Sumas Window Composite Decking Built for Kendall's Climate
A deck in Kendall sits outside year-round, which means it takes on everything this part of Whatcom County throws at it: salt-tinged marine air that works on fasteners and hardware, driving rain that gets pushed sideways by wind instead of falling straight down, and a long moss season that keeps shaded surfaces damp for months at a stretch. Composite decking holds up well against all of that when it's installed correctly, but "composite" isn't a single product with one installation method — it's a category, and the substructure, fastening, and drainage details underneath the boards matter just as much as the decking itself.
This page covers composite decking specifically for Kendall properties — what the local climate asks of a deck, what a correct install actually involves, how our process works from design through final walkthrough, and why a crew that already works this area brings something a first-timer to the region won't.
What Kendall's Climate Demands From a Deck
Salt Air and Fastener Corrosion
Salt-tinged air moving through this part of Whatcom County accelerates corrosion on lower-grade fasteners, joist hangers, and hidden fastener clips over time. A deck that looks fine on installation day can develop rust streaks and weakening hardware within a few years if the substructure wasn't built with corrosion-resistant, exterior-rated fasteners from the start. This is a detail that's invisible once the boards are down, which is exactly why it has to be right the first time.
Driving Rain and Substructure Drainage
Rain here rarely falls straight down. Wind pushes it sideways and up under the deck surface, into the gaps between boards and against the ledger connection where the deck meets the house. If the substructure doesn't shed that water — through correct board spacing, joist protection, and a properly flashed ledger — moisture works its way into places it can sit for weeks rather than draining or drying out.
Moss, Algae, and Surface Traction
Shaded sections of a deck, especially under trees or on the north side of a house, stay damp longer here than they would in a drier climate. That supports moss and algae growth on the board surface, which isn't just a look problem — it makes the deck slick and reduces traction underfoot for months during the wetter part of the year. Board texture, gap spacing, and airflow underneath the deck all affect how much moss actually takes hold.
Composite vs. Other Decking Materials
Composite isn't the only option, and it isn't automatically the right one for every project. Here's how the common choices compare for a deck that has to deal with this region's weather.
| Material | Moisture Behavior Here | Typical Maintenance | Realistic Lifespan |
|---|---|---|---|
| Composite (capped) | Resists moisture absorption and rot; won't splinter or warp with correct install | Periodic washing to clear moss and pollen film | 25-30+ years |
| Pressure-treated wood | Absorbs moisture, prone to warping, checking, and splintering in a wet climate | Regular sealing/staining, ongoing board replacement | 10-15 years before major repair |
| Cedar | Naturally rot-resistant but still absorbs moisture without upkeep | Sealing every 1-2 years to hold color and resist moss | 15-20 years with consistent maintenance |
| PVC/vinyl decking | Fully moisture-proof; doesn't absorb water at all | Low; occasional washing | 25-30+ years |
Composite lands in a middle ground that works well for most Kendall homeowners: far less upkeep than wood, a more traditional look and feel underfoot than straight PVC, and moisture behavior that's well suited to a climate where a deck rarely gets a long stretch to fully dry out between rain events.
What a Correct Composite Deck Install Involves
Ledger Board Flashing
Where the deck attaches to the house is the single most important connection on the whole structure, both structurally and for moisture control. The ledger needs proper flashing — typically metal flashing integrated with the house's weather-resistive barrier — so that water running down the siding sheds away from that connection instead of tracking behind it. A ledger that's lag-bolted on without correct flashing is one of the most common sources of hidden rot behind a deck in a wet climate.
Substructure Protection
Joist tape over the tops of pressure-treated joists, corrosion-resistant joist hangers, and stainless or coated structural screws all matter more here than they would in a dry inland climate. The substructure is the part of the deck that never gets inspected again once decking is installed, so it has to be built to outlast the boards on top of it.
Joist Spacing and Board Direction
Composite boards generally need tighter joist spacing than solid wood decking, and picture-frame borders, diagonal patterns, or curved layouts often require closer spacing still, per the manufacturer's specification. Skipping this step is a common shortcut that shows up later as bounce or sag in the deck surface.
