Sumas Roofing Composite Decking Built for Kendall's Wet Side of Whatcom County
Kendall sits close enough to the foothills and far enough from any real wind break that its homes take a steady beating from moisture nine months out of the year. Driving rain off the Nooksack valley, heavy morning dew, and a moss season that can run from October through May all work against wood decking in ways that show up fast — cupping boards, black streaking, soft spots near the ladder. Composite decking was built to shrug off exactly that kind of climate, but only when it's installed with the local conditions in mind, not just bolted down to a generic spec sheet.
We've done deck work across Sumas and the surrounding rural lots long enough to know that a deck plan that works fine in a dry inland town doesn't automatically work here. Framing height, drainage gaps, fastener choice, and even which composite board profile we recommend all shift once you factor in how much standing moisture this area actually sees.
What Kendall's Climate Actually Does to a Deck
Salt Air and Driving Rain
Whatcom County isn't coastal in the way Bellingham's waterfront is, but weather systems moving through still carry enough moisture-laden air to accelerate corrosion on exposed metal fasteners and hardware. Combined with wind-driven rain that hits decks at an angle rather than straight down, water gets pushed under railings, into end-grain cuts, and behind ledger boards if those areas aren't properly flashed and sealed.
The Long Moss Season
Moss doesn't care what your decking is made of — it cares about shade, moisture, and airflow. Composite boards resist moss growth far better than untreated wood because they don't have the same porous surface for spores to latch onto, but moss will still colonize the surface if a deck sits under tree cover with poor ventilation underneath. Left alone through a wet Whatcom winter, moss turns a deck surface slick and dangerous long before it does any real structural harm.
Freeze-Thaw Cycling
Kendall gets enough cold snaps each winter that any water trapped in a joint, a fastener hole, or an unsealed cut edge will freeze, expand, and slowly work a board loose. This is less dramatic than what you'd see in the mountains, but over five or six winters it's enough to loosen hidden fasteners and open gaps that let more water in — a slow feedback loop that ends with a deck that looks fine from ten feet away and feels spongy up close.
Why Composite Makes Sense Here
Composite decking is a blend of wood fibers and plastic (usually polyethylene or polypropylene), capped or coated to resist moisture absorption. For a property in Kendall, the appeal isn't cosmetic — it's that composite doesn't rot, doesn't need annual staining, and handles repeated wet-dry cycles without the surface checking that eventually splinters cedar or pressure-treated pine.
That said, composite isn't maintenance-free, and we tell every homeowner that up front. It still needs periodic washing to keep pollen, algae film, and moss spores from building up, and the substructure underneath — the joists, ledger, and fasteners — still needs to be built correctly, because composite boards are only as good as what they're screwed into.
Composite vs. Wood vs. PVC — Honest Comparison for This Climate
| Factor | Wood (cedar/PT pine) | Composite | Full PVC |
|---|---|---|---|
| Moisture resistance | Moderate — needs annual sealing | High — capped boards shed water well | Highest — fully synthetic |
| Moss/algae resistance | Low — porous surface holds spores | Good — smoother surface, still needs washing | Very good |
| Upfront cost | Lowest | Mid-range | Highest |
| Long-term maintenance | Highest — staining, sealing, board replacement | Low — occasional cleaning | Lowest |
| Feel underfoot in cold weather | Natural, warms quickly | Solid, some flex depending on board | Can feel harder/colder |
| Typical warranty structure | Manufacturer warranty on lumber grade only | 25-50 year fade/stain warranty common | Similar to composite, often longer |
We install composite most often in Kendall because it lands in the sweet spot for this climate: it costs less than full PVC, handles the moisture and moss pressure far better than wood, and the warranty structure most manufacturers offer actually means something given how much wet weather these boards see every year.
What a Correct Composite Deck Build Involves
Framing and Substructure
This is where most deck problems actually start, regardless of what decking material sits on top. For Kendall properties we build with proper joist spacing for composite span ratings (composite typically needs tighter joist spacing than wood — usually 16" on center, sometimes less depending on the board), and we use corrosion-resistant fasteners and hardware given the moisture exposure. Ledger board flashing gets extra attention here; a poorly flashed ledger is the single most common source of hidden rot we find on older decks in this area.
Drainage and Airflow
Composite boards need a gap — both between boards and at the perimeter — to let water drain through rather than pool on the surface. Underneath, we make sure there's enough clearance and airflow so the substructure can dry out between rain events instead of sitting damp for days, which is exactly the condition moss and mildew need to take hold.
Fastening
Hidden fastener systems are standard on most composite jobs now, and they matter more here than in a drier climate — every exposed screw head is a potential entry point for water and a future rust streak. We match fastener type to the specific board manufacturer's spec, since composite expands and contracts with temperature more than solid wood and needs fasteners that account for that movement.
Edges, Cuts, and Trim
Every cut edge on a composite board exposes the core material underneath the cap, and an unsealed cut is a weak point for moisture intrusion over time. Fascia boards, picture-frame trim details, and stair stringers all get finished properly rather than left as raw cuts.
Our Process for a Kendall Deck Project
- On-site assessment — we look at drainage on the lot, tree cover and shade patterns (a big factor in moss risk), existing structure if it's a tear-off, and how the deck ties into the house.
- Material selection — we walk through board options and color/finish choices based on your budget and how much sun or shade the deck actually gets.
- Framing and structural work — joists, ledger flashing, footings if needed, all built to current code for the span and load.
- Composite installation — hidden fastener systems, proper board gapping, trim and edge finishing.
- Final walkthrough — we go over maintenance basics with you before we leave the job site.
Signs Your Current Deck Needs Composite Replacement, Not Just Repair
- Boards that stay dark or damp-looking days after the last rain
- Soft or spongy spots when you walk across the surface
- Persistent moss or green film that returns within weeks of cleaning
- Visible gaps or movement where the deck ties into the ledger board
- Fasteners that are rusted, popped up, or missing entirely
- Railings that flex or feel loose when leaned on
If you're seeing two or more of these, it's usually worth a real inspection rather than another round of patch repairs — patching a failing substructure just delays the same conversation for another year or two.
Maintenance That Actually Keeps Composite Looking Good Here
Composite decking cuts the maintenance load dramatically compared to wood, but "low maintenance" isn't "no maintenance" — especially with Kendall's moss season working against you most of the year.
| Task | Frequency | Why it matters here |
|---|---|---|
| Rinse/sweep debris off surface | Every few weeks in fall | Wet leaves trapped on boards feed moss and algae growth |
| Soap-and-water wash | 2-3 times per year | Removes pollen film and early moss spores before they take hold |
| Check fastener/railing tightness | Annually | Freeze-thaw cycling can loosen hardware over several winters |
| Clear under-deck airflow paths | Annually | Blocked airflow underneath keeps the substructure damp longer |
Why a Locally Experienced Crew Matters for This Job
Composite decking installation isn't exotic work, but doing it well in a climate like Kendall's takes judgment calls that a crew unfamiliar with this area might not think to make — how tight to set drainage gaps given how much rain this valley actually sees, which fastener grade actually holds up, where moss pressure will be worst based on tree cover and sun exposure on your specific lot. We work this area regularly, which means we're not guessing at how Whatcom County's wet season behaves — we're building around it every time.
If you're weighing a new composite deck or replacing an aging wood deck in Kendall, we're happy to walk the site with you, look at drainage and sun exposure, and put together a straightforward estimate with no pressure attached.