Anacortes Siding Why Composite Decking Makes Sense on Guemes Island
Guemes Island sits right in the path of everything the Salish Sea throws at it. Homes here get salt-laden air off Rosario Strait, wind-driven rain that comes in sideways more often than straight down, and long stretches of gray, damp weather that keep everything in shade wet for days at a time. A deck on Guemes Island isn't just outdoor furniture — it's exposed structure that has to hold up to conditions most inland Skagit County homes never see. Composite decking, when it's specified and installed correctly, handles that exposure far better than untreated or even pressure-treated wood, which is why it's become the default choice for most of the deck rebuilds and new builds we do out here.
What the Marine Climate Actually Does to a Deck Over Time
It helps to understand the specific ways this environment attacks a deck, because it changes which details actually matter.
Salt Air and Fasteners
Salt in the air accelerates corrosion on anything metal — screws, joist hangers, flashing, railing brackets. A deck built with standard coated fasteners can start showing rust streaks and fastener failure years before the decking itself wears out. On an island property, every metal component in the build needs to be rated for coastal or marine exposure, not just "exterior use."
Driving Rain and Board Ends
Wind-driven rain doesn't fall politely from above — it gets pushed into board ends, under railings, and behind fascia. Cut ends of composite boards are more vulnerable to moisture intrusion than the factory-capped face, so how those ends are treated, sealed, or covered matters more here than it would on a sheltered inland deck.
Moss, Algae, and Shade
Guemes Island's tree cover and marine humidity add up to a long moss season, often stretching from fall through spring. Any deck surface that stays shaded and damp will grow moss and algae if it isn't ventilated and drained properly underneath, regardless of what the decking is made of. This is as much a structural and drainage issue as it is a cosmetic one.
Choosing the Right Composite Board for This Environment
Not all composite decking is built the same way, and the differences matter more in a marine climate than they do in a dry inland yard. Here's how the main categories compare for a Guemes Island install:
| Board Type | Moisture & Salt Resistance | Maintenance | Best Fit |
|---|---|---|---|
| Capped composite (wood-plastic blend, polymer shell) | Strong — capped face resists moisture and staining | Occasional wash; cut ends need sealing | Most Guemes Island homes; good balance of cost and durability |
| Mineral-based composite | Very strong — low water absorption throughout the board | Low; holds up well in shaded, damp spots | Waterfront or heavily shaded sites with persistent moisture |
| Uncapped composite (older-style) | Weaker — absorbs moisture, prone to staining and mold | Higher; needs more frequent cleaning and sealing | Generally not recommended for this climate |
We don't push one brand or product line on every job. The right board depends on how exposed the deck is to wind and salt spray, how much shade it sits in, and what the homeowner wants to spend on upkeep. What we won't do is install uncapped or budget-tier composite in a spot that's shaded and damp most of the year — it's a maintenance headache we can see coming from the first site visit.
Cost Factors on a Guemes Island Project
Composite decking costs more upfront than pressure-treated wood, but a well-installed composite deck typically needs far less spent on maintenance and repair over its life. Beyond the board tier chosen — capped composite versus mineral-based, for example — the biggest cost factors on a Guemes Island project are usually the condition of the existing substructure and whether it can be reused or needs to be rebuilt, the size and complexity of the layout including railings and stairs, and modest additions to scheduling tied to ferry access. We walk through all of this during the estimate so there aren't surprises once work starts.
What a Correct Composite Deck Install Actually Involves
The Substructure Comes First
Composite decking is only as good as what's underneath it. On Guemes Island projects we pay particular attention to joist material and coating (galvanized or coated steel components rated for coastal exposure), proper joist spacing for the specific composite board being used — composite often needs tighter spacing than wood framing lumber — and ledger flashing where the deck ties into the house, since that's one of the most common places water gets into a structure it shouldn't.
