Moisture Management & WRB Installation in Seattle
Your siding is only as good as what’s behind it. We make sure the invisible layer that protects your home actually works — because in Seattle, water always finds a way in if you let it.
WA License #GPGENGC830KD — Verify
Hardie Certified Installer★ 5-Star Rated on Google
Seattle & EastsideGP General Corp builds Pacific Northwest wall assemblies that actually drain — across Seattle, the Eastside, and Snohomish County we detail the weather-resistive barrier, flashings, and drainage plane so water gets out before it reaches framing. WA license GPGENGC830KD, MBAKS member, rated 5.0 on Google. Real installed rates on our pricing page; free written quote after an on-site assessment.
By Paul Gubenya — Owner, James Hardie Certified Installer · WA License #GPGENGC830KD · MBAKS Member · Rated 5.0 on Google · (425) 344-9635
What Homeowners Say
Real reviews from our Google profile — unedited, from real projects.
“We recently had Paul with GP General repair a damaged corner protector and sidings. His estimate was reasonable, his availability was timely, and his job was excellent. Our home hadn’t been re-painted in a while and the paint had considerably faded, yet he was able to match the color perfectly. Now we know who to turn to when in need of another repair work.”
“GP General replaced LP siding on our garage. Paul was very thorough when he came out to do the estimate; he listened to my concerns and was able to work out solutions on the spot. His crew did a great job and were very courteous. They also were careful about cleaning up (I didn’t find any nails!). Really happy with the job and can recommend GP General.”
“I highly recommend GP General Corp for siding replacement. We recently had our wood siding replaced with James Hardie lap siding, and Paul and his team did an excellent job.”
The Invisible Layer That Determines Whether Your Siding Job Lasts
Most homeowners never think about what’s behind their siding. And honestly, you shouldn’t have to. But here’s the thing — the layer between your siding and your house’s bones is what determines whether your siding job lasts 10 years or 40.
Recent project: See HydroGap WRB integrated with custom metal flashing on a Bellevue modern new construction →
I’m Paul, and I run GP General Corp. I’ve been stripping old siding off Seattle-area homes for years, and what I find behind it is usually the reason I got called in the first place. This page is my attempt to explain what a weather-resistive barrier does, why most older homes around here don’t have one that works, and what we do differently so you don’t end up calling someone like me again in a decade.
Ready to talk about your project?
Free walk-through with Paul. No-pressure quote. Honest assessment of what your home needs.
What Is a WRB, and Why Should You Care?
WRB stands for weather-resistive barrier. That’s the industry term. In plain English, it’s the waterproof layer between your siding and the wood structure of your house.
Think of it this way: your siding is the umbrella. It stops most of the rain. But if you’ve ever walked two blocks in a Seattle sideways downpour, you know an umbrella doesn’t catch everything. Wind-driven rain gets past it. Water wicks upward through capillary action at the bottom edge. Condensation forms behind it on cold mornings.
The WRB is the rain jacket underneath the umbrella. When water gets past your siding — and it will — the WRB is the thing that keeps it from soaking into your wall sheathing, insulation, and framing. A good WRB also lets water vapor escape from inside the wall so moisture doesn’t get trapped. It blocks water coming in while letting vapor breathe out. That’s the whole job.
Without a functioning WRB, your siding is basically decorative. It looks great on the outside while water slowly rots your house from the inside.
What We Actually Find Behind Old Siding in Seattle
This is the part of the job most homeowners never see — until it’s too late.
Last month we pulled cedar shingles off a 1978 home in Wallingford. No WRB. None. Just cedar nailed directly onto bare plywood sheathing. The entire north wall was black with mold in every single stud bay.
A 1993 Kirkland home had a single layer of 15-lb felt paper as its only weather barrier. After 30 years, the paper had dried out, torn at every staple hole, and pulled away from the sheathing.
Even a correctly installed WRB can fail if there’s no drainage path behind the siding. This is exactly why we pair every WRB installation with a proper rainscreen drainage system.
If your home was built before 2005 in the Seattle area, there is a very good chance your WRB is either missing, improperly installed, or a product that has degraded past the point of doing its job.
