How is composite decking different from PVC or capped polymer decking?

Composite decking is typically a blend of wood fibers and plastic, capped with a protective outer layer on most modern boards, while PVC/capped polymer decking is fully synthetic with no wood content. Composite generally costs less and still gives a wood-grain look, while PVC offers slightly better moisture and mold resistance since there's no organic material in the board at all. Both are strong choices in a wet coastal climate; the right pick usually comes down to budget and desired appearance.

What should I ask a contractor before hiring them for a deck build on the island?

Ask whether they carry proper licensing and insurance, whether they've built decks specifically in San Juan County's marine climate, and whether they'll show you the substructure and hardware plan before covering it with decking. Ask for a written estimate that breaks out substructure repair separately from the decking install, since those are two different scopes of work. A contractor who's vague about framing details or fastener specs is worth a second look.

Do all composite decking brands perform the same way?

No — composite decking varies significantly by manufacturer in terms of cap technology, fade resistance, and how well the board resists moisture and staining over time. Lower-tier composite without a full protective cap can be more prone to fading and moisture absorption at cut edges. We select boards based on the specific project and are upfront about the trade-offs between tiers rather than pushing one brand across every job.

Can composite decking be installed directly over an old wood deck?

Generally no — composite decking needs to be installed on a substructure that meets the manufacturer's spacing and support requirements, and an old wood deck's framing often doesn't match those specs or may already have hidden moisture damage. In most cases the framing needs to be inspected and often rebuilt or reinforced before new composite boards go down. Skipping that step is one of the more common reasons composite decks develop problems early.

Does composite decking need special care to handle San Juan County's moss season?

Composite decking resists moss growth better than untreated wood, but it isn't immune, especially in shaded or poorly ventilated areas of the deck. Periodic cleaning and making sure the space underneath the deck has airflow to dry out between rains go a long way toward keeping moss from taking hold. A deck built with proper drainage and spacing from the start needs less intervention later.

Composite Decking in Friday Harbor: What Holds Up

Decking Built for Friday Harbor's Marine Climate

Friday Harbor sits close enough to the water that salt air, driving rain off the Strait, and a long damp season all work on a deck's surface and substructure year-round. A deck that would hold up fine in a dry inland climate can start showing problems here within a few seasons — not because the material failed outright, but because it wasn't detailed or installed with San Juan County conditions in mind. Composite decking, done correctly, is one of the more sensible answers to that climate, but "composite" isn't a single product with one set of rules. The board brand, the substructure underneath it, and the way the crew handles fasteners and drainage matter as much as the decking itself.

This page is about composite decking specifically for homes in and around Friday Harbor — what the local conditions demand, what a correct install actually involves, and what to check before you hire someone to build or replace a deck here.

Why Friday Harbor's Climate Is Hard on Decks

San Juan County's marine environment brings a few specific stresses that decking has to tolerate:

Salt-laden air: Airborne salt accelerates corrosion on fasteners, brackets, and any exposed metal hardware near the water.
Persistent moisture: Long stretches of damp, overcast weather keep wood substructure and end grain wet longer than in drier climates, which is exactly the condition mold, rot, and moss need.
Moss and algae growth: A long moss season means anything that stays shaded and damp — the underside of boards, joist tops, north-facing rail sections — is a candidate for growth if it can't dry out between rains.
Driving rain: Wind-driven rain gets under rail caps, into fastener holes, and behind poorly flashed ledger boards, which is where hidden rot usually starts.

None of this means composite decking is a bad fit for Friday Harbor — it's actually a strong fit, since good composite boards don't absorb moisture the way wood does and won't feed rot the way a wood deck surface can. But the framing underneath, the fasteners, and the way the deck is built to shed water all still have to be right, because composite boards sitting on a poorly built or unprotected substructure just hide a problem instead of solving it.

What a Correct Composite Deck Install Involves

The Substructure Comes First

The decking material gets most of the attention, but the framing underneath is what determines whether the deck lasts. In this climate, that means:

Pressure-treated framing rated for ground contact where applicable, with joists sized and spaced to the manufacturer's spec for the composite board being used (composite often requires tighter joist spacing than wood decking, especially at angles or stair treads).
A ledger board properly flashed against the house, with a water-resistant barrier between the ledger and the wall — this is one of the most common failure points on any deck near the water.
Joist tape or another moisture barrier on top of the framing, so rain that gets between the boards doesn't sit directly on bare wood.
Proper airflow underneath the deck so the substructure can actually dry out between wet spells instead of staying damp for weeks at a time.

