Flat roofs fail at the seams and the drains. That's where we start.
No roof is truly flat; a good one is pitched just enough to move water to a drain or a scupper. When it doesn't, water sits, freezes, thaws and finds the weakest seam. We fix the drainage along with the membrane.
Shingles need a pitch of at least about 2 in 12 to shed water. Below that, from porch roofs and rear additions on older Des Moines houses to the tops of brick commercial buildings downtown and along Ingersoll, you need a membrane.
| Membrane | Best for | Notes |
|---|---|---|
| TPO (white) | Commercial roofs, large additions | Heat-welded seams, reflects summer sun, the most common new flat roof today |
| EPDM (black rubber) | Porches, garages, small additions | Forgiving, long track record, seams taped or glued; dark color absorbs heat |
| Modified bitumen | Residential low slopes, heavy foot traffic | Layered asphalt sheets, tough surface, good for decks over living space |
| Coatings | Sound older roofs that need more years | Silicone or acrylic over a dry, sound membrane; not a fix for a wet roof |
What fails on Iowa flat roofs
- Ponding. Water that sits more than a couple of days after rain shortens a membrane's life and finds every seam. In winter it freezes.
- Seams and flashing. Where the membrane turns up a parapet, a wall or a curb is where leaks begin.
- Clogged drains and scuppers full of leaves and cottonwood fluff, which turn a small roof into a pond overnight.
- Wet insulation under the membrane, which stays wet and keeps feeding leaks until it's cut out and replaced.
On a repair, we find the source, cut out wet insulation, and patch with the same membrane. On a replacement, we add tapered insulation where water ponds, so the new roof drains the way the old one never did.
Flat roof prices
| Work | Typical range | What moves it |
|---|---|---|
| Seam or flashing repair | $350 – $1,000 | Membrane type, access |
| Porch or small addition, new EPDM or mod-bit | $1,500 – $4,500 | Size, decking |
| TPO replacement, per square foot | $8 – $14 | Insulation, tear-off, drains |
| EPDM replacement, per square foot | $7 – $12 | Size, details |
| Tapered insulation to fix ponding | $2 – $5 per sq ft added | Depth needed |
Ranges are typical for Des Moines-area homes in 2026 and are here to help you plan. Your real price comes after the free inspection, written down, before any work starts.
On the roof
Questions about flat & low-slope roofs
Why does my flat roof always pond?
The structure has sagged, the drain is set too high, or the roof was never sloped. Tapered insulation during a replacement is the permanent fix.
Can I walk on my flat roof?
Occasionally, carefully, in soft shoes. If you need regular access to a unit or a deck, ask about walkway pads or a tougher membrane.
White or black?
White TPO keeps buildings cooler in summer; black EPDM absorbs a little winter sun. For most homes the difference is small; for commercial buildings with big roofs, white usually wins.
Do coatings work?
On a dry, sound roof, they can add years. On a roof with wet insulation underneath, they trap the problem.
How long does a flat roof last?
A well-installed TPO or EPDM roof commonly lasts 20 to 30 years, longer when the drainage is right.
Do you fix porch roofs on older houses?
Often. Many older Des Moines porches have low slopes that were shingled anyway and leak at the house wall. A membrane or metal porch roof fixes that.