The WRB Products We Use (and Why We Chose Them)
There are dozens of WRB products on the market. We’ve narrowed it down to two that we trust for Seattle’s climate.
This is what goes on every GP General siding project unless the homeowner upgrades. HydroGap looks like regular housewrap, but it has tiny built-in spacer bumps on the surface that create a 1mm drainage gap.
For most Seattle homes, especially those getting James Hardie fiber cement or cedar siding, HydroGap is the right balance of performance and budget.
For homeowners who want the best available protection. This is a peel-and-stick membrane that bonds directly to the sheathing. No staple holes. No seam gaps.
Tyvek HomeWrap is the most common WRB in residential construction. It works fine — when it’s installed correctly. But in Seattle’s climate, we think you need more than “fine.”
The 5 Places Where Moisture Gets Into Your Walls
Water doesn’t sneak in randomly. It follows the same paths on almost every house.
The bottom edge of every window is a shelf that collects water. This is the single most common failure point we see.
A kickout flashing is a small metal diverter that catches water and kicks it out into the gutter. Without it, hundreds of gallons per year pour behind the siding. We see severe dry rot damage at missed kickout locations.
The lowest row of siding is closest to the ground and most likely to stay damp.
Every hole in your wall is a potential entry point.
This is also where a rainscreen gap is critical — it gives trapped moisture an exit path at these tricky junctions.
Not sure where to start?
We’ll come out, look at your siding, and give you a straight answer — even if the answer is “you don’t need us yet.”
How We Install WRB on Every Project
We walk the bare sheathing with a moisture meter, bay by bay.
Damaged OSB or plywood gets cut out and replaced. If there’s rot in the framing, we address that too.
We start at the base of the wall and work upward so each course laps over the one below it — like shingles.
Every window and door gets a sill pan membrane, jamb flashing, and a head flashing that ties into the WRB above.
Each pipe, vent, hose bib, and wire entry gets individually flashed with compatible flashing tape.
Before any siding goes up, we inspect the complete WRB installation. If we’re installing a rainscreen system, the furring strips go on after this inspection passes.
What Happens When Contractors Skip This Step
Proper WRB installation adds roughly $1,500 to $3,000 to a siding project. Skipping it saves that money on day one. But a typical Seattle dry rot repair runs $8,000 to $15,000.
The $2,000 you “saved” by skipping the WRB turns into $15,000 or more in repairs within a decade.
Moisture Management — Across Seattle Neighborhoods
Common Questions About Moisture Management in Seattle
Does my house already have a WRB?
Maybe. Homes built before the mid-1990s often have no WRB at all. During any siding replacement project, we assess the existing WRB as part of our standard process.
Can you install a new WRB without replacing the siding?
Not really. The siding has to come off, the WRB goes on the bare sheathing, and then the siding goes back up.
How much does proper WRB add to a siding project?
Roughly $1,500 to $3,000 on a typical Seattle-area home for our standard HydroGap drainable housewrap installation.
Is WRB required by building code in Seattle?
Yes. The Washington State Building Code requires a weather-resistive barrier behind all exterior cladding. Our installations exceed code requirements.
What is a WRB and why does it matter more than the siding?
WRB stands for weather-resistive barrier — the sheet material (house wrap or self-adhered membrane) that goes between your framing and your siding. It’s the actual water barrier on your home. The siding just protects the WRB from UV and physical damage. If the WRB fails, your walls rot regardless of how nice your Hardie or cedar looks. In Seattle’s climate, the WRB detail is more important than the material choice. See how we install Hardie over a proper WRB.
How long does Tyvek HomeWrap last in Seattle?
Tyvek is rated for 4 months of UV exposure during construction. Once covered by siding, it should last 30+ years — if installed correctly. “Correctly” means: laps facing downhill, properly taped seams, window flashing integrated before siding goes up, no reverse-laps at penetrations. Most Seattle WRB failures are installation errors, not material failure.
What’s the difference between Tyvek, ZIP System, and liquid-applied WRB?
Tyvek (DuPont): most common mechanically-fastened house wrap. Good in most applications. $0.25-0.35/sq ft.
