Flat roof replacement and repair in St. Louis
Many St. Louis City homes, including brick two-families, four-families, rowhouses and rear additions, have flat or low-slope roofs. They use a membrane, not shingles, and need a roofer who does residential flat roofs. One call connects you with one.
Why flat roofs are common in St. Louis
About a quarter of homes in the City of St. Louis are in buildings with two to four units, and 56% of City homes were built before 1940 (Source: U.S. Census ACS 2024). Many of those brick flats and rowhouses have flat or low-slope roofs hidden behind parapet walls. In the County, flat roofs show up more on porches, additions and mid-century homes.
Flat roof materials
| Material | What it is | Good to know |
|---|---|---|
| TPO | A white single-ply membrane, heat-welded at the seams | Reflects sun; a common choice for full replacements |
| Modified bitumen | Asphalt-based rolls, torch-applied or self-adhered, often in two plies | Tough and familiar to many St. Louis crews; often used over existing built-up roofs once they're torn off |
| EPDM | Black rubber sheet, glued or ballasted | Long-lived; seams are taped or glued |
| Built-up / tar and gravel | Layers of felt and hot asphalt | Common on older buildings; usually replaced with one of the above |
The right choice depends on the roof's slope, the drains, how the roof meets the parapet walls, and budget. Ask each roofer why they recommend their material.
What makes a flat roof job different
- Drainage. Water has to reach a drain, scupper or gutter. Low spots where water ponds shorten the life of any membrane. Tapered insulation can fix the slope.
- Parapet walls and flashing. On brick buildings, the membrane runs up the inside of the parapet and under a metal cap or counter-flashing. Old, cracked mortar can let water in behind new flashing.
- Tear-off and the deck. Old built-up roofs are heavy and can hide rot. Expect a per-sheet price for deck repairs.
- Insulation. A replacement is the cheapest time to add insulation above the deck.
What a flat roof costs
Missouri has no widely published flat-roof average comparable to the RSMeans shingle figures. Our estimator uses $6–$11 per square foot for a residential membrane replacement, which is our assumption and is labeled as one. Tear-off of multiple old layers, tapered insulation, parapet work and access on three-story buildings push costs up. Try the estimator
Permits
In the City, re-roofing with like material and 25% or less new sheathing usually doesn't need a permit. Switching materials (for example, from built-up to TPO) likely counts as "not replacement of like material," which needs a permit, so ask your roofer or the City before you sign (Source: City of St. Louis). In St. Louis County, roofs under 4:12 slope need a permit for re-roofing where the County enforces the code (Source: St. Louis County). Permits, City vs. County
Flat roof repair
Small blisters, open seams and flashing failures can often be repaired. A roof that ponds badly, leaks in several places or has a soft deck usually needs replacement. Roof repair
Sources
Last reviewed October 22, 2026.
- American Community Survey 2024 1-year: tables B25034, B25035, B25024 (via Census Reporter), U.S. Census Bureau. Accessed October 22, 2026.
- When a residential building permit is needed, City of St. Louis Building Division. Accessed October 22, 2026.
- Residential re-roofing checklist and guide for asphalt shingles, St. Louis County Department of Transportation and Public Works. Accessed October 22, 2026.