Flat and low-slope roofing
Half the houses around here have a flat section somewhere — over the kitchen, over a porch, or the whole roof if it is a rowhome. It fails differently from a pitched roof and it gets fixed differently.
Flat roofs are not actually flat. They are built with a slight fall so water runs to a drain or a scupper, and most of their problems come from that fall being lost — the deck sags, water sits, and standing water finds every seam. Shingle technique does not transfer here: a low-slope roof is a membrane job, and it is the seams and the terminations that matter.
In this part of Delaware County that means the rear additions on twins and rowhomes, porch and bay roofs, and dormer tops. In Philadelphia it usually means the whole roof.
The systems used here
- EPDM rubber membrane — a single large sheet, few seams, long-established. The usual choice for a rear addition or a porch roof.
- Polyglass SBS modified bitumen — a torch- or self-adhered granulated system, used on rowhome roofs and where a tougher walkable surface is wanted.
- Roll roofing — the budget option, and honestly a short-term one. It is offered where the budget requires it, and you get told what it is.
- Protective coatings — where an existing membrane is sound but tired, a coating can buy real time for a fraction of a replacement.
What actually fails
- Seams and laps opening up as the membrane ages and moves.
- Terminations and flashing where the flat roof meets a wall or the pitched roof above it.
- Ponding water sitting in a low spot long after the rain has stopped.
- Drains and scuppers blocked, so water backs up above the flashing line.
- Blistering, where trapped moisture under the membrane expands in the sun.
- Old patch-on-patch repairs that have become the problem themselves.
Why the rear addition cannot just have shingles put on it: the residential code does not permit asphalt shingles on a slope shallower than 2:12, and between 2:12 and 4:12 it requires a doubled underlayment. That is not a preference or an upsell — it is the reason a low-slope roof needs a membrane and the reason a shallow porch roof legitimately costs more per square foot than the main roof above it.
The other thing worth knowing: the joint where a low-slope rear roof meets the main pitched roof is the most common leak point on a Delaware County twin, and the part most often done badly. The membrane has to be carried up under the shingle course properly, not sealed across with a bead of caulk.
Customers on this kind of work
I had a significant roof leak on my flat roof of my rental property in Havertown that caused some ceiling drywall damage. I called about 5-6 reputable companies in the area not knowing if I needed a repair or replacement.
Related work
Roof Repair
Most leaks are a flashing problem, not a whole-roof problem. The job is to find out which one you have.
More on thisCommercial Roofing
Small commercial and mixed-use buildings — the same low-slope trade, on a bigger deck.
More on thisGet a straight answer about your roof
James will come and look at it properly, tell you what he finds, and put the price in writing. Estimates are free and there is no sales pitch.
Roof leaking right now? Call (215) 837-9135 — the phone is faster than a form.