ZIP System (Huber): integrated sheathing + WRB in one panel. More airtight, faster install. $1.20-1.80/sq ft.
Liquid-applied (Prosoco, Henry Blueskin): rolled or sprayed membrane that fully bonds to sheathing. Best moisture protection but 3-4x the cost of Tyvek. Best for high-performance or hillside homes. We use all three depending on the project.
Do I need a rainscreen behind my siding?
In Seattle? Effectively yes. Rainscreen systems create a 3/8″ ventilated cavity behind the siding that lets bulk water drain, equalizes pressure during wind-driven rain, and dries the back of the cladding. Mandatory for cedar (without it, cedar fails in 8-12 years). Highly recommended for Hardie (doubles the life of the WRB). Adds about $3-5 per sq ft to the project.
What’s kick-out flashing and why does every contractor miss it?
Kick-out flashing is the piece of metal that directs water AWAY from your wall where your roof meets a wall. Without it, all the water from half your roof runs down behind your siding. It’s prevented by a piece of bent metal that takes 5 minutes to install — and missing it causes 90% of the wall rot we see in Seattle. Every bent-metal detail like this is where bad contractors cut corners — and where a good Seattle siding contractor earns the money. See examples of what happens when it’s missed.
Can I install new siding over old WRB?
Sometimes, but rarely recommended. If your current Tyvek is 30 years old, there’s no way to know if it’s still watertight at every penetration. And you can’t test it — you’d have to open the wall. Our standard practice: replace WRB on every re-side. Adding a few thousand dollars now is infinitely cheaper than redoing the project in 15 years.
What causes WRB failure in Seattle specifically?
Three things, ranked by frequency: (1) Bad installation at windows — head flashing not integrated with WRB above. (2) UV exposure during a long construction delay. (3) Poor laps or reverse-laps where water can get behind the barrier. Material failure of modern housewraps is rare. Install failure is common.
What is the difference between Tyvek and a drainable WRB like HydroGap?
Standard Tyvek is a flat housewrap that blocks bulk water but provides no drainage path; HydroGap is a drainable WRB with built-in 1mm spacers that create a continuous drainage cavity behind the siding. In Seattle’s climate, the drainage cavity is what makes the difference between siding that lasts 10 years and siding that lasts 30. Plain Tyvek relies on the siding itself to never let water through — an unrealistic standard for any cladding over time. HydroGap (or DuPont’s Tyvek DrainWrap) accepts that water will get past the cladding occasionally and gives it a path to drain out the bottom and dry. Our standard Seattle install uses HydroGap Drainable on every Hardie, cedar, and LP project.
How long does a WRB last behind siding before it needs replacement?
A correctly installed WRB lasts 30–50 years behind siding in Seattle — longer than most cladding materials it sits behind. The failure modes for WRB are UV exposure during construction (Tyvek degrades after 4–9 months in sunlight, HydroGap after 12 months), nail and fastener perforations that aren’t self-sealing, and improper laps at horizontal seams. A WRB installed shingle-style with all penetrations flashed and the cladding installed within the UV exposure window will outlast everything else on the wall. We don’t replace WRB on its own — if you’re re-siding, it’s coming off with the old cladding regardless.
Can rainwater really get behind siding even with a good WRB?
Yes — that’s the entire reason the WRB exists. No siding system is 100% waterproof, and the WRB is the secondary drainage plane that catches and drains what gets past the cladding. Wind-driven Seattle rain pushes water past the back of lap siding, behind butt joints, around windows, and through any caulk failure. A flat Tyvek wrap will bounce most of it but leaves any trapped water sitting against the sheathing. A drainable WRB plus a vented rainscreen cavity gives that water somewhere to go — out the bottom of the wall through a continuous gap. That’s why we install HydroGap Drainable + 3/8”–3/4” rainscreen furring on every Seattle re-side.
Not Sure What’s Behind Your Siding?
We’ll assess your home’s current weather protection and give you an honest recommendation.
GP General Corp · WA License #GPGENGC830KD — Verify · Seattle, WA
Moisture management WRB — see the work
Real projects from our crew — photos, specs, and the problems they solved.