Flat Roof TPO + EPDM Installation
Why this matters
Flat + low-slope roofs dominate commercial + light industrial - strip malls, restaurants, office buildings, multifamily. Single-ply membrane (TPO + EPDM) replaced built-up roofing (BUR) + modified bitumen for most new installations 2010+. Per-square-foot pricing. A 10,000 sq ft commercial roof runs . Specialty trade within roofing - but contractors who handle low-slope work capture commercial accounts that recurring service residential-only roofers can't.
TPO vs EPDM (the two dominant single-plies)
TPO (Thermoplastic Polyolefin)
- White (highly reflective) - Energy Star + LEED cool-roof credit
- Heat-welded seams (hot-air welder)
- 25 - 30 year typical lifespan
- More dimensional stability + chemical resistance than EPDM
- Higher installed cost
- Better aesthetic; preferred for visible roofs
- Brands: GAF EverGuard, Carlisle Sure-Weld, Firestone UltraPly, Johns Manville TPO
EPDM (Ethylene Propylene Diene Monomer)
- Black (or white-coated) rubber-like membrane
- Adhesive OR seam-tape seams
- 30 - 50 year typical lifespan (longer than TPO)
- More flexible in cold; less reflective
- Lower installed cost
- Easier to repair
- Brands: Firestone RubberGard, Carlisle Sure-Seal, Versico VersiGard
Decision: which membrane
TPO is better for:
- Hot climates (reflective)
- Visible roofs (white, clean look)
- Where Energy Star / LEED matters
- Where chemical exposure possible (HVAC oils, etc.)
EPDM is better for:
- Cold climates (flexibility at low temp)
- Concealed roofs (aesthetic less important)
- Tight budget
- Maximum lifespan focus
Both perform well in residential low-slope + commercial.
Roof preparation
Existing roof condition assessment
- Tear-off OR overlay decision (most jurisdictions allow 1 overlay; 2+ requires tear-off)
- Substrate condition: dry rot, soft spots, sag
- Drainage: positive slope to drains; standing water indicates problem
- Insulation: foam-board OR mineral wool typical under membrane
Substrate options
- Wood deck: plywood OR OSB
- Concrete deck: poured concrete
- Steel deck: corrugated metal
- Lightweight concrete: gypsum-based
Insulation board
- Polyisocyanurate (polyiso): standard; R-6 per inch nominal
- Mineral wool: fire-rated where needed
- EPS / XPS: older / specialty applications
- Tapered insulation: directs water to drains; specified per roof
Installation method options
TPO methods
- Mechanically attached: fasteners + plates secure membrane to deck through insulation. Most common; affordable.
- Fully adhered: bonding adhesive attaches membrane to insulation. Premium; better at high-wind sites.
- Ballasted: stone or pavers hold membrane in place. Older method; not common for new.
- Self-adhered: peel-and-stick. Limited applications.
EPDM methods
- Fully adhered: bonding adhesive; most common residential + commercial EPDM
- Mechanically attached: similar to TPO; less common
- Ballasted: stone-weighted; older method
TPO mechanically-attached install
- Tear off OR overlay prep: remove old to deck OR clean for overlay; deck inspection + repair
- Insulation board: mechanically attached OR adhered; R-20 to R-30+ commercial; tapered for drainage
- Cover board (if specified): 1/4" - 1/2" Dens-Deck / Securock; puncture + fire resistance
- Lay membrane: 10 - 12 ft panels perpendicular to short dimension; 6" seam overlap
- Fasten + plate: TPO-rated screws + 3" plates per wind-uplift design (zone-specific)
- Weld seams: hot-air welder at 800 - 1,100°F; consistent speed; probe-test EVERY weld
- Detail work: bonded drain boots; pipe flashings; curb wraps; parapet + corner accessories
- Walk + inspect: every seam tested; photo documentation; customer walk + sign-off
EPDM fully-adhered install (residential low-slope)
Similar to TPO but:
- Bonding adhesive applied to insulation OR cover board AND membrane back
- Allow tack-up time per adhesive
- Roll membrane carefully to release bubbles
- Seams: 6" overlap with seam tape OR seam adhesive
- Sealed with bonding tape rolled tight
- Detail work + walls similar to TPO
Common installation mistakes
Insufficient slope
- Standing water on TPO + EPDM accelerates degradation
- Verify drainage to all drains; add cricket or tapered insulation if needed
Welder temperature too high (TPO)
- Membrane char + lose physical properties
- Strip weld at burn point
Welder temperature too low (TPO)
- Cold weld; fails physical test
- Risk: appears welded but separates under stress
Bonding adhesive too dry / too wet (EPDM)
- Per adhesive spec (some are "wet" set; others "dry-tacky")
- Wrong technique = membrane not bonded properly
Improperly fastened around penetrations
- Mechanical fastener too close to membrane edge or seam = leak path
Skipped seam testing
- Test EVERY seam with probe
- 1-foot probe test under tension; passing weld holds full pull
Wrong walkway / wear pad placement
- HVAC service paths need walkway pads
- Without them, foot traffic damages membrane over years
NEVER skip the SLOPE + DRAINAGE inspection before bidding a flat-roof job. The membrane is only as good as the underlying drainage. A perfectly-installed roof on a substrate with negative slope or clogged drains will pool water + fail in 5 - 8 years. Verify positive slope to all drains, drainage system condition, + interior gutter / scupper performance. Quote tapered insulation + drainage repair as separate line items where needed. Customer who pays for membrane only on a poorly-drained roof is the customer who calls back at year 6 + you eat the warranty.
Inspection + warranty
- Manufacturer warranty: 15, 20, 25, OR 30 year - only valid with certified installer + inspection
- Workmanship warranty: from contractor; 5 - 15 year typical
- Insurance carrier inspection: often required at completion for commercial
- Annual inspection: recommended for full warranty + customer asset protection
References
- ARMA (Asphalt Roofing Manufacturers Association)
- Carlisle, GAF, Firestone, Johns Manville installation manuals
- NRCA (National Roofing Contractors Association) standards
- ANSI / SPRI ES-1 (wind uplift for low-slope roofs)
- IRC R905.11 + IBC Chapter 15 (low-slope provisions)
- Manuall internal: Metal Roofing Installation