# Flat Roof Replacement Federal Way WA | Residential Low-Slope & TPO | Federal Way Roofing

> Residential flat and low-slope roof replacement for Federal Way homes — additions, porches, and full low-slope sections — with drainage correction built into the job, not an afterthought.

URL: https://federalwayroofing.net/flat-roof-replacement/

## Price

$550-$950 roofing square (100 sq ft) installed. reconciled from 2026 national TPO/EPDM installed-pricing data scaled to residential-size sections — see the commercial roofing page for full commercial-scale pricing.

## What's included

- On-site inspection covering membrane condition, seams, and drainage slope
- A written price before any work starts, identifying the cause of any existing ponding
- TPO or EPDM membrane installation to manufacturer wind and code spec
- Tapered insulation where the existing slope doesn't drain correctly — not just a new membrane over the same drainage problem
- Flashing and termination detail work at walls, parapets, and penetrations
- Deck inspection and sheathing repair where standing water has caused damage
- A King County or Federal Way building permit pulled as part of the job
- Full cleanup and haul-away of the old roofing

## Process

01. **Free on-site inspection** - We check the membrane, every seam, and whether water is actually draining off the roof within 48 hours of rain — a real problem in this climate if it isn't.
02. **Permit and scope** - We pull the permit and specify membrane type and any drainage correction needed, in writing.
03. **Tear-off and install** - Deck repaired where ponding has caused damage, then membrane and flashing installed to spec.
04. **Inspection and walkthrough** - Final inspection confirming the roof drains correctly, cleanup, and a walkthrough before we leave.

## When it's needed

- Standing water that doesn't drain within 48 hours after rain
- Visible membrane seams separating or bubbling
- A leak at a wall, parapet, or penetration on a flat section
- Ponding staining or darkening visible on the membrane surface
- An addition or porch roof original to a home built decades ago
- Previous patches that haven't stopped a recurring leak

## FAQ

**Why does my flat roof keep holding water?**

Usually because the original slope was never adequate, or has settled over time — a new membrane over the same bad slope just delays the same problem. We check drainage specifically and recommend tapered insulation where it's actually the cause, rather than only replacing the membrane.

**TPO or EPDM for a residential flat section?**

TPO is more common now for its reflectivity and heat-welded seams; EPDM has a long track record and slightly lower material cost. For a residential addition or porch roof, either performs well if installed correctly — the bigger factor is usually drainage design, not membrane choice.

**How long does a flat roof last in this climate?**

A properly installed and correctly-draining TPO or EPDM system commonly reaches 20-25 years. Standing water from poor drainage is the single biggest thing that shortens that in the PNW's wet winters.

**Is this the same service as your commercial roofing?**

Same membrane systems, different scale — this page covers residential-size flat sections like additions and porch roofs. For a full commercial building, see our commercial roofing page.