One of the major items on This Old House TV’s Charlestown project checklist was a new roof. Homeowner Dan Beliveau wanted to attain a historic look while staying within his budget—no easy task.
The Charlestown row house had originally been topped with slate, a material befitting its Victorian character. As architect Jack French noted during the project’s early assessment: “This house used to have a slate roof. It’d be nice to put slate back on, but the stuff is very expensive.” That prompted This Old House general contractor Tom Silva’s colleague Steve to suggest an alternative: “There is that imitation slate made from rubber that we used in Billerica. It’s worth thinking about here.”
The house’s roof has two sections: the mansard, highly visible from the street, and the flat top section. Slate would be ideal but the cost was prohibitive. Laminated or architectural shingles were more cost effective but did not match the scale of the house. Dan selected scalloped asphalt shingles for the mansard because they matched the scale of the adjoining buildings, had a 25- to 30-year life expectancy and their cost was reasonable. He had hoped to select a shingle with a similar life expectancy for the top section but this proved difficult.
The choice of scalloped shingles for the mansard was particularly fitting. As This Old House Magazine has noted, diamond- and scallop-shaped asphalt shingles “recall French slate commonly found on 19th-century mansard roofs,” and on a steeply pitched surface like a mansard, the clipped corners of two-ply laminated shingles can “evoke the shape and thickness of American Victorian slate.”
In the end, Dan selected an EDPM roof system. The major components are EPDM membrane sheets which, by themselves, last for up to 60 years. The flashing material is the weak link in the system, lasting only 13 to 16 years. For each item protruding through the roof’s surface-everything from skylights to plumbing vents-we have to cut a hole through the long lasting membrane and install flashing along the cuts. The more holes in the roof membrane, the more flashing necessary and the lower the chance that the roof’s life span can stretch closer to that of the membrane itself.
Pro Tip: Roofing contractor Mark Mulloy, who worked on the project, emphasizes that penetrations are the critical vulnerability: “It’s never the roofing itself that leaks. Ninety-nine percent of the time, it’s going to happen at the seams and edges, so that’s where we put most of our attention.”
At vent stacks and other penetrations, Tom Silva stretches a special rubber collar over the pipe and glues it to the EPDM, then seals it with glued strips of uncured rubber—which, unlike EPDM, has no “memory” and can be stretched without springing back and wrinkling—and finishes with a bead of tri-polymer caulk for an extra layer of protection.
Manufacturers are already at work improving the short life of flashing on EPDM roofs. One such step is the use of self-sealing flashing, in which adhesive is manufactured right on the flashing itself, providing a strong, consistent joint. An additional improvement involves the use of primers. Just as a primer helps a wall better accept paint, so too a primer used at a joint can provide a superior surface to accept the adhesive.
To ensure that the Charlestown roof would get increased life from the EPDM membrane roof, we doubled the flashings. Combining innovations in flashing materials with some tried and true methods, we put together a roof system that should give Dan and Heather a sense of security when the wind is howling and the rain is falling.
