Flat Roof Calculator: 2026 Cost for TPO, EPDM, PVC and Modified Bitumen

A flat roof (technically a low-slope roof, usually 1/4 inch of fall per foot or less) is common on garages, porches, additions, row houses and modern homes. It can't shed water like shingles do, so it's covered with a continuous waterproof membrane instead. That changes both the materials and the price.

Flat roof cost at a glance (2026)

• EPDM rubber: about $5.50–$9.00 per sq ft installed
• TPO (white, single-ply): about $6.50–$10.50 per sq ft
• PVC: about $8.00–$13.00 per sq ft
• Modified bitumen (torch-down or peel-and-stick): about $5.00–$9.00 per sq ft
• Built-up roof (tar and gravel): about $5.50–$9.50 per sq ft

A typical 400 sq ft garage roof lands around $2,600–$4,600. A 1,500 sq ft flat roof on a house usually runs $9,500–$17,000 once tear-off and insulation are included. These are our own typical 2026 estimates, so always compare them with local quotes.

How the flat roof calculator works

Enter the length and width of the roof, pick a membrane, and say whether the old roof comes off. The calculator adds 10% for parapet walls, flashing and seams, then prices tear-off, tapered insulation (which creates slope so water drains), new drains or scuppers, and adjusts labor for your ZIP code.

What changes the price most

Tear-off and wet insulation

Removing one layer runs roughly $1.00–$2.00 per sq ft. If the old insulation is soaked, it all has to go — that's the most common surprise on flat roof jobs.

Ponding water

Water sitting more than 48 hours shortens membrane life. Tapered insulation adds about $1.50–$3.00 per sq ft but fixes the cause instead of the symptom.

Drains, scuppers and parapets

Each new drain or scupper adds a few hundred dollars. Tall parapet walls need membrane wrapped up and over them, which adds material and labor.

Which membrane should you pick?

• EPDM: lowest cost, proven, easy to patch — good for garages and small additions
• TPO: white surface cuts cooling bills in hot climates; the most popular choice today
• PVC: best against grease and chemicals (near kitchen exhausts) and very durable seams
• Modified bitumen: tough under foot traffic; good for roof decks you walk on

On a flat roof, the details — edges, drains and seams — fail long before the membrane does. Pay for good flashing work.

Frequently asked questions

How long does a flat roof last?

EPDM and TPO usually last 20–30 years, PVC 25–30, modified bitumen 15–20 and built-up 15–25 with good maintenance.

Can I put a new flat roof over the old one?

Sometimes, if there's only one existing layer and the insulation is dry. Most codes allow two layers maximum, and a core cut is the only way to know what's underneath.

Is a flat roof cheaper than a shingle roof?

Per square foot it's often similar or a bit higher, but flat roofs are usually smaller and need no steep-slope safety gear, so total jobs can be cheaper.

Do I need a permit for a flat roof?

Most US cities require one for a full replacement. Use our roofing permit calculator to estimate the fee.