How to Price Window Replacement: UPVC, Aluminium and Timber Trade Supply Rates

Quick Answer: A standard 1,200×1,200mm UPVC casement supply-and-fit prices at £450–£750 in 2026, aluminium £700–£1,200 and a sash timber sash window £1,400–£2,800. Build the quote bottom-up: frame supply, glass upgrade, fitter day rate (£280–£450), finishings (silicone, trims, internal reveal making good) and FENSA notification (£3–£8 per window through your scheme provider). Never price by linear-metre — wider windows scale non-linearly because of glass cost steps and lift requirements.

Summary

Pricing windows looks straightforward — until you've done a survey and realised the supplier price covers the frame and unit only, the customer wanted obscure glass in the bathroom, the sill is 200mm deep stone that you'll have to box round, and the upstairs bay needs scaffolding because the access platform won't reach. Most window quotes that go bad go bad on the things outside the frame: lifting gear, internal making-good, FENSA notification fees, mid-job upgrades to acoustic glass, and trickle vents under Approved Document F.

Trade prices in 2026 sit roughly 12–18% above 2024 levels because of energy-efficiency-driven Building Regs Part L changes and the U-value uplift to 1.4 W/m²K (replacement) and 1.2 W/m²K (new dwelling) under SAP 10.2. Aluminium prices have softened slightly as suppliers absorb LME aluminium volatility, but timber sash windows continue to climb because of rising softwood and labour cost, especially Accoya and engineered laminated softwood. Always quote against a measured survey, never off the customer's tape measure — opening tolerance and structural lintel issues account for most loss-making jobs.

This guide covers UK trade supply rates, fitter day rates, FENSA scheme economics, the Part L compliance checks Building Control or your competent person scheme will require, and the line items most fitters miss.

Key Facts

Quick Reference Table — UK Trade Supply Costs 2026

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Window type Size (mm) Trade supply (frame + glass) Supply + fit (single window) Notes
UPVC casement, A-rated 600×900 £160–£220 £340–£480 Bathroom, single opener
UPVC casement 1,200×1,200 £230–£320 £450–£700 Standard front room
UPVC casement 1,800×1,200 £340–£460 £600–£900 Wide kitchen/lounge
UPVC tilt-and-turn 1,200×1,200 £290–£420 £550–£800 Triple gasket, premium
UPVC sliding sash (mock Georgian) 900×1,500 £580–£780 £900–£1,300 Astragal bars, balanced
Aluminium casement 1,200×1,200 £450–£650 £700–£1,100 Polyester powder-coat
Aluminium slim-sash flush 1,200×1,500 £750–£1,100 £1,150–£1,700 Architectural
Engineered timber casement 1,200×1,200 £550–£800 £950–£1,400 Factory finished
Box sash (engineered softwood) 900×1,800 £1,150–£1,650 £1,650–£2,400 Cords or spiral balance
Box sash (Accoya) 900×1,800 £1,650–£2,400 £2,200–£3,200 50-year warranty
Bay (3-sided UPVC) 2,400×1,200 £680–£980 £1,150–£1,800 Plus loadbearing post if structural
French doors (UPVC) 1,500×2,100 £550–£780 £950–£1,400 Pair, low threshold
Roof window (Velux GGL MK06) 780×1,180 £280–£400 £550–£900 Plus flashing kit

Frame prices assume A-rated 4-20-4 double-glazed sealed unit, argon-filled, warm-edge spacer. Triple glazing adds 22–35% to the supply cost; toughened safety glazing adds £18–£35/m² where critical-location regs apply.

Detailed Guidance

Building the quote line by line

A defensible quote breaks every window into seven cost categories. Don't merge them — clients query opaque quotes and the line-item structure also helps you spot where you've under-priced.

  1. Frame and unit supply — quoted from your supplier, not retail. Always confirm the price includes the BFRC energy rating, hardware (handles, espagnolette, restrictors), trickle vents, and any astragal bars or Georgian grids if specified.
  2. Glass spec uplifts — toughened (BS EN 12150), laminated (BS EN 14449), acoustic (BS EN 12758), obscure pattern, low-e plus solar control. Each adds a per-m² premium.
  3. Lifting and access — ladder work for ground floor; tower scaffold for first floor; full system scaffold for bay/oriel and anything above 4m. Don't price as "labour" — it's separate.
  4. Fitter labour — day rate × number of windows ÷ daily throughput. Include a half-day buffer for the last day for cleaning, sealing and snagging.
  5. Internal make-good — silicone bead (always included), reveal repointing, plaster patching, sill repair or replacement. The customer's expectation here is the most common pricing dispute.
  6. External make-good — render or brick repair around the new frame, lead flashing tucking back into chase, drip detail.
  7. Notification and certification — FENSA scheme fee, Building Control involvement if you go that route instead, and the certificate sent to the customer.

