Waterproof Deck Installation
Licensed: CSLB #1106627 
Insured and Bonded 
Why Choose Us
Trusted
Our Works
Added home value
Total labor time
Estimated lifespan
Added home value
Total labor time
Estimated lifespan
Added home value
Total labor time
Estimated lifespan
Added home value
Total labor time
Estimated lifespan
Added home value
hours
Total labor time
Estimated lifespan
Client
Reviews
GOOGLE GUARANTEED
— Mark T., Seattle homeowner
— William Tikhonenko
— Ruvim Gaidaichuk
— Davyd Brovkin
— Anatolii Dobrolevskyi
“Cold Flooring” in the Sun: Myth or Reality?
In summer, you want to step out onto the terrace barefoot and avoid the heat. This leads to a popular question: is there a deck that doesn’t heat up at all in the sun? The short answer is no; any material will heat up in direct sunlight. However, the difference in heat can be quite […]
How to care for a wood or wood-polymer composite deck
Yes, both wood and modern composite decks are designed to withstand the elements. But their lifespan and appearance directly depend on regular cleaning, proper chemical treatments, and careful winter maintenance. In the US, manufacturers’ recommendations are consistent: dirt and organic matter are the main enemies; harsh cleaning products and excessive water pressure are a common […]
Is Your Deck Poorly Built? Three Warning Signs to Check Today
A terrace isn’t just for relaxation. It’s a space subject to loads, wind, moisture, and cyclical heating. Errors in joints accumulate and then suddenly erupt: a wobbly fence, a sagging span, a damp “house joint.” Therefore, the reaction “we’ll figure it out some other time” is inappropriate. Our blog covers many topics related to home […]
Spring is the best time for a deck: start the season right
Building a deck involves more than just choosing deck boards and railings. It also involves weather windows, soil management, delivery schedules, permits, and inspections. In spring, these factors combine to create a more predictable picture: the ground has thawed, temperatures have stabilized, and permit departments and contractors aren’t yet overwhelmed with summer requests. As a […]
Steel deck framing: the fire-safe solution your home really needs
Forest fires are becoming a reality in an increasing number of regions. Therefore, the discussion of decking has long since moved beyond aesthetics. The key lies not only in the decking, but in the foundation itself. It is the framework that determines the fire resistance of the entire structure and influences how it will respond […]
FAQ
Places where we provide services
What “Waterproof Deck” Actually Means
“Waterproof deck” can mean two different things — and the difference matters for pricing and complexity:
1. Waterproof deck over living space (also called “roof deck” or “occupied-over deck”). The deck acts as a roof — space below is living area (basement, garage, interior room). Water must NOT penetrate. Requires continuous waterproof membrane + structural wood or concrete substrate + walking surface on top. Total system: 4-6 inches thick minimum.
2. Under-deck drainage on a standard deck. Deck is traditional framing with gaps between boards. Separate drainage system below the deck catches water and redirects it. Creates dry space below for outdoor furniture, hot tub, storage. Water passes through the deck surface — only the under-deck area stays dry.
These are completely different products. The first costs $45K-$120K; the second costs $8K-$20K as an add-on to a standard deck.
LGC builds both. The right choice depends on what’s below the deck and what you want to do with that space.
Waterproof Deck Over Living Space (Type 1)
When you need this: Your deck sits over a finished basement, garage, or interior room. Any water leak floods the space below. Examples: second-story decks with a garage below, decks over basement walkouts, decks over enclosed patios.
System components (bottom-up):
- Structural substrate. Treated wood subframe (rated for the deck’s live load + snow load + furniture), sloped 1/4″ per foot minimum toward drains.
- Underlayment. Temporary protection against construction moisture.
- Waterproof membrane. One of:
- TPO (thermoplastic polyolefin) — heat-welded, 60 mil standard. 20-30 year warranty. $5-8/sqft material + install. Most common for residential.
- PVC — similar to TPO, heat-welded. 25-40 year warranty. $6-9/sqft.
- Liquid-applied — peel-and-stick rubberized asphalt or elastomeric coating. Flexible, good for complex shapes. $4-7/sqft. 15-20 year lifespan typical.
- Hot-mopped asphalt — traditional, fewer contractors work with it now. 15-20 years.
- Protection layer. Drainage mat or slip sheet protects membrane from top layer.
- Walking surface. Options:
- Pedestal pavers — concrete or porcelain, rest on adjustable pedestals. No penetrations. Best for pedestal-friendly layouts. $8-15/sqft installed.
