Roofing & Exterior
Dry Underneath, Not Just Covered
Waterproof deck surfaces and dry-below systems for the Northwest: proper membranes, real slope, drainage and under-deck ceilings that turn the space beneath an elevated deck into dry, usable square footage.
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Signs to watch
Is this you?
It rains through the deck onto the patio below
An open-board deck drips everything that lands on it straight through, so the space underneath is only usable when it isn't raining — which in the Northwest is a narrow window. A dry-below system captures and drains that water instead.
You want a real room under the deck
A covered, drained space beneath an elevated deck becomes an outdoor room you use in October — dry seating, storage, a hot tub — instead of a muddy gap. It's usable square footage most homes are leaving on the table.
The waterproof surface is failing or leaking
Coated and membrane deck surfaces have seams, penetrations, and slope that all have to be right, and when one lets go water gets under the system and into the framing. Ponding, blisters, or stains below are the signs it's time to look.
Stains or drips where the deck meets the house
Water tracking in at the ledger, a post penetration, or a drain is the quiet version of the same problem, and it's rotting framing you can't see. Finding the true entry point is the actual skill — the drip is rarely under the leak.
Your options
Keep the water on top of the system, moving where you want it
For the surface itself, we install waterproof membrane and coated deck systems with the slope, seams, and flashing detailed to shed water rather than trap it. For dry-below, we build the drainage layer that hangs under an elevated deck — a sloped membrane or panel system with gutters and downspouts — plus a finished under-deck ceiling, so the space beneath stays dry and usable. Every waterproof detail lives or dies on three things: real slope so water can't pond, sealed penetrations at posts and rails and drains, and flashing at the ledger treated like the roof detail it actually is. When there's already a leak, we diagnose the entry point before we quote a fix, because guessing wastes your money on the wrong repair.
The method
How we do it
- 01
Diagnose slope, penetrations, and any leak
We check slope and drainage, inspect penetrations and ledger flashing, and trace any active leak to its real entry point — photographing everything before we quote.
- 02
Fixed-price quote on the right system
You approve the number before work starts, with the membrane or dry-below system matched to your deck and how you want to use the space below spelled out plainly.
- 03
Install, seal, and water-test
Membrane or drainage layer set to real slope, penetrations and ledger sealed and flashed, drainage plumbed, under-deck ceiling finished if specced — then a water test before final walkthrough.
Straight numbers
What waterproofing runs
A waterproof surface on an existing deck is one range; a full dry-below system with drainage, gutters, and a finished under-deck ceiling is a larger one, and diagnosing and repairing an existing leak depends on how far the water traveled. Deck size, height, slope corrections, and finish level move the number most. We quote fixed prices, and if a leak has already reached the framing we'll show you what we found in photos before pricing the repair.
Where we do this work
Waterproof Decks & Dry-Below Systems: straight answers
Can you make the space under my existing deck dry?
Often yes — an under-deck drainage system hangs a sloped membrane or panel layer beneath the joists, catches everything that comes through the boards, and channels it to gutters and a downspout. Add a finished ceiling and you've turned a drippy gap into a dry, usable room. Whether it fits depends on the deck's height and framing, which we check in person.
My waterproof deck is leaking — can it be fixed, or does it all come off?
It depends where and why it's failing. Membrane and coated systems leak at seams, penetrations, and slope problems, and often the fix is targeted once we find the real entry point. But if water has been getting under the system for a while, it may have reached the framing — so we diagnose first and show you what we find before quoting, rather than guessing.
Why does slope matter so much?
Because a waterproof surface only works if water leaves it. Any flat or reverse-sloped spot ponds, and standing water finds every seam and penetration eventually. Getting real, consistent slope built into the surface and the drainage layer is the single detail that separates a system that stays dry from one that leaks in a few seasons.
Does the framing underneath need to be different for a waterproof deck?
Sometimes. A waterproof surface and a dry-below system add weight and change how water moves, and the framing, slope, and drain locations all have to suit that. Where the structure or the details call for it, engineering and permits may apply, and those requirements vary by jurisdiction — we check yours and build to it rather than assume.
Get the waterproof decks & dry-below systems conversation started.
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