7 Window Replacement Mistakes to Avoid

Most window replacement regrets are not about the windows — they are about decisions made in the two weeks before signing. After thousands of Quebec installations, the same seven mistakes come up again and again, and every one of them is avoidable with information you can gather in an afternoon. Here they are, with the questions that prevent each one.

Mistake 1: Choosing on Price Alone

When three quotes land at $12,000, $16,000 and $21,000 for "the same" ten windows, the numbers are almost never describing the same project. The low bid typically gets there through builder-grade frames, double glazing where triple belongs, no low-E upgrade, thinner installation details and a crew paid by the opening rather than by the job done right. None of that is visible in a one-page quote — which is exactly why price-only comparison fails.

The honest comparison is line by line: exact model and series, U-factor and Energy Rating for the configuration quoted, glass package per orientation, installation method (insertion versus full-frame), what happens to interior casings and exterior cladding, disposal, and warranty terms for both product and labour. Ask each bidder to state these in writing; the cheap quote usually stops being comparable by the third line.

Windows are a 25-to-40-year purchase in which the product is only part of the cost of ownership. A $4,000 saving that delivers 1990s thermal performance costs itself back in Hydro-Québec bills and comfort over a decade, then keeps costing. Value the quote over the life of the window, not over the week you sign it.

Mistake 2: Ignoring Installation Quality

A mid-range window installed impeccably outperforms a premium window installed carelessly — every time, in every climate, and especially in this one. The window itself is a sealed, factory-tested unit; the 20 millimetres around it are hand-made on your wall in a day. Air leakage, water infiltration and frame distortion nearly always originate in that perimeter joint, not in the product.

Proper installation in Quebec means the opening is shimmed square and plumb, the perimeter is insulated with low-expansion foam (not stuffed fiberglass, not left hollow), the exterior joint gets a backer rod and quality sealant, sill flashing directs water out, and the interior air-vapour barrier is made continuous with the window. Each skipped step is invisible on day one and expensive by year five — drafts, frost at the casing, rot in the rough sill.

Interrogate the installation, not just the brochure: who actually installs (employees or subcontractors paid per opening), what is the crew's method for air sealing, will they show you a mid-job opening, and is installation labour warranted in writing for at least five years? Our guide to professional window installation details what a correct job looks like step by step, so you know what you are paying for and what to verify.

Mistake 3: The Same Glass on Every Orientation

Ordering one glass package for the whole house is simpler for the seller and worse for you. A south-facing window in Quebec can harvest meaningful free heat all winter if it carries a moderate-to-high solar gain coating; that same coating on a large west-facing window turns the living room into a greenhouse on July afternoons. North-facing glass sees little direct sun and should simply chase the lowest possible U-factor.

The specification language is SHGC — solar heat gain coefficient. As a working rule for Quebec: south facades tolerate and often benefit from SHGC around 0.35 to 0.45; west (and to a lesser degree east) facades with big glass want lower, 0.25 to 0.35, to blunt summer overheating; north facades prioritize U-factor and triple glazing over any solar consideration. Street noise is also orientation-specific — asymmetric glass thicknesses or laminated panes on the street side cost little when ordered up front.

A good consultant asks about orientations, shade trees, room overheating and noise before quoting. If every window in your quote shows identical glass, nobody engineered anything — they copied a default. It costs nothing to ask for the SHGC per facade; it costs a lot to live with the wrong one.

Mistake 4: Skipping Permits and the RBQ Check

Two administrative steps get skipped in the excitement of choosing colours, and both can bite hard. First, permits: many Quebec municipalities require one when window dimensions, locations or exterior appearance change, and boroughs with heritage overlays — Plateau-Mont-Royal, Outremont, Old Longueuil and dozens more — regulate even like-for-like replacement on visible facades, down to material and divided-lite pattern. An unpermitted change can mean redoing a facade at your expense; a quick call to the borough costs nothing.

Second, the contractor's licence. In Quebec, installing windows for a client legally requires an RBQ licence (Régie du bâtiment du Québec), which comes with mandatory bonding and defined recourse if the work is deficient or the company disappears. Verifying takes two minutes on the RBQ's public register: confirm the licence is active, in the right category, and registered to the exact business name on your contract — not a similar name, not "the licence of a friend."

