How To Install A Deck On A Flat Roof

Flat roofs aren't architecturally logical, as rain and snow will shed much more than quickly off a sloped roof. Yet for celebrated Modernistic-style buildings like This Old House's Cambridge Boob tube project, flat roofs are at the cadre of the architecture, meant to reflect the broad horizontal lines of the natural landscape.

Of course, you don't need to alive in a modern business firm to bargain with a flat roof. Traditional homes often take sections of flat roof—over shed dormers, above porches and garages, and on balconies. And their horizontal lines abound in the West and in urban areas.

But apartment roofs have a pounding from harsh weather, which is why they rarely last as long as a good sloped roof. Fortunately, modern materials for roofing flat roofs have improved considerably over the past two decades; some behave warranties of up to xx years, approaching those for sloped roofing.

"If y'all build and flash ane correct—and proceed it make clean—a skillful flat roof won't leak," says TOH full general contractor Tom Silva, who had seven different apartment roofs to debate with on the Cambridge project house. He sealed them all with a mucilage-down EPDM rubber membrane organisation, a favorite of his because it's calorie-free, quick to install, and requires no special equipment.

It'south so piece of cake, in fact, that a handy homeowner could practise information technology himself. And then we watched Tom put down EPDM on a minor section at the project house to larn how a pro makes a flat roof smooth, potent, and watertight.

Step ane

The Importance of Building it Correct

Sheathing goes downward quickly on a roof that isn't sloped and thus provides some basis. Merely the horizontal lines of this viii ½-by-xiii-foot flat roof section at the Cambridge Boob tube project house, make it vulnerable to heavy snow and pooling rainwater, which is why information technology must be built to last.

Step 2

Frame the Roof

"The most of import thing to know about a flat roof," says Tom, "is that information technology'southward not flat." To preclude water from pooling and eventually invading the home, flat roofs are always built on a slight incline—at least 1⁄8 inch per foot. Many slope in several directions, like squashed hip roofs, toward scupper holes that connect to downspouts.

Step iii

Sheathe With Plywood

On pinnacle of the framing goes five⁄8-inch plywood sheathing with a ane⁄8-inch gap at all the joints to allow for expansion and contraction.

Footstep 4

Screw Down Underlayment

The canvas-rubber roofing textile that Tom is using requires a substrate chosen iso board—½-inch-thick rigid foam (fabricated of polyisocyanurate) with a special fiberglass bankroll. The iso board (a flat version of the aforementioned material he orders custom-fitted for larger roofs) cuts easily with a utility pocketknife and anchors to the plywood capsule with screws and large galvanized steel washers. Information technology provides a soft, protective base for the rubber. Tom makes sure to stagger the joints and to fit the pieces tightly against each other, equally iso board doesn't expand and contract like plywood.

Step five

Create Askew Corners

On 2 sides, the roof abuts a parapet (a short wall mutual effectually flat roofs), besides as a wall for the third floor; here the rubber roof volition need to stitch the walls and mucilage to the sheathing. To keep h2o from pooling at these inside corners, Tom rips 2x4s lengthwise on a 45-degree bevel with a table saw. Then he screws them into the joint between the roof and the wall to create a gradual transition.

Pace 6

Dry-Fit The Roofing

Before putting down the rubber, Tom does a quick sweep-downward to remove whatever debris that could puncture the new roof. EPDM (which stands for ethylene propylene diene monomer) comes in 10-foot-broad rolls and cuts easily with shears or a utility knife. Tom cuts a piece large enough to cover the roof plus an actress 9 inches all around. He takes the piece and spreads it into place and then folds it back in half. (This roof is small plenty to require only a unmarried sail. On larger roofs, Tom overlaps sections about half dozen inches, but doesn't mucilage the seams until the very end.) To negotiate a vent stack, Tom would cutting a pigsty in the rubber slightly larger than the pipe, then slide the safety downwards over information technology.

Step 7

Glue Downwards the Rubber

Using a ¼-inch-nap paint roller on an extension pole, Tom spreads the glue over the exposed section of iso lath and the corresponding folded-over condom. Like ordinary contact cement, the gum goes on both surfaces and bonds instantly the moment the ii meet. So later letting information technology dry to the affect, he gets down on his knees and advisedly spreads the rubber over the iso board, pushing as much from the within of the fold as he can to prevent wrinkles. He doesn't selection upward the rubber or it will stretch from its own weight, and so spring dorsum, causing it to lay down unevenly. "You only get one shot," says Tom. Working in sections, he finishes the rest of the roof, smoothing out air bubbles with the now-dry roller before gluing the edges up the wall and parapet and 6 inches down over the front of the roof.

Had in that location been a seam to contend with, Tom would kickoff clean it with a special solvent, then apply a black rubber-to-rubber adhesive. Considering seams are so vulnerable, he would also glue a 12-inch-broad strip of uncured safe (which, unlike EPDM, has no "memory," pregnant it can be stretched without springing back and wrinkling) onto the seam itself. At vent stacks, he would stretch a special rubber collar over the pipe and glue it to the EPDM, and then seal it with glued strips of uncured condom and a bead of tri-polymer caulk.

Pace 8

End the Edges

At within vertical corners, Tom cuts and overlaps the EPDM, then uses condom adhesive to glue information technology downwards tightly. He also seals this seam with uncured rubber. To keep the vertical sections from peeling off the walls, Tom screws on metallic brackets called termination stops, then cuts off the excess above the brackets. He runs a dewdrop of tri-polymer caulk along the peak edge of the brackets to seal them. Later he will nail downwards a custom lead-coated copper flashing over the front edges of the roof, then gum down a 12-inch strip of uncured safe over the flashing's top blast edge. The off-the-rack alternative to custom flashing is a galvanized baste edge specially fabricated for apartment roofs. Chosen a gravel end, it works on whatever kind of flat roof and comes in many colors. In one case the flashing is in place, the roof is ready to face the elements.

Source: https://www.thisoldhouse.com/roofing/21017452/building-a-flat-roof-right

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