Deck Waterproofing & Underdeck Systems in Southwest Washington
An elevated deck in our climate takes on months of rain every year, and where that water goes determines whether the framing underneath lasts — and whether the space below the deck is usable at all. Our team installs waterproof deck membranes and under-deck drainage (dry-below) systems that capture water at the deck surface and channel it away, correct the ledger flashing where most deck leaks start, and use rot-resistant framing throughout, so you get a durable upper deck and a genuinely dry, usable space underneath.
- Waterproof deck membrane systems (vinyl or coated)
- Under-deck drainage / dry-below ceiling systems
- Ledger-board flashing correction at the house connection
- Rot-resistant, pressure-treated, or engineered framing
- Gutter and downspout integration for under-deck drainage
- Composite and waterproof-rated decking surfaces
- Structural inspection of existing decks before waterproofing
- Covered, dry storage or living space created under an elevated deck
- Corrosion-resistant fasteners and structural connectors
- Repair of rot found during tear-off, before waterproofing goes in
Typical Timeline
Typically 1 – 3 weeks
Structural & Moisture Assessment
We inspect the existing deck's framing, ledger connection, and any current drainage, checking for rot or water damage before scoping the waterproofing system.
System Design
We design the waterproof membrane or dry-below drainage system, plan how it collects and channels water to a gutter or downspout, and confirm how the ledger flashing will be corrected at the house.
Structural Repair & Ledger Correction
Any rot-damaged framing is replaced, and the deck ledger — one of the most common sources of hidden water intrusion — is properly flashed where it attaches to the house.
Waterproofing & Drainage Installation
The waterproof membrane or under-deck drainage system is installed and integrated with gutters and downspouts so collected water discharges away from the foundation.
Decking & Finish
New decking is installed over the waterproofed structure, and — for a dry-below system — the underdeck ceiling is finished so the space below is ready to use as covered, dry outdoor living.
Plan Your Remodel With Confidence.
Tell us about your kitchen, bathroom, siding, or deck project and we'll help you plan the scope, materials, and budget that fit your home — free, no obligation, in a single conversation. Then book a consultation with our licensed Southwest Washington crew.
Free consultation · No obligation · Licensed & insured
What's an under-deck drainage system, and do I need one?
It's a system installed beneath an elevated deck's surface that catches water coming through the deck boards and channels it to a gutter, keeping the space underneath dry. If you have — or want — usable space under a raised deck, whether for storage, a patio, or simply a dry walkway, this is what makes it possible in a climate that gets rain most of the year.
Why do deck ledgers leak so often?
The ledger board — where the deck attaches to the house — is one of the most common failure points because it requires flashing that's easy to install incorrectly or skip entirely. Water gets behind the ledger, into the rim joist, and into the house framing before it's ever visible. We correct ledger flashing as a standard part of every deck waterproofing project.
Can this be added to an existing deck, or only new construction?
Both. We regularly retrofit waterproofing and under-deck drainage onto existing decks, which usually means removing the current decking, inspecting and repairing the framing underneath, correcting the ledger flashing, and installing the system before new decking goes back down.
Will a waterproof membrane affect how the deck looks?
No — the membrane and drainage system sit beneath the visible decking surface. From above, you still choose composite or wood decking in the look you want; the waterproofing works out of sight to protect the structure and, if you're finishing the space below, keep it dry.
Do you repair rot you find during this project?
Yes. If we find rot-damaged framing, sheathing, or ledger connections when we open up the deck, we repair it before installing any waterproofing — sealing a system over damaged wood would only hide the problem.
We provide deck waterproofing & underdeck systems to homeowners throughout the Vancouver metro, Clark County, the Columbia River Gorge, and the Lewis River and Cowlitz County corridor. Each community has its own page with local permitting and housing detail.
Plan your deck waterproofing & underdeck systems project with our in-depth guides.
Talk to a real project manager
Have Questions? Call Now for a Free In-Home Consultation.
Mon–Fri 7 AM–6 PM · Licensed & insured · No obligation
George S · Your Project Manager
Ready to Start Your Remodeling Project?
Get a free, no-obligation estimate from Southwest Washington's remodeling and exterior specialists. Licensed, insured, and ready to build.
In Southwest Washington, a deck spends more of the year wet than dry. The difference between a deck that lasts and one that rots is almost never the boards you can see — it is the waterproofing, flashing, and drainage you can't. We build and repair decks so that rain is carried off the surface, away from the ledger, and clear of the load-bearing framing, the same structural discipline we bring to a residential deck or patio and to dry rot & siding repair when moisture has already found a way in.
- Waterproof deck membrane systems (vinyl or coated)
- Under-deck drainage / dry-below ceiling systems
- Ledger-board flashing correction at the house connection
- Rot-resistant, pressure-treated, or engineered framing
- Gutter and downspout integration for under-deck drainage
- Composite and waterproof-rated decking surfaces
- Structural inspection of existing decks before waterproofing
- Covered, dry storage or living space created under an elevated deck
- Corrosion-resistant fasteners and structural connectors
- Repair of rot found during tear-off, before waterproofing goes in
Almost every deck failure in a wet climate traces back to water that got into the structure and wasn't seen. When a membrane or the ledger flashing fails, moisture reaches the load-bearing wood and drives dry rot that is invisible from the surface — the deck can look fine right up until it isn't. Our work addresses both the damage and the path the water was taking, so the repair actually lasts.
- Waterproof deck membranes and coatings sized for constant Pacific Northwest moisture.
- Correct ledger flashing where the deck attaches to the house — the most common leak point.
- Under-deck drainage (dry-below) systems that turn the space below an elevated deck into usable, covered outdoor living.
- Rot-resistant framing, joists, posts, and hardware, with structural repair where rot has already started.
- Positive drainage and slope so standing water never sits against wood.
- Permits and inspections for structural work, with documentation for your records.
The following government agencies, industry organizations, and official resources provide additional information relevant to your remodeling project.
We provide deck waterproofing to homeowners across the Vancouver metro, Clark County, the Columbia River Gorge, and the Lewis River and Cowlitz County corridor. Each community has its own dedicated page with local permitting, climate, and project detail — and each regional hub covers the surrounding areas we also serve.
Ready to Start Your Remodeling Project?
Get a free, no-obligation estimate from Southwest Washington's remodeling and exterior specialists. Licensed, insured, and ready to build.