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 double-glazed replacement runs roughly £4,500–£10,500 installed; aluminium £8,000–£20,000; timber £9,000–£28,000 depending on timber and 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 frame material for replacement windows in homes. It requires no painting and resists moisture, and modern multi-chamber profiles with low-E double glazing comfortably meet the Building Regulations Part L limit for replacement windows set out below.

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-finished timber frames can last for decades if the paint or stain finish is renewed at the interval the maker recommends. Softwood frames need repainting more often 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 slimmer sightlines than 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 good modern aluminium windows to meet the same 1.4 W/m²K Part L limit. Powder coating gives a durable factory finish in almost any RAL colour that needs no repainting for many 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 above aluminium alone, so expect quotes toward the top of the aluminium range or beyond, 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 materialLowTypicalHigh
uPVC casement (double-glazed)£3801£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

The cited prices in this table were published in 2016 and brought to 2026. What that means.

Larger windows, complex shapes, and non-standard configurations attract premiums. Budget extra where upper-floor windows need scaffolding or a MEWP, and ask for it to be priced separately.

Whole-house guide prices (3-bed semi, 10 openings)

Frame materialLow (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 typeCentre-pane U-valueTypical added cost over standard DGU
Standard double (4-16-4, air-filled, uncoated)about 2.8 W/m²K-
Low-E double (4-16-4, argon, hard coat)about 1.5 W/m²K+£20–£40/unit
Low-E double (4-16-4, argon, soft coat)about 1.0–1.2 W/m²K+£40–£70/unit
Triple-glazed (argon, two low-E coatings)about 0.5–0.8 W/m²K+£80–£150/unit
Acoustic glass (laminated outer pane)as for the low-E unit it is built into+£60–£120/unit
Self-cleaning glassas for the low-E unit it is built into+£30–£60/unit

The best soft-coat low-E glass now reaches a centre-pane U-value of about 1.0 W/m²K in a double-glazed unit and as low as 0.5 W/m²K in a triple-glazed one.2

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 or better, or a Window Energy Rating of band B.3 Most low-E argon-filled DGUs in a decent frame meet this comfortably. Using an installer registered with a competent person scheme such as FENSA or Certass means the installer self-certifies Building Regulations compliance and you do not need to notify building control yourself.3 Keep the certificate, as buyers’ solicitors ask for it.

Planning in Conservation Areas

Window replacement is usually permitted development in England for houses: you do not need planning permission for new windows of similar appearance to those used in the construction of the house.4 However, two exceptions apply:

Conservation areas: Many councils have made an Article 4 Direction withdrawing permitted development rights for changes to front elevations in conservation areas.4 Where one applies, replacing wooden sash windows with uPVC, or any change to the window design or materials visible from a public highway, needs a planning application (householder application, £548 fee in England from 1 April 2026).5 The application will usually need a heritage statement explaining how the proposed windows suit the character of the area. Conservation officers strongly prefer slim-profile aluminium or traditionally-detailed timber over uPVC in most conservation areas.

Listed buildings: Replacing windows almost always needs Listed Building Consent, as do many internal changes, whether or not the windows are visible from a public road.4 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.6

Flats: Replacing windows in a flat usually needs the freeholder’s or managing agent’s consent, because the lease often makes the windows part of the building they control, so check this before ordering.4

Outside conservation areas with an Article 4 Direction, and for unlisted houses, your installer registers the work through its competent person scheme and you 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 any asbestos-containing materials around older frames, such as panels or boards, need specialist disposal)
  • Low-expansion foam or other sealing around the frame, with membranes where the detail needs them
  • Internal render and plaster making-good
  • External 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. Under the 2021 edition of Part F it does not matter whether the old windows had trickle vents or not. If they did, the replacements need ventilators at least as large. If they did not, the installer has to show the dwelling’s ventilation is no worse than before, and the standard way to demonstrate that is ventilators of 8,000 mm² equivalent area in habitable rooms and kitchens and 4,000 mm² in bathrooms.7 Unless the house has mechanical ventilation with heat recovery or continuous mechanical extract, that means trickle vents on effectively every replacement window. Fitting sealed windows without them 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 often replace several standard windows a 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.

References (7)

Figures in this note were checked against the sources below on 30 September 2026. Superscript numbers in the text point to them. Every source the site cites, by topic.

