Plenty of New Jersey homes have at least one flat or low-slope section: a back porch roof, a kitchen addition, a dormer, a garage, or the whole roof on a Hoboken or Jersey City rowhouse. Shingles cannot be used on those areas because water does not run off fast enough. Instead you have three common choices: TPO, EPDM and modified bitumen.
Here is how they compare in plain terms, and which one we usually recommend for homes in New Jersey.
Quick comparison
| TPO | EPDM | Modified bitumen | |
|---|---|---|---|
| What it is | White single-ply membrane, seams heat-welded | Black synthetic rubber sheet, seams taped or glued | Asphalt-based rolls, torched or self-adhered in layers |
| Color | White (reflects heat) | Black (absorbs heat) | Usually gray or granulated |
| Seams | Welded, very strong | Glued or taped, the weak point | Overlapped layers |
| Best for | Most homes and additions, sunny roofs | Simple, wide-open roofs with few penetrations | Small areas, heavy foot traffic |
Installed flat roofing in New Jersey typically runs about $5 to $12 per square foot depending on the system, the insulation underneath and how much old roofing comes off. See our roof replacement cost guide for how that compares to shingles.
TPO: our usual recommendation
TPO is a white membrane that comes in wide sheets. The seams are welded together with hot air, so they become one continuous piece. That matters, because seams are where flat roofs leak. The white surface reflects summer sun, which keeps a room under a flat roof noticeably cooler.
The downside: TPO needs to be installed by a crew with the right welding equipment and experience. A bad weld leaks just like a bad glue seam.
EPDM: proven rubber
EPDM has been around for decades. It is tough, flexible in the cold and handles our freeze-thaw winters well. The black surface absorbs heat, which is less ideal over a living space in July. The seams are glued or taped rather than welded, and seam failure is the most common EPDM repair we see.
Modified bitumen: the old standby
Modified bitumen is a modern version of the old tar-and-gravel roof. It holds up well to foot traffic, which makes it a reasonable choice for a roof deck you walk on. It is heavier and the installation is more involved.
The part that matters more than the membrane
No flat roof works if water sits on it. Most flat roof leaks we fix trace back to:
- Ponding water from sagging decking or no slope to the drain. Tapered insulation fixes this.
- Bad edges and walls where the flat roof meets the house or a shingled roof.
- Clogged drains and scuppers, especially under trees.
Ask any contractor how they plan to handle drainage before you ask what membrane they use.
Which one should you pick?
For most New Jersey homes, porch roofs and additions, we recommend TPO for the welded seams and cooler surface. EPDM is still a solid choice for a simple roof with few penetrations. Modified bitumen makes sense for small areas and spots with a lot of foot traffic.
Not sure if your flat roof can be repaired? See flat vs. pitched roofs for how the two age differently, or have us take a look.
Frequently asked questions
How long does a flat roof last?
A properly installed TPO or EPDM roof with good drainage can last for decades. Ponding water, poor seams and foot traffic shorten that a lot.
Can you put a new flat roof over the old one?
Sometimes, if there is only one existing layer and the decking is sound. In most cases we recommend removing it so we can check the wood and fix the slope.
Can I walk on a flat roof?
Occasional careful foot traffic is fine. If you plan to use it as a deck, tell your contractor so they can choose the right system and add walkway protection.
Get your flat roof checked
Herts handles flat roof repair and replacement on homes and small buildings across New Jersey. Call 908-206-4240 or request a free estimate.