Seattle Two Different Materials, One Big Decision
If you're replacing siding in Seattle, you've probably run into two names over and over: James Hardie and LP SmartSide. Both get marketed as upgrades over vinyl, and both look good in a showroom. But they are not variations on the same product — they're built from fundamentally different materials, and that difference matters more here than almost anywhere else in the country. Seattle's combination of near-constant drizzle, driving winter rain off the Sound, salt-laden air in neighborhoods close to Puget Sound, and a moss season that can run eight months out of the year puts exterior building products through a specific kind of stress test.
This page lays out what each product actually is, how they hold up under King County weather, and why we standardized our installs on James Hardie fiber cement instead of offering both. We're not going to tell you LP SmartSide is junk — it isn't, and plenty of houses around the region wear it without major issues. What we will do is walk through the real trade-offs so you can make an informed call.
What James Hardie Actually Is
James Hardie siding is fiber cement: a mix of Portland cement, sand, and cellulose fiber pressed into boards and panels, then cured. It contains no wood. That's the core fact that drives most of the differences below — fiber cement doesn't rot, doesn't feed insects, and doesn't swell or delaminate when it gets wet, because there's no organic wood fiber for moisture to break down.
The HZ5 Engineering
Hardie's HZ5 product line is engineered specifically for climates like ours — freeze-thaw cycles, prolonged damp exposure, and moisture-driven mold and mildew pressure. It's the version we install on every job in the Seattle area, not the HZ10 line built for hot, dry southern climates.
ColorPlus Factory Finish
Most Hardie boards we install come with the ColorPlus finish — a baked-on, multi-coat finish applied in a controlled factory environment rather than painted on-site after installation. It resists fading and holds up to UV exposure far longer than field-applied paint, and it comes backed by its own separate finish warranty.
What LP SmartSide Actually Is
LP SmartSide is engineered wood siding — strand board made from wood fiber, resin, and wax, treated with a zinc borate preservative and coated with a resin-saturated overlay to resist moisture. It's a genuine improvement over old-school OSB siding products from decades ago, and it costs less than fiber cement. LP has also improved the product's moisture engineering significantly over the years.
But it's still wood at its core. That's not a flaw — it's just a fact that changes how the product needs to be installed, sealed, and maintained, especially in a climate that stays wet for most of the year.
How Each Product Handles Seattle's Climate
Moisture and Rot Resistance
This is the big one. Seattle doesn't get hit with brief, heavy storms and then dry out — it gets sustained, driving rain for days at a stretch, especially in the wetter months, plus fog and dew that keep exterior surfaces damp even between rain events. Fiber cement doesn't care. It's inorganic, so prolonged dampness against the board doesn't create a path to rot.
Engineered wood siding is more installation-sensitive in wet climates. LP SmartSide's factory treatments protect the face of the board, but the vulnerable points are the cut edges, seams, and any spot where the factory coating gets breached during installation — nail heads, trim joints, corner details. If those aren't sealed correctly and maintained over time, moisture can work its way into the wood fiber core. In a hot, dry climate that's a minor risk. In a Puget Sound climate with months of standing damp, it's a much bigger one.
Moss and Mildew
Anyone who's owned a home in King County knows moss doesn't stay on the roof — it creeps onto north-facing siding, fence lines, and anywhere shade and moisture linger. Fiber cement's non-organic surface doesn't feed mold or mildew growth the way wood-based products can if organic buildup is left to sit. Surface growth on Hardie is a cleaning issue; on wood-based siding, prolonged organic growth against the surface can become a moisture and coating issue too.
Salt Air
Homes closer to the Sound, in neighborhoods like West Seattle, Alki, or along the Duwamish waterfront, deal with a low but steady dose of salt-laden air. Salt exposure accelerates the breakdown of fasteners, caulking, and coatings on any exterior product. Fiber cement's cement-based composition isn't affected by salt the way organic materials and some coatings are, and Hardie's factory finish is built to hold up to coastal exposure.
