By Andrew P. DiGiammo
In the coastal area where I design and build homes, it's often important to make the most of the views, light, and breezes that a shoreline site offers. Many times, I find that a high deck is the best way to reveal a beautiful ocean view, or perhaps just to catch a glimpse of the water over dunes or neighboring buildings.
Working primarily in the Shingle Style, which typically involves a lot of dormered spaces under roofs, I often end up setting those decks into the roofline above a lower-story room. It's also convenient in many cases to build a deck on top of one of the many-sided projecting rooms I like to use for catching light, views, and oceanside breezes. In house after house, I've found that a deck sitting on a roof provides a lot of value for the owner. It makes sense to me, in light of my own experience, that the "widow's walk" has been such a popular element on homes in this area through the years.
When I started to use rooftop decks more than 12 years ago, I looked around at some examples built by others. EPDM rubber membranes make an excellent low-slope roof covering, and it's not hard to build a deck sitting on sleepers that rest on the membrane itself; but I've never liked that method. For one thing, the sleepers tend to compress the foam-board underlayment used for those EPDM systems, creating a slight trough or depression in the roof surface. And they tend to dam up the water that should flow freely off the roof. Debris and grime quickly start to collect in the low spots around the sleepers and, after a few years, accumulate on the roof just below the walking surface.
To avoid those problems, I worked out a design that suspends the deck frame an inch or two above the rubber roof, supported by parapet half-walls that rise above the roof plane as a continuation of exterior or interior house walls (see Figure 1). That way, the deck structure never contacts the roof surface at all — instead, a continuous drainage space lets water (and dirt) flow freely off.
The author's design for rooftop decks protects the structure and living space of the room below with a continuous EPDM roof. To allow free drainage and protect the roofing, the deck frame is suspended from the parapet walls.
On the other hand, the deck still shades the watertight EPDM surface and protects it from damaging sunlight. That extends the service life of the rubber (which is good for 30 years or more, even when it isn't shaded). I've built at least 25 roof-and-deck combinations using this design over the last dozen or so years, all exposed to harsh seaside conditions that can eat the enamel off a doorknob in about three months — and I haven't had a single callback.
For an example of how it's done, I'll use the deck we installed over a bumpout room on the same Rhode Island custom home that I described in "Shearwalls for Coastal Homes" (2/04). On that house, a projecting octagon room facing the ocean served the design in several ways: It efficiently opened up interior space; it provided nice views, light, and air; and it also helped to stiffen the house frame against coastal windstorm forces. With parapet walls, a rubber roof, and a deck assembly placed above it, the room serves yet another function: It supports a protected but open upper-story deck, graced with a nice view and plenty of sunshine.
Roof Framing
The room's roof framing, which is also the ceiling framing for the room below, really resembles a floor frame more than the usual roof frame (Figure 2).
Figure 2.The ceiling joists of the room below the deck are ripped to provide a slight pitch away from the house, then sheathed with 1/2-inch plywood (left). Strapping helps ensure a flat drywall ceiling (right).
The house walls do the work of supporting the above-roof walking deck, and the deck framing itself is sized to carry the design dead and live loads for our area, including snow loads. So although it is capable of considerably more, the roof-ceiling frame for the room isn't actually subjected to loading much beyond its own weight. Depending on the dimensions of the space, I'll use 2x8s or 2x10s for joists, with 1x4 strapping on the underside and 1/2-inch plywood sheathing on the upper side. We rip the tops of the joists to provide a pitch of about an inch, creating a gentle slope away from the house.
