Ferndale Siding Composite Decking Built for Life on the Spit
Semiahmoo sits out on a narrow spit between Semiahmoo Bay and Drayton Harbor, right at the edge of Blaine and the Canadian border. Water sits on more than one side of most properties out here, which means homes get salt-laden air and wind-driven rain from multiple directions rather than one prevailing exposure. That's a harder environment for an outdoor deck than almost anywhere else in Whatcom County, since a deck has no wall or roofline to shield it from any of it.
Composite decking has become the material most homeowners on the spit land on, and for good reason — but "composite" covers a wide range of products, and not all of them hold up the same way out here. This page covers what a Semiahmoo deck actually needs from its decking material, what a correct composite installation involves, and how our process works for a project on this specific stretch of coastline.
What This Climate Does to a Deck
Salt Air From More Than One Direction
Because Semiahmoo has water on more than one side, salt-laden air doesn't come from a single prevailing direction the way it might a few miles inland. It reaches a deck from multiple angles across most of the year. Salt accelerates corrosion in exposed fasteners, brackets, and railing hardware, and it also degrades lower-grade finishes and coatings faster than a more sheltered inland site would. A fastener that starts corroding loses holding strength well before it looks obviously bad, which matters on a structure people walk and stand on.
Driving Rain and Open Wind
With very little to break the wind out on the spit, rain doesn't just fall straight down here — it gets pushed sideways with real force, driving up under railings, into ledger connections, and between deck boards that aren't gapped correctly for it. A decking surface that sheds water fine on a calm day can still trap moisture the moment wind gets involved, and on Semiahmoo, wind is involved more often than not.
A Moss Season That Runs Most of the Year
Mild temperatures and near-constant humidity give moss and mildew a long growing season across this part of Whatcom County, and a waterfront location like Semiahmoo doesn't shorten it. Shaded and north-facing deck areas are usually first to show it, since horizontal surfaces hold water longer than a vertical wall and stay damp between rain events. Any decking material with surface porosity gives moss something to grip onto.
Why Composite Fits This Environment
Composite decking is made from a blend of wood fiber and plastic, which gives it more resistance to moisture, staining, and insect damage than solid wood without the higher cost or installation sensitivity of cellular PVC. That middle position is exactly why it's become the most common decking choice for homes on the spit — most homeowners here want something that performs well against salt air and driving rain without the ongoing sealing schedule that wood demands or the premium cost of full PVC.
Not every composite product is engineered the same way, though, and the difference matters more in a climate like this one than it would somewhere drier and more sheltered.
Capped vs. Uncapped Composite
Capped composite boards have a plastic shell wrapped around the wood-fiber composite core, sealing it off from direct moisture contact. Uncapped composite is the core material alone, with no protective shell. In a salt-air, high-moisture environment like Semiahmoo, that cap layer is doing real work — it's the difference between a board that needs occasional washing and one that gradually absorbs moisture at exposed surfaces, fades unevenly, and becomes more susceptible to mold and mildew staining over time. We install capped composite for that reason, and we're straightforward with homeowners about why an uncapped product costs less up front but tends to cost more in appearance and upkeep over the years on a site this exposed.
| Material | Handling Salt Air & Wind-Driven Rain | Moss Resistance | Typical Upkeep |
|---|---|---|---|
| Capped composite | Strong — cap layer blocks direct moisture absorption | Good on most product lines | Occasional washing |
| Uncapped composite | Moderate — exposed fiber can absorb moisture over time | Fair; more prone to buildup | Periodic cleaning, closer watch on edges |
| Cellular PVC | Excellent — no wood fiber to absorb moisture at all | Strong, smooth non-porous surface | Occasional washing |
| Cedar | Moderate — natural resistance, but needs sealing | Fair when sealed and maintained regularly | Regular oiling or sealing |
| Pressure-treated wood | Weak against sustained salt exposure over time | Poor without regular treatment | Regular sealing or staining |
Cellular PVC is worth mentioning here too, since some homeowners on more exposed lots ask about it directly. It contains no wood fiber at all, so it doesn't absorb moisture even at cut edges or fastener holes the way composite can if the cap is compromised. It costs more than composite and can flex a bit more under heavy point loads, but for a deck sitting closest to the water, some homeowners decide the added moisture resistance is worth it. We install both and will lay out the honest trade-offs for your specific lot rather than steering everyone to the same product.
