Roofing materials
EPDM rubber roofs for Philadelphia flat roofs
EPDM is the black rubber sheet you see on a lot of re-roofed Philly rowhomes. It's been used on flat roofs for decades, it handles our freeze-thaw winters well, and it's easy to patch. Here's how it holds up, where it's weak, and when it's the right call.
The material
What EPDM is, and how it goes on a rowhome
EPDM (ethylene propylene diene monomer) is a synthetic rubber made in wide, flexible sheets. Because the sheets are large, a typical 14- to 16-foot-wide rowhome roof can often be covered with one piece or just a few, which means very few seams.
It comes in different thicknesses, commonly 45, 60 and 90 mil. Thicker sheets resist punctures better and are worth asking about if people walk on the roof. It's mostly black, though white EPDM is also made.
On Philadelphia rowhomes it's usually fully adhered: glued down over insulation board or a cover board after the old roof is torn off. Edges are finished with metal drip edge or termination bars, and walls, curbs and pipes get pre-formed flashing pieces.
Properly installed and maintained, an EPDM roof typically lasts 20 to 30 years.
Signs an EPDM roof needs work
If you already have a rubber roof, watch for:
- Seams lifting or opening at the edges of a lap
- Rubber pulled tight and "tenting" away from the base of a wall
- Punctures or tears from foot traffic or dropped tools
- Old patches curling up at the corners
- Flashing pulling away from a chimney, hatch or vent
- A chalky, worn surface on a roof that's 15+ years old
Pros & cons
Where EPDM shines, and where it falls short
Strengths
- Few seams. Big sheets mean fewer places for water to get in.
- Cold-weather flexibility. It stays pliable through freeze-thaw cycles instead of cracking.
- Easy to repair. A puncture can be cleaned, primed and patched years later.
- Long track record. Roofers have decades of experience installing and fixing it.
- No open flame. It's glued and taped, not torched, which matters on attached houses.
Weak spots
- Black EPDM absorbs summer heat right above the top floor
- Seams are the weak point if they weren't primed and taped carefully
- Softer surface can be punctured by debris, tools or deck furniture
- Older installs can shrink slightly and pull at walls and edges
- Coating it later needs a primer made for rubber
The detail that matters
Seams and flashing: where EPDM roofs succeed or fail
The rubber itself rarely wears out early. Problems almost always start where two pieces meet or where the roof turns up a wall. Modern installs join sheets with a primer and factory-made seam tape. Older roofs often used liquid adhesive alone, and those seams are the first thing to check on a rubber roof that's 15 or more years old.
On a rowhome, the walls matter just as much. The rubber runs up each parapet and party wall, and the top edge has to be held tight and covered so water can't run behind it. At the property line, the new rubber also has to tie into whatever your neighbor has, which may be tar, torch-down or another rubber roof.
Ask before you hire: how will the seams be done, how will the rubber be finished at the top of each wall, and how will it meet the neighbors' roofs? Clear answers to those three questions say a lot about the installer.
The work
What installing an EPDM roof involves
Tear off & repair
Old layers come off down to the boards, and any rotted boards are replaced.
Insulation & cover board
Board goes down to insulate and give the rubber a smooth base, sometimes tapered to improve drainage.
Glue down the sheet
The rubber is unrolled, left to relax, then bonded with adhesive. Seams are primed and taped.
Flash & finish
Walls, curbs, pipes and the hatch get flashing, and the edges get drip edge or termination bars.
Planning your job
What affects the price
For an EPDM roof, these make the biggest difference:
- What has to come off first. Old layers, and any rotted boards found under them.
- Sheet thickness and color. Thicker rubber and white EPDM differ from standard black.
- Insulation. How much is added, and whether it's tapered to fix ponding.
- Walls and openings. Parapets, party walls, chimneys, hatches, skylights and vents all need flashing.
- Roof shape and size. Including a back-building roof done at the same time.
- Access. Getting rolls of rubber up three stories without a rear alley.
See what your roof likely needs with the Roof Problem Checker.
Related pages
- Flat roof materials compared: EPDM next to TPO and modified bitumen
- Flat roof replacement: the full replacement process
- Silver coat roof replacement: moving from tar to a modern membrane
- Flat roof coating: extending an aging rubber roof
- TPO roofing: the white, heat-welded alternative
- Modified bitumen roofs: torch-down and self-adhered
- South Philly flat roof repair: rowhome roofs and party-wall seams
EPDM rubber roof questions
Will a black rubber roof make my top floor hotter?
A black roof does absorb more summer heat than a white one. Good insulation under the rubber reduces the effect a lot. If the top floor is already uncomfortable, ask about white EPDM, a TPO membrane or a reflective coating.
Can a rubber roof be patched, or does it need replacing?
Most punctures, tears and small seam failures can be patched. The area is cleaned, primed and covered with a rubber patch. Replacement makes sense when the seams are failing across the roof, the rubber has shrunk away from the walls, or water has soaked the insulation underneath.
Can I put a deck or walk on an EPDM roof?
You can, with care. Walkway pads where people walk regularly, and protection pads under deck sleepers, keep the rubber from being worn through. A thicker sheet is worth considering if the roof will see regular traffic.
Is EPDM better than TPO for a rowhome?
Neither is better everywhere. EPDM has fewer seams on a narrow roof and is easy to repair. TPO is white, so it reflects heat, and its seams are welded. The right choice depends on your roof, how hot your top floor gets, and the installer's experience with each.
Have a different question about rubber roofs? Call and ask a local roofer.
(215) 702-6130