When I built the combination shed/ playhouse featured in the June/July 2010 issue of HANDY (see “Double-Duty Shed,” p. 40), I could have used any roofing material. I chose Pro-Panel II roofing (manufactured by Metal Sales Manufacturing Corp. in Rogers, Minnesota) because it has a commercial appearance that complements the shed’s style. Metal roofs have become increasingly popular for use on residential structures, so I was interested in learning more about these products. Here’s an overview of what I discovered when I installed the roof on my shed.
There are two basic types of metal roofing: exposed-fastener and concealed-fastener. Exposed-fastener roofing is the type that most DIYers can install. It is fastened with screws — no specialized tools are required. It is also typically less expensive than concealed-fastener roofing. The materials for my roof cost roughly $225 (double the cost of asphalt shingles).
This stuff is heavy-duty. Most panels and flashing components are made from 24- to 30-gauge galvanized steel or Galvalume, and many manufacturers offer a 45-year warranty. The panels and flashing components are fabricated in much the same way that seamless gutters are made: Prepainted steel comes off a roll and is pushed through a break or form. The flashing is available in standard lengths (10 ft. is common); the panels are 3 ft. wide and cut to any length you specify. Although you can order lengths ranging from 5 to 45 ft., it’s hard for me to imagine a DIYer handling a panel longer than 16 ft.
Most metal-roof components are fabricated to order at regional facilities to minimize transportation expenses, so you must plan ahead — it might take a couple weeks to receive your materials.
Determining all of the seals, screws and flashing components that you’ll need can be a little confusing. When you place your order, bring a detailed drawing of your roof so the distributor (in my case, a clerk at the home center’s contractor desk) can help you figure out what you need. It took about 45 minutes for the distributor to put together the order, including one 10-minute phone call to get a couple of questions answered by the manufacturer.
Because the panels are bundled and shipped in stacks that are very heavy and awkward to handle, home delivery is worth the extra expense. Once you remove the strapping, two people can lift a single panel into place.
The panels are fastened to the roof with self-tapping wood screws that feature rubber gaskets under the heads. The panels are secured to each other at the overlaps with 1/4 x 7/8-in. self-tapping metal stitch screws. Molded foam closure strips fill the gaps between the panels and the eaves and between the peak flashings and the panels. All flashing overlaps are sealed with a bead of butyl tape sealant (also available from the manufacturer).
The edges (especially freshly cut ones) are very sharp. I wore Ansell ProGrade Series Cut Protection Gloves. They feature rubber palms that grip the metal sheets and are made with a fabric that incorporates Kevlar (which is used in body armor). The only downside to these gloves is that they are hot.
The easiest method I found for cutting the panels was to use a jigsaw equipped with a metal-cutting blade (photo 1). A power metal shear would work even better, but I don’t own one. The panels can also be cut with a manual metal snip (aviators snips), but that method isn’t easy. The pros often score the panels with a utility knife and break them. This works on flat areas, but you need a deep score line, so use a heavy-duty blade.
One essential consideration
I had to learn a hard lesson that wasn’t included in the manual: the importance of positioning the panels so that the rake (angled roof edge) flashings connect correctly.
Unless your roof exactly matches the width of the panels, you will have to trim the excess. The rake or gable flashing is designed to fasten to a specific section of the roof panel (either on a ridge or on a flat section between the ridges). If you simply attach the roof panels and cut the overhanging excess off of the last panel, the rake flashing may not fit correctly, and you’ll have to either order a different piece of flashing (which may take a couple of weeks to arrive) or remove all the screws, shift the panels a couple of inches and trim the opposite overhanging edge so that both rake flashings fit. Due to time constraints, I had to remove all the screws and move the panels (not a fun process).
A better option for the DIYer building a small roof is to lay the panels out on the ground, check how the flashing is designed to fit and then determine how much to cut off of one or both outside panel edges. You might be able to cut the excess off of one panel, but you might have to split the difference and cut some off of both rake-edge panels. Metal-roof contractors have experience and will calculate where to make these cuts or will have multiple flashing types on hand to deal with these variables.
Manufacturers of metal roofing include instructions that explain how to prep the underlayment and install the components. You may also want to ask whether the company offers any online videos or DVDs that show the process.
It took only a few hours to install my 8- x 12-ft. roof. The instructions and photos that follow explain how I did the job; however, the system that you install may be slightly different. Be sure to follow the instructions provided with your materials.
The first step is to prep the roof deck. Staple a layer of 30-pound building felt over the sheathing. Then attach 1x4 strips over the felt, spacing them 24 in. OC. (You can attach the metal roof panels directly over the felt, but in this case the sheathing also acts as the interior ceiling, and the 1x4 strips add the necessary thickness to prevent the screws from popping through the ceiling.) Next, attach a piece of eave flashing along the bottom edge of the roof (photo 2). If your shed will have a gutter, the eave flashing must overlap the side of the gutter.
Next, attach foam inside-closure strips over the eave flashing (photo 3). These soft strips are shaped to fill and seal the gaps between the panels and the flashing. Apply a bead of butyl tape sealant to the top of the closure strip.
Position the first panel so that the end overhangs the eave by roughly 3/4 in. Attach the panel with self-tapping gasket-head wood screws. (I used 1-in. screws.) Drive a row of screws into each 1x4 strip (photo 4).
Place the next panel on the roof. Overlap the high ridges along the edge of each panel. Fasten the panels by driving self-tapping metal stitch screws through the overlapping high ridges (photo 5). Space the screws 12 in. apart up for the full length of the overlapping ridges. Attach the rest of the panel to the roof with wood screws in the same way you attached the first panel. Continue to attach panels until the roof is covered.
Next, install the rake or gable flashing over the sloped front and back edges of the shed roof. Apply a bead of butyl tape sealant along the line where the flashing will contact the roof panel. Attach the top of the flashing to the roof by driving a row of wood screws though the flashing, tape sealant and roof panel and into the sheathing. Then attach the front face of the flashing to the rafter face with wood screws. The rake flashing pieces that I used were 10 ft. long, so I had to cut and attach an additional short length of flashing. The flashings must overlap by at least 2 in. and are sealed with a couple of pieces of tape sealant (photo 6).
Finally, install the peak flashing (or “peak condition,” as the manufacturer referred to it). Adhere foam outside-closure strips to the roof panels with a bead of butyl tape sealant. Next, place another bead of sealant over the closure strip and then place the peak flashing on top (photo 7). Fasten the flashing by driving a metal stitch screw into each of the roof panel high ridges.