Seattle Two Different Materials, One Big Decision
If you're replacing siding in Seattle, you've probably come across both James Hardie fiber cement and LP SmartSide engineered wood. They get compared often because they occupy similar price territory and both promise an upgrade over vinyl or aging cedar. But they are fundamentally different materials with different long-term behavior, especially in a climate like ours — salt-laden air off Puget Sound, months of driving rain, and a moss season that seems to start earlier every year.
This isn't a knock on LP as a company. LP SmartSide is a legitimate, engineered product that has improved a lot over the decades. We simply don't install it, and we think King County homeowners deserve a clear, honest explanation of why — not marketing spin from either side.
What LP SmartSide Is
LP SmartSide is an engineered wood product: strand-based substrate (similar in concept to OSB) that's treated with zinc borate for insect and fungal resistance, then coated with a resin-saturated overlay and primed at the factory. It's lighter than fiber cement, easier to cut without special dust precautions, and holds paint well when new.
Its core vulnerability is still wood. The strand substrate is engineered to resist moisture better than raw lumber, but it is not moisture-proof. Cut edges, seams, and fastener penetrations need to be properly sealed and kept sealed for the life of the siding. In a climate that delivers sustained wet weather for much of the year, that maintenance margin matters — a failed caulk joint or a scratch left unprimed doesn't just peel, it can let moisture into the substrate itself, and swollen or delaminating engineered wood doesn't shrink back down once it dries.
What James Hardie Fiber Cement Is
James Hardie siding is cement, sand, and cellulose fiber, cured into a rigid board. There's no wood substrate to swell, rot, or feed fungal growth. It's non-combustible, which matters more each year as wildfire smoke and ember exposure become part of the regional conversation even on this side of the Cascades. It resists moss and mildew staining far better than wood-based products, which is a real advantage under our shaded, damp eaves and north-facing walls where moss thrives.
James Hardie also makes a climate-specific HZ10 product engineered for the Pacific Northwest's wet weather pattern, and finishes it with the ColorPlus factory-baked finish rather than relying entirely on field-applied paint. That factory finish carries its own multi-year warranty against fading and peeling, which shifts a lot of the durability burden off the installer and onto a controlled manufacturing process.
Side-by-Side Basics
| Factor | James Hardie Fiber Cement | LP SmartSide |
|---|---|---|
| Core material | Cement, sand, cellulose fiber | Engineered strand wood |
| Combustibility | Non-combustible | Combustible (wood-based) |
| Moisture behavior | Does not swell or rot | Can swell/delaminate if seals fail |
| Finish | Factory-baked ColorPlus available | Factory-primed; often field-painted |
| Maintenance sensitivity | Low once installed to spec | Higher — seams/cuts need ongoing sealing |
Where LP SmartSide Genuinely Makes Sense
We'd be doing you a disservice if we pretended there's no case for it. LP SmartSide is lighter, which can simplify installation on certain structures. It takes fasteners easily and is a familiar product for crews used to working with wood siding profiles. For a homeowner on a tighter budget who understands and accepts the maintenance commitment — regular inspection of seams and caulking, prompt touch-up of any damage — it can perform reasonably well, particularly in drier climates.
Seattle isn't a drier climate. Between the rain totals, the marine humidity, and the salt air that reaches well inland from the Sound on windy days, the maintenance window that keeps engineered wood siding performing well is narrower here than in most of the country. That's the trade-off homeowners need to weigh honestly, not a defect in the product itself.
Why We Standardized on Hardie
We made a decision, several years back, to install only James Hardie fiber cement. It's not because every wood-based or composite product is bad — it's because after years of doing this work throughout King County, we found that fiber cement, installed correctly, holds up to our specific weather pattern with the least ongoing homeowner burden. No substrate swelling to worry about, strong moss and mildew resistance, a non-combustible core, and a factory finish backed by a substantial transferable warranty. When we put our name behind an installation, we want the material underneath it to be the reason that job still looks right in twenty years, not a maintenance schedule the homeowner has to stay on top of.
If you're weighing siding options for a home in Seattle or elsewhere in King County, we're happy to walk through what James Hardie would look like on your specific house — colors, product lines, and what correct installation involves. Reach out for a free, no-pressure estimate.