Replace windows — what to order? — Which Machine, Which Providers?
- Recommended class
- Kunststoff/Holz/Alu
- Typical duration
- 1-2 Tage/Fenster
- Cost estimate
- 400-1.500 €/Fenster
Overview
Replacing windows is one of the most common renovation tasks for commercial and residential properties across the UK, offering improved thermal efficiency, noise reduction, and enhanced aesthetic appeal. Whether you're upgrading single-glazed units to modern double or triple-glazed systems, or replacing damaged frames, understanding what equipment and materials to order is essential for a smooth installation process. The choice between uPVC, timber, or aluminium frames depends on building regulations, heritage constraints, and performance requirements, with each material requiring specific handling equipment and installation techniques.
For most standard window replacement projects, the equipment needed is relatively straightforward: scaffolding or tower platforms for safe access, basic hand tools, sealants and installation materials, and appropriate lifting equipment for larger units. A typical residential window replacement takes 1-2 days per window depending on size and complexity, with costs ranging from £400 for a simple uPVC casement window to £1,500 or more for larger timber or aluminium units with high-performance glazing. Professional installers will typically bring their own tools, but for trade professionals managing multiple installations, investing in proper access equipment, accurate measuring tools, and quality finishing materials ensures compliance with Building Regulations Part L (energy efficiency) and Part F (ventilation) requirements while maintaining warranty coverage from window manufacturers.
Step-by-step
1. Survey and measure existing openings
Conduct accurate measurements of all window openings, recording width, height, and depth at multiple points as openings may not be perfectly square. Check wall construction type (cavity, solid, timber frame) as this affects fixing methods and reveals. Photograph existing installations noting how frames are secured, DPC positioning, and internal finishing details. Assess access requirements and identify any obstacles for delivery and installation. Document any structural concerns, lintel condition, or masonry damage that may require remedial work before new windows can be fitted.
2. Specify and order replacement windows
Select appropriate window systems based on building type, thermal performance requirements (U-values typically 1.4 W/m²K or better for Building Regulations compliance), and aesthetic considerations. Order windows with correct frame depth for wall thickness, specifying opening configurations, glazing specification (double or triple-glazed, gas fills, coatings), hardware (handles, locks, restrictors), and colour/finish. Include essential accessories: cavity closers, DPC trays, sill extensions, cills, and trim. For heritage or conservation areas, ensure specifications meet planning requirements. Lead times typically range from 2-6 weeks depending on material and customisation level.
3. Arrange access equipment and site preparation
For ground floor installations, a simple step platform may suffice, but first floor and above require scaffold towers or fixed scaffolding with proper edge protection and load-rated platforms. Arrange delivery to coincide with installation schedule, ensuring storage space is weatherproof and secure. Prepare internal areas with dust sheets and protective coverings. Set up waste containment for old frame removal, arranging appropriate skip or waste collection for glass, timber, uPVC, or aluminium recycling. Ensure all necessary tools are available: spirit levels, packers, sealant guns, drills, fixings, expanding foam, and finishing materials.
4. Remove existing windows carefully
Before removal, remove any window furniture and carefully cut through sealant lines with a knife. Extract glazing units or panes safely, disposing of glass appropriately with proper handling to prevent injury. Cut through frame sections to ease removal without damaging surrounding masonry or internal plaster. Remove fixings and extract frame sections, inspecting reveals for damage, dampness, or inadequate lintel support. Clean opening thoroughly, removing old sealant, mortar debris, and dust. Check reveals are sound and level; repair any masonry damage and ensure DPC is intact. Verify opening dimensions against new window specifications before proceeding.
5. Install new window frames and secure
Position new frame in opening using packers to achieve level, plumb, and square alignment, typically with 3-5mm tolerance. Maintain consistent gap around perimeter for fixing and sealing (usually 10-20mm depending on wall construction). Drill through frame into masonry at manufacturer-specified centres (typically 150-600mm from corners then maximum 600mm intervals), using appropriate fixings for wall type: frame anchors for masonry, screws for timber. Check regularly with spirit level during fixing process. Avoid over-tightening fixings which can distort frames. Install DPC cavity trays and closers correctly to prevent water ingress while maintaining cavity insulation continuity.
6. Seal, insulate, and finish installation
Fill gaps between frame and masonry with low-expansion foam, avoiding over-application which causes frame distortion. Apply appropriate sealant to external perimeter joints using colour-matched products suitable for movement and weather exposure. Fit internal cavity closers and any additional trim pieces. Install window boards and cills with proper falls for water drainage, sealing all joints. Internally, finish reveals with plaster or trim as appropriate, ensuring no gaps expose insulation. Fit glazing units or beads if supplied separately, ensuring correct edge clearances and secure retention. Test all opening sashes for smooth operation, correct lock engagement, and proper sealing. Provide client with warranty documentation, care instructions, and ventilation guidance to meet Building Regulations compliance.
