Bellingham Siding What "New-Construction Windows" Actually Means
New-construction windows are built with a nailing fin around the perimeter of the frame. That fin gets fastened directly to the wall sheathing, then integrated into the water-resistive barrier (WRB) and flashed in layers before siding goes back on. This is different from a pocket or insert replacement window, which slides into an existing frame and leans on that old frame's condition to keep water out. New-construction windows are the right call any time the siding is coming off anyway, when a wall is being reframed or resized for a bigger opening, or when the existing frame has already taken on water damage and needs to go. For a lot of Sehome homes — especially older ones near campus that have had additions, remodels, or siding replacements over the years — this is the more thorough option, and it's the one that actually resets the water management at that opening instead of working around a compromised one.
Why This Matters More in Sehome Than It Might Elsewhere
Sehome's mix of older single-family homes, converted rentals, and infill construction near Western Washington University means a lot of window openings that have been touched more than once — added onto, re-sided, or fitted with replacement windows at some point without addressing the flashing underneath. Bellingham's building stock skews older than a lot of Western Washington suburbs, and older openings are exactly where new-construction windows earn their keep: you're not just swapping glass, you're rebuilding the flashing assembly at that wall from scratch. That's a meaningfully different job than popping a new sash into an old frame, and it's worth doing right the first time rather than patching around a leak that's already found its way into the wall.
The Regional Climate Reality
Whatcom County doesn't get the heaviest rainfall in the state, but it gets a lot of low-intensity, wind-driven rain over many months, plus proximity to salt air off Bellingham Bay that accelerates corrosion on unprotected fasteners and metal flashing. Add in a long moss and algae season — cool, damp conditions for much of the year that let organic growth take hold on north-facing walls and anywhere water sits instead of shedding — and you've got a climate that punishes shortcuts at window openings specifically. A gap in the flashing that would go unnoticed in a drier climate becomes a slow leak here, because the wall never really gets a chance to dry out between rain events. This is the backdrop for everything we do differently on a new-construction window job in this area:
- Driving rain means face-sealing alone (caulk and hope) isn't enough — the assembly needs to shed water mechanically, not just rely on sealant
- Salt air means fastener and flashing material choice actually matters, not just fit and finish
- Long wet seasons mean any trapped moisture has months to do damage before a dry spell shows up
- Moss and algae growth on north and shaded walls means drainage paths at sills and trim need to stay clear, not just watertight
What a Correct Installation Actually Involves
Sequencing Matters as Much as the Window Itself
The window unit is only part of the job. The flashing sequence around it — sill pan first, then side flashing lapped over the pan, then the head flashing lapped over the side flashing and integrated with the WRB above — has to go in a specific order so that water draining down the wall is always directed outward, never behind the next layer down. Get that shingle-lap sequence backwards or skip a layer, and you've built a funnel instead of a barrier. It doesn't leak on day one. It leaks in year three or four, after enough wind-driven rain events have found the gap, and by then the damage is inside the wall cavity where nobody can see it until the siding or trim starts showing stains.
The Sill Pan Is Non-Negotiable
A sloped, corner-dammed sill pan under the window is cheap insurance against the single most common failure point in any window installation: water that gets past the sash and needs somewhere to go besides straight down into the framing. In a climate with this much sustained rain, we treat the sill pan as a standard part of the job, not an upsell.
Fastener and Flashing Material Choice
Given the salt air off the bay, we pay attention to galvanic compatibility — making sure flashing metal, fasteners, and the window frame material don't set up a corrosion reaction against each other over time. It's a small detail that doesn't show up in a walkthrough but shows up ten years later if it's ignored.