Fasteners and Hardware

Given the salt air around Friday Harbor, hardware choice isn't cosmetic — it's a durability decision. Structural connectors, joist hangers, and fasteners should be rated for coastal or marine exposure, not general-purpose galvanized hardware that's fine inland but corrodes faster here. Hidden fastener systems for the decking surface should also be matched to the specific composite board being used, since not all clip systems are interchangeable across brands.

Drainage and Spacing

Board spacing, end-gapping, and any picture-frame or border detailing need to account for expansion and contraction — composite boards move with temperature more than people expect, and gaps that are too tight in one season can cause buckling in another. Drainage at the perimeter and around any posts or footings also needs to direct water away from the structure, not let it pool against framing.

Composite vs. Wood vs. PVC: How They Compare Here

Factor	Composite	Wood (cedar/PT)	PVC/Capped Polymer
Moisture resistance	Good — resists rot, doesn't absorb water into the board core the way wood does	Poor without ongoing maintenance; end grain and cut edges are vulnerable	Very good — fully synthetic, minimal moisture absorption
Moss/algae resistance	Moderate to good, varies by brand and cap quality	Poor — wood surfaces feed moss and mildew readily in shaded, damp areas	Good — smooth, non-porous surface
Maintenance	Low — periodic cleaning, no staining or sealing needed	High — annual sealing/staining recommended to hold up to marine exposure	Low
Upfront cost	Mid	Lowest	Highest
Typical lifespan (climate-adjusted)	25-30+ years with correct install	10-15 years before major repair/replacement, shorter near salt air	25-30+ years

Wood is still a reasonable choice for homeowners who want that look and are committed to annual maintenance, but it's the highest-upkeep option in a climate that's actively working against unsealed wood most of the year. Composite tends to be the middle ground most Friday Harbor homeowners land on — meaningfully lower maintenance than wood without the top-end cost of full PVC systems.

What Drives Cost on a Friday Harbor Composite Deck

Composite decking projects vary widely in price, and most of that variation comes down to a handful of factors rather than the brand name on the board:

Substructure condition: A full tear-off and rebuild of rotted framing costs more than resurfacing a deck with sound framing underneath.
Height and access: Elevated decks, decks over slopes, or decks with limited equipment access add labor time.
Railing and stair complexity: Custom rail systems, glass panels, or multi-level stairs add cost beyond the flat deck surface.
Board tier: Composite lines range from basic capped composite to premium multi-tone or fully capped polymer boards, with a real price spread between them.
Site logistics: Ferry-dependent material delivery and job scheduling can factor into island project timelines and costs more than mainland jobs.

We give homeowners an honest range for their specific project rather than a one-size number, because a straightforward resurface and a full rebuild with new footings are not the same job.

How We Approach a Composite Deck Job

On-site assessment: We look at the existing structure (if there is one), check for hidden moisture damage at the ledger and framing, and talk through what the homeowner actually wants from the deck — entertaining space, low-maintenance priority, matching the home's exterior, etc.
Substructure evaluation and repair plan: Any rot, undersized framing, or corroded hardware gets addressed before a single composite board goes down. Building over a bad substructure just delays the problem.
Material selection: We walk through composite board options and hardware suited to marine exposure, matched to the homeowner's budget and maintenance expectations.
Build: Framing, moisture barrier, decking installation with correct spacing and fastening, and railing/stair work as needed.
Final walkthrough: We check drainage, board seams, and hardware before calling the job done, and go over basic care so the deck stays looking right through the wet season.

Signs an Existing Deck Needs Attention

If you already have a deck in the Friday Harbor area, a few warning signs are worth checking before they become bigger repairs:

Soft or spongy spots underfoot, especially near the house or stair connections
Visible moss or dark staining that keeps returning after cleaning
Rust streaking around fastener heads or brackets
Gaps or movement at the ledger board where the deck meets the house
Boards that have cupped, warped, or separated at the seams

Any of these can be a sign that moisture is getting into the substructure, which is worth addressing before it spreads to framing that's expensive to replace.

Why Local Experience Matters for This Job

Composite decking isn't a difficult product to install badly — it's a fairly forgiving material to work with on the surface. The part that separates a deck that lasts from one that needs rework in a few years is whether the crew understands what San Juan County's marine air and moss season actually do to framing, fasteners, and drainage over time. A crew that only occasionally works on the islands may default to mainland-standard hardware and spacing that isn't matched to this environment. We work in and around Friday Harbor regularly, so the coastal-rated hardware, proper flashing, and drainage detailing aren't an upcharge or an afterthought — they're just how we build a deck meant to hold up here.

If you're considering a new composite deck or replacing one that's showing its age, we're happy to take a look and give you a straightforward, no-pressure estimate — just fill out the form below.