Commercial Deck Waterproofing · CSLB #1060736
Deck Waterproofing for California Commercial & Multifamily Properties
Deck waterproofing is what keeps water out of the structure — and, on a deck over living space, out of the rooms below. It’s all we do here: wood-framed, composite and Trex, and rooftop decks for California’s apartment communities, condominiums, HOAs, and hotels. Built as an integrated system — membrane, flashing, drainage, and joist protection together — not a paint-on coating that fails at the seams.
- CSLB #1060736 Licensed California contractor
- 9+ yrs Waterproofing commercial decks
- SB 721 / 326 Built to pass inspection
- Commercial Multifamily, HOA & mixed-use only
01 Why it matters
The waterproofing is the only thing between the deck and the structure
On a deck, the waterproofing is the layer standing between the walking surface and the wood underneath — and on a rooftop deck or a deck over living space, between the deck and the rooms below. When it fails — a cracked coating, unprotected joists, water passing between open composite boards — it goes straight into the framing, or straight into the ceiling below.
In California, every elevated deck is an exterior elevated element, inspected under SB 721 (rentals) or SB 326 (HOAs) every six to nine years. Water intrusion is exactly what those inspections look for — and a deck with failed or missing waterproofing is the most common reason an assembly gets flagged.
Deck waterproofing done right — a continuous membrane or under-deck system, protected joists, correct slope, and flashing tied into the wall — stops that failure before it starts and clears the inspection cycle with nothing to remediate. Getting the waterproofing right is the cheapest way to protect the whole deck and everything under it.
By the time water shows on the ceiling below, it’s already been in the framing for years. The waterproofing is what buys you those years — or costs them.
02 The D&B difference
What proper deck waterproofing actually includes
We waterproof the deck as one integrated assembly — surface, membrane, flashing, drainage, and joist protection built together by one CSLB-licensed crew under one warranty. That’s what separates real deck waterproofing from a coating contractor rolling product over unprotected boards.
A system, not a coating
The membrane is integrated with the flashing, the drainage, and the wall’s weather-resistive barrier — so there are no seams at the wall, posts, or ledger for water to find. Waterproof deck coatings on their own don’t fix the interfaces where decks actually leak.
Wood, composite & rooftop decks
Any deck substrate. On a solid-surface deck we install a membrane; on an open-board wood or composite/Trex deck we protect the joists and — where there’s space below to keep dry — add an under-deck drainage system.
Built to pass inspection, and keep the space below dry
Detailed to hold up through the SB 721 / 326 inspection cycle and documented for the compliance file — and, over living space, built as a true waterproof deck, not just a drainage tray. One vendor accountable, not a chain of subcontractors.
03 How a project runs
How to waterproof a deck — start to finish
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01
Assessment
We inspect the surface, flashing, drainage, and joists, note whether the deck is over living space, take moisture readings, and check whether water is already in the structure — then choose the system.
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02
Prep & repair
We remove failed coatings or boards as needed, repair wood rot and joists, apply joist protection, and correct the slope to drain.
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03
Membrane or under-deck system
On a solid-surface deck we install a continuous membrane tied into flashing at the wall, posts, and ledger. On an open-board deck we protect the framing and, to keep the area below dry, install an under-deck drainage system.
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04
Surface & drainage
We finish with the specified surface — traffic/deck coating, pedestal pavers, or re-decking — and verify positive drainage, and the under-deck ceiling finish where applicable.
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05
Documentation & handoff
We walk the deck with you and hand over as-built documentation for the SB 721 / 326 compliance file.
04 Scope
What’s included in a D&B deck waterproofing job
Complete deck waterproofing — from substrate repair through a sealed, traffic-rated deck, handled in-house by one licensed crew so there’s no seam between trades to fail later.
- All deck substrates — wood-framed, composite / Trex, and rooftop / roof decks
- Continuous waterproofing membrane (fluid-applied or sheet) integrated with flashing and the weather-resistive barrier
- Under-deck drainage systems — keep the space, ceiling, and area under the deck dry
- Waterproofing a deck over living space — a true waterproof membrane rated for habitable space below
- Joist protection — joist tape and flashing so water off the boards doesn’t rot the framing
- Slope correction so water drains off the deck, not into it
- Deck surfaces — traffic/deck coatings, pedestal pavers, or re-decking
- Rooftop / roof-deck waterproofing over occupied space
- Deck repair and waterproofing combined — rot and joist repair before the membrane
- As-built documentation for the SB 721 / 326 compliance file
Systems we install: fluid-applied (liquid) membranes · sheet membranes · deck / traffic coatings · pedestal-paver assemblies · under-deck drainage systems — matched to your substrate and whether there’s living space below
05 Investment
How much deck waterproofing costs
Every deck is quoted after an on-site assessment — but this rate reflects typical recent commercial and HOA work and helps you budget deck waterproofing early.