- Composite decking on sleepers — Trex or TimberTech boards on pressure-treated sleepers laid on membrane. Walking surface looks like a traditional deck. $12-20/sqft installed.
- Stamped concrete overlay — poured directly on membrane (specific membrane types only). $15-25/sqft installed.
Total cost for a 300 sqft waterproof deck over living space: $45,000 – $85,000 typical.
Under-Deck Drainage (Type 2)
When you use this: Standard outdoor deck (no habitable space below), but you want to use the area under the deck as a dry patio for hot tub, outdoor furniture, storage, or workshop space.
System components:
Under-deck drainage installs BELOW the deck joists, catches water that falls between the deck boards, and redirects it to a gutter / downspout.
Main types:
- Trex RainEscape — vinyl trough + downspout system. Panels snap between joists. 20-year warranty. $3-6/sqft (additional to deck cost). Best all-around choice.
- UnderDeck (Color Guard) — similar panel system, different connection detail. Comparable pricing.
- DryJoist / DeckDrain — aluminum pan system that clamps to joists. More robust, more expensive. $6-10/sqft.
Installation happens during deck construction — retrofit after the fact is possible but costs 2-3× more.
Ledger Flashing — Water Management Starts Here
Even on a non-waterproof deck, water management begins at the ledger. An improperly flashed ledger causes more PNW deck failures than any other single issue. Over 8-12 years, water wicks behind the ledger board, rots the house rim joist, and eventually the connection fails.
Our standard ledger detail:
- Z-flashing (metal) installed above ledger, turned up behind siding 4″ minimum
- Peel-and-stick Vycor membrane under and behind the ledger
- Sealant at all penetrations (ledger bolts, lag screws)
- Drip edge extending 1/2″ beyond ledger face
- Gap between ledger and siding for drainage
This applies to every deck, not just waterproof decks. It’s the detail we won’t compromise on, and it’s the difference between a 25-year deck and a 7-year failure.
Waterproof Deck Process
Step 1: Evaluation. What’s below the deck? Living space, garage, or exterior? This determines Type 1 vs Type 2. We also assess existing drainage, slope, and any existing water damage.
Step 2: Design + engineering. For Type 1, structural engineer designs the substrate for the specific live load + membrane requirements. Typical engineering fee: $600-1,500.
Step 3: Permit. Waterproof deck over living space requires full permit. Clark County, Portland PP&D, etc. — same process as new deck construction. Engineer stamp on drawings.
Step 4: Substrate construction. Build sloped treated-wood subframe per engineering spec. Drainage plan, scupper or downspout placement.
Step 5: Membrane installation. TPO/PVC welded, tested for leaks. Corners, curb details, drain penetrations all flashed. This is the critical step — done by us or by roofing subcontractor (depending on project scope).
Step 6: Walking surface. Pedestal pavers, composite-on-sleepers, or specified final surface. Railings installed with minimal penetrations.
Step 7: Final inspection + warranty documentation. County sign-off. Written warranty from LGC on installation (5 years workmanship). Membrane warranty from manufacturer (20-30 years).
Timeline: 10-16 weeks for full waterproof deck over living space. 2-4 weeks for under-deck drainage add-on.
Waterproof Deck Pricing — 2025 Ranges
Type 1 (over living space):
| Project | Typical range |
|---|---|
| 200 sqft waterproof deck, TPO + pavers | $35,000 – $55,000 |
| 300 sqft waterproof deck, TPO + composite decking | $50,000 – $80,000 |
| 400 sqft waterproof with railings + stairs | $65,000 – $105,000 |
| Luxury 500+ sqft, PVC + premium finish + custom railings | $95,000 – $150,000+ |
Type 2 (under-deck drainage add-on):
| Deck size | Trex RainEscape | Aluminum pan system |
|---|---|---|
| 300 sqft | $3,000 – $6,000 | $6,000 – $10,000 |
| 500 sqft | $5,500 – $10,000 | $10,000 – $16,000 |
About LGC Remodeling & Larry Zagoriy
LGC Remodeling is led by Larry Zagoriy, owner and lead contractor. Larry has been building decks, patios, pergolas, and outdoor living spaces across Clark County and the Portland metro for over 15 years, with 100+ completed outdoor living projects.
CSLB License #1106627 — Licensed, Bonded & Insured. Verify license at California State Licensing Board.
Call Larry directly at (360) 356-6008 or email info@lgcremodeling.com for a free on-site estimate. LGC Remodeling, 1616 NW 13th Street, Battle Ground, WA 98604.
