Deck Waterproofing & Flashing in Mercer Island, WA
Walkable waterproof coatings, slope fixes and flashing that keep water out of your walls and ceilings. When coatings wear through or flashing is missing at doors and walls, the leak often shows up far from where water gets in. We trace it to the source, replace any wet framing, correct slope and flashing, and finish with a walkable surface that drains away from the house. We serve homeowners across Mercer Island and nearby Bellevue and Seattle.
Before
AfterNew siding and trim around the window
Why waterproofing comes up so often in Mercer Island
Lake-facing walls, decks over living space, and complex rooflines make waterproofing a priority on Mercer Island. Older homes were built before kick-out flashing and window pans were standard, and newer homes sometimes have membrane failures at deck-to-wall transitions. We install kick-out flashing at roof corners, metal ledger and Z-flashing, sill and door pans, and self-adhered membranes. For decks and balconies over occupied space, we apply a full waterproof membrane with slope and drainage. Every detail is lapped so water moves out and away, which matters on an island exposed on every side.
Mercer Island’s homes range from 1940s and 50s cottages in East Seattle and the North End to mid-century ramblers in neighborhoods like Mercerwood, and many large newer houses built on the island’s slopes and shoreline. Older homes often have cedar or wood lap siding, while newer ones use fiber cement, stucco or mixed cladding. Lots tend to be sloped and wooded, with daylight basements and decks that step down toward Lake Washington views. Waterfront homes along East and West Mercer Way often have docks, boathouses and multi-level terraces.
Surrounded by Lake Washington, Mercer Island gets wind from almost every direction depending on the storm, and lake-facing walls take wind-driven rain. Steep, wooded slopes keep many homes shaded and damp, and dense trees around Pioneer Park and along the Mercer Ways drop needles that clog gutters. Long wet winters mean wood rarely dries out between fall and spring. Large windows and decks oriented toward the water are the most exposed parts of most homes.
Our crew comes out from our Woodinville office, and we also work in nearby Bellevue, Seattle, Medina and Kirkland.
When to call about waterproofing in Mercer Island
- Rot or stains under windows and doors
- Streaks down the wall below a roof edge
- Stains or drips on the ceiling below a deck or balcony
- Cracked, peeling or soft deck coating
- A deck that slopes toward the house
Our waterproofing process, step by step
Trace the leak
Moisture readings, inspection openings and photos to find the real source.
Repair the substrate
Rotted plywood, joists or sheathing are replaced before sealing.
Correct slope and details
Proper slope, sill pans and flashing at every edge and door.
Apply the system
Primer, membrane and walkable top coat applied in layers.
Water test
We test the problem areas and show you the finished details.
Recent waterproofing projects near Mercer Island
What we do in Mercer Island
Leak investigation
We trace leaks to the source before anything is sealed.
Door and sill pans
Pan flashing under doors, where many balcony leaks start.
Kick-out flashing
Diverts roof water away from the wall at roof-to-wall joints.
Window head flashing
Flashing and tape around windows to stop leaks into the wall.
Slope correction
Fix flat or back-sloped decks so water drains away from the wall.
Walkable deck coatings
Waterproof coating systems for decks and balconies over living space.
Neighborhoods and permits in Mercer Island
North End homes near I-90 and Luther Burbank Park include many older houses with original siding and small decks. East Seattle and the west side face Seattle across the lake, catching weather on west walls. Mercerwood and the central island have mid-century homes under heavy tree cover. The South End and properties along East Mercer Way sit on steep, wooded slopes where tall decks and daylight basements are common.
Patching small areas of trim, siding or decking with identical material rarely needs a permit. Steep-lot deck rebuilds, structural work and larger replacements usually call for one. The City of Mercer Island handles that review, and we confirm the requirements with them up front, submit what is needed, and keep inspections on the calendar.
Deck and balcony surface options
| System | Best for | Expected life | Maintenance |
|---|---|---|---|
| Recoat existing membrane | Sound surface with a worn top coat | A few years per top coat | Keep drains clear, recoat when worn |
| New walkable membrane | Decks and balconies over living space | 10–15+ years | Top coat every few years |
| Membrane under decking | Dry space under a deck with a wood or composite surface | 15+ years | Keep gaps and drains clear |
| Rebuild, slope and membrane | Wet or rotted plywood, flat or back-sloped deck | 15+ years | Top coat every few years |
What waterproofing typically costs in Mercer Island
| Project | Typical scope | Price range | Timeline |
|---|---|---|---|
| Flashing repair | Kick-out, head flashing or a door pan at one spot | $600 – $2,500 | 1 day |
| Recoat a balcony | Prep and top coat over a sound membrane | $1,500 – $4,500 | 2–3 days |
| New walkable membrane | Full membrane system on a deck or balcony | $5,000 – $14,000 | 4–7 days |
| Rebuild and waterproof | New plywood, slope correction, flashing and membrane | $12,000 – $30,000+ | 1–3 weeks |
These are typical 2026 ranges we see for waterproofing in Mercer Island and nearby cities. Your price depends on what we find once the area is open, access and height, and the materials you choose. Every estimate is free, in writing and based on an on-site inspection with photos.
Waterproofing in Mercer Island: cost and timing
Most common causes
Doors without sill pans
Water that gets under a threshold runs into the subfloor and the room below.
Decks that slope toward the house
Flat or back-sloped surfaces push water against the wall and door thresholds.
Missing kick-out flashing
Roof water runs down the wall instead of into the gutter and soaks the siding and framing.
What drives the price in Mercer Island
Waterproofing in Mercer Island depends on the size of the deck or balcony, how much substrate has to be replaced, slope correction and how many doors and walls need new flashing. Recoating a sound surface costs far less than rebuilding a wet one. You get a written price after we trace the leak.
Typical timeline
A recoat over a sound deck usually takes a few days including cure time. Rebuilding plywood, slope and flashing takes about one to two weeks, depending on weather.
Backed by a 24-month workmanship warranty
Written scope
You know exactly what is included before work starts, with photos of what we found.
Our own crew
The people who quote your job are the people who do it, start to finish.
Clean site daily
Debris is hauled away and your yard is left the way we found it.
24 months covered
If our workmanship fails within two years, we come back and make it right.
What homeowners near Mercer Island say
“I had a great experience working with Eco Home Repair on a water damage project. Water was leaking into the house through the chimney, which caused mold and water damage issues. Eco Home Repair handled everything smoothly and professionally. They replaced the…”
“I hired Eco Home Repair to do a leak repair under my balcony, deck waterproofing and slope correction, and underlying rot repair. They were professional, quick, and fairly priced; kept me in the loop throughout the whole process and was honest about what…”
“Very professional, quick to respond, and able to schedule the work on short notice they treated our home and deck with care and did an excellent job. I would definitely hire them again for a future project.”
5.0 average from 106 reviews on Google, Thumbtack, Angi, HomeAdvisor and Yelp. Read our reviews on Google.
Questions Mercer Island homeowners ask about waterproofing
Why does my Mercer Island home have rot on more than one side?
Can you coat over my existing deck in Mercer Island?
Why is water leaking under my deck or balcony?
Do you fix leaks around windows?
Why does my ceiling leak only in heavy rain?
More from our crew in Mercer Island
Waterproofing near Mercer Island
Tell us about your waterproofing project in Mercer Island
- Licensed, bonded & insured
- Free on-site estimates
- 24-month workmanship warranty
Book a free waterproofing inspection in Mercer Island
We inspect the damage on-site, show you photos of what we find and give you a written price before any work starts.