Getting a new flat roof right from day one
On new construction, the most important flat roof decisions happen before the membrane goes on: how the roof slopes to drains, where the drains and scuppers are, how insulation is arranged, and how the membrane turns up and flashes at walls and doorways. Get those right and a flat roof performs well for decades. Get them wrong and no membrane will keep up with ponding water.
Projects we install flat roofs on
- Rear additions and kitchen bump-outs
- Porch, portico and sunroom roofs
- Detached garages and accessory dwelling units
- Contemporary homes with flat or very low-slope roofs, increasingly common among new homes in Bethesda and Chevy Chase
- Roof decks over occupied space, with a membrane and walking surface designed together
- Small commercial buildings. See commercial roofing.
Design details we coordinate
- Slope: built into the framing or created with tapered insulation, so water does not pond
- Drainage: internal drains, edge scuppers or gutters sized for the roof area
- Wall and door transitions: membrane turned up behind siding and under door thresholds to the proper height
- Penetrations: HVAC curbs, vents and skylights flashed as the roof is installed
- Tie-ins: where a new flat roof meets an existing pitched roof, a detail that needs careful layering
- Structural deck: wood or steel decking on joists.
- Tapered insulation: boards cut to a slope, so a "flat" roof actually drains.
- Membrane: TPO, EPDM or modified bitumen; the continuous waterproof layer.
- Wall flashing: membrane turned up the wall and secured with a termination bar. Most flat-roof leaks start here.
- Coping cap: metal cap that sheds water off the top of the parapet.
- Drain at the low point, with a strainer to keep leaves out. Keep it clear.
- Positive drainage: water moves to the drain instead of ponding and aging the membrane.
Choosing the membrane
For most new residential flat roofs we install TPO or EPDM. Modified bitumen is a good choice where the roof will see foot traffic or equipment. For a comparison of the systems, see flat roof replacement. The same membranes apply to new roofs.
New low-slope roofs on additions, terraces and infill homes
New low-slope roofing in this area comes from two sources. The first is the rear addition or second-story pop-top on an older Bethesda or Chevy Chase house, where a flat roof is the only way to add space under an existing eave line or to keep the addition below a height limit. The second is the contemporary infill house now being built on redeveloped lots, with parapet walls, flat or very low-slope planes and sometimes an occupied roof terrace. Both benefit enormously from decisions made before the framing goes up, because slope built into the structure drains better and costs less than slope added afterward in tapered insulation.
Designing it early also fixes the two details that cause most new flat-roof problems. Parapets need through-wall flashing and a properly detailed coping, not sealant at the top; and drains need an overflow path, so that a single blocked outlet during one of our summer downpours does not turn into several hundred pounds of standing water over a finished ceiling. Roof terraces add a third: the wearing surface, usually pedestal pavers over the membrane, has to sit low enough to be usable while still leaving the flashing high enough above the finished walking level, and railing posts belong on the structure rather than through the field of the membrane.
Penetrations get planned at the same time rather than cut in later. Skylights are set on curbs tall enough for a low-slope roof as part of skylight installation, and mechanical curbs, vent stacks and solar conduit are grouped so the membrane has as few interruptions as possible. Where the new low-slope roof meets the existing shingle roof and wall above it, that transition is built with step and kick-out flashing integrated into the courses, which is why we coordinate it with shingle roof installation on the same project and with the overall roof installation schedule on a new build. Scupper and drain discharge is tied into the house's gutters and downspouts through gutter installation so the water actually leaves the property.
Flat Roof Installation across Bethesda, North Bethesda and Chevy Chase
We provide flat roof installation throughout southern Montgomery County, including Bethesda, MD (20814, 20816, 20817) , North Bethesda, MD (20852) , and Chevy Chase, MD (20815) . Each area page covers the housing types, permit considerations and storm history particular to that community.
Frequently asked questions
How much slope does a flat roof need?
Flat roofs are not truly flat. They need enough slope to move water to drains or edges. Your membrane manufacturer and the building code set minimum slopes, and we design to meet or exceed them.
Can I put a deck on top of a flat roof?
Yes, if it is designed for it. The structure, membrane, protection layer and deck surface all need to work together, and structural work like a roof deck typically requires a building permit. We confirm permit requirements with Montgomery County DPS or your municipality before work starts.