What drives the number
- Deck substrate and its condition — wood, composite, or rooftop, and how much repair it needs
- Membrane on a solid-surface deck vs. joist protection + under-deck drainage on an open-board deck
- Whether the deck is over living space or a rooftop over occupied rooms — adds scope
- Extent of joist and framing repair
- Deck surface selected — coating vs. pavers vs. re-decking
- Number of decks and site access across the building
Ranges reflect typical recent commercial and HOA work. Sealing over a sound existing surface is the cost-effective route where the substrate allows; a failed or over-living-space deck needs full prep and a rated membrane. Final price follows a site assessment — request a free estimate, no obligation.
06 Project example
A recent deck waterproofing project
An apartment community in the Central Valley had a large elevated wood-framed deck — the shared common area outside the clubhouse — failing quietly: the surface coating had cracked, the joist tops were unprotected, and water was working its way into the framing. D&B stripped the failed coating, repaired and sistered the decayed joists, taped the joist tops so the boards could no longer feed water into the frame, installed a continuous membrane tied into flashing at the building wall and posts, and finished with pedestal pavers sloped to drain. The deck reopened as a safe common area and went into the property’s SB 721 file with no remediation findings.
The deck looked fine from the top — the damage was down in the joists. They caught it, saved the framing, and waterproofed it properly instead of coating over the rot. Regional Property Manager · Central Valley apartment community
07 Client feedback
What property managers say
Our wood decks had rot starting under the coating and unprotected joists. D&B repaired the framing, taped the joists, and did the membrane and flashing properly — not just a coat of paint over the problem.
We have composite decks over a covered patio, and water was coming right through between the boards. They installed an under-deck drainage system and the space below finally stayed dry.
Our rooftop deck was leaking into the units below. One crew handled the repair, membrane, and flashing, documented it for our SB 326 file, and the job came in on budget.
08 FAQ
Deck waterproofing questions
How do you waterproof a deck?
Five steps: assess the surface, flashing, drainage, and joists; prep and repair the substrate and framing; correct the slope; install a continuous membrane (or, on open-board decks, protect the joists and add an under-deck system); then apply the deck surface. The membrane, flashing, and joist protection — not the coating alone — are what actually keep water out.
How do you waterproof under a deck and keep the space below dry?
Two different situations. To dry out an open area beneath an elevated deck, we install an under-deck drainage system — panels or troughs below the boards that channel water off to a gutter, keeping the under-deck ceiling and space dry. When the deck is over living space, that isn’t enough on its own: waterproofing a deck over living space means a true waterproof membrane on a solid substrate, rated for habitable rooms below.
How do you waterproof a rooftop or roof deck?
A rooftop deck is a roof first and a deck second — so roof-deck waterproofing starts with a continuous membrane detailed into every penetration, drain, and wall, then a traffic-rated surface or pedestal pavers over it. Waterproofing a roof deck over occupied space is the highest-stakes deck we do, and we document it for the SB 721 / 326 file.
Can a composite or Trex deck be waterproof?
Not on its own. Composite and Trex boards resist moisture and shed water off the top, but water still passes between the boards to the framing and whatever’s below — so a composite deck isn’t a waterproof deck by itself. We make it one either with an under-deck drainage system beneath the boards, or with a waterproof membrane on a solid substrate under a composite finish. That’s the honest version of “Trex waterproof decking.”
How do you waterproof a wooden deck?
On a wood deck we repair any rot in the boards, joists, and ledger first, apply joist protection so water off the surface can’t rot the framing, then install a membrane integrated with flashing at the wall and posts, with correct slope to drain. Waterproof wood for decks starts with protecting the framing, not just sealing the surface.
What’s the best waterproofing for a deck?
There’s no single best deck waterproofing product — the right system depends on the substrate and whether there’s living space below. We match fluid-applied membranes, sheet membranes, deck coatings, pedestal pavers, or under-deck drainage to your deck, rather than using one coating for everything. That’s what makes the best waterproofing for decks: the right system for that deck, installed as one assembly.
Do you protect the deck joists?
Yes. Waterproofing decking joists — taping or flashing the tops of the joists — keeps water that gets between the boards off the framing, which is where wood decks quietly rot. On any deck we waterproof, joist protection is part of the scope, not an add-on.
Are you deck waterproofing contractors near me in California?
We’re CSLB-licensed deck waterproofing contractors (#1060736) serving the Bay Area, Central Valley, and Sacramento. Instead of searching for deck waterproofing contractors near you, you can call one contractor who handles the repair, membrane, flashing, joists, and surface in-house.
09 Start here
Start your deck waterproofing with a free estimate
Send us photos or tell us about your decks — we’ll assess the substrate, flashing, joists, and drainage and give you a free estimate covering system, timeline, and cost. No obligation.
CSLB #1060736 · 9+ years · Insured & Bonded · Serving the Bay Area, Central Valley & Sacramento
