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Q.The low-slope roof on the addition I'm building has an ornamental iron railing at the edge. Since the roof won't be used as a deck, it's just there for appearance. Given that high strength isn't a requirement, I'm wondering if there's some way to fasten the railing that doesn't involve penetrating the roofing and creating potential leaks.

A.Harrison McCampbell, an architect and moisture-intrusion consultant in Brentwood, Tenn., responds: Your concern about through-fastening is justified - it makes little sense to apply a carefully waterproofed membrane and then poke it full of holes.

It is technically possible to put a railing on the roof that is held in place by gravity alone. A simple way to do that would be to weld each of the railing columns to steel base plates. But first check your local code to make sure that the area where the railing will go is clearly defined as a roof, not a deck. This will probably depend on how accessible it is to the building's occupants - whether it can be reached through a door, by climbing out a window, or only by using a ladder. If the area could be considered a deck under the code, the railing should conform fully with the code requirements for that application - anything less is asking for trouble.

  • Base plates supporting an ornamental rooftop railing (one not required by code) stand on scraps of membrane roofing, which protect the roof from abrasion (top). If a true railing is called for, a correctly detailed post penetration is necessary (above).
    Base plates supporting an ornamental rooftop railing (one not required by code) stand on scraps of membrane roofing, which protect the roof from abrasion (top). If a true railing is called for, a correctly detailed post penetration is necessary (above).

Either way, make sure the roof itself is properly designed and built to last. Provide the structural deck with enough slope to allow water to flow away from the building the addition will be attached to - 1/8 inch per foot is a practical minimum - and toward the roof edge or drain. Install a fully adhered waterproofing membrane, making sure to terminate it properly by turning it up and under the main building's moisture barrier and extending it fully over the drip edges. If there is an access door, the deck level should be at least 4 to 6 inches below it so that there's enough vertical space to turn the membrane up, terminate it, and counterflash it with the overhang of the door sill.