Semiahmoo Siding New-Construction Windows Are a Different Job Than Replacement Windows
Most people who call us about "windows" are picturing a retrofit — pulling an old unit out of a finished wall and dropping a new one into the existing opening. New-construction windows are a different project entirely. There's no finished wall, no old flashing to work around, and no interior trim to protect. Instead, you're building the moisture-management system for that opening from scratch: the weather-resistive barrier, the flashing, the sill pan, and the siding that ties into all of it. Get that sequence right on a new build in Lynden and the window will perform for decades. Get it wrong, and you won't see the problem until the drywall is already up and the water has been finding its way in behind the wall for a season or two.
Because we're a siding contractor first, we see new-construction window installs from the outside — literally. We're the trade responsible for the drainage plane that has to work with those windows, not around them. That perspective matters, because a window that's technically "installed" but not integrated correctly with the WRB and siding is one of the most common sources of hidden water damage in new homes.
What Lynden's Climate Actually Does to a Window Opening
Lynden sits inland from Semiahmoo Bay and the Strait of Georgia, but Whatcom County's marine weather doesn't stop at the coastline. Damp, salt-tinged air off the bay pushes east across the lowlands on a regular basis, and it combines here with the same driving rain, low winter sun angle, and long stretches of overcast, wet weather that define this whole corner of the state. For a window opening, that combination means near-constant exposure to moisture from multiple directions — wind-driven rain hitting the wall at an angle, not just falling straight down, and humid air that never really dries the framing out between storms.
Wind-Driven Rain and Flashing
Straight-down rain is easy to shed. Wind-driven rain gets pushed sideways and upward into gaps that a sill pan and proper flashing are designed to catch. If the flashing laps are backwards, if the sill pan isn't sloped and sealed correctly, or if the head flashing doesn't extend far enough past the jambs, water will find the one path of least resistance and follow it straight into the wall cavity. On a new build, this is the single most consequential detail in the entire window install.
Moss, Algae, and a Long Wet Season
Whatcom County's moss and algae season runs long — north- and west-facing surfaces that stay shaded and damp for months at a time are where it takes hold first. Around window openings, that usually means trim boards, sills, and the siding-to-window transition, especially where debris or a poor drip-cap detail lets water sit instead of shedding. It's not just cosmetic — sustained moss growth holds moisture against wood trim and accelerates rot underneath it.
What a Correct New-Construction Window Install Involves
Rough Opening Prep and WRB Integration
Before a window ever goes in, the rough opening needs to be square, properly sized per the manufacturer's specs, and the weather-resistive barrier (housewrap or a fluid-applied WRB) needs to already be in place and lapped correctly at the opening. Skipping straight to "hang the window" without this step is how gaps and reverse-lapped seams end up buried in the wall.
The Flashing Sequence
There's a correct order to this, and it doesn't vary by opinion — it's dictated by how water actually flows downhill:
- Sill pan flashing installed first, sloped to drain outward, with back and end dams so water can't run back into the wall
- Window set into the opening, shimmed level and square, fastened per the manufacturer's nailing schedule
- Jamb flashing applied over the nailing fin on both sides
- Head flashing installed last, lapping over the jamb flashing and integrated up under the WRB above the opening
- WRB seams taped and shingle-lapped over the top of all flashing so water is always directed outward and downward, never into a seam
Nail-Fin Attachment and Sealant
Nailing-fin windows need to be fastened at every hole the manufacturer specifies — skipping fasteners to "save time" is a warranty and performance risk, not just a labor shortcut. Sealant matters too: it belongs at specific points in this sequence (typically behind the fin at the sides and top, never a solid bead across the bottom of the sill, which would trap any water that does get past the sill pan instead of letting it drain).
Choosing the Right Window for This Climate
New construction is the one time you get to pick the window itself, not just install what's already there. In a marine climate like ours, that decision should weigh moisture tolerance and condensation resistance as heavily as looks or price. Vinyl and fiberglass frames handle sustained damp exposure with the least maintenance. Wood-clad windows can look great and perform well, but the cladding has to be detailed correctly at every joint, because any point where moisture reaches the wood core becomes a long-term liability in a climate this wet.
| Frame Material | Moisture Tolerance | Maintenance | Fit for Lynden's Climate |
|---|---|---|---|
| Vinyl | High — won't rot or corrode | Low | Solid, budget-friendly default for most new builds |
| Fiberglass | High — very stable, minimal expansion/contraction | Low | Strong choice for larger openings or higher-end builds |
| Wood-clad | Depends entirely on cladding detail quality | Moderate to high | Fine if flashed and sealed precisely; unforgiving of shortcuts |
| Aluminum | Low without thermal breaks — prone to condensation | Moderate | Usually not our first recommendation for residential in this climate |
Where Windows and Siding Have to Work as One System
This is the part that gets missed when a window crew and a siding crew never talk to each other. The window's flashing has to be lapped correctly with the WRB, and the siding then has to be installed so it sheds water down and over that flashing without trapping anything behind it. If the siding trim gets nailed on before the flashing sequence is confirmed, or if the drainage plane behind the siding doesn't continue cleanly past the window opening, you've created a gap in an otherwise sound system — and it's usually invisible until there's a problem inside the wall.
Because we handle both the exterior envelope and the trim details around openings, we treat the window and the siding as one continuous water-management system on every new build, not two separate trades' worth of separate work.
Our Process on New Builds in Lynden
New construction gives us more control than a retrofit, but it also means more coordination with the builder or general contractor. Here's how we approach it:
- Review the plans and rough openings before framing is closed up, confirming sizes and locations match the window schedule
- Inspect the WRB installation for correct lapping before any window goes in
- Install sill pans, set windows, and run the full flashing sequence per manufacturer instructions and current code
- Coordinate timing with siding installation so the drainage plane stays continuous from the top of the wall to the bottom
- Final inspection of every opening — flashing laps, fastening, and sealant placement — before siding closes it in for good
Before we let siding close in a single window opening, we check for these on every unit:
- Sill pan present, sloped outward, with end dams intact
- Flashing lapped in the correct shingle-style order — sill, then jambs, then head
- Every nailing-fin hole fastened per the manufacturer's schedule
- Sealant placed at the sides and top only — sill left free to drain
- WRB taped and lapped over the head flashing, no exposed seams
- Unit set level, square, and plumb with even reveals
Common Problems We See When This Sequence Gets Rushed
Reversed flashing laps are the big one — installed in the wrong order so water is funneled into the wall instead of away from it. We also see sealant used as a substitute for proper flashing, which might pass a quick look but fails once the sealant ages and cracks, usually a few years down the road, well after the crew that installed it is gone. And we see WRB that was cut around the opening but never properly taped or lapped back over the flashing — a gap that's invisible once the siding goes up but sits there waiting for the first real wind-driven storm.
Why It Matters to Hire a Crew That Already Works This Area
A window and flashing detail that works fine in a dry climate can fail here simply because the volume and direction of water this region deals with is different. A crew that installs windows and siding across Whatcom County knows to plan for wind-driven rain from the direction it actually comes from here, to size overhangs and drip details with our moss season in mind, and to never treat sealant as a substitute for correct flashing sequencing. That's not a marketing point — it's the difference between a wall that stays dry for thirty years and one that needs opened up in five.
Get a Straight Answer on Your New Build
If you're building new in Lynden and want the window and siding details planned out correctly from the start — not patched together after the fact — we're glad to walk through your plans with you. Use the form below to request a free, no-pressure estimate, and we'll give you a straightforward read on what your build needs.