Window Replacement Cost Guide: UPVC, Aluminium & Timber UK

Quick Answer: Standard UPVC casement window replacement runs £450–£900 supply-only and £200–£350 to fit per opening. Aluminium adds 60–120% to UPVC supply cost; timber 80–150%. All replacement glazing must be FENSA, CERTASS or Building Control notified under Building Regulations Part L 2021 and Part F, with U-values not exceeding 1.4 W/m²K for whole-window.

Summary

Window replacement is one of the most quoted jobs in domestic trade. Pricing it badly costs you either the job or your margin, and the gap between a winning quote and a losing one is often less than £80 per opening. This guide breaks down how to build a defensible price from trade supply, labour, ancillaries and compliance.

The market is split three ways: UPVC dominates volume (around 75% of UK domestic replacements), aluminium has taken share at the premium end (slimmer sightlines, larger openings), and timber holds its ground in conservation areas, period properties, and bespoke commissions. Each carries a different cost base, install time, and risk profile.

Most quotes fail on three things: forgetting the ancillaries (cills, reveals, trickle vents, FENSA registration), under-pricing the make-good (plaster damage, render cutting, internal redecoration) and not building enough contingency for surprises behind old frames (rotten lintels, missing cavity trays, lead flashing). Build these into your standard quote template and you'll stop losing money on jobs you thought were profitable.

Key Facts

• Trade vs retail — Window fabricators offer 20–40% trade discount on list. Don't quote retail. Open a fabricator account (Anglian Trade, Eurocell, Liniar, Veka) and your margin doubles.
• UPVC casement supply (standard sizes) — 600×900 £180–£260; 1200×1200 £280–£380; 1800×1200 £420–£550 trade pricing, white frames, A-rated double glazed.
• Aluminium adds 60–120% to UPVC supply for similar size — slim sightlines, more colours, thermally broken frames standard.
• Timber adds 80–150% to UPVC. Factory-finished engineered timber (Mumford & Wood, Bereco) is mid-range; conservation-grade hardwood top-end.
• Triple glazing adds £80–£150 per pane on top of double-glazed unit price.
• Building Regs Part L 2021 — Replacement windows must achieve whole-window U-value ≤1.4 W/m²K (or Window Energy Rating Band B).
• Building Regs Part F — Background ventilation (trickle vents) required unless dwelling has continuous mechanical ventilation.
• FENSA/CERTASS registration — £8–£12 per installation, mandatory unless using Building Control notification (£200–£400 per dwelling).
• CDM — Domestic clients on jobs under 30 days/500 person-days don't require CDM principal designer, but you still need safe systems of work.
• Lead time — UPVC 5–10 working days, aluminium 3–6 weeks, timber 4–8 weeks. Build deposit terms around this.
• Standard labour — 2-fitter team installs 4–6 standard openings per day for straight replacement (like-for-like).
• Lintels — Pre-cast concrete or Catnic steel lintels often need replacement on pre-1960s properties. Budget £80–£200 plus 2–3 hours' labour per opening.
• Cill thickness — UPVC standard cill 85mm or 150mm projection. Specify on order; site-cutting wastes time.
• Glass thickness — Standard 4–20–4 double glazing 28mm overall. Acoustic, security and Low-E options change cost.
• Toughened glass mandatory — In critical locations under BS 6262-4: within 800mm of floor in doors, within 300mm of doors, below 800mm in low-level glazing.

Quick Reference Table

Detailed Guidance

Building the supply price

Trade fabricators publish list prices, then apply a trade discount based on volume — typically 25% standard account, 35% for monthly volume, 40%+ for large national installers. If you're new, expect 20–25% off list. Quote off your actual trade price, never list.

Add hardware upgrades line-by-line: anti-snap cylinders (£8–£15 per door/window), shootbolt locks (£15–£30 extra), chrome handles (£8–£25 per handle), Georgian bars (£35–£60 per pane), foiled finishes (anthracite, oak, golden oak — 12–25% uplift on white).

