Commercial roofing refers to the roofing systems used on non-residential buildings — offices, warehouses, retail centers, industrial facilities, schools, and similar structures. The term covers both the roof type and the specialized materials, design, and installation practices that differ meaningfully from a house roof.
Commercial vs. Residential Roofing
The most visible difference is slope. Commercial roofs are typically flat or low-slope, while residential roofs are steep-sloped. OSHA officially defines a “low-slope” roof as one with a slope of less than 4:12 (a rise of less than 4 inches for every 12 inches of horizontal run) — the category nearly all commercial roofs fall into.
That low slope isn’t a cost-cutting shortcut — it’s a functional choice. A low-slope design maximizes usable interior space, makes it far simpler to install and service rooftop HVAC units, solar arrays, and other equipment, and costs less to build across the large roof areas common on commercial buildings. See our guide to why commercial buildings use low-slope roofs for the engineering details.
The tradeoff is drainage. A steep residential roof sheds water by gravity almost automatically; a low-slope commercial roof has to be engineered with deliberate slope and drainage points to move water off the surface at all — which is why drainage design, not just membrane choice, is central to how commercial roofs are built and maintained.
What Commercial Roofs Are Made Of
Because commercial roofs are low-slope, they use fundamentally different materials than the shingles, wood shakes, or tile common on houses. The dominant commercial systems are:
- TPO — a heat-welded, reflective single-ply membrane, the most widely installed system on new commercial construction today.
- EPDM — a synthetic rubber single-ply membrane with the longest field-proven track record of the major systems.
- Modified bitumen — a multi-ply, asphalt-based system, often used to replace existing torch-down or built-up roofs.
- PVC — a heat-welded single-ply membrane valued for chemical and grease resistance.
- Metal (standing seam) — the longest-lasting option, at a higher upfront cost.
See our full systems comparison for how these differ on cost, lifespan, and best fit, or our materials guide for the membrane, insulation, and flashing components that make them up.
Owning a Commercial Roof: What’s Different
Beyond materials, commercial roofing involves a different ownership process than a residential roof:
- Scheduled inspections — typically twice a year, and often required to keep manufacturer warranties valid. See our inspection guide.
- Licensed, certified contractors — commercial installation requires specific system certification, permitting, and code compliance (fire rating, wind uplift, insulation R-value) that residential re-roofing typically doesn’t. See our guide to choosing a commercial roofing contractor.
- Higher project cost and complexity — driven by roof size, system choice, and code requirements. See our cost guide.
- Planned repair vs. replacement decisions — commercial roofs are actively managed assets, not a one-time purchase. See our repair-or-replace tool.
Frequently Asked Questions
Is commercial roofing always flat?
Not perfectly flat, but almost always low-slope. A small minority of commercial buildings use steep-slope residential-style materials, but the overwhelming majority use low-slope systems built for a slope under roughly 4:12.
Can a residential roofer install a commercial roof?
Not well. Commercial roofing uses different materials, installation methods (heat-welding, adhesive-seaming), and code requirements than shingle roofing. Look for a contractor with specific manufacturer certification in the system you’re installing, not just general roofing experience.
What size building counts as commercial roofing?
It’s defined by building use and roof type more than square footage — any non-residential building with a low-slope roof (offices, retail, warehouses, schools, industrial facilities) falls under commercial roofing, regardless of size.