Fire Resistance
Fiber cement is non-combustible — it won't ignite or contribute fuel to a fire. Engineered wood siding, even with fire-retardant treatments, is still a wood product and carries a different risk profile than cement-based siding. Wildfire smoke and occasional dry-season fire risk have become a more regular late-summer concern even on the wet side of the state, and it's a factor more Seattle homeowners are weighing than they were a decade ago.
Installation Sensitivity
Both products perform close to their design specs only when installed correctly — but the margin for error is different. LP SmartSide's performance depends heavily on proper sealing at every cut edge, joint, and fastener penetration, done consistently across the whole house, and maintained over the life of the siding. Miss a few details, or let caulking fail years down the road without recaulking, and you've created entry points for moisture in a product whose core is moisture-sensitive.
Hardie is also installation-sensitive — manufacturer specs on fastening, clearances, and joint treatment matter and get skipped by unlicensed crews all the time — but because the board itself doesn't rot, an installation gap is far less likely to turn into a structural problem down the road. That's a meaningful difference in a market where reliable, spec-trained crews aren't always easy to find.
Side-by-Side Comparison
| Factor | James Hardie Fiber Cement | LP SmartSide |
|---|---|---|
| Core material | Cement, sand, cellulose fiber | Engineered wood strand |
| Combustibility | Non-combustible | Combustible (treated) |
| Moisture vulnerability | Low — inorganic core | Moderate — depends on seal integrity |
| Finish | ColorPlus factory finish available | Factory primed or pre-finished options |
| Typical upfront cost | Higher | Lower |
| Manufacturer warranty (material) | Long-term, transferable | Long-term, transferable |
| Maintenance driver | Periodic cleaning, recaulk trim joints | Recaulking, coating upkeep, edge sealing |
Cost Factors to Weigh, Not Just Sticker Price
LP SmartSide almost always wins on upfront material cost. That's real and we won't pretend otherwise. But the fair comparison isn't just the install invoice — it's the total cost over the years you own the house.
| Cost Factor | What to Consider |
|---|---|
| Upfront material + install | LP SmartSide typically lower; Hardie typically higher |
| Repainting / refinishing | ColorPlus-finished Hardie goes far longer between repaints than field-painted wood siding |
| Caulk and seam maintenance | Ongoing on both products, but the stakes are higher on wood-based siding if skipped |
| Resale / buyer perception | Fiber cement is widely recognized by Seattle-area buyers and appraisers as a premium, low-maintenance material |
| Insurance considerations | Non-combustible materials can factor into some homeowner insurance conversations |
What to Ask Any Contractor Before You Sign
- Are they installing to the manufacturer's written spec for our specific climate zone (HZ5 for fiber cement), not a generic national spec?
- Do they carry manufacturer certification or training on the specific product line they're installing?
- What's covered by the material warranty versus the workmanship warranty, and is either transferable if you sell the house?
- How are seams, corners, and penetrations (vents, lights, hose bibs) detailed and sealed?
- Will they show you the flashing and moisture-barrier plan before siding goes up, not just after?
- What ongoing maintenance will the product require, and will they put that in writing?
Why We Only Install James Hardie
We made a decision to stop offering multiple siding systems and standardize on one: James Hardie, specifically the HZ5 product line with ColorPlus finish. It's not because LP SmartSide is a bad product on paper — it's because of what we've learned installing and servicing exterior products across King County for years. In a climate defined by driving rain, long moss seasons, and salt exposure near the water, we wanted a material where the core itself isn't the thing standing between a good outcome and a moisture problem. Fiber cement gives us that. It also gives homeowners a factory finish that holds its color for years, a transferable warranty that adds real value at resale, and a non-combustible product that simplifies one more variable in an unpredictable climate.
We'd rather do one product exceptionally well, trained and certified to spec, than offer a menu of options and hope every crew gets every detail right on all of them.
If you're weighing siding options for a home in Seattle or elsewhere in King County, we're happy to walk your specific house, look at your exposure, and give you a straight answer — including where fiber cement is or isn't the right call for your budget. Reach out for a free, no-pressure estimate and we'll go through it in person.