Low slope, zero leaks
Flat & TPO Roofing
TPO and low-slope membrane systems for additions, townhomes, and modern Seattle builds.
- Lifespan
- 20 – 30 years
- Range
- $12,000 – $28,000
- Warranty
- Manufacturer + 5-yr GripGo
What it is & how it works
Flat & TPO Roofing in plain English
Flat and low-slope roofs are everywhere in the Seattle area — mid-century ramblers, modern townhomes in Ballard and Columbia City, rear additions, dormers, and garage roofs. They don't shed water like a pitched roof, so they need a true waterproof membrane. We install TPO, the proven single-ply membrane that stands up to Pacific Northwest rain, moss, and ponding water.
TPO (thermoplastic polyolefin) is a heat-welded single-ply membrane: every seam is fused with a hot-air welder into one continuous waterproof sheet — no glue, no tar, no open flame. White TPO reflects summer sun to keep upper floors cooler, and the smooth surface resists the moss and algae that eat Seattle asphalt roofs. It handles our nine-month rainy season, standing water on dead-flat sections, and freeze-thaw cycles without cracking. We taper insulation to push water to drains and scuppers, because on a flat roof the drainage design matters as much as the membrane.
Understanding your options
Tiers, styles & what's included
Tap any tier to see exactly what's in it, what it costs relative to the others, and who it fits best.
Option 1TPO Membrane (Our Standard)
TPO Membrane (Our Standard)
The modern replacement for torch-down and tar-and-gravel. White, reflective, and heat-welded into a single sheet.
- 60 or 80 mil thickness (we recommend 80 mil for Seattle)
- Hot-air welded seams — stronger than the membrane itself
- Reflective white surface (Energy Star rated)
- 20 – 30 year manufacturer warranties available
- Resists moss, algae, UV, and ponding water
Option 2Tapered Insulation & Drainage
Tapered Insulation & Drainage
On a flat roof, water that sits is a leak waiting to happen. We build the slope into the insulation so water moves to drains.
- Tapered ISO insulation creates positive drainage
- Eliminates ponding at low spots and around drains
- Adds R-value — warmer in winter, cooler in summer
- Cricket saddles behind chimneys and skylights
Option 3Where Flat Roofs Show Up in Seattle
Where Flat Roofs Show Up in Seattle
We replace and repair flat sections on every style of local home.
- Modern townhomes (Ballard, Fremont, Columbia City, Capitol Hill)
- Mid-century ramblers with low-pitch sections
- Rear additions and kitchen bump-outs
- Dormers, porch roofs, and garage roofs
- Mixed roofs: pitched shingle main roof + flat addition
Option 4System Details (Every GripGo Flat Roof)
System Details (Every GripGo Flat Roof)
Flat roofs fail at the edges, seams, and penetrations. Our system over-builds all three.
- Full tear-off and deck inspection before any membrane goes down
- Every seam probed and tested after welding
- Fully welded flashing at vents, skylights, and walls — no caulk-only details
- Drip edge and gutter integration so water leaves the roof cleanly
- Walkway pads at HVAC and service access points
- 10-year workmanship warranty on every install
The system
Anatomy of a full roof system
A roof is a stack of layers — each one has a job. Here's what goes into every one we build, in plain English.
- Ridge cap & ventLets hot air escape from the attic peak
- Shingles / tiles / shakesThe visible weather layer
- Synthetic underlaymentSecondary water barrier across the whole deck
- Ice & water shieldPeel-and-stick at eaves, valleys, and penetrations
- Roof decking (sheathing)The plywood/OSB nailing surface
- Rafters + soffit intakeStructure and fresh-air inlet that balances the ridge vent
The honest take
Advantages & things to consider
Advantages
- Heat-welded seams — one continuous waterproof sheet, nothing to peel apart
- Handles ponding water and nine months of Seattle rain
- White reflective surface cuts summer heat upstairs
- Smooth membrane resists moss and algae growth
- Lightweight — no structural changes needed on most homes
- Easier and cheaper to repair than tar-and-gravel or torch-down
Things to consider
- Not walkable like a deck — foot traffic needs walkway pads
- Quality varies by manufacturer; we only install membranes with proven Seattle track records
- Requires a specialist crew — a bad weld is a hidden leak (our welds are probed and tested)
Is this right for your home?
Quick fit check
What GripGo inspects
Free on-site inspection checklist
Every quote starts with a real inspection — not a driveway guess. Here's what we look at before we write a single number down.
Membrane seams and heat-welded laps
Perimeter and edge flashing
Curbs, penetrations, and pipe boots
Drains, scuppers, and overflow paths
Ponding areas and slope-to-drain
Insulation moisture (infrared where needed)
Common questions
What Seattle homeowners ask us about flat & tpo roofing
Is TPO better than torch-down for Seattle?+
For most homes, yes. TPO seams are heat-welded into one sheet with no open flame (safer install), the white surface reflects heat instead of absorbing it, and repairs are simpler. Torch-down still makes sense on some small roofs with heavy foot traffic — we'll tell you honestly which fits your roof.
My flat roof ponds water after it rains. Is that a problem?+
Ponding that disappears within 48 hours is normal. Water that sits longer accelerates wear and finds seams. The fix usually isn't a new membrane — it's tapered insulation that rebuilds the slope so water reaches the drains. We check drainage on every flat roof inspection.
Can you put TPO over my existing flat roof?+
Sometimes, if there's only one existing layer and the deck and insulation are dry. We scan for trapped moisture first — covering wet insulation guarantees mold and deck rot. If the old roof is wet or there are two layers, we tear off.
How much does a flat roof replacement cost in Seattle?+
Most residential flat and low-slope sections run $12,000 – $28,000 depending on size, tear-off, insulation, and how many penetrations (vents, skylights) need flashing. A small porch or dormer section can be much less. Every quote starts with a free on-site inspection and a written price.
How long does TPO last in the Pacific Northwest?+
20 – 30 years with proper installation and occasional drain cleaning. The membrane itself handles our rain and mild freezes easily — what kills flat roofs here is clogged drains, ponding water, and bad seam welding. All three are install-quality issues, which is why crew experience matters more on flat roofs than any other type.
Related services
Also worth a look
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The Pacific Northwest workhorse — affordable, proven, 30+ year lifespan.
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Composite / Synthetic Roofing
The look of slate or cedar — engineered to outlast both, with 50-year warranties.
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Metal Roofing
Standing seam and metal shingle — 40 to 70+ year lifespan, energy-efficient.
Learn moreReady when you are
Free inspection, honest recommendation, no pressure. That's how we've done it since day one.