What's the difference between new-construction and replacement windows?

New-construction windows have a nailing flange that attaches to the wall sheathing before siding goes on, giving full access to flash and seal the opening properly. Replacement windows fit into an existing frame without disturbing the exterior wall, which limits how the opening can be re-flashed.

How should I vet a contractor for new-construction window installation?

Ask specifically how they flash the sill, jamb, and head of each opening, not just what window brand they install — the flashing sequence is what actually prevents leaks. Also ask whether the same crew handles both windows and siding, since gaps between trades are a common source of water problems.

Do you install every window brand and material?

We work with several established vinyl, fiberglass, and clad-wood manufacturers and will discuss trade-offs for your specific project. We generally steer new builds away from bare wood frames in this climate due to the maintenance burden from sustained shade and moisture, though we'll install what a homeowner specifically wants after discussing that trade-off.

What glass package is worth it for a Whatcom County home?

Low-E glass is standard practice here and helps with both energy performance and comfort near large window walls. Beyond that, glass upgrades depend on your specific exposure — a heavily shaded or waterfront wall may warrant different specs than a typical in-town lot, which we'll go over during your estimate.

Does Bellingham's weather actually change how windows should be installed compared to drier parts of Washington?

Yes — wind-driven rain and sustained shade-related moisture mean flashing sequence and sealant choice matter more here than in drier climates where a simpler installation might get away with fewer safeguards. We build in sill pan drainage and shingle-lapped flashing on every new-construction opening specifically because of how often and how hard this area gets rained on.

New-Construction Windows for Bellingham Homes

Why New-Construction Windows Need a Different Approach in Bellingham

Building new in the Bellingham area means dealing with a specific mix of weather that a lot of window packages simply aren't built for: salt-laden air off the Puget Sound and the bays, long stretches of driving rain that comes in sideways off the water, and a moss and mildew season that can stretch for most of the year in shaded, north-facing exposures. New-construction windows sit inside a fresh wall assembly with no old flashing, no old caulk lines, and no prior mistakes to work around — which is exactly why it's worth getting the material, the flashing detail, and the installation sequence right the first time. A window that's a poor fit for this climate won't show its weaknesses on day one. It shows them two or three wet seasons later, as soft trim, fogged glass, or staining around the frame.

Glenhaven Siding Company works new-construction and major remodel projects throughout Whatcom County, including Bellingham, and we treat window installation as part of the building envelope — not a separate trade dropped in after the fact. The window opening, the flashing, the siding, and the weather-resistive barrier all have to work together as one system, or moisture finds the seam between them.

What "New-Construction" Windows Actually Means

New-construction windows are built with a nailing flange (sometimes called a nail fin) that attaches directly to the wall sheathing before siding goes on. That's different from a replacement or "pocket" window, which is sized to slide into an existing frame without disturbing the exterior wall covering. The distinction matters for performance:

New-construction windows let us flash directly to the sheathing and weather-resistive barrier, which is the strongest, most predictable way to manage water at the opening.
They allow the window to be set square and level in the rough opening before any interior or exterior finish work covers up mistakes.
They give us full access to shim, insulate, and air-seal the gap around the frame — something you can't do well once siding and trim are already in place.

If you're building new in Bellingham or doing a full re-side down to the sheathing, you're almost always in new-construction window territory, even if the framing itself isn't brand new.

What Local Homes Need From a Window Package

Salt Air and Coastal Exposure

Homes closer to Bellingham Bay and the surrounding waterways deal with airborne salt that accelerates corrosion on hardware, screens, and lower-quality frame components. This doesn't mean every window needs marine-grade everything, but it does mean we pay attention to hardware finish and frame material on homes with more direct water exposure, rather than defaulting to whatever's cheapest.

Driving Rain

Wind-driven rain doesn't just hit a window head-on — it gets pushed sideways and upward under sills and around corners. Windows and their flashing details need to shed water that's moving in directions a simple bead of caulk was never designed to handle. This is a flashing and sequencing issue as much as a product issue, which we cover below.

Moss, Shade, and Sustained Moisture

Many Bellingham lots have significant tree cover or north-facing walls that stay damp for days after a storm. That kind of sustained moisture is hard on wood trim, promotes moss and mildew growth on sills, and can slowly break down caulk and sealants that aren't rated for constant wet exposure. Detailing and material choice both need to account for surfaces that may not fully dry out between rain events for weeks at a time.

Frame Materials: What Holds Up and What Doesn't

There's no single "best" window material — the right call depends on budget, exposure, and how the home is built. Here's how the common options compare for Whatcom County's climate specifically:

Material	Moisture Behavior	Maintenance	Best Fit
Vinyl	Won't rot; handles constant damp well	Low — occasional cleaning	Most new builds and value-focused projects
Fiberglass	Very stable, minimal expansion/contraction in wet-cold swings	Low	Higher-exposure walls, larger openings, longer-term owners
Aluminum-clad wood	Good exterior protection, but relies on flawless sealing at joints	Moderate — interior wood still needs attention	Homeowners wanting a wood interior look with exterior protection
Bare wood	Poor in sustained damp/shade without diligent upkeep	High	Only where owners commit to regular refinishing

We don't install bare wood windows on new construction in this climate as a matter of professional standard — not because wood windows are inherently bad, but because Whatcom County's shade, moisture, and moss conditions demand a maintenance schedule most homeowners underestimate. Clad-wood or fiberglass gets you the interior wood look with far less long-term risk.

