Most Twin Cities homes are pitched, shingled roofs — but a lot of them have a flat or low-slope section somewhere. A porch roof, a garage, an addition, a dormer, a mid-century or modern flat-roof design. And here's the thing I tell homeowners all the time: that flat section is a completely different roof than your shingles, and it can't be roofed the same way. I've put down flat membranes on plenty of houses around the metro, often right alongside the shingle work on the same home. Here's what you should know.
The short answer
Shingles need slope to shed water — they don't belong on a flat or low-slope roof, period. A flat section on your house needs a membrane system (TPO, EPDM, or modified bitumen) with sealed seams and proper flashing where it meets the rest of the roof and the walls. Done right, a residential flat roof lasts 20–30 years and carries our lifetime workmanship warranty, same as any residential roof we install. Done with shingles on too shallow a pitch, it leaks — and that's the call I get most.
Why your flat section can't be shingled
Shingles work by overlapping and shedding water downhill. Take away the slope and water sits on them, works backward under the laps, and gets in. There's a minimum pitch below which shingles simply don't belong, and a lot of porch, addition, and garage roofs fall below it. If a contractor wants to shingle your low-slope section to keep it cheap and matching, that's a leak waiting to happen. The right answer is a membrane — even though it looks different from your shingles.
What we put on residential flat roofs
The same systems we use commercially (here's how they compare), sized to a house:
- TPO — a white, energy-efficient welded membrane; a clean choice for most residential flat sections.
- EPDM — proven rubber, flexible in Minnesota cold, great on porches and additions.
- Modified bitumen — tough and layered, good on small or cut-up flat areas.
On homes with combination roofs — and we see a lot of those in places like Edina, Minnetonka, and around the lakes, where additions and remodels have left metal, flat, and shingle all on one house — the flat membrane has to tie cleanly into the other materials. That transition flashing is exactly where a lot of houses leak, and it's where doing all the trades in-house pays off: one crew, one warranty, no finger-pointing between a shingler and a flat-roof sub.
Common problems on residential flat roofs
- Shingles where there should be a membrane — the number-one cause of low-slope leaks on houses.
- Bad transition flashing — where the flat section meets a wall or the pitched roof above it.
- Ponding water — a flat section that doesn't drain right holds water and breaks down early.
- Neglect — flat roofs are out of sight, so they're out of mind until they leak. A quick look twice a year catches problems while they're cheap.
What it costs
A residential flat or low-slope section is usually a smaller job than a whole commercial roof, but it's priced the same way — by the system, the tear-off, and the detail work. Most home flat-roof sections land in the $8,000–$15,000 range depending on size and how it ties into the rest of the roof; a small porch can be less, a large modern flat-roof home more. The detail work at the transitions and flashings is where the value is — and where the cheap jobs cut.
A note on storm damage
Flat roofs take hail and wind too, and the damage can be harder to spot than on shingles — a bruised or punctured membrane, a lifted seam, dinged metal flashing. If a storm rolled through and you've got a flat section, it's worth having it looked at, especially before you assume your claim only covers the shingled part of the roof. (We've got a full guide to hail damage and insurance claims in Minnesota if you're dealing with a recent storm.)
FAQ
Can you put shingles on a flat or low-slope roof?
No — not below a minimum pitch. Shingles shed water by slope, and on a flat or low-slope section water sits and works backward under them, causing leaks. Low-slope sections need a membrane system (TPO, EPDM, or modified bitumen) with sealed seams, not shingles. A contractor who shingles your flat section to keep it cheap is setting up a future leak.
How long does a flat roof on a house last?
A properly installed residential flat or low-slope membrane typically lasts 20–30 years in Minnesota, similar to commercial systems. Lifespan depends on installation quality — especially seams and transition flashings — and on drainage. Standing water and neglected flashings are what cut it short.
Why does my porch or addition roof keep leaking?
The most common reason is that a low-slope section was shingled when it should have a membrane, or the flashing where it meets the wall or main roof was done poorly. Both let water in no matter how many times you patch the surface. The fix is usually a proper membrane and reworked transition flashing.
How much does it cost to replace a flat roof section on a house?
Most residential flat or low-slope sections run $8,000–$15,000 depending on size, tear-off, and how the section ties into the rest of the roof. A small porch can be less; a large modern flat-roof home, more. The transitions and flashing detail are where the real labor — and the leak protection — live.
Do residential flat roofs come with a warranty?
Yes. We back residential flat and low-slope work with our lifetime workmanship warranty, the same as any residential roof we install, plus the membrane manufacturer's warranty. Always get the warranty terms in writing and confirm they cover the seams and flashings.
My house has flat, metal, and shingle all on one roof — can one company do it?
Yes, and you want one company that self-performs all of it. Combination roofs are common on remodeled and lake-area homes, and the leaks almost always show up at the transitions between materials. One crew handling every trade means one warranty and no finger-pointing between a shingler and a flat-roof subcontractor.
Got a flat or low-slope section on your home that's leaking or due? Call Modern Exterior Systems at 952-206-6339 for a free inspection — we do flat roofing and full roof replacement under one roof, one warranty, across the Twin Cities.
Modern Exterior Systems is a women-owned, family-operated roofing and exterior contractor based in Eden Prairie, MN, serving Minneapolis, St. Paul, and the Twin Cities metro. Owner Joe Dvorak brings 20+ years of hands-on construction experience, manufacturer certifications, NRCA membership, and a LIFETIME workmanship warranty on residential projects. BBB Accredited with an A+ rating.