When Building Control gets involved instead of FENSA

You can replace windows under either route: through a Competent Person Scheme (FENSA, CERTASS, Assure) where the installer self-certifies, or via a Building Control application where the local authority inspects and certifies. For straightforward like-for-like swaps, FENSA is faster and cheaper. Building Control becomes the only route when:

A Building Control Application (BCA) typically costs £200–£450 for a domestic window replacement and the inspection adds 1–2 site visits.

Critical-location safety glass

Approved Document K and BS 6262-4 mandate safety glass (toughened or laminated) in:

Pricing without confirming the survey checked these dimensions is the single most common reason a replacement quote ends up unprofitable — the supplier substitutes toughened glass at a £25–£70 premium per pane, and you swallow the cost.

Bay windows, oriels and structural lintels

Bay-window replacement is the highest-risk product category. The original bay frame may be load-bearing in a Victorian terrace or Edwardian semi. The replacement must either retain the structural strap-and-tie connection above the bay or include a new structural post and lintel. Always:

A "simple" bay swap that turns into a structural job typically costs an extra £600–£1,400 on materials and £300–£700 on labour. Include this as a contingency on every bay quote.

Sash windows: balance type, lift weight and Listed Buildings

The two main sash window mechanisms are cord-and-weight (traditional) and spiral spring balance (modern). Cord-and-weight requires deep boxes either side of the frame to house lead or cast-iron weights — typically 100–125mm — and is non-negotiable in Listed Buildings or Conservation Area-restricted properties. Spiral balance fits in a narrower frame but is less suitable for very heavy sashes (>20kg).

Listed Building Consent applies to any sash replacement on a Grade I, II* or II property and to many Conservation Area properties. Plan a 6–10 week lead time for application and decision. Refusal is common where modern double-glazed units are proposed for a Grade II* — slimline 12mm units (£250–£400/m² premium) or single-glazed with secondary glazing are usually the only routes through.

Trickle vents under Part F (June 2022)

Since 15 June 2022, Approved Document F has required trickle vents in replacement windows in habitable rooms (8,000 mm² equivalent area) unless background ventilation is otherwise provided (e.g. continuous mechanical extract). Bathrooms and kitchens require 4,000 mm² in wet rooms with intermittent extract.

A common pricing trap: customers sometimes ask for "no trickle vents — they're ugly." You cannot legally deliver this on a FENSA notification — the fitter is the one who self-certifies compliance. Either provide alternate background ventilation (mechanical) or fit the trickle vent. Document the conversation in writing.

Frequently Asked Questions

Should I price doors and windows together as a package?

Yes — supplier discount tiers usually break around 5–10 frames. Combined orders unlock the next discount band, so a job with 8 windows plus a bifold or sliding door set often comes in 8–12% cheaper than the same items priced individually. Quote the package price but break the cost out by line item so the customer can see what they're paying for.

How much should I add for unforeseens?

A measured survey reduces unforeseens significantly, but lintel failure, hidden rot in timber sub-frames, and undersized openings still occur. Add a 5–8% contingency for UPVC supply-and-fit, 8–12% for timber/sash, and 12–18% for bay and structural-bay work. Mark unforeseens out as a separate line in the quote so the customer doesn't think you've padded the price.

What's the cost of a single window replacement on a UK 3-bed semi (homeowner-friendly)?

A typical front-room casement on a UK 3-bed semi costs £450–£900 supply-and-fit in 2026 for UPVC, £700–£1,200 for aluminium, and £1,400–£2,400 for engineered timber. Whole-house replacement (8–10 windows on a 3-bed semi) usually lands at £4,500–£9,500 for UPVC and £8,000–£16,000 for aluminium or timber. The price depends on size, glass spec, access, and whether trickle vents are needed (post-June 2022 they almost always are). Always get itemised quotes — it's the easiest way to compare like-for-like.

Do I need scaffolding for first-floor windows?

Working at Height Regulations 2005 require a safe means of access, but not necessarily scaffold. For first-floor casements you can use an alloy tower (£60–£90/day hire) or scaffold-tower hybrid system. Anything above 4.5m to the cill or with no firm ground for tower legs needs system scaffold. Always check tile/slate roof eaves clearance — many pre-1970 properties have only 50–80mm of overhang and full scaffold is the only safe access.

How do I price replacement on a Conservation Area property?

Slow down and confirm whether Article 4 Direction is in force — many London and southern Conservation Areas restrict permitted development on windows and require planning permission for any change of frame material. Default to like-for-like in style, opening pattern, and glazing-bar layout. Price a slimline 12mm sealed unit (£250–£400/m² premium) and budget 4–8 weeks lead time for both the planning decision and the manufacture. Always include a planning fee allowance (£206 householder application fee 2026) and a planning consultant fee if the case is borderline.

Regulations & Standards