The Installation Details That Actually Protect the Opening

The window product matters less than most people assume. What actually determines whether a window leaks in five years is the installation sequence around it. On a new-construction opening, we follow a layered, shingle-style approach so every layer sheds water onto the layer below it, never behind it:

Sill pan flashing installed first, sloped slightly outward so any water that gets past the window drains back out, not into the wall cavity.
Jamb flashing up both sides, lapped over the sill pan.
Window set into the opening, shimmed square and plumb, fastened per the manufacturer's schedule — not just at the corners.
Head flashing installed last across the top, lapped over the jamb flashing and integrated with the weather-resistive barrier above it.
Air sealing around the interior gap with an appropriate low-expansion product — overfilling with foam can bow the frame and cause the window to bind or seal poorly.

Skipping or reversing any of these steps — a common shortcut on rushed jobs — is exactly how water ends up inside a wall that looks fine from outside for years before the damage shows.

Our Process, Start to Finish

For new-construction and full re-side projects in the Bellingham area, our sequence looks like this:

Walk-through and measure: we confirm rough opening sizes against the window order and check the wall assembly (sheathing type, weather-resistive barrier) before anything ships.
Product selection: we go over frame material, glass package, and hardware options based on the home's exposure — waterfront, shaded, or a more typical in-town lot.
Flashing and set: sill pan, jamb, and head flashing installed in sequence as above, window set square and shimmed, fasteners driven to spec.
Integration with siding: trim and siding tied into the flashing system so water sheds outward at every layer, not just at the window itself.
Final check: operation, seal, and sightlines confirmed before we call the opening done.

Because we also handle siding, we're looking at the window opening as part of the whole exterior envelope rather than an isolated task — which matters when the siding crew and the window crew are the same people and there's no gap for details to fall through between trades.

Common Mistakes We See on Local New Builds

Some of the recurring issues we run into on new-construction homes and additions around Bellingham and Whatcom County:

Caulk used as the primary water barrier instead of proper flashing — caulk is a supplement, not a substitute.
Sill pans left flat or sloped the wrong direction, trapping water instead of draining it.
Windows fastened only at the corners, leaving the frame free to bow under wind load.
Weather-resistive barrier lapped incorrectly at the head flashing, sending water behind the barrier instead of over it.
Foam sealant overfilled around the frame, causing binding or uneven compression on the seal.

None of these show up on a walkthrough right after installation. They show up after a wet winter, which is exactly why sequencing and inspection during the build matter more than they might seem to at the time.

Checklist: What to Confirm Before Your Windows Go In

Rough openings measured and confirmed against the actual window order, not just the plan set
Sill pan flashing product and slope specified in writing, not left to on-site improvisation
Frame material matched to the wall's sun/shade exposure and proximity to open water
Fastening schedule follows the manufacturer's spec, not just "enough to hold it up"
Weather-resistive barrier lap sequence planned before the window crew and siding crew hand off work to each other
Interior air-sealing product specified (low-expansion foam or backer rod, not standard high-expansion foam)

Cost Factors Worth Understanding

We don't quote new-construction window pricing without seeing the plans and openings, but the main variables that move the number are consistent from project to project:

Factor	Effect on Cost
Frame material (vinyl vs. fiberglass vs. clad-wood)	Vinyl typically lowest; fiberglass and clad-wood run higher
Glass package (standard vs. upgraded low-E, tempered where required)	Upgrades add cost per opening but improve comfort and code compliance
Number and size of openings	Larger and more numerous openings raise both material and labor cost
Wall exposure (waterfront, high wind, heavy shade)	May push toward higher-spec flashing and hardware, adding modest cost
Access and building stage	Easier access during framing keeps labor lower than retrofitting later

The honest advice: don't shop window packages purely on the sticker price per opening. A cheaper window installed with a compromised flashing detail costs far more once you account for the repair down the road.

Why a Bellingham-Experienced Crew Matters

Window flashing details that work fine in a dry inland climate aren't automatically right for Whatcom County's rain and shade patterns. A crew that already works new-construction projects in and around Bellingham has seen which flashing sequences actually hold up here, which frame materials are worth the upgrade on exposed walls, and which shortcuts show up as callbacks two winters later. That local repetition is worth more than a generic installation manual, because it's been tested against this specific climate, not a national average.

If you're planning a new build or a full re-side in Bellingham or elsewhere in Whatcom County, we're happy to walk the site, look at your plans, and put together a straightforward estimate — no pressure, no upsell script, just an honest look at what your project actually needs. Use the form below to get started.