Hidden Fasteners and Board Gapping
Most composite systems use hidden fastener clips between boards rather than face screws, which gives a clean surface but requires consistent gapping for both drainage and the board's normal expansion and contraction with temperature. Gaps that are too tight trap water and debris between boards; gaps that are inconsistent look poor and can affect how the fastener clips perform over time.
Cut-End Sealing and Ventilation
Any board end that gets field-cut for length needs the cut edge treated or capped according to the manufacturer's instructions, since an unsealed cut end can wick moisture into the board core over time even on a fully capped composite product. Underneath the deck, enough clearance and airflow needs to exist to let moisture from a long wet season actually evaporate rather than sit trapped against the substructure.
What Affects the Cost of a Composite Deck
| Factor | Why It Matters |
|---|---|
| Composite board tier | Fully-capped, all-sides-protected boards cost more up front and generally outperform partially capped or uncapped composite in a wet climate |
| Substructure material | Pressure-treated wood framing is standard; aluminum substructure costs more but removes wood-to-moisture exposure entirely |
| Size and layout complexity | Multiple levels, curves, picture-framing, and diagonal patterns add material and labor beyond a simple rectangle |
| Railing system | Composite, aluminum, and cable railing all vary widely in material cost and installation time |
| Old deck removal | Demolishing and hauling away an existing deck adds labor that a new-build project doesn't have |
| Permitting and structural work | Whatcom County permit requirements and any footing or ledger structural upgrades affect both cost and timeline |
We'll walk through actual numbers for your specific project during an estimate rather than quoting off a generic price-per-square-foot range that doesn't account for your home's ledger condition, layout, or site access.
How Our Process Works
- Site visit and design: We look at the ledger connection, existing structure if there is one, drainage slope of the yard, and how much sun and shade the deck will actually get before recommending a layout.
- Permit and structural review: Footings, ledger attachment, and span requirements get checked against current code before any material is ordered.
- Substructure build: Framing goes in with corrosion-resistant hardware, joist tape, and spacing set for the specific composite product and pattern you've chosen.
- Ledger flashing and waterproofing: The house connection is flashed and integrated properly before decking ever goes down over it.
- Decking installation: Boards go in with correct gapping, hidden fasteners, and sealed cut ends, following the manufacturer's specification for this climate.
- Railing, stairs, and fascia: Finish components are installed and checked for level, secure attachment, and code-compliant spacing.
- Final walkthrough: We go over the finished deck with you, including basic care specific to this climate, before calling the job done.
Living With a Composite Deck Through a Long Moss Season
Composite decking is low-maintenance compared to wood, but "low-maintenance" doesn't mean "no maintenance" in a climate like this. A periodic wash — plain water and a soft-bristle brush, or a cleaner rated for composite decking — keeps moss and the fine green film that builds up on shaded boards from taking hold. Gaps between boards should stay clear of leaves, needles, and dirt, since packed debris in a drainage gap defeats the purpose of the gap in the first place. Pressure washers should be used carefully, if at all, and never at close range or high pressure directly on composite boards, since that can damage the cap layer that's doing the actual moisture protection.
- Sweep or rinse debris out of board gaps a few times a year, more often under trees
- Wash shaded, moss-prone areas before moss gets established rather than after
- Check the ledger area and any flashing you can see for signs of staining or moisture
- Keep planters, rugs, and furniture feet from sitting in one spot long enough to trap moisture underneath
- Confirm railing connections and stair stringers annually, since hardware works loose over time regardless of decking material
- Address any soft or spongy spots immediately rather than waiting for a scheduled inspection
Why Hiring a Crew That Already Works Kendall Matters
A crew that regularly builds decks in and around Kendall has already seen which ledger connections tend to leak, how fast underspecified hardware corrodes in this air, and which corners of a yard hold moss no matter what board texture you choose. That's practical knowledge that shows up in small decisions throughout the build — decisions a crew unfamiliar with this specific stretch of Whatcom County might not think to make at all. It also means someone who's still local and reachable years down the road if a warranty question or a loose railing connection comes up, rather than a crew that did one job in the area and moved on.
If you're planning a new deck or replacing an aging one in Kendall, we're glad to walk the site with you and talk through what a correct build looks like for your specific yard and budget. Use the form below to request a free, no-pressure estimate.