Glass options matter for high-spec quotes: Pilkington K-glass standard, Activ self-cleaning adds £15–£30 per pane, acoustic laminated 6.4mm or 8.4mm adds £30–£80 per pane for road-noise installations, P5A security laminated for ground-floor BS EN 356 compliance adds £40–£90 per pane.

Fit labour calculation

Use 2 fitters at £180–£240 per day each (London £240–£320). Standard straight replacement of 4–6 openings = 1 day. Build the labour rate per opening:

• Ground-floor single casement: 1.5–2 fitter hours = £55–£90 labour
• First-floor casement with scaffold tower: 2.5–3 hours = £90–£140
• Bay window or large 3+ pane unit: 4–6 hours = £140–£260
• French doors: 3–4 hours = £105–£175
• Above-ground bay or oriel: full day for one opening, factor scaffold

Add 10% to standard labour for difficult access, lath-and-plaster reveals, listed/conservation work, or hardwood timber installs (more careful handling).

Ancillaries and make-good

This is where most quotes lose money. Cost every item separately on the worksheet:

• External silicone seal — included
• Internal trim/architrave — £25–£60 per opening if replacing, £0 if existing reused
• Internal plaster make-good — £45–£120 per opening (small patch to full reveal)
• External render make-good — £50–£150 per opening if render cut
• Lintel replacement — £150–£400 fitted if needed
• Cavity tray retrofit — £80–£200 per opening if missing (uncommon but high-stakes)
• Asbestos textured coating around opening — survey first, isolate, do not disturb. Add specialist removal cost.
• Skip hire — £180–£280 per skip for one-day jobs, £350–£500 weekly hire
• Scaffold or tower hire — Tower £80–£120/week, scaffold £400–£900 per elevation per week

Make these explicit line items on the quote. Customers who see them itemised understand the price; customers given a total feel cheated when extras appear.

Compliance and certification

All replacement windows in dwellings need Building Regulations sign-off under Part L (energy) and Part F (ventilation). Three routes:

1. FENSA-registered installer — £8–£12 per installation, certificate emailed to homeowner. FENSA notifies Building Control. Most common route.
2. CERTASS — Similar to FENSA, slightly different scheme. £8–£11 per cert.
3. Building Control notification — £200–£400 per dwelling. Used by non-CPS-registered installers. Disruptive — inspector must visit. Avoid where possible.

Include the FENSA/CERTASS cost in your quote as a separate line. Don't absorb it.

Trickle vents: required under Part F unless dwelling already has continuous mechanical ventilation (MVHR or whole-house extract). Budget £20–£40 per vent.

Lintel inspection: Pre-1960 properties often have under-spec or rotted lintels. Inspect before final order. New Catnic steel CG90 lintel £40–£80 supply; pre-cast concrete £25–£60. Allow 2–3 hours' labour per replacement.

Bay windows — pricing nuance

Bay windows are the highest-margin replacement opportunity but the easiest to mis-quote. Key cost drivers:

• Type of bay — splayed (3-section angled), square (3-section 90°), oriel (cantilevered, no posts to ground)
• Structural posts — Loadbearing posts under window frame? Survey before quoting. Replacement bay must include load path.
• Cill condition — Sub-cill or canopy roof often deteriorated. Budget make-good £150–£400.
• Above-bay roof — Lead or tiled canopy. Inspect, may need re-leading or re-felting. £200–£800.

Quote bays at 25–35% margin, not the 15–20% you might use on standard casements. The risk of surprise is much higher.

Aluminium-specific pricing

Aluminium has different drivers from UPVC. Key cost factors:

• Sightlines — Slim 60mm sightline frames cost 20–40% more than standard 80mm.
• Colour — RAL colour matching £80–£150 surcharge per order. Anthracite (RAL 7016) cheapest, fully bespoke RALs most expensive.
• Thermal break — All compliant aluminium has thermal break. Don't be sold non-thermally-broken industrial frames for domestic.
• Hinges and handles — Aluminium quality fittings (D&E, GU, Sobinco) cost more than UPVC equivalents.

