A premium window installed wrong performs worse than a budget window installed right. That's not a slogan — it's what 46 years of tearing out other people's work has taught us. Here is what a correct full-frame installation actually involves, step by step, including the parts that disappear behind the trim. At each step, we'll tell you what skipping it costs — because almost every failure we're called out to fix traces back to one of these corners.
Step 1: Tear-Out to the Rough Opening
We remove the old sash, frame, interior stops, and exterior trim down to the bare rough opening — the structural lumber the original builder framed. This is slower than leaving the old frame in place, but it's the only way to see what four decades of weather have done underneath.
What cutting this corner costs you: an insert stuffed into a rotten frame seals rot inside your wall, where it keeps spreading on your dime.
Step 2: Inspect and Repair the Sill and Framing
With the opening bare, we check the sill, jack studs, and header for rot, insect damage, and water staining. Soft wood gets cut out and replaced with sound lumber — not coated in filler and painted over. In Treasure Valley homes from the '70s through the '90s, we find repairable sill damage in roughly one opening out of every ten.
What cutting this corner costs you: new windows anchored to compromised framing — the fasteners have nothing solid to hold, and the rot bill compounds every year it hides.
Step 3: Sill Pan Flashing
Before the new window goes anywhere near the opening, we build a waterproof pan across the sill: flexible flashing membrane run across the bottom and turned up the jambs, with a back dam so water can only drain outward. Here's the honest truth the industry doesn't like to say out loud: water will get past your window someday. A seal ages, a gasket shrinks, wind drives rain sideways. The pan is what decides whether that water drips harmlessly back outside or feeds a colony of rot inside your wall. ASTM E2112, the national installation standard, treats pan flashing as fundamental — yet it's the most commonly skipped step in residential work because nobody can see it after lunch.
What cutting this corner costs you: the first failed seal drains into your framing instead of your flowerbed. This is the difference between a $0 non-event and a $6,000 wall rebuild.
Step 4: Set the Window — Plumb, Level, Square, Shimmed at Lock Points
The window goes in dry-fit first. We shim it plumb, level, and square, checking diagonals — because a frame that's out of square by an eighth of an inch will fight you at the lock forever. Shims go where the engineering wants them: under the jambs at lock points and hinge points, at the meeting rail on hung windows, never randomly. Shims transfer load; a shim in the wrong place is a pressure point that distorts the frame.
What cutting this corner costs you: sashes that stick every August, locks that need a hip-check to engage, and a "drafty window" that's really a parallelogram.
Step 5: Fasten Per the Manufacturer's Schedule
Every manufacturer publishes a fastening schedule — which fasteners, where, how many, how far from corners. We follow it exactly, and not just because it's right: the fastening schedule is a warranty condition. Improvised fastening voids coverage on the very window you just paid for.
What cutting this corner costs you: a manufacturer's warranty claim denied on inspection, ten years from now, when you need it most.
Step 6: Low-Expansion Foam — and Only Low-Expansion
The gap between frame and framing gets filled with low-expansion, window-and-door-rated foam. High-expansion foam — the cheap stuff — generates real pressure as it cures, enough to bow a vinyl or fiberglass frame inward until the sash binds. We foam in controlled passes and never pack the gap.
What cutting this corner costs you: a brand-new window that won't open by spring, with a bowed frame no adjustment can fix.
Step 7: Exterior Flashing Tape, Shingle-Lapped with the WRB
Outside, flashing tape seals the window flange to the weather-resistive barrier — jambs first, head last, every layer lapped shingle-style so gravity carries water over each joint, never behind it. The head flap of the WRB comes down over the head tape. Order of operations is everything here; tape applied bottom-over-top is a funnel pointed into your wall.
What cutting this corner costs you: a wall that leaks only in wind-driven rain — the hardest, most expensive kind of leak to diagnose.
Step 8: Interior Air Seal
Inside, we seal the frame-to-framing joint with backer rod and sealant or a continuous foam seal. The exterior layer sheds water; the interior layer stops air. They're different jobs. Skip the interior seal and warm indoor air leaks into the wall cavity all winter, condensing against cold sheathing.
What cutting this corner costs you: drafts you'll blame on the window, and hidden condensation that wets the insulation around every opening.
Step 9: Exterior Trim and Casing
Exterior trim goes back on — or new casing, matched to the house — bedded in sealant where it meets siding, with clean joints and back-caulked ends. On older Boise homes we mill trim to match the original profiles rather than flattening a 1948 house with stock brickmould.
What cutting this corner costs you: curb appeal, obviously — but also open trim joints that wick water behind the siding.
Step 10: Adjustment and Lock Tuning
Last, we tune each unit: sash travel, tilt latches, lock engagement, weatherstrip contact. A lock should close with two fingers. Then we walk you through the operation of every window before we load the trucks.
What cutting this corner costs you: a punch list you discover one window at a time, after the crew is gone.
Why We Can Promise Every Step Happens
Every one of these steps is performed by Wood Windows employees — AAMA-certified installers on our payroll, not the lowest bidder on a subcontractor list. Same crews, same standard, every house, for 46 years. If you'd like to see it done right on your home, the measure is free: call (208) 376-2200 or use the form on this page.
Frequently Asked Questions
What is sill pan flashing and why does it matter?
A sill pan is a waterproof tray — formed from flexible flashing membrane or a rigid pan — installed across the bottom of the rough opening before the window goes in. Every window seal eventually admits some water. The pan catches it and drains it back outside instead of letting it soak the framing. It's invisible when the job is done, which is exactly why cut-rate installers skip it.
Why does the type of expanding foam matter in a window install?
High-expansion foam generates enough pressure as it cures to bow a vinyl or fiberglass frame inward — sashes bind, locks misalign, and the window never operates right again. Low-expansion, window-and-door-rated foam seals the gap without deforming the frame. It costs a little more per can, which is why you should ask what your installer uses.
How long does it take to install one window correctly?
A full-frame installation done right — tear-out, opening inspection, sill pan, setting, fastening, foam, flashing tape, interior seal, and trim — typically runs 60 to 90 minutes per window. An insert replacement in a sound frame runs closer to 30 to 45. If someone promises a whole house in half a day with a two-man crew, steps are being skipped.
Does Wood Windows use its own installers?
Yes. Every installation is performed by Wood Windows employees — AAMA-certified crews on our payroll, in our trucks, covered by our insurance. We have never subcontracted installation in 46 years, because the install determines whether a good window performs like one.
Sources & Testing Data
Last reviewed 2026-07-06 by Wood Windows Inc — (208) 376-2200