Replacing windows is one of the most impactful changes you can make to a home’s thermal performance, appearance, and security — and one of the most expensive if you choose the wrong product for the building or misread planning rules before ordering.
For a typical three-bedroom semi with ten window openings, a full uPVC replacement runs £5,000–£9,000 installed; timber would be £9,000–£20,000+; aluminium sits in between at £8,000–£18,000 depending on configuration. The right choice depends on the property type, planning constraints, budget, and aesthetic intent.
Frame Materials Compared
uPVC windows
Unplasticised polyvinyl chloride is the UK’s most common window frame material, accounting for roughly 65% of residential replacements. It requires no painting, resists moisture, and the modern multi-chamber profiles achieve U-values of 1.2–1.4 W/m²K for the frame alone — compliant with Building Regulations Part L requirements (the overall window assembly including glass must achieve ≤1.4 W/m²K for replacements in existing dwellings as of 2022 standards).
Advantages: lowest purchase cost, no maintenance painting, wide availability, good energy performance
Limitations: cannot be repaired as easily as timber when damaged; some planners dislike the appearance in sensitive contexts; less suited to slim-line glazing bars; colour options beyond white, cream, and anthracite grey add cost
Timber windows
Engineered timber windows (Accoya, modified pine, or European oak) have the best environmental credentials per frame and are preferred in conservation areas, listed buildings, and period properties. Modern factory-primed or pre-finished timber frames last 30–40 years with appropriate maintenance (repainting every 8–12 years). Softwood frames require more frequent repainting (every 5–8 years) and are vulnerable to rot if maintenance lapses.
Advantages: planning-acceptable in conservation areas and listed buildings; repairable; excellent appearance for period properties; can match original profiles precisely; sustainable timber options available
Limitations: highest upfront cost; ongoing maintenance cost and programme; delivery lead times often 8–14 weeks for bespoke joinery; heavier than uPVC or aluminium
Aluminium windows
Thermally broken aluminium frames offer ultra-slim sightlines (60–70 mm face widths vs 80–100 mm for uPVC) and are the material of choice for contemporary extensions and large glazed openings. The thermal break — a polyamide strip separating inner and outer aluminium sections — prevents cold bridging, allowing modern aluminium frames to achieve U-values of 1.0–1.5 W/m²K. Powder coating gives a durable factory finish in any RAL colour without repainting for 20–30 years.
Advantages: slim profiles for maximum glass area; very durable powder-coated finish; wide colour range; suited to large openings; appropriate for modern design
Limitations: higher cost than uPVC; thermally inferior to composite (timber-aluminium) windows without a quality thermal break; some cheaper aluminium products lack an adequate break, producing cold frames and condensation
Composite (timber-aluminium) windows
A timber inner frame clad with aluminium externally. These combine the warmth and workability of timber inside with the low-maintenance exterior of aluminium. Favoured in Scandinavian-influenced builds and high-end renovations. Costs are typically 20–40% above aluminium alone, at £1,200–£3,500 per window depending on size.
Cost per Window
The table below covers casement windows (the most common format) at a medium residential size of approximately 900 × 1,050 mm — supply and fit, including removal of old window, making good, and all ironmongery. Bay windows and sash windows are listed separately.
| Frame material | Low | Typical | High |
|---|---|---|---|
| uPVC casement (double-glazed) | £380 | £600 | £900 |
| uPVC casement (triple-glazed) | £500 | £750 | £1,100 |
| Aluminium casement (double-glazed) | £700 | £1,100 | £1,800 |
| Aluminium casement (triple-glazed) | £900 | £1,400 | £2,200 |
| Timber casement (double-glazed, softwood) | £750 | £1,200 | £2,000 |
| Timber casement (double-glazed, hardwood/Accoya) | £1,100 | £1,800 | £2,800 |
| uPVC sash (double-glazed) | £600 | £950 | £1,400 |
| Timber sash (double-glazed) | £1,200 | £1,800 | £3,000 |
| Aluminium bifold (per pane, minimum 3 panes) | £700 | £1,000 | £1,600 |
Larger windows, complex shapes, and non-standard configurations attract premiums. Add 15–25% for first-floor installation requiring scaffolding or a MEWP.
