Anacortes Exterior Why Decks on Guemes Island Face Different Conditions Than the Mainland
Guemes Island sits just across Guemes Channel from Anacortes — close enough that the ferry crossing takes only a few minutes, but far enough removed from Fidalgo Island's more sheltered, built-up shoreline that homes here deal with a different set of conditions than a deck built in town. With open water on more than one side and Rosario Strait exposed to the north and west, the island catches marine weather with less to break it up than a typical inland Skagit County lot tucked behind trees or neighboring structures. A deck has no roof over it and sits outside year-round, so it takes that exposure more directly than almost anything else attached to a house.
Composite decking exists largely to hold up better against that kind of exposure than wood does, but "composite" covers a wide range of construction quality, and how a board is built changes how it actually performs on an island like this one. This page covers what a Guemes Island home actually needs from its decking material, what a correct composite install involves out here, and why the details — and the logistics of building on an island — matter more than they would on a typical mainland job.
What Guemes Island's Climate Does to a Deck
Salt Air Off the Channel and Strait
Guemes has open water on more than one side, and salt-laden air moves across the island more consistently than it does at a property set back from the water on the mainland. That air accelerates corrosion in any exposed metal — fasteners, brackets, railing hardware, post connectors — and it works on a deck continuously, not just during storms. A fastener that's started corroding loses holding strength well before it looks obviously bad, which is why fastener grade isn't a place to cut corners on a deck out here.
Driving Rain and Wind Across Open Water
Storms crossing the Strait and the Salish Sea don't arrive as straight-down rain. Wind pushes it sideways, driving it up under railings, into ledger connections, and between deck boards that aren't gapped correctly. A deck surface that sheds water fine on a calm day can trap moisture the moment wind gets involved, and on an island with open exposure on multiple sides, wind is involved more often than it is at a sheltered inland site.
A Moss Season That Runs Most of the Year
Guemes Island's mix of open shoreline and heavily wooded interior — a lot of fir and madrona cover across the island — keeps humidity high and gives moss and mildew a long growing season. Horizontal deck surfaces are usually among the first places it takes hold, since they hold water longer than a vertical wall and stay damp between rain events. Shaded decks tucked under tree cover or facing north are typically first to show it, and any decking material with real surface porosity gives moss something to grip onto.
What "Composite Decking" Actually Means
Composite decking is generally a blend of wood fiber and plastic, and the ratio, plastic type, and finishing process vary significantly between manufacturers and product lines. Two distinctions matter most for an island climate like this one.
Capped vs. Uncapped Composite
Capped composite boards wrap a plastic shell around a wood-plastic composite core, protecting it from moisture absorption, staining, and UV degradation. Uncapped composite — the older style of the product — leaves that core exposed on all sides, so it absorbs moisture more readily and is more prone to fading, mold growth, and surface wear over time. In a salt-air, high-humidity environment like Guemes Island, that difference shows up faster than it would somewhere drier, which is part of why we standardize on capped composite for island installs.
Where PVC Fits In
Some manufacturers also build fully cellular PVC decking, which contains no wood fiber at all. PVC resists moisture absorption completely and some lines run cooler underfoot, but it can flex more than composite under heavy point loads and typically costs more. We'll walk through whether capped composite or PVC makes more sense for a given deck based on sun and shade exposure, budget, and how the space will actually get used — there isn't one right answer for every lot on the island.
Composite Decking Compared to the Alternatives
Homeowners weighing decking material for a Guemes Island property are usually choosing among a handful of real categories. Here's how they generally hold up against this specific combination of salt air, driving rain, and moss:
| Material | Handling Salt Air & Moisture | Moss Resistance | Upkeep |
|---|---|---|---|
| Cellular PVC | Excellent — no wood fiber to absorb moisture | Strong, smooth non-porous surface | Occasional washing |
| Capped composite | Strong — cap layer resists moisture and staining | Good on most product lines | Occasional washing |
| Uncapped composite | Moderate — some moisture absorption at exposed fiber | Fair; more prone to buildup over time | Periodic cleaning |
| Cedar | Moderate — natural resistance, but needs sealing | Fair when sealed and maintained on schedule | Regular oiling or sealing |
| Pressure-treated wood | Weak against sustained salt exposure over time | Poor without regular treatment | Regular sealing or staining |
The gap between a well-suited material and a poorly-suited one shows up faster here than it would at a drier, more sheltered inland property, simply because the island climate gives every weak point more to work with.
