Seattle Siding LP SmartSide shows up on a lot of bid sheets in the Puget Sound area, and it's not a bad product on paper. It's an engineered wood siding — strand-based substrate treated with resin and zinc borate, then coated — and it installs faster and lighter than fiber cement. If you've gotten a quote that includes it, you deserve a straight answer on why our crews don't put it on Seattle homes. This isn't about trashing the product. It's about what happens to wood-based siding over years of King County weather, and why we standardized on something else.
What LP SmartSide Gets Right
To be fair to the product: SmartSide is engineered to resist the fungal decay that plagues old-school hardboard siding from the 1980s and 90s. The zinc borate treatment and resin binders are a real improvement over what came before it, and LP backs it with a warranty. It's also lighter than fiber cement, which can shave labor time and cost on a job. For a lot of markets — drier climates especially — it performs reasonably well when installed and maintained correctly.
Why We Don't Put It on Homes Here
Our reservation isn't about the factory product itself — it's about how wood-based siding behaves once it's on a wall in a marine climate for fifteen, twenty, thirty years. A few things drove our decision:
It's Still Wood at the Core
Strand board is engineered, but it's still cellulose. Any wood-based siding depends on cut edges, seams, and fastener penetrations staying properly sealed and primed for the life of the product. Miss a caulk joint, let a butt seam open up, or have a roofer nick the bottom course during a re-roof, and you've created a path for moisture to reach untreated wood fiber. Once that happens, the clock starts on swelling, delamination, and soft spots — and by the time you see it from the ground, the damage is usually already inside the wall.
Seattle's Climate Doesn't Give Wood Siding a Break
This is the core of it. Seattle sits on Puget Sound, which means salt-laden air working on fasteners and trim year-round, plus driving rain off the water that hits siding at an angle most siding details weren't drawn for. Add King County's long, gray moss season — where north-facing walls and anything shaded by a big Douglas fir stay damp for weeks at a stretch — and you've got close to the worst-case environment for a product that needs its protective coating and sealed edges to stay intact. Fiber cement doesn't care about any of that, because there's no wood fiber for moisture to find.
Maintenance Becomes the Homeowner's Job
SmartSide's performance is tied directly to caulking and repainting on schedule — miss a cycle or two and you're exposed. Most homeowners don't track a strict recaulk-and-repaint calendar, and in a rainy climate that gap matters more than it would somewhere dry. We'd rather install something that doesn't put that much weight on maintenance discipline to avoid moisture problems.
Installation Sensitivity
Wood-based siding is less forgiving of installation shortcuts — clearance from grade, flashing at every horizontal transition, gap sealing at trim — because the consequence of a mistake is decay, not just a cosmetic issue. We hold every crew to a strict install spec regardless of product, but we'd rather that spec be protecting a material that isn't organic in the first place.
Why We Install James Hardie Instead
James Hardie fiber cement is sand, cement, and cellulose fiber cured into a dense, non-combustible board — there's no wood fiber left to decay, swell, or feed moss and mildew. Hardie's HZ5 product line is specifically engineered for climates like ours: freeze-thaw cycling, sustained damp, and coastal moisture exposure. The ColorPlus factory finish is baked on under controlled conditions, which holds color and resists the fading and touch-up patchwork you get with field-applied paint, and it carries a real transferable warranty that follows the house to the next owner.
None of that means Hardie is maintenance-free — it still needs proper caulking at joints and periodic repainting eventually. But the failure mode if you fall behind is cosmetic, not structural. That's the trade-off that matters most in a market with our rainfall and our moss pressure.
The Bottom Line
LP SmartSide is a legitimate product, and in the right climate with disciplined maintenance it can hold up fine. We just don't think a wood-fiber product with a maintenance-dependent moisture barrier is the right call for homes exposed to Puget Sound salt air, sideways rain, and months of shade and moss every year. Fiber cement removes that risk at the source, which is why it's the only siding we put our name behind.
Comparing the Two
| Factor | LP SmartSide | James Hardie Fiber Cement |
|---|---|---|
| Core material | Engineered wood strand | Cement, sand, cellulose fiber |
| Moisture vulnerability | Decays if seals/coating fail | Non-organic, won't rot |
| Combustibility | Combustible (wood-based) | Non-combustible |
| Finish | Field-primed, needs repainting | Factory ColorPlus, longer color life |
| Maintenance dependency | High — coating/caulk critical | Lower, mainly cosmetic upkeep |
If you're weighing siding options for a Seattle-area home and want a straight comparison based on your house, your exposure, and your budget, we're happy to walk the property with you and put together a free, no-pressure estimate.