Drainage and Airflow Underneath
A deck that traps moisture underneath will grow moss and mildew no matter what's on top. We grade and, where needed, add drainage below the deck surface so water moves away instead of sitting, and we leave enough clearance and airflow underneath — especially on lower, shaded decks — to let the structure dry out between rain events instead of staying wet for weeks at a stretch.
Fastening and Board Layout
Hidden fastener systems are standard on most composite decks now, and they matter even more here because every exposed screw head is a future rust spot and a future leak point. We also plan board layout and expansion gaps around the actual manufacturer specs for the product being installed — composite expands and contracts with temperature more than people expect, and gaps that are too tight will buckle over a Skagit County winter-to-summer swing.
Railings, Fascia, and Trim
Cut ends, post bases, and fascia joints are where a lot of amateur composite installs fail early. We treat or cap cut ends per the manufacturer's requirements, use post bases and railing hardware rated for coastal exposure, and detail fascia so water sheds away from the board ends instead of collecting behind them.
Our Process for a Guemes Island Project
Site Visit and Planning
Because Guemes Island is ferry-access only, we plan our site visits and work days around the ferry schedule rather than treating it like a same-day drop-in. That means the initial measure-and-assess visit, material delivery, and the install crew's time on the island are all planned as a sequence, not squeezed in piecemeal — which keeps the project moving instead of stalling out waiting on a missed sailing.
Material Ordering and Staging
Composite decking, fasteners, and hardware are ordered and staged ahead of the install so the crew isn't making extra ferry trips mid-project for a forgotten box of screws. For larger jobs we confirm quantities and lead times early, since composite board runs can have longer order windows than dimensional lumber.
Installation and Cleanup
Once the crew is on-island, the goal is to complete framing, decking, and railing work in a continuous run rather than spreading it across disconnected visits. We haul debris and packaging off the island rather than leaving it for the homeowner to deal with, and we walk the finished deck with the homeowner before we call the job done.
Maintaining a Composite Deck in This Climate
Composite decking is genuinely lower-maintenance than wood, but "low-maintenance" doesn't mean "no maintenance" — especially with this much moss pressure and salt air. A simple seasonal routine keeps a composite deck looking and performing the way it should:
- Rinse or sweep the deck surface regularly through fall and winter to keep moss spores and organic debris from taking hold
- Clean the gaps between boards where debris collects and holds moisture against the substructure
- Check railing posts, hardware, and fastener points once or twice a year for early rust or corrosion
- Keep gutters and downspouts near the deck clear so runoff isn't dumping extra water onto or under the deck surface
- Trim back overhanging branches where possible to reduce shade and speed drying time after rain
- Use a composite-safe cleaner for moss or algae buildup rather than a pressure washer alone, which can damage the capped surface
Permitting and Shoreline Considerations
Many Guemes Island properties sit close enough to the water that deck and structure work can fall under Skagit County shoreline regulations, in addition to standard building permit requirements. Setback rules, height limits, and permitted footprint can vary depending on exactly where a property sits relative to the shoreline, and on whether the work counts as a repair, a replacement, or new construction. We don't guess on this — we check what applies to the specific property before finalizing a design, and we handle the permitting conversation as part of the project rather than leaving it for the homeowner to sort out separately.
Why Hire a Crew That Already Works Guemes Island
A composite deck installed with mainland assumptions — standard fasteners, no ferry planning, no allowance for shade and moss pressure — tends to show problems within a few years even though the decking material itself is rated for decades. Working Guemes Island regularly means we already know to spec coastal-rated hardware by default, plan around the ferry instead of getting caught by it, and design drainage and airflow for a site that stays damp longer than most. That local familiarity is the difference between a deck that needs real attention in year three and one that's still doing its job with minimal upkeep well past year ten.
If you're planning a new deck or replacing an aging one on Guemes Island, we're glad to take a look and talk through what makes sense for your specific site. Use the form below to request a free, no-pressure estimate — there's no obligation, and no pressure to book anything on the spot.