New-Construction vs. Insert Windows — Which Fits Your Project
| Factor | New-Construction Window | Insert / Pocket Window |
|---|---|---|
| Siding involvement | Siding must be removed at the opening (or is already off) | Existing siding and trim stay in place |
| Water management | Full flashing assembly rebuilt from the sheathing out | Relies on the existing frame's condition and seal |
| Best fit | New builds, additions, re-siding jobs, or frames with existing damage | Sound existing frames where siding isn't being disturbed |
| Opening size changes | Straightforward to resize the rough opening | Limited to the existing opening dimensions |
| Typical project pairing | Full siding replacement or new construction | Standalone window replacement |
If your siding is already coming off, new-construction windows are almost always the better long-term choice — you're paying for the tear-out and re-flashing either way, so it makes sense to reset the whole assembly rather than reuse an old frame of unknown condition.
Our Process for a Sehome Job
1. On-Site Assessment
We look at the existing openings, the condition of the sheathing and WRB where exposed, and how the current siding and trim were installed. This tells us whether we're dealing with straightforward new-construction openings or whether prior water intrusion needs to be addressed before new windows go in.
2. Prep and Tear-Out
Old windows and surrounding siding come out, sheathing is inspected and repaired if there's rot or soft spots, and the opening is squared up and sized for the new units.
3. Flashing and Window Install
Sill pan, side flashing, window installation per manufacturer spec, then head flashing integrated with the WRB above — each layer lapped correctly before the next goes on.
4. Siding and Trim Restoration
Trim and siding are brought back around the new openings, matched to the surrounding wall as closely as the existing material allows.
5. Final Check
We walk the openings with you before calling the job done, checking operation, seals, and that drainage paths at sills are clear.
Frame Materials Worth Considering in This Climate
Vinyl, fiberglass, and clad-wood are all viable in Whatcom County, and the right choice depends on your budget, the style of the house, and how much upkeep you want to take on. Vinyl is low-maintenance and cost-effective, and modern vinyl frames handle the wet climate well. Fiberglass costs more but holds up to temperature swings and moisture with very little movement over time. Clad-wood gives you a wood interior with a weather-resistant exterior shell, which suits older or more traditional Sehome homes where matching the existing character matters, but it comes with a higher price point and more attention needed at the cladding seams. We'll talk through the honest trade-offs for your specific house rather than pushing one option across the board.
Cost Factors to Expect
| Factor | Why It Moves the Price |
|---|---|
| Number and size of openings | More and larger windows mean more flashing work, not just more glass |
| Existing damage found during tear-out | Rotted sheathing or framing found once siding is off needs repair before windows go in |
| Frame material | Vinyl, fiberglass, and clad-wood carry different material costs |
| Opening resizing | Changing rough opening dimensions adds framing work beyond a like-for-like swap |
| Siding type being restored | Matching trim and siding around new openings varies by material and how the original was installed |
We give a firm number after we've actually looked at the openings — not a phone estimate — because the flashing and prep work is where the real cost variation lives, not the windows themselves.
What to Check Before You Hire Anyone for This
- Do they treat the sill pan and flashing sequence as standard, or as an add-on you have to ask for?
- Will they inspect sheathing condition once siding is off, before installing new windows over a hidden problem?
- Do they have experience with this specific climate — driving rain and long wet seasons — or mostly drier-climate installs?
- Are they clear about the difference between new-construction and insert windows, and which one your project actually needs?
- Will they give you a written scope that includes flashing and siding restoration, not just "window installed"?
Why Local Experience with Sehome Homes Matters
A crew that's worked in Sehome and around Bellingham knows what the older housing stock in this part of the city tends to hide once siding comes off — prior remodels, inconsistent past flashing work, and wall assemblies that weren't always built to current standards. That's not a knock on the neighborhood; it's just what you find in a city with a lot of housing built across many decades. Knowing that going in means fewer surprises mid-project and a more accurate estimate up front, instead of change orders once the walls are open.
If you're planning new construction, an addition, or a full siding replacement in Sehome and want windows installed the right way from the sheathing out, we're happy to take a look and put together a free, no-pressure estimate — no obligation, just an honest read on what your project needs.