What does a commercial flat-roof replacement cost and how long does it take?

Commercial low-slope roofs (industrial, office, restaurants, multifamily) follow different economics than residential shingle work. The biggest cost variables are not material choice — they are tear-off vs. recover, insulation requirements, and how much HVAC equipment lives on the roof.

Per-square-foot cost ranges (installed, in the Bay Area, 2026 prices):

• 60-mil TPO over existing roof (recover): $8–$11 / sq ft. Available only when the existing roof is dry, the deck is sound, and a recover is code-allowed (max two roof layers in California Title 24).
• 60-mil TPO with full tear-off + new ISO insulation: $11–$16 / sq ft. The right call when the existing roof is wet, leaking, or already at two layers.
• 80-mil PVC (restaurants, hotels, chemical exposure): $13–$19 / sq ft. The chemical-resistant choice — kitchen grease, HVAC condensate, refrigerant don’t degrade PVC the way they degrade TPO.
• Modified bitumen (multi-ply SBS): $9–$13 / sq ft. The conservative choice for low-budget industrial; less premium aesthetics but battle-tested 20–25 year life.

Code adders to know about:

• Title 24 cool-roof requirement: any commercial flat-roof replacement must meet minimum solar reflectance. White TPO and PVC pass by default; black EPDM does not without a coating.
• Insulation R-value upgrade: California Title 24 requires R-25 minimum on most commercial roofs. Existing roofs often have R-15 or less — the upgrade adds $1–$2.50 / sq ft depending on thickness.
• Equipment curb modifications: when raising the roof for insulation, every HVAC curb, drain, and exhaust stack has to be raised too. Budget $300–$800 per curb.

Timeline: about 1 day per 1,500–2,500 sq ft once material is on site, plus 1–3 weeks for permit and material lead time. We schedule commercial jobs around tenant operations — restaurants get overnight or weekend installs; warehouses are usually weekdays during normal hours.