While you are checking, confirm liability insurance and CNESST compliance for the crew working on your property. A contractor who hesitates on any of these is telling you how the rest of the project will go. The paperwork takes one evening; skipping it puts your only real recourse in the shredder.

• Call your municipality or borough: is a permit required, and are there heritage rules for the facade?
• Verify the RBQ licence number on the public register — active, correct category, exact company name
• Ask for proof of liability insurance and CNESST registration
• Keep copies of permit, licence check and contract together for warranty and resale

Mistake 5: Windows That Fight the House

Replacement is the moment a house's face changes for decades, and style mistakes are the ones you see every single day from the curb. The classics: white vinyl casements punched into a century home that always had wood double-hungs with divided lites; a modern black frame on one facade elevation while the rest stays almond; chunky replacement frames that shrink the glass area and make the facade look like it is squinting.

Respect the architecture's logic. Heritage-influenced homes generally want vertical proportions, traditional profiles and lite patterns close to the originals; postwar bungalows carry horizontal sliders and picture windows naturally; contemporary builds reward slim frames and large uninterrupted glass. Colour deserves the same discipline — black and dark commercial tones flatter some facades and overwhelm others, and exterior colour is essentially permanent on your schedule, not fashion's.

Two practical safeguards: replace by whole facade rather than one window at a time, so profiles and colours stay consistent; and look at real installed projects on houses like yours, not showroom samples. Manufacturers offer hybrid options — one colour outside, another inside — so the interior design debate does not have to be settled on the lawn.

Mistake 6: Not Reading the Warranty Before Signing

"Lifetime warranty" is a marketing phrase, not a contract term — the contract is the fine print, and the fine print varies enormously. The questions that matter: how long is the sealed glass unit covered against fogging (the most common failure), is that coverage prorated after year ten, are hardware and weatherstripping included, does coverage transfer to the next owner, and — most often forgotten — who pays the labour to remove and reinstall a failed unit in year eight?

Product and installation warranties are separate documents from separate parties. The manufacturer covers the unit; the installer covers the perimeter work — and a supplier who subcontracts installation may cover it barely or not at all. A serious installer warrants labour in writing for five years or more; if a draft appears at year three, that document decides whether the fix is free or $400 per opening.

Read both documents before signing, not when the first seal fails. Note the claim procedure and keep your invoice, spec sheets and photos in one file — warranty claims settle fastest when the serial numbers and dates are one email away.

Mistake 7: DIY Measuring and Ordering

Ordering windows to your own measurements is the mistake with the least sympathy after the fact, because custom-made windows are non-returnable. A rough opening is measured at three widths and three heights, taking the smallest of each, with diagonals checked for square and allowances made for shimming, sill slope and the installation method — insertion frames measure completely differently from full-frame replacements. A tape held across the old casing gets several of those wrong at once.

The failure modes are all expensive. Too big and the frame will not enter the opening — a reorder measured in weeks and dollars. Slightly too small and the installer bridges the difference with foam and extension trims: legal, but thermally weaker, uglier, and leak-prone at the sill. Old Quebec houses add their own traps, with openings out of square by two centimetres and no two "identical" windows actually identical.

Professional measurement solves the risk and moves the liability. When the installer measures, a wrong size is their reorder, not your problem — one more reason the measure-and-install package from one responsible company beats supplying your own windows to a third-party crew. Use your tape for budgeting; let the contract measurements come from the party who answers for them.

Getting It Right: A One-Evening Checklist

Every mistake above is prevented before signature, none after. The pattern behind all seven is the same: the visible part of the decision (price, colour, brochure specs) crowds out the invisible part (installation method, orientation engineering, paperwork, fine print) — and the invisible part is where the money and comfort live.

Spend one evening with this checklist and the three quotes on the table. If a bidder cannot answer these questions in writing, that silence is itself the answer.

• Line-by-line quote comparison: model, U-factor, ER, glass per orientation, installation method, disposal, warranties
• Installation method described in writing — shims, low-expansion foam, backer rod and sealant, sill flashing, air barrier continuity
• SHGC specified per facade; noise glass considered on street side
• Permit confirmed with the borough; RBQ licence verified on the public register
• Style, profile and colour checked against the whole facade, with installed references
• Both warranty documents read: sealed unit term, proration, transferability, labour coverage
• Final measurements taken by the installer, and stated as their responsibility in the contract

Frequently Asked Questions