As a certified installer of just about any type of roofing you can think of, my company enjoys a competitive advantage when working with products whose manufacturers restrict the number of installers per geographic region; to get the material, a homeowner typically has to go through a certified installer. This year, my crew and I spent several days on a full-house remodel in Cohasset, Mass., replacing existing EPDM roofing with Sentinel Copper Art (soprema.us), a European-made 60-mil, polyester-reinforced PVC membrane. It has actual powdered copper metal incorporated into its chemical mix, resulting in a single-ply waterproofing membrane that weathers, or oxidizes, over time to a classic copper patina.
This PVC material has a number of benefits. Its reinforcing scrim provides high puncture resistance, which is an important feature around here because seagulls drop clams on the roofs, and the shells make sharp shards when they break. Unlike EPDM, ponding conditions don’t void the warranty, so a no-slope roof is actually a go with PVC. That’s because once you weld the seams, they’ll never separate again, period. Another plus is that while EPDM can leach nasty solvents into the runoff, PVC sheds clean water, making it a great choice for cisterns and agricultural water capture.
The windows on the second floor of this house looked out over a couple of low-slope roof areas, and the owners wanted to see something more attractive there than black EPDM, or even white PVC or TPO. (A white roof has about 88% reflectivity, forcing us to wear shades during installation.) When I showed them a sample of the copper membrane, they were sold on the look. We sell Copper Art roofing starting at an installed cost of about $10 per square foot. Compared with solid copper, that’s maybe one-third the cost, and it’s probably three times faster to install, too. The following slideshows will demonstrate the steps we took to complete this re-roofing project.
Installing the Roof Membrane
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Deck preparation, underlayment, laying out the “field” membrane, mechanical fastening, seam work, and tools.
Play slideshowUnderlayments
After stripping the old roofing and fiberboard underlayment, we installed new, 1/2-inch-thick polystyrene underlayment as a smooth base for the membrane. Unlike fiberboard, polystyrene underlayment doesn’t absorb water, ensuring a dry base in the event we have to leave it temporarily exposed. Also, once fiberboard gets wet, it pretty much stays wet and can even promote rotten plywood sheathing—it’s the cheap stuff and we never use it.
Raised perimeter trim around one of the areas of the roof called for additional build-up, so we installed 1-inch-thick R-Max Thermasheath-3 as underlayment there. For both the 1/2-inch and the 1-inch thicknesses, we fasten the underlayment using common screw-down plate fasteners on nominal 2-foot centers.
Mechanical Fastening Preferred
When rolled out, the 60-mil Sentinel Copper Art membrane is heavy enough that it lays flat. It comes in 63-inch-long rolls, which weigh roughly 150 lbs. and covers 344 sf. It can be installed fully adhered using a flocking-backed membrane and approved adhesives, or it can be mechanically fastened, which is the method we typically use. Certain applications or specifications do require adhesive bonding, but it’s overkill in most residential situations.
Mechanical fastening avoids the prep, the volatile goo, and the 50°F low-temperature limitation that go with the fully adhered method. Mechanical fastening also satisfies high-wind code requirements, a real concern on an oceanfront property like this one. We use proprietary, 2.4-inch “membrane stress plates”—we call them “seam plates”—along the upper edge of each 6-foot-wide course, on 12-inch centers. These plate fasteners have barbs and ribs on the underside to better resist membrane uplift. The 6-inch overlap of the next membrane course covers the fasteners. Along the roof’s perimeter, a heavy-gauge drip edge fastened with roofing nails secure the membrane to the deck.
Heat-Welded Seams
Welding PVC is straightforward, though it takes some practice. Click here to see a short video demonstration. We heat the seams briefly by slipping a torch nozzle under the membrane edge, and then immediately press the pieces together using a seam roller. You should see a little bit of white smoke wafting out of the seam as you work.
We use a Leister hand-held, 1,500W torch, with power adjustable from 80W to 1,500W, and a temperature scope from 100°F to about 1,300°F. (On smaller jobs like this one, the hand-held torch is sufficient, but on large, commercial-scale work, we break out the “robot,” which semi-automates seam welding and can crank along at up to 10 feet per minute.) While cold weather doesn’t delay installation (you can even weld PVC in the rain), you do have to adjust the welding temperature upward to compensate. Likewise, in hot weather, you need to lower the welding temperature accordingly.
What you’re looking for is a characteristic “bleed” at the seam edge, where molten material is squeezed out ahead of the seam roller. That tells you that you have a fully welded bond. We use a pointed probe to check for any loose spots that would void the manufacturer’s warranty.
Perimeter Flashing and Accessories
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Roof-to-wall flashing, fastening the roof membrane at the perimeter edge, and accessories
Play slideshowPerimeter Flashing
We cut both cover strips and terminal flashing from the roll, according to need. To terminate the membrane against a wall or parapet, we cut the sheet to the junction and fasten the edge with stress plates. Then we fold a cover strip up the wall, using a full bead of caulk along the upper edge and nailing it in place. A few tack-welds hold the strip in place pending full seam-welding. Measuring 6 inches out along the roof plane, we then snap a line and trim the cover strip to it. Pre-formed inside and outside corner flashing is available from the manufacturer, and is the way to go for these junctures.
Along the roof’s perimeter, we install PVC-clad, heavy-gauge stainless drip edge with a bonded, weldable PVC coating. The drip edge is nailed off with stainless steel roofing nails at a rigorous 3- to 4-inch on-center spacing (replacing membrane stress plates along this edge). To finish it off, we then seal it under a weld-down cover strip. Because there’s a tendency during welding for the membrane to deform at any sharp corners, we round all the cover-strip terminations.
When mechanically-fastened membrane is first installed, it’s common to see slight waves in the surface where the material hasn’t fully relaxed onto the substrate. Over time, as the material responds to temperature cycling, the material settles to a flat, smooth appearance.
Photos by Dave Holbrook and Matt Quigley
