HomeFlat Roof and Commercial Roofing in Sioux Falls
Flat roof repair in Sioux Falls
A flat roof still needs a fall of at least a quarter inch per foot so water drains, and it takes a membrane, never shingles. That goes for a porch, a garage, an addition or a small commercial building.
What kinds of flat roofs are there?
Six systems cover nearly all of them: built-up roofing, modified bitumen, EPDM rubber, TPO, PVC, and sprayed foam or a liquid-applied roof. The residential code sets rules for each.
In a cold climate, watch the seams. EPDM seams are glued or taped, and contractors report that freeze-thaw can open old lap seams. TPO and PVC seams are heat-welded.
Sioux Falls averages about 97 freeze-thaw days a year. On an old EPDM roof, have the seams checked.
How much slope does a flat roof need?
At least 1/4 inch of fall per foot, or 2 percent, for every membrane under the model residential code (section R905). Sioux Falls now lists the 2024 edition with local changes, but the posted amendment is still a draft, so confirm the rule for your roof with Building Services at 605-367-8670. Coal-tar built-up roofs may go down to 1/8 inch per foot.
| Roof system | Minimum slope |
|---|---|
| Built-up roofing | 1/4 inch per foot (2%); coal-tar 1/8 inch (1%) |
| Modified bitumen | 1/4 inch per foot (2%) |
| EPDM (thermoset single-ply) | 1/4 inch per foot (2%) |
| TPO and PVC (thermoplastic single-ply) | 1/4 inch per foot (2%) |
| Sprayed polyurethane foam | 1/4 inch per foot (2%) |
| Liquid-applied roofing | 1/4 inch per foot (2%) |
Shingles need far more. Asphalt shingles go only on roofs with at least 2 inches of rise per foot, with a double layer of underlayment up to 4 inches. A porch roof flatter than that needs a membrane.
We took these figures from published copies of the code and could not check them against the official text. The city also has a draft ordinance adopting the 2024 code for permits issued after 15 October 2026. It renumbers the sections and keeps the same slopes. Whether it passed is unconfirmed.
Is standing water on a flat roof a problem?
If it is still there two days after the rain, yes. The national roofing contractors’ association defines ponding as water that stays on a roof more than 48 hours after the last rain, in weather that lets it dry.
Cold adds strain of its own. A Canadian national research digest found that membranes held to the deck take thermal strain in severe cold. The strain stayed below breaking point, by a thin margin, and was worst at the joints in the insulation. Sioux Falls averages 24.9 days a year with a low at or below zero.
Cold also limits repairs. One membrane maker starts its cold-weather procedures at 40 F, and its self-adhering EPDM goes on only at 20 F and rising, TPO at 25 F and rising. With 162 nights a year at or below freezing, ask the contractor how they handle a winter leak.
How do flat roofs hold up to hail?
Ask for the membrane’s FM 4470 hail class. The standard has three:
| Class | Rated for | Test |
|---|---|---|
| Moderate Hail (MH) | Hail under 1.75 inches | 2-inch steel ball, 1.19 lb, dropped 81 inches |
| Severe Hail (SH) | 1.75 to 2 inches | Same ball dropped 141.5 inches |
| Very Severe Hail (VSH) | 2 inches and up | 2-inch ice ball fired at 53 to 58 ft-lb on new, sun-weathered and heat-aged samples |
Very Severe Hail is the newest class, added between 2016 and 2018 depending on the source. Shingles use other tests (FM 4473 and UL 2218).
Hail here reaches those sizes. NOAA logged 36 reports of hail 1.75 inches or larger in Minnehaha, Lincoln, Turner and McCook counties from 2015 to June 2026. On 5 August 2021, 3.5-inch stones fell north of Sioux Falls.
Wind matters too. On 28 August 2021 it tore most of the rubber membrane off part of the Lennox High School roof. The record of Sioux Falls hail and wind storms since 2010 has the rest. If a storm just hit, start with what to check after hail.
Should I coat, restore or replace a flat roof?
Check underneath first. Restoration guidance calls for core cuts down to the deck, about one per 40 to 50 squares, plus a moisture survey such as infrared, checked against the cores.
Isolated wet spots can be cut out and replaced before a coating or a new layer goes on. Widespread wet insulation points to tear-off. One industry training course puts the line at 20 to 25 percent wet.
Where water ponds, pick the coating with care. Coating sellers agree silicone holds up better under standing water than acrylic, which can soften, swell or blister. Only vendors make that claim.
A new roof over the old one is not allowed where the existing roof is water-soaked or too deteriorated to work as a base, or already has two or more layers (residential code R908.3.1.1). A home inspectors’ chart gives an aluminum roof coating 3 to 7 years. We found no confirmed warranty terms for other coatings.
Whichever way you go, get a roof inspection with a written report first.
How long does a flat roof last?
EPDM has the best evidence. A 2025 survey of 569 roofing professionals by the EPDM industry association put its expected life at about 25 to more than 40 years, depending on thickness and how it is attached. A 2010 study by the same group found every 30-year-old roof it examined still performing. Both come from the industry.
The other numbers are thin. A home inspectors’ chart gives built-up roofs 30 years, modified bitumen 20 and EPDM 15 to 25. TPO is sold with guarantees of up to 30 years. That is a warranty term. A PVC maker’s study of 44 roofs aged 9 to 34 years found most samples still beat the standard for new membrane.
We found no published life in years for TPO, PVC, modified bitumen or built-up roofs from the national contractors’ association or the big manufacturers. For shingles and metal, see how long a roof lasts in South Dakota.
Does a commercial roofer need a license in Sioux Falls?
No. The City of Sioux Falls says it does not require commercial building contractors to be licensed at this time, and it has no separate commercial roofing license. Apartment buildings count as commercial.
Each commercial project still goes through plan review and permits, the city says. The fee schedule prices commercial permits, commercial roofing included, on the value of the work, starting at $40 for $1 to $2,000. Whether a commercial reroof needs a permit is unconfirmed. Call the city’s plans examiners at 605-367-8248 before work starts.
Homes are different. Shingling a house, duplex or townhome inside city limits takes a city Residential Roofing and Repair Contractor license, with an exam, a $20,000 compliance bond and $300,000 in liability insurance. That license covers shingling with no structural changes, so ask the city which license membrane work on a house needs.
On a home, check the roofer’s city license. On a commercial building there is none to check. Get the membrane maker, its hail class and the warranty in writing.
Questions about flat roof repair in Sioux Falls
How much does flat roof repair cost in Sioux Falls?
We found no published Sioux Falls price for flat roof repair or replacement. A contractor needs to see the roof, and on a bigger roof check how wet the insulation is, before quoting.
Can you put shingles on a flat roof?
No. Asphalt shingles need at least 2 inches of rise per foot, with a double layer of underlayment below 4 inches. Flatter roofs need a membrane.
How long does a rubber roof last?
A 2025 EPDM industry survey put expected life at about 25 to more than 40 years, depending on thickness and attachment. A home inspectors’ chart gives it 15 to 25.
What flat roof holds up best to hail?
Look for the FM 4470 hail class. Very Severe Hail is rated for stones 2 inches and up, Severe Hail for 1.75 to 2 inches, so ask for the rating in writing.
Do I need a permit for a commercial roof in Sioux Falls?
The city says every commercial project goes through plan review and permits, but we could not confirm when a reroof needs one. Ask the city’s plans examiners at 605-367-8248.
Get a free flat roof quote
Tell us about the job, for a home or a business, and a local roofing contractor will call, text or email to set up a visit. The quote is free.