What is the difference between TPO and EPDM?

TPO is white/reflective, heat-welded at seams, and offers better energy savings. EPDM is black rubber, glued or taped at seams, extremely durable, and slightly less expensive. Both typically last 20–30+ years with proper installation.

What are standard membrane roll sizes?

TPO: 10' × 100' (1,000 sq ft) is the most common, also 6' and 12' widths. EPDM: 10', 20', 40', and 50' widths in lengths up to 200', allowing large areas to be covered with fewer seams.

How much overlap do TPO seams need?

Most TPO manufacturers require a minimum 6-inch seam overlap, with 1.5 inches of actual heat weld width. The remaining 4.5 inches provides a pocket that must be probed for weld integrity.

What attachment methods are used?

Three main methods: Fully adhered (glued to substrate), mechanically attached (screwed through membrane and insulation), and ballasted (loose-laid with river rock or pavers). Each has different material requirements.

How much adhesive is needed?

For fully-adhered EPDM: bonding adhesive covers about 60 sq ft per gallon. For TPO, the adhesive type and substrate vary the rate. Always check the specific product's data sheet for spread rates.

Can I install membrane over old roofing?

In many cases, yes. A cover board (polyiso, gypsum, or HD polyiso) is placed over the existing roof, and the new membrane is installed on top. This avoids tear-off costs but adds weight. Check local codes for maximum number of roof layers.

TPO / EPDM Membrane Calculator

Calculate TPO or EPDM single-ply membrane roofing material needed. Accounts for field area, parapet wrap, seam overlaps, and adhesive requirements.

Roof Length

Roof Width

Parapet Height

Parapet Perimeter

Roll Width

Overlap Width

Additional Waste

Deck Area

2,400 sq ft

Parapet Wrap

500 sq ft

Seam Overlap Waste

90 sq ft

3 seams

Total Membrane Needed

3,289 sq ft

Rolls Needed

1,000 sq ft per roll

Planning notes, formulas, and examples

About the TPO / EPDM Membrane Calculator

TPO (thermoplastic polyolefin) and EPDM (ethylene propylene diene monomer) are the two dominant single-ply membrane systems for flat and low-slope commercial and residential roofs. Proper material estimation must account for the field area, parapet and curb wrap-ups, seam overlaps (typically 6 inches for TPO, 3–6 inches for EPDM), and perimeter terminations.

This membrane calculator helps you estimate the total membrane area needed by adding the deck area, parapet wrap, and overlap waste. It also provides an adhesive or fastener estimate based on the system type (fully adhered, mechanically attached, or ballasted).

Accurate membrane estimation prevents mid-project shortages that cause schedule delays and potential warranty issues from using material from different production lots.

When This Page Helps

Membrane roofing is purchased by the roll (typically 10' wide × 100' long), and seam overlaps waste 8–15% of the material. This calculator accounts for overlaps, parapet wrap, and field area to give an accurate roll count.

How to Use the Inputs

Enter the deck area (length × width) of the flat roof.
Enter the parapet height and total parapet perimeter for wall wrap calculations.
Enter the overlap width and roll width for seam waste.
Review the total membrane area and estimated roll count.
Add 5–10% contingency for field waste (cutting, penetrations).

Formula used

Deck Area = Length × Width
Parapet Wrap = Parapet Perimeter × (Parapet Height + 6") × 2 sides
Overlap Waste = (Deck Area / Roll Width) × Overlap Width × Deck Length
Total = Deck Area + Parapet Wrap + Overlap Waste
Rolls = Total / Roll Area

Example Calculation

Result: 3,400 sq ft, 4 rolls

Deck = 60 × 40 = 2,400 sq ft. Parapet wrap = 200 × 2.5 ft = 500 sq ft. Overlap waste: 4 seams × 0.5 ft × 60 ft = 120 sq ft. Total ≈ 3,020 sq ft. With 10% waste: ~3,322 sq ft. 4 rolls (1,000 sq ft each) needed.

Tips & Best Practices

TPO seams are heat-welded and must be a minimum of 6 inches wide for warranty.
EPDM seams use contact adhesive or seam tape (typically 3–6 inch overlap).
Always run membrane sheets perpendicular to the roof slope for proper drainage.
For fully-adhered systems, calculate adhesive based on manufacturer's spread rate.
Parapet wrap should extend at least 8 inches up the wall face and be terminated with a metal bar.
Penetration details (pipes, HVAC curbs) require extra patch material — order accordingly.

TPO vs. EPDM: Choosing the Right System

TPO reflects sunlight (especially white TPO), reducing cooling costs. It's the dominant choice for new commercial construction. EPDM is preferred for its reliability, lower material cost, and ease of repair. Both last 20–30+ years, and the choice often depends on local climate, contractor expertise, and energy goals.

Attachment Methods

Fully adhered systems provide the best wind uplift resistance and are required in high-wind zones. Mechanically attached systems are faster to install and work well in most conditions. Ballasted systems are the least expensive but require a roof structure that can support 10+ lbs/sq ft of ballast.

Seam Integrity

Seams are the most vulnerable point on any single-ply roof. TPO's heat-welded seams form a molecular bond stronger than the sheet itself. EPDM's adhesive or tape seams require careful preparation and pressure-rolling. Both systems should have seams inspected and probed after installation.

Sources & Methodology

Last updated: February 8, 2026

Frequently Asked Questions

TPO is white/reflective, heat-welded at seams, and offers better energy savings. EPDM is black rubber, glued or taped at seams, extremely durable, and slightly less expensive. Both typically last 20–30+ years with proper installation.