Signs your flat roof needs replacement
- Leaks at several seams or the same area leaking again after repairs
- Widespread blisters, cracks or alligatoring across the surface
- Membrane shrinking and pulling away from walls, curbs and edges
- Soft spots or wet insulation found in test cores
- Ponding that has worsened as the deck or insulation has compressed
If the damage is confined to one area, flat roof repair may be the better value. We will tell you which.
Choosing a replacement membrane
| Membrane | Strengths | Good fit for |
|---|---|---|
| TPO | Heat-welded seams; light color reflects sun and keeps the roof cooler | Additions, mid-century flat roofs, commercial roofs |
| EPDM | Flexible, proven, simple to repair | Residential flat roofs, porches, roofs with many penetrations |
| Modified bitumen | Multi-ply, tough surface that tolerates foot traffic | Roofs with rooftop equipment or regular access |
We recommend a system based on how the roof is used, drainage, rooftop equipment, budget and appearance from upper windows. We do not push one product for every roof.
What a flat roof replacement includes
- Tear-off of the existing membrane and wet or damaged insulation
- Deck inspection and repair
- New insulation, with tapered insulation to improve slope toward drains where possible
- New membrane installed to the manufacturer's specifications
- New flashing at walls, parapets, curbs and penetrations, plus new edge metal
- Drains, scuppers and gutters checked and tied into the new roof
- 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.
Flat roofs on Bethesda and Chevy Chase homes
Many flat roofs here sit next to a pitched shingle roof, on a rear addition, sunroom or porch. The transition between the two is a frequent leak point, so we detail it carefully and, when the main roof is also aging, quote both together. See roof replacement. In the Chevy Chase Village Historic District, roofing material changes visible from the street go through the Historic Preservation Commission's Historic Area Work Permit process. Its guidelines apply "moderate scrutiny" to roofing materials visible from the public right-of-way.
Drainage and insulation decisions that outlast the membrane
On a flat roof replacement the membrane you choose matters less than where the water goes. A great many older low-slope roofs in this area were framed essentially dead level over a wood deck, and decades later the framing has taken a set and holds water in the middle of every bay. Laying a new membrane over that geometry buys you a new warranty on the same problem, because standing water plus our freeze-thaw winters is what opens seams in the first place. Replacement is the one opportunity to fix the slope itself with tapered insulation, to build crickets that move water toward the outlets, and to re-pitch scuppers and reset drain bowls at the true low points.
It is also the only practical moment to correct the details around the edge. Raising the assembly changes every height on the perimeter, so the roof-to-wall counterflashing gets rebuilt into the wall rather than surface-sealed, door and threshold heights onto a roof terrace get resolved, and skylight curbs get raised to a proper height above the finished membrane instead of being reflashed at the old height, which is the usual reason a skylight on a flat roof leaks in wind-driven rain. Those heights, set once during replacement, are what determine whether the roof is quiet for the next twenty years. If you have units that are already failing, doing skylight replacement in the same project costs far less than reopening the membrane later.
Membrane selection then comes down to the room underneath. A reflective white TPO or PVC surface noticeably reduces summer heat gain in a bedroom or family room directly below a flat roof, which is a real comfort difference on a west-facing rear addition in August; EPDM is more forgiving and simpler to repair cleanly years later, which is why we still specify it on small porch and bay-window roofs. Either way the discharge has to be carried properly once it leaves the roof, so interior drains, downspouts and scupper outlets get sized and tied into the system we install under gutter installation. If the roof has life left and the problem is localized, we will say so and do flat roof repair instead; for new additions and new construction the work is designed from scratch under flat roof installation.
Flat Roof Replacement across Bethesda, North Bethesda and Chevy Chase
We provide flat roof replacement 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
Can a new flat roof go over the old one?
Sometimes a recover is allowed, but only when the existing roof and insulation are dry and the deck is sound. In most residential cases we recommend a full tear-off so we can find and fix wet insulation and deck damage.
Is a white roof worth it?
A light-colored membrane such as white TPO reflects more sunlight than black EPDM, which can reduce heat gain in rooms directly below. Whether it is worth it depends on the room below, insulation levels and how visible the roof is.
How long does a flat roof replacement take?
Small residential flat roofs are often completed in a day or two. Larger roofs, tapered insulation, or many curbs and penetrations take longer. Your estimate includes a planned schedule.