Semiahmoo Siding Building a Deck for Point Roberts' Marine Exposure
Point Roberts sits on its own peninsula at the bottom of the Tsawwassen headland, surrounded on three sides by the Salish Sea. That geography is part of what makes it a great place to build an outdoor living space — and part of what makes decking here harder to get right than in a typical inland Whatcom County neighborhood. Salt-laden air off the water works on metal fasteners and hardware year-round. Driving rain off the water finds gaps in flashing and framing that would stay dry a few miles inland. And the long, wet moss season that defines the Pacific Northwest coast doesn't spare horizontal deck boards, especially on the shaded or north-facing sides of a house.
None of that means composite decking is a bad fit for Point Roberts — it's usually the opposite. But it does mean the install has to account for conditions that a generic decking crew, unfamiliar with this stretch of coastline, might not plan for. This page covers what a correct composite deck build looks like here, what to expect from our process, and why local experience with this specific peninsula matters.
Why Composite Makes Sense in This Climate
Composite decking — a blend of wood fiber and recycled plastic, usually with a protective outer cap — was developed specifically to resist the two things that wear out wood decks fastest: moisture cycling and UV. In a climate like Point Roberts', where boards go from soaked to sun-baked and back again for months at a stretch, that resistance matters more than it would somewhere drier.
What Composite Doesn't Solve
Composite isn't maintenance-free, and it isn't immune to moss, mildew, or algae staining — those grow on any horizontal surface that stays damp and shaded, composite included. What composite does solve is rot, splintering, and the endless refinishing cycle that comes with a wood deck exposed to this much rain. The trade-off is a different maintenance routine, not zero maintenance, and we'll walk homeowners through exactly what that looks like before they commit to a product.
What a Correct Installation Involves
Most composite deck problems we get called to fix in this area didn't start with the decking material — they started with the substructure or the fastening underneath it. The visible boards are only as good as what's holding them up.
Substructure and Framing
In a salt-air environment, the framing choice matters as much as the decking choice. We frame with pressure-treated lumber rated for ground contact where it's near grade, and we pay close attention to joist spacing — composite boards typically require tighter joist spacing than wood (often 12" on-center instead of 16") to avoid sagging over time, especially at deck ends and stair stringers. Manufacturer span tables exist for a reason, and skipping them is one of the most common shortcuts we see on decks that develop a bounce or a wave within a few years.
Fasteners and Hardware
This is the detail that separates a deck built for the coast from a deck built anywhere else. Standard electro-galvanized fasteners corrode faster in salt air than they would inland. We spec stainless steel or heavy hot-dip galvanized hardware for ledger connections, joist hangers, and structural fasteners, and hidden composite fastening clips rated for exterior marine exposure for the board-to-joist connections. It costs more up front than using whatever's on the shelf at a big-box store, but it's the difference between hardware that lasts the life of the deck and hardware that starts staining or failing in five to seven years.
Flashing, Ledger Attachment, and Drainage
Driving rain off the water tends to find the one gap in flashing that wouldn't matter in a calmer climate. Where the deck attaches to the house, we flash the ledger board properly with self-adhering membrane and metal flashing to keep water from tracking behind siding — this is one of the most common failure points on older decks in this area, and it's invisible until it isn't. We also grade and gap the decking to shed water quickly rather than letting it pool, since standing water is what feeds moss and mildew growth even on capped composite boards.
Composite vs. Other Decking Materials
| Material | Performance in Salt Air / Rain | Moss & Mildew Resistance | Long-Term Upkeep |
|---|---|---|---|
| Pressure-treated wood | Prone to swelling, splitting, and fastener corrosion staining | Low — porous surface holds moisture | Annual cleaning, periodic staining/sealing |
| Cedar | Naturally rot-resistant but still absorbs moisture over time | Moderate — needs regular cleaning | Refinishing every 2-3 years to hold appearance |
| Capped composite | Strong — cap layer resists moisture absorption and salt exposure | Moderate — surface growth still needs periodic washing | Occasional cleaning, no staining or sealing |
| PVC decking | Very strong — fully synthetic, no wood fiber to absorb moisture | Moderate — same surface cleaning needs as composite | Occasional cleaning, higher upfront cost |
For most Point Roberts homeowners, capped composite lands in the sweet spot between upfront cost and long-term performance in this climate. PVC is worth discussing for decks with heavy shade or ground-level moisture exposure where an all-synthetic board makes sense, but it's a smaller share of what we install here.