Common aluminium fabricators: Origin, Smart Systems, Reynaers, Schueco. Premium aluminium installs at £900–£1,800 per opening.

Timber-specific pricing

Timber breaks into three tiers:

• Engineered factory-finished softwood — Roseview, Quickslide range, £400–£700 supply per casement opening. 60-year warranty common.
• Engineered factory-finished hardwood (sapele, oak, accoya) — £600–£1,100 supply, longer life, conservation-acceptable.
• Bespoke joinery (sliding sash, custom profiles) — £900–£2,200+ supply per opening, often required for listed buildings.

Timber needs maintenance painting at 5–8 year intervals — flag this to clients in the quote so they don't return claiming it's "rotting" when it just needs refinishing.

Frequently Asked Questions

Do I need planning permission to replace windows?

Generally no for like-for-like replacement in standard dwellings. Planning permission is required for: listed buildings (always), conservation areas (often, depending on Article 4 Direction), flats above ground floor, and significant changes (e.g. installing oriel or bay where none existed). Always check with the local planning authority before quoting if any doubt — refusal mid-project costs you the job and damages reputation.

What's the difference between FENSA and CERTASS?

Both are government-authorised competent person schemes for window and door installation, registered under MCS-like frameworks. FENSA is larger (originally GGF-backed). CERTASS is the alternative (TICA-backed). Functionally equivalent — both let you self-certify Building Regs compliance for replacement windows. Pick one and stick to it; annual fees £400–£700.

Can I quote without specifying the U-value?

You can quote a total, but you must specify a compliant product. Under Part L 2021, replacement windows must achieve whole-window U-value ≤1.4 W/m²K, OR Window Energy Rating Band B or above. Quote A-rated as standard — it's barely more expensive than B-rated and removes any compliance argument.

When do I need toughened/safety glass?

Under BS 6262-4 critical-location rules: any glazing within 800mm of finished floor level in a wall, any glazing within 300mm of a door (either side, full door height plus 300mm), and any glazing within doors. Use toughened (BS EN 12150) or laminated (BS EN 14449) — both meet Class 1B of BS 6206. Toughened is cheaper; laminated is preferred for security and acoustic.

How do I price scaffold for upper-floor windows?

Tower hire £80–£120 per week for single openings, but only if access permits. Full scaffold £400–£900 per elevation per week for multiple upper openings. Add £200–£400 erect/strike. If property has 3+ first-floor windows on one elevation, scaffold is usually cheaper and safer than working from tower.

Regulations & Standards

• Building Regulations Part L1B 2021 — Conservation of fuel and power in existing dwellings; U-value limits for replacement glazing

• Building Regulations Part F 2021 — Ventilation; trickle vent requirements

• Building Regulations Part Q — Security in dwellings (new build only, but informs hardware spec)

• BS 7950:1997 — Specification for enhanced security performance of casement and tilt/turn windows

• BS 6262-4:2018 — Glazing for buildings: code of practice for safety related to human impact

• BS EN 12150 — Glass in building: thermally toughened soda lime silicate safety glass

• BS EN 14351-1 — Windows and doors: product standard, performance characteristics

• PAS 24:2022 — Enhanced security performance for doorsets and windows (required for new dwellings)

• FENSA scheme rules — fensa.org.uk

• CERTASS scheme rules — certass.co.uk

• CDM Regulations 2015 — Construction (Design and Management); applies to all construction work

• Building Regulations Approved Document L (Volume 1) — energy efficiency for dwellings

• Building Regulations Approved Document F (Volume 1) — ventilation requirements

• FENSA — find a competent person scheme — registration and notification

• CERTASS — competent person scheme — alternative CPS

• Glass and Glazing Federation guidance — industry technical documents

• bifold door pricing guide — pricing companion for sliding and bifold doors

• conservatory pricing guide — related glazing-heavy project pricing

• fensa and certass — competent person scheme detail

• building control — when to notify, approved inspector route