What a Correct Composite Deck Build Involves Here
The decking boards get most of the attention when homeowners picture a new deck, but on Guemes Island the substructure and fastening details underneath are what actually determine how long it lasts. A build done right for this island includes:
- Framing material suited to sustained moisture exposure — pressure-treated lumber rated for the application, sized correctly for the span and load
- 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 deck surface where the product allows, reducing exposed metal and giving a cleaner walking surface
- Correct board gapping for drainage and material movement, so wind-driven rain and standing moisture can actually drain and dry between boards
- Proper ledger board flashing where the deck ties into the house, since that connection point is one of the most common places moisture gets in on a poorly built deck
- Joist spacing matched to the specific composite product's span rating rather than a generic wood-framing layout
- Railing and post attachment sized for the site's actual wind exposure, especially on elevated decks or lots with open water views
- Ventilation and grading 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 show up a few winters later, as a soft joist, a loosening railing post, or fastener corrosion staining the boards around it — and on an island, that's a repair trip that takes real planning to schedule, not a same-day fix.
Getting Materials and a Crew to the Island
Building on Guemes Island adds a logistics layer that a mainland Anacortes job doesn't have. Every board, fastener, and tool has to cross on the ferry, and the ferry runs on its own schedule with limited capacity per sailing — it's not a resource a job can treat as unlimited. That changes how a deck project needs to be planned from the estimate forward: material takeoffs need to be accurate the first time, deliveries need to be staged and complete rather than trickled over multiple trips, and the crew's day needs to be built around sailing times rather than around when the crew happens to be ready to head out.
Get that planning wrong and the cost shows up as wasted ferry trips, a crew standing around waiting on a missing bundle of boards, or a job that stretches out longer than it needs to. Get it right, and island logistics are mostly invisible to the homeowner — the crew shows up with what they need, works a full day, and doesn't need to make repeat trips for things that should have been on the truck the first time.
How Our Process Works
We start with a site visit to look at what's actually there — existing structure condition if it's a replacement, drainage and grade around the deck area, sun and shade exposure through the day, and how much wind and water exposure the specific lot sees. From there we talk through composite and PVC options that fit the budget and how the space will actually get used, whether that's a quiet spot off the house or a larger deck built for entertaining.
Permitting for decks on Guemes Island generally falls under Skagit County's standard 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, we plan material delivery and crew scheduling around the ferry from the start, so the actual build follows the sequence above without avoidable delays — substructure and framing first, sized and fastened for the site's real exposure, then the composite surface, railing, and any stairs or trim work. We finish with a walkthrough covering what the specific product you chose actually needs going forward, which for most modern composite is minimal, but not nothing.
What Composite Decking Still Needs From You
Composite decking is low-maintenance compared to wood, not maintenance-free. A little routine care goes a long way toward getting the full life out of it in this climate:
- 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 needles so water and airflow can move through 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 brush 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 with time
Why It Matters That We Already Work Guemes Island
A crew that mostly builds decks on the mainland can still install composite decking competently, but a Guemes Island job has variables that don't come up as often in Anacortes proper — ferry-dependent material staging and scheduling, corrosion-grade fastener requirements from sustained open-water salt exposure, and moss pressure that runs longer here than it does at more sheltered sites. Working this island regularly means we're not learning those requirements on your project. We've worked out how to plan a materials list so nothing gets left on the mainland, which composite lines actually hold up against this specific combination of salt air, driving rain, and moss, and which fastener grades and framing details are worth the extra time rather than an upsell.
That familiarity also shows up in smaller judgment calls — how to orient a deck for the wind and water exposure a particular lot actually sees, and being straightforward about what a deck here realistically needs to last versus what's just an extra line item. If you're weighing a new composite deck or a replacement on Guemes Island, we're happy to come out, walk the site, and lay out the options plainly. Reach out below for a free, no-pressure estimate.