles is a great way to maximize the service life of the new roof while saving on roof tear-off costs.
You can attach the panels into furring or lathing strips. For a more budget-friendly option, you consider attaching the panels directly through the shingles into the roof deck below.
Metal Roofing Installation: Final Thoughts
Correct metal roof installation is essential to the longevity and structural integrity of the entire building façade. Take the time to do it properly; your roof will serve you well for years.