What a Correct Composite Deck Installation Involves
The decking boards get most of the attention when homeowners picture a new deck, but on a Semiahmoo property, the framing, fasteners, and drainage details underneath are what actually determine whether the deck holds up. A composite deck built correctly for this stretch of coastline includes:
- Framing material rated for sustained moisture exposure, sized correctly for the span and load the deck will actually carry
- Stainless steel or coastal-grade corrosion-resistant fasteners throughout — not standard hardware that starts corroding in salt air within a few seasons
- Hidden fastener systems on the decking surface where the product allows, cutting down exposed metal and giving a cleaner walking surface
- Board gapping set to the manufacturer's spec for drainage and thermal movement, since composite expands and contracts more than wood with temperature swings
- Joist spacing matched to the specific composite product's span rating rather than a generic framing layout
- Proper ledger board flashing where the deck ties into the house — one of the most common places moisture gets into a poorly built deck
- Railing and post attachment sized for the wind exposure the specific lot sees, which on the spit can be significant even on a modest-sized deck
- Grading and airflow underneath the deck so moisture doesn't sit against the framing between storms
Skip any one of those and the deck usually still looks fine on day one. The problems — a soft joist, a loosening railing post, fastener corrosion staining the boards around it — tend to show up a few winters later, once the exposure has had time to work on the weak point.
Design Considerations for Semiahmoo Properties
Beyond material and structure, a few site-specific questions matter more on the spit than they would on a typical inland lot. Wind exposure affects how open a railing design can realistically be versus how much a partial screen or glass panel earns its keep as a windbreak. Elevation and grade around waterfront and condo-adjacent lots affect drainage design and whether the substructure needs extra attention to keep water from sitting underneath. Sun and shade patterns across the day affect which decking color will hold up best against fading and which parts of the deck need the most moss-resistance priority. None of these are one-size-fits-all answers, and a deck designed around a specific Semiahmoo lot performs differently than a stock layout dropped onto any site.
How Our Process Works
We start with a site visit to look at what's actually there — existing deck condition if it's a replacement, drainage and grade around the area, wind exposure through the day, and how directly the lot faces the bay or harbor. From there we talk through composite product options that fit the budget and how the space will get used, and we're direct about which grade of composite makes sense for a given lot's exposure versus which one is more than the situation calls for.
Permitting on Semiahmoo generally follows the standard Whatcom County setback, structural, and elevation requirements, and we handle that as part of the job rather than leaving it for the homeowner to sort out. Once permitted, the build follows the sequence above — substructure and framing first, sized and fastened for the site's actual exposure, then the decking surface, railing, and any stairs or trim. We finish with a walkthrough of what your specific composite product actually needs going forward, which for a quality capped product is minimal, but not nothing.
What Your Deck Still Needs From You
Composite decking cuts down maintenance significantly compared to wood, but "low-maintenance" isn't "no-maintenance," especially in this climate. A few things worth keeping on a routine:
- Rinse or wash the deck surface periodically to clear salt residue, pollen, and organic buildup before it works into the cap layer
- Keep gaps between boards clear of leaves and debris so water and airflow can move the way the design intends
- Check railing posts and hardware once a year for early corrosion or loosening, especially heading into the wet season
- Trim back overhanging branches or plants that hold moisture against the deck or block sun and airflow across the surface
- Address any soft framing or standing water underneath right away — that's a structural issue, not a cosmetic one, and it doesn't improve on its own
Why It Matters That We Already Work This Stretch of Coastline
A crew that mostly builds decks further inland can still put one together competently, but a Semiahmoo job has variables that don't come up as often even a few miles into Blaine — corrosion-grade fastener requirements from salt exposure on more than one side, wind loads tied to open water exposure, and moss pressure that runs longer here than in more sheltered towns. Working this specific area regularly means we're not guessing at those requirements on your project. We've seen which composite lines actually hold up against Semiahmoo's particular combination of salt air, driving rain, and moss, and which fastener grades and framing details are worth the extra attention rather than an upsell.
That familiarity also shows up in smaller judgment calls — how to orient a deck for the wind a specific lot actually sees, or being straightforward about what a deck here realistically needs to last versus what's just an extra line item on an estimate.
Whether you're replacing a tired deck, building new, or just want an honest read on what composite decking would take on your Semiahmoo property, we're happy to walk the site with you and lay out the options plainly. Reach out below for a free, no-pressure estimate.