Cost breakdown
| uPVC casement window (1200×1200mm) | £400-650 | Standard white, double-glazed, per unit supply only |
|---|---|---|
| Timber or aluminium window (1200×1200mm) | £700-1,500 | Higher specification materials, factory-finished, per unit |
| Scaffold tower or access equipment hire | £80-200 | Per week, or £150-400 for fixed scaffold for whole property |
| Installation materials and fixings | £30-60 | Per window: packers, fixings, sealant, foam, cavity closers |
| Window boards and cills | £40-120 | Depending on material (uPVC, timber, stone) and length |
| Waste removal and recycling | £100-250 | Skip hire or waste collection for whole project |
| Labour (professional installation) | £150-300 | Per window, including removal and fitting, varies by complexity |
Common pitfalls
- Measuring openings at only one point — frames won't fit square openings that are actually out of tolerance, causing delays and potential remanufacturing costs of £300-800 per window
- Failing to check or repair lintel condition before installation — structural movement can crack new frames and glass within months, requiring reinstallation at full cost
- Over-tightening frame fixings during installation — distorts uPVC or aluminium frames preventing proper sash operation and seal performance, voiding manufacturer warranties
- Incorrect DPC or cavity closer installation — allows water penetration into cavity causing damp patches, mould growth, and potential insulation damage requiring costly remedial work
- Not maintaining ventilation requirements under Part F — modern sealed windows without adequate trickle vents or alternative ventilation cause condensation and potential Building Control compliance issues
- Installing windows without appropriate certification — lack of FENSA, CERTASS, or Building Control sign-off affects property saleability and insurance, requiring retrospective certification costing £200-500
FAQ
- Do I need Building Regulations approval to replace windows?
- In England and Wales, replacement windows must comply with Building Regulations Part L (energy efficiency) and Part F (ventilation). Most installations are covered by Competent Person Schemes (FENSA, CERTASS, etc.) where the installer self-certifies compliance and registers the work, providing a certificate within 4-6 weeks. If you're installing windows yourself or using a non-registered installer, you must notify Building Control before starting work and pay inspection fees (typically £200-500). Listed buildings and properties in conservation areas require additional planning permission. Scotland and Northern Ireland have separate but similar requirements under their respective building standards.
- What's the real cost difference between doing it myself versus hiring professionals?
- DIY window replacement saves labour costs (£150-300 per window) but requires competent skills, proper tools, and Building Control notification adding £200-500 for inspections. You'll need scaffold hire (£80-200/week), tools if not owned, and accept responsibility for any installation errors affecting performance or causing damage. Professional installers provide warranty coverage (typically 10 years insurance-backed), handle Building Regulations compliance through Competent Person Schemes, have appropriate public liability insurance, and complete work faster with proper equipment. For a typical 10-window house replacement, professional installation costs £4,000-8,000 all-in versus £3,000-5,000 DIY when factoring in materials, equipment hire, and compliance costs, but without the same guarantees or insurance protection.
- Which window material should I choose: uPVC, timber, or aluminium?
- uPVC is most cost-effective (£400-650 per standard window), requires minimal maintenance, offers good thermal performance, and suits most modern properties, though colour options beyond white cost 20-30% more. Timber (£700-1,200) is often required in conservation areas, offers authentic aesthetics for period properties, excellent thermal performance when properly specified, but requires maintenance every 5-8 years with painting or staining. Aluminium (£800-1,500) provides slim sightlines preferred for contemporary design, maximum durability, and excellent security, with thermally-broken frames achieving good U-values, but typically costs most. For listed buildings, planning authorities often mandate timber. Choice also depends on exposure (coastal areas suit uPVC or aluminium better than timber) and desired lifespan (aluminium 45+ years, uPVC 25-35 years, timber 30+ years with proper maintenance).
- How do I ensure new windows meet current thermal performance standards?
- Building Regulations Approved Document L requires replacement windows to achieve a whole-window U-value of 1.6 W/m²K or better (England & Wales; Scotland requires 1.4 W/m²K). This is typically met with modern double-glazing using low-emissivity (Low-E) coatings, argon or krypton gas fills, and thermally efficient frames with insulated or broken-thermal-bridge construction. Manufacturers provide Window Energy Ratings (WER) from A++ to E, with A-rated windows offering U-values around 1.2-1.4 W/m²K. Triple glazing (U-values 0.8-1.0 W/m²K) exceeds requirements but costs 20-40% more and may not be cost-effective based on energy savings alone. Ensure your installer provides documentation proving compliance — either through Competent Person Scheme certification or Building Control approval — as this affects property sale and EPC ratings.
- What's the typical lead time and how should I schedule the work?
- Standard uPVC windows typically have 2-3 week lead times from order to delivery, while bespoke timber or aluminium can take 4-8 weeks depending on supplier and specification complexity. Order windows only after accurate site measurements, as manufacturing errors are costly to rectify. Schedule installation during dry weather if possible, as properties are exposed during replacement — budget 4-6 hours per window opening. For whole-house projects, installers often complete 3-5 windows per day with a two-person team. Arrange scaffold before window delivery if needed for upper floors. Consider occupant disruption: noise, dust, temporary loss of security and weatherproofing mean many homeowners schedule work when properties are vacant or during warmer months when temporary openings are more tolerable.
- What warranties and insurance should I expect with new windows?
- Reputable window manufacturers provide 10-year guarantees on frames and mechanisms, with sealed glazing units typically warranted for 10 years against seal failure or condensation between panes. Professional installers should offer installation warranties (usually 2-10 years) covering fitting defects, leaks, or operational issues. Critically, ensure your installer provides insurance-backed guarantees (IBG) through schemes like GGFi or FENSA — these protect you if the company ceases trading, covering remedial work for typically 10 years. Check public liability insurance (minimum £2 million) covers any installation damage. For DIY installations, you receive manufacturer warranties on products but no installation warranty, and must ensure compliance yourself. Keep all certification documentation as it's required for property sales and can affect home insurance if missing.