Our Process, Step by Step
- On-site assessment — we look at sun/shade exposure, drainage, existing framing condition, and how close the deck sits to the water or prevailing wind.
- Design and material selection — board color, profile, and railing system, matched to the home and budget.
- Permitting — Point Roberts falls under Whatcom County jurisdiction, and most deck projects here require a building permit depending on height and attachment to the structure. We handle that process rather than leaving it to the homeowner.
- Demolition of the old deck (if applicable), with an inspection of the ledger and framing underneath for hidden rot before anything new goes up.
- Framing and flashing — built to the joist spacing and flashing standards the decking manufacturer requires, not just what's minimally code-legal.
- Decking installation — hidden fastening, proper board gapping, and stair/railing integration.
- Final walkthrough — we cover care instructions specific to the product installed before we consider the job done.
Getting Crews and Materials to Point Roberts
Point Roberts is a U.S. exclave — reaching it by land means crossing the Canadian border twice, once each direction, even though it's technically part of Whatcom County. That logistics reality trips up crews and suppliers who don't already have a routine for it. Material deliveries need to be planned around border processing, and a contractor unfamiliar with that reality can turn a straightforward project timeline into a frustrating one, with delayed lumber or hardware sitting at the crossing while a crew waits on-site. We plan Point Roberts jobs around that reality rather than treating it as an afterthought, which keeps timelines realistic instead of optimistic.
Maintaining a Composite Deck in This Climate
Composite decking cuts down on maintenance, but "low-maintenance" and "no-maintenance" are not the same thing, especially with the moss season this area sees every fall and winter.
- Rinse or sweep debris (needles, leaves, seed pods) off the deck regularly — trapped organic matter under debris is what feeds moss and mildew growth on any decking surface.
- Wash the deck surface once or twice a year with a soft-bristle brush and a cleaner made for composite decking — avoid pressure washers on close settings, which can damage the cap layer.
- Check and clear gaps between boards so water keeps draining instead of pooling.
- Inspect railing posts and stair connections annually for any looseness, which is often the first sign of a fastener issue rather than a decking issue.
- Trim back overhanging vegetation where possible to reduce shade and let the deck surface dry out between rain events.
What Drives the Cost
| Factor | Why It Matters Here |
|---|---|
| Board tier (capped composite vs. PVC) | PVC costs more upfront but handles constant moisture exposure with less surface concern |
| Substructure condition | Salt-air corrosion on old fasteners and framing often means more replacement than expected |
| Deck height and railing code requirements | Elevated decks require engineered railing systems, which adds material and labor |
| Access and delivery logistics | Border-crossing delivery timing can affect scheduling and, occasionally, material staging costs |
| Square footage and layout complexity | Curves, multiple levels, and stairs add labor time beyond a simple rectangular deck |
We give straightforward, honest estimates rather than lowball numbers that grow once demolition uncovers hidden framing problems — which, on older Point Roberts decks facing the water, is common enough that we plan for the possibility upfront in our assessment.
What to Ask Before Hiring Anyone for This Job
- Do they carry Washington state contractor licensing and liability insurance?
- Will they pull the required Whatcom County permit, or leave that to you?
- What fastener and hardware grade do they use for structural connections?
- Do they follow the decking manufacturer's span tables and joist spacing requirements, or build to generic wood-deck spacing?
- Have they worked in Point Roberts before, and do they have a plan for material delivery logistics?
A crew that already has answers to these questions — rather than answers they're improvising on the spot — is generally a crew that's done this work here before.
Ready to Talk Through Your Deck
Every property along this stretch of coast handles wind, salt, and rain a little differently depending on elevation and exposure. If you're weighing a new composite deck or replacing an aging wood one in Point Roberts, we're happy to take a look and talk through what makes sense for your home. Reach out for a free, no-pressure estimate — there's a form right below to get started.