  1. 1costvery strongCambridge Architectural Research for the Department for Business, Energy and Industrial Strategy.RN-TC86A6A price, true at 2016, brought forward on the Construction Output Price Index. Cambridge Architectural Research's April 2017 report updating the cost assumptions behind government energy efficiency modelling. Prices individual retrofit measures, loft and cavity and solid wall insulation, glazing, heating controls, with the installed cost and the assumptions behind it. Its value is that it shows the working; its limit is that the prices are true for 2017 and must be escalated, not quoted.
  2. 2technicalsupplier figurePilkington (NSG Group), guidance.RN-87UV88A glass maker's product page for a soft-coat low-E glass. It gives centre-pane U-values of 1.0 W/m²K in a double-glazed unit and as low as 0.5 W/m²K triple-glazed.
  3. 3technicalvery strongMinistry of Housing, Communities and Local Government.RN-L0FCJXThe in-force U-value tables a DIY insulation or door note must quote, with the exact numbers. Table 4.2, limiting U-values for new fabric elements in existing dwellings, sets roof 0.15, wall 0.18, floor 0.18, swimming pool basin 0.25, window 1.4 or Window Energy Rating Band B minimum, rooflight 2.2, doors with more than 60 per cent of the internal face glazed 1.4 or Doorset Energy Rating Band C minimum, and other doors 1.4 or Doorset Energy Rating Band B minimum. Table 4.3, for existing elements, gives a roof threshold of 0.35 and an improved value of 0.16, which is the figure a loft insulation note needs: paragraph 4.12 says a retained element whose U-value is higher than the column (a) threshold, for example through a loft or garage conversion, should be upgraded to the column (b) value. Paragraph 4.13 allows a lesser upgrade only where the improved value is not technically or functionally feasible or would not achieve a simple payback of 15 years or less. Paragraph 4.8 requires a replacement element to be no worse than the one it replaces as well as meeting Table 4.2. Paragraph 4.10 gives the heritage exception: where character must be maintained, a centre pane U-value of no more than 1.2 or low-emissivity secondary glazing. Note 9 records that the timber window concession of 1.6 or Band C ended on 14 June 2023. The 2021 edition came into force on 15 June 2022; a 2026 edition exists at https://assets.publishing.service.gov.uk/media/69c122a6cfa346b9d4704a55/ADL1_2026.pdf.
  4. 4technicalvery strongPlanning Portal, guidance.RN-LIPHMWThe Planning Portal on planning permission for doors and windows: usually not needed for repairs, maintenance and minor improvements including replacing windows like for like, with the exceptions that catch people, listed buildings, conservation areas, flats, and where permitted development rights have been removed.
  5. 5technicalvery strongMinistry of Housing, Communities and Local Government (GOV.UK), a government page.RN-JM9I1NThe schedule of planning application fees in England from 1 April 2026. Fees rise annually with the September CPI under the 2023 amendment regulations; September 2025 CPI was 3.8%, so every fee from April 2025 rose by that and is charged from 1 April 2026. The table lists the new amount for each application type, which is the statutory figure a council must charge rather than a guide price.
  6. 6technicalvery strongThe National Archives, guidance.RN-AKNVL3Section 9 of the Listed Buildings Act 1990 makes it a criminal offence to carry out works to a listed building in breach of section 7, punishable by a fine or imprisonment.
  7. 7technicalvery strongMinistry of Housing, Communities and Local Government.RN-QD1SFFTable 1.1 sets minimum intermittent extract rates: kitchen with a cooker hood extracting outside 30 l/s, kitchen without one 60 l/s, utility room 30 l/s, bathroom 15 l/s, sanitary accommodation 6 l/s. Extract terminals and fans other than cooker hoods should be as high as practicable and no more than 400mm below the ceiling; a cooker hood should sit between 650mm and 750mm above the hob if the manufacturer gives no figure. Table 1.7 requires background ventilators of at least 8000mm2 equivalent area in habitable rooms and kitchens for a dwelling, 10,000mm2 for a single-storey dwelling. Background ventilators should be at least 1700mm above floor level and at least 500mm from a fan in the same room. On replacement windows, paragraph 3.14 says new windows must carry background ventilators no smaller than the originals, and paragraph 3.15 gives the fallback minimums where the old size is unknown: 8000mm2 habitable rooms, 8000mm2 kitchen, 4000mm2 bathroom. Paragraph 3.32 confirms that replacing an extractor fan or cooker hood on existing cabling is not notifiable.

  1. What Does It Cost To Retrofit Homes?, Cambridge Architectural Research for the Department for Business, Energy and Industrial Strategy, accessed 15 September 2026. Priced at 2016; brought to 2026 on the Construction Output Price Index, housing repair and maintenance (Great Britain), published by Office for National Statistics, a factor of 1.2292. assets.publishing.service.gov.uk

  2. Pilkington Optitherm S1 Plus, Pilkington (NSG Group), accessed 30 September 2026. pilkington.com

  3. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments, HM Government (GOV.UK), accessed 30 September 2026. assets.publishing.service.gov.uk

  4. Doors and windows: planning permission, Planning Portal, accessed 30 September 2026. planningportal.co.uk

  5. Fees for planning applications in England from 1 April 2026, Ministry of Housing, Communities and Local Government (GOV.UK), accessed 7 September 2026. assets.publishing.service.gov.uk

  6. Planning (Listed Buildings and Conservation Areas) Act 1990, section 9, legislation.gov.uk, accessed 30 September 2026. legislation.gov.uk

  7. Approved Document F: Ventilation, Volume 1: Dwellings, 2021 edition, HM Government (GOV.UK), accessed 10 September 2026. assets.publishing.service.gov.uk