A Goof-Proof Roof

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 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.

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.

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.