Whole-house guide prices (3-bed semi, 10 openings)
| Frame material | Low (estimate) | Typical (estimate) | High (estimate) |
|---|---|---|---|
| uPVC, double-glazed | £4,500 | £7,000 | £10,500 |
| uPVC, triple-glazed | £5,500 | £8,500 | £12,500 |
| Aluminium, double-glazed | £8,000 | £13,000 | £20,000 |
| Timber, double-glazed | £9,000 | £16,000 | £28,000 |
Glazing Options
The glass unit is as important as the frame. Most UK replacements use argon-filled double-glazed units (DGUs) with one or two low-emissivity (low-E) coatings. Triple-glazed units add a second air or gas gap and a further coating.
| Glazing type | Centre-pane U-value | Typical added cost over standard DGU |
|---|---|---|
| Standard double (4-16-4, air-filled) | 2.8 W/m²K | — |
| Low-E double (4-16-4, argon, one coating) | 1.6 W/m²K | +£20–£40/unit |
| Low-E double (4-16-4, argon, two coatings) | 1.1 W/m²K | +£40–£70/unit |
| Triple-glazed (4-12-4-12-4, argon, two coatings) | 0.6–0.7 W/m²K | +£80–£150/unit |
| Acoustic glass (laminated outer pane) | 1.4 W/m²K | +£60–£120/unit |
| Self-cleaning glass | 1.4 W/m²K | +£30–£60/unit |
Building Regulations Part L (as amended in England in 2022) requires replacement windows in existing dwellings to achieve a whole-window U-value of ≤1.4 W/m²K. Most low-E argon-filled DGUs in a decent frame meet this comfortably. The Competent Person Scheme certificate from a FENSA or CERTASS-registered installer is required — this self-certifies Building Regulations compliance and is required for conveyancing.
Planning in Conservation Areas
Window replacement is usually permitted development in England for most residential properties — you do not need planning permission for like-for-like or similar replacements. However, two exceptions apply:
Conservation areas: The Article 4 Direction removes permitted development rights for many changes to front elevations in conservation areas. Replacing wooden sash windows with uPVC, or any change to the window design or materials visible from a public highway, typically requires a planning application (householder application, approximately £206 fee in England as of 2026). The application requires a Heritage Statement explaining how the proposed windows match the character of the area. Conservation officers strongly prefer slim-profile aluminium or traditionally-detailed timber over uPVC in most conservation areas.
Listed buildings: All window replacements (and many internal changes) require Listed Building Consent, irrespective of whether they are visible from a public road. This applies even in Grade II listed buildings where the windows were not specifically mentioned in the listing description. Unauthorised work to a listed building is a criminal offence, not merely a planning breach.
Flats: Replacing windows in a flat almost always requires the freeholder’s or managing agent’s consent and may require a variation of lease — check this before ordering.
Outside conservation areas and for non-listed houses, submit a FENSA notification via your installer and keep the certificate. No planning involvement is required.
What to Look For in a Quote
A like-for-like replacement should include:
- Removal and disposal of existing frames (check if lead flashings or asbestos-containing putty in pre-1980 frames needs specialist disposal)
- Foam, membrane and low-expansion fire-rated foam around the frame
- Internal render and plaster making-good
- Exernal mastic sealant in an appropriate colour
- Ironmongery: handles, stays, trickle ventilators (Part F of Building Regulations requires background ventilation in replacement windows — usually a trickle vent in the frame)
Avoid quotes that do not mention ventilation: Part F requires trickle vents in replacement windows where the existing window had them, or where the dwelling has no other background ventilation. Fitting sealed windows without trickle vents is a common shortcut that creates condensation and Building Regulations non-compliance.
Lead Times and Disruption
Standard uPVC windows from a national installer: 3–6 weeks. Bespoke timber joinery: 8–14 weeks. Aluminium from specialist fabricators: 5–10 weeks.
A pair of experienced fitters can replace 3–5 standard windows per day. Expect one to two rooms to be open to the outside while frames are changed — manageable in summer, more disruptive in winter. Plan the sequence so you are never leaving external walls open overnight.
