Window & Door Installation: Costs, FENSA Compliance & How to Get Quotes

Replacing windows and doors is one of the best investments you can make in your property — improving energy efficiency, security, noise insulation, and kerb appeal. But it's also expensive, and the market is full of high-pressure sales tactics, mis-sold products, and cowboy installers.

So how much should you expect to pay for new windows? What's FENSA certification and why does it matter? What's the difference between uPVC, timber, and aluminium? And how do you find a trustworthy installer who won't overcharge or botch the job? This guide explains window and door costs, FENSA and Building Regulations requirements, material options, and how SpecConnect can connect you with verified installers quickly.

How much do new windows cost?

uPVC windows (supply and fit)

• Casement window (standard size, double-glazed): £400-£700 per window
• Bay window (3-panel): £1,200-£2,500
• Sash window (uPVC, double-glazed): £800-£1,400 per window

Timber and aluminium windows

• Timber casement (double-glazed): £800-£1,500 per window
• Aluminium casement (powder-coated): £900-£1,800 per window
• Bi-fold doors (3-panel, 3m wide): £3,000-£7,000
• Sliding patio doors (2.5m wide): £2,500-£5,000
• uPVC composite front door: £800-£1,500
• Whole house uPVC (8-10 windows): £4,000-£7,000
• Whole house aluminium: £9,000-£18,000
• London and South East: Add 20-30%

What is FENSA and why does it matter?

FENSA (Fenestration Self-Assessment Scheme) is the government-authorised competent person scheme for window and door installations in England and Wales. It matters because: all replacement windows and doors must comply with Part L (energy efficiency) of Building Regulations; FENSA installers self-certify their work so no separate Building Control application is needed; installations come with a 10-year insurance-backed warranty; and buyers' solicitors will ask for FENSA certificates for any windows installed after 2002.

Without FENSA certification, you must apply for Building Regulations approval separately (£300-£600), lose the insurance-backed warranty, and may face difficulty when selling your property. Always verify FENSA registration before signing a contract.

uPVC vs timber vs aluminium: which is best?

• uPVC: affordable, low maintenance, good insulation (20-30 year lifespan) — best for modern homes and rental properties
• Timber: beautiful, can be repainted, suitable for listed buildings — requires maintenance (painting every 5-10 years)
• Aluminium: slim frames, very strong, powder-coated in any colour (30-40 year lifespan) — best for modern architecture and large glazed areas
• Composite (front doors): timber core with uPVC or GRP skin — best combination of strength, insulation, and low maintenance

Energy efficiency: U-values and Window Energy Ratings

Building Regulations Part L requires windows to meet minimum energy efficiency standards. The maximum U-value allowed is 1.6 W/m²K. Good-quality double glazing achieves 1.2-1.4 W/m²K; triple glazing 0.8-1.0 W/m²K. Look for low-E (low-emissivity) coating, argon or krypton gas fill between panes, and warm-edge spacer bars. Windows are rated A++ to E — A-rated windows are the most efficient.

Do you need planning permission for new windows?

Most replacement windows do NOT need planning permission if they are the same size and style as the originals, not on a listed building, and not in a conservation area (front-facing may need permission). You WILL need permission if changing window size or position, the property is listed, or it's a front-facing window in a conservation area. Always check with your local council before proceeding.

Common window and door problems and how to avoid them

• Condensation between panes: seal failure — replacement sealed unit required (should be covered under warranty if under 10 years)
• Draughts around frames: poor installation — installers should use expanding foam and sealant around frames
• Windows won't open or close properly: incorrect installation, frame not square — insist on re-fitting before final payment
• Water ingress: poor sealing — sills should slope outwards, sealant should be continuous with no gaps

How to avoid cowboy window installers

• ❌ High-pressure sales tactics ('special offer ends today')
• ❌ No FENSA registration
• ❌ Demands large deposit upfront (more than 20%)
• ❌ Can't provide references or show previous work
• ✅ Get 3 written quotes
• ✅ Verify FENSA registration on the FENSA website
• ✅ Check reviews online (Google, Checkatrade, Trustpilot)
• ✅ Use verified platforms like SpecConnect where installers are FENSA-checked

How SpecConnect connects you with FENSA-certified installers

Finding reliable window installers usually means enduring aggressive sales pitches, waiting weeks for quotes, and dealing with pushy reps. SpecConnect removes that friction. You upload details of your project — photos of existing windows, measurements, style preferences. The app shares these with FENSA-registered installers covering your area. Most SpecConnect users receive competitive window quotes within a few hours. SpecConnect is free to use for homeowners and property managers. It covers 35+ trade categories beyond windows — electricians, plumbers, builders, roofers, and more.