I've replaced a lot of commercial flat roofs around the metro — office buildings, warehouses, retail, mixed-use office-warehouse combos, up to four stories. TPO and EPDM mostly, some modified bitumen, both ballasted and fully adhered. So I know the part that actually keeps a building owner up at night isn't the membrane. It's "how long is my roof going to be torn open, and is the work going to leak."
The short answer
A commercial flat roof replacement in the Twin Cities usually means a full tear-off down to the deck, new insulation to code, and a new single-ply (TPO or EPDM) or modified-bitumen system, sequenced so your building stays dry and operating the whole time. Most jobs run from a few days to a couple of weeks depending on size, access, and rooftop equipment, and price in the $5–$12 per square foot range. The contractor's job is to do it without flooding your tenants or shutting you down.
What's different about a commercial flat roof
A house gets one roof. A commercial building gets a roof full of obstacles: HVAC units, exhaust fans, drains and scuppers, curbs, skylights, parapet walls, and sometimes solar or satellite gear. Every one of those is a penetration — a place water wants in — and every one has to be flashed right. On a warehouse or office-warehouse roof, the open field is the easy part. The detail work around all that equipment is where the job is won or lost, and it's where the cheap bids cut corners.
Height and access change the job too. Getting material and crew up onto a four-story roof safely — and getting the old roof down — is real planning, real equipment, and a real line item. It's not the same as a one-story strip mall you can reach with a ladder.
Systems we install on commercial roofs
- TPO — my default for most commercial fields. White, energy-efficient, heat-welded seams. Reflects heat off the building in summer. (See how TPO, EPDM, and mod-bit compare.)
- EPDM — proven rubber, excellent on ballasted systems and buildings that take abuse.
- Modified bitumen — tough and layered, good for smaller or cut-up roofs and high-traffic areas.
- Ballasted or fully adhered — we do both, and we match the attachment method to your building's structure and wind exposure.
Keeping you operating during the job
This is the part owners care about most. We phase the work so we're never opening more roof than we can close before weather, we protect the interior and your tenants, and we coordinate around your hours where it matters — a retail roof over an open store gets handled differently than a vacant warehouse. The goal is simple: no surprise leaks into occupied space, and no shutting you down.
Repair vs. replacement on a commercial roof
Not every commercial roof needs replacement. If the membrane has life left and you've got isolated failures — a few bad seams, a failed drain, storm damage in one area — a targeted repair plus a maintenance plan is often the smarter spend, and I'll tell you that honestly. Replacement is the call when the membrane is at end of life across the field, when there's trapped wet insulation under it, or when you're spending more on patches every year than the roof is worth. A core sample and a real inspection tell us which.
Pricing and warranty
Commercial flat roof replacement runs roughly $5–$12 per square foot installed, driven by size, tear-off, insulation, roof height/access, and the number of penetrations. On commercial work, we back the job with a 10-year workmanship warranty plus the manufacturer's membrane warranty — and we put the scope in writing, line by line, so you can see exactly what you're buying. Get any commercial roofing bid in writing with the warranty terms spelled out; a lump-sum number with a vague warranty is a red flag.
FAQ
How much does a commercial flat roof replacement cost in the Twin Cities?
Most run $5–$12 per square foot installed, so a mid-size building lands anywhere from the low five figures into six figures depending on square footage. Size, tear-off, insulation, roof height and access, and the number of rooftop penetrations drive the number. An on-roof inspection and measurement is the only way to price it accurately.
How long does a commercial flat roof replacement take?
Anywhere from a few days for a small single-story roof to a couple of weeks for a large or complex building. Roof access, rooftop equipment, weather, and whether the building stays occupied all affect the timeline. We phase the work so the building stays dry and operating throughout.
Can you replace our roof while we stay open?
Yes — that's standard on retail and office work. We phase the tear-off so we never open more than we can close, protect occupied space below, and coordinate around your operating hours where it matters. The whole point is no surprise leaks into your space and no shutdown.
What's the best flat roof system for a warehouse or office building?
For most Twin Cities commercial buildings, a TPO or EPDM single-ply — ballasted or fully adhered to suit the structure — is the workhorse. TPO adds an energy-efficient reflective surface; EPDM is proven rubber for high-abuse roofs. Modified bitumen fits smaller or cut-up roofs. We match the system to your building.
Do I need to replace the whole roof or can it be repaired?
It depends on whether the membrane has life left. Isolated seam failures, a bad drain, or localized storm damage are often repairs. Replacement makes sense when the membrane is failing across the field, there's wet insulation trapped underneath, or annual patch costs are climbing. We take a core sample and inspect before recommending either.
Do you work on multi-story commercial buildings?
Yes — we've done flat roof work on buildings up to four stories, including office, warehouse, retail, and mixed-use office-warehouse combinations. Height and access are planned into the job with the right hoisting and safety setup.
Need a commercial flat roof looked at? Call Modern Exterior Systems at 952-206-6339 for a free on-roof inspection and a line-by-line written proposal — flat roof replacement for office, warehouse, and retail 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 and NRCA membership. Commercial work is backed by a 10-year workmanship warranty plus manufacturer warranty. BBB Accredited with an A+ rating.
