Windows and doors are one of the most visible, and most expensive, decisions in any UK renovation. Replacing every window in a typical three-bed semi costs £4,000–£12,000 in 2026, a new composite front door runs £1,000–£3,000 fitted, and a set of bifolds to open up a kitchen-diner adds £2,000–£10,000 depending on width and material. Get the frame material, glazing spec and door type right first time and you avoid an expensive second pass a decade later.

The market has genuinely fragmented by priority. Some households are chasing the lowest U-value they can afford under Part L; others are matching a conservation area’s leaded lights or timber sashes pane-for-pane; others just want a wider opening onto the garden without a full extension. What follows sets out the rules a replacement has to satisfy, the numbers that decide whether a glazing upgrade is worth paying for, and the traps that turn a straightforward job into a second one.1

The five rules every replacement window has to satisfy

Replacing a window or an external door is notifiable building work in England, and five separate parts of the Building Regulations bite on it at once. Most disputes with an installer come from a homeowner knowing about one of them and not the other four.2

Part L, thermal performance. Approved Document L Volume 1 Table 4.2 sets the limiting standards for new fabric elements in existing dwellings. A window must achieve a maximum U-value of 1.4 W/(m²·K) or a Window Energy Rating of Band B as a minimum. A rooflight is 2.2. A door with more than 60% of its internal face glazed must reach 1.4 or Doorset Energy Rating Band C; any other door 1.4 or Band B. External fire doorsets are allowed 1.8.1 Two details catch people out. First, paragraph 4.8 requires a replacement element to be no worse than the element it replaces as well as meeting Table 4.2, so you cannot downgrade a good window because the minimum is lower. Second, the transitional concession that let timber windows sit at 1.6 or Band C ended on 14 June 2023; since 15 June 2023 the full 1.4 or Band B standard applies to timber too.1

Part L again, if you make the opening bigger. If a window is enlarged or a new one created, the total area of windows, roof windows, rooflights and doors should not exceed 25% of the total floor area of the dwelling, unless compensating energy efficiency measures are taken elsewhere.1 This is the rule that quietly constrains a wall of glass onto the garden in a small house.

Part F, ventilation. Approved Document F is explicit about replacements. If the existing windows have background ventilators, the replacements must include them, they must be no smaller than the originals, and they must be controllable. If the original size is unknown, or the existing windows had no ventilators at all, the fallback minimum equivalent areas are 8,000 mm² in a habitable room, 8,000 mm² in a kitchen and 4,000 mm² in a bathroom.3 Note that these are equivalent areas, not free areas, and the whole-dwelling figures in Table 1.7 rise to 10,000 mm² per habitable room and kitchen in a single-storey dwelling.3 Trickle vents explains why this is the requirement installers most often leave out of a quote.

Part K, safety glazing. Approved Document K Diagram 5.1 defines the critical locations: glazing below 800 mm from floor level in a wall, and glazing below 1500 mm in a door or within 300 mm of either edge of a door. In those locations glass must break safely, satisfying Class 3 of BS EN 12600:2002, or Class 2 where it sits in a door or door side panel with a pane width exceeding 900 mm.4 The code of practice behind this, and the source of the requirement that safety glass be permanently marked, is BS 6262-4:2018.5 The classes themselves come from BS EN 12600:2002, the pendulum impact test that grades flat glass by the drop height it survives and by how it breaks.6 If a pane in a critical location has no visible mark in the corner, it is not certified safety glass, whatever anyone says.

Part B, escape. Where a window serves as an emergency escape window, it needs an unobstructed openable area of at least 0.33 m², with a minimum height of 450 mm and a minimum width of 450 mm, and the bottom of the openable area no more than 1100 mm above the floor.7 Replacing an escape window with a smaller-opening unit is a common and serious error, particularly with tilt-and-turn or fixed-light designs, and it matters most in a loft conversion.

PartWhat it governsThe figure
LThermal performanceWindow 1.4 W/(m²·K) or WER Band B; rooflight 2.2; doors 1.4 or DSER Band B/C
LEnlarged or new openingsGlazing and doors not more than 25% of dwelling floor area
FBackground ventilation8,000 mm² habitable room and kitchen, 4,000 mm² bathroom, or no worse than existing
KSafety glazingBelow 800 mm in a wall, below 1500 mm in or beside a door
BEscape windows0.33 m² openable, min 450 × 450 mm, cill no higher than 1100 mm
QSecurity (new dwellings only)Doorsets and accessible windows tested to PAS 24

Whether all of this is checked by Building Control or self-certified depends on your installer. FENSA Limited and Certass are both authorised competent person schemes, which means a registered installer can self-certify the work and the scheme operator notifies the local authority on your behalf.8 Replacement windows walks through that process and realistic per-window costs from £300 to £1,500.

Window Frame Materials and Styles

Frame material is the single biggest driver of both cost and appearance. Our uPVC vs timber vs aluminium windows comparison sets out installed costs from £300 (uPVC) to £1,800 (aluminium) per window, alongside the U-values and conservation-area rules that often decide the question for you.

The honest way to choose is to work out which constraint is binding. If the property is in a conservation area or the planning consent conditions the window profile, the material is chosen for you and the only real decision is repair or replace. If sightlines matter, because you want the largest possible glass area in a fixed opening, aluminium wins on frame slenderness and pays for it in cost and in a slightly worse frame U-value than a well-made uPVC or timber alternative. If the budget is binding and the house is unlisted, uPVC does the job and meets Part L without difficulty. Timber sits in the middle on cost and at the top on maintenance, and buys you the ability to repair rather than replace in twenty years, which is a real long-run saving that rarely appears in a comparison quote.1

Once the material is settled, the opening style still affects both price and ventilation. Our guide to casement windows and their tilt-and-turn and bay alternatives compares them from around £300 to £1,000 per unit supplied and fitted. Check the openable area against the Part B figures above before you commit to a style, not after.7

Glazing and Energy Performance

This is where most of the money is either well spent or wasted, and where the marketing is least reliable.

A rating is not a U-value

A Window Energy Rating runs from A++ down to E and is an energy balance, not a heat-loss figure. The British Fenestration Rating Council calculates it from three factors: solar gain, counted positive; thermal transmittance, the heat lost out through the window, counted negative; and air leakage, also negative.9 That is why a south-facing window with a high solar transmittance can carry a better letter than a window with a lower U-value. Approved Document L accepts either route, so a product can comply by hitting 1.4 W/(m²·K) or by achieving Band B, and the two claims are not interchangeable.1 When comparing quotes, insist on the same measure across all of them.

What actually moves the number

The Glass and Glazing Federation publishes typical values for a range of insulating glass unit configurations in a standard PVC-u frame, and the table is the clearest available answer to whether triple glazing is worth it.10

UnitConfigurationLow-E coatingsGasCentre pane UgWhole window UwWER
28 mm double4-20-41Air1.51.6−13 (C)
28 mm double4-20-41Argon1.21.3+7 (A)
28 mm triple4-8-4-8-41Argon1.31.4−9 (B)
28 mm triple4-8-4-8-42Argon1.01.1+2 (A)
36 mm triple4-12-4-12-42Argon0.81.1+22 (A++)
44 mm triple4-16-4-16-42Argon0.60.9+36 (A++)

GGF typical values with warm-edge spacer. Ug to BS EN 673, Uw to BS EN ISO 10077.

Read the third row against the second. A 28 mm triple-glazed unit with a single low-E coating performs worse than an argon-filled double unit of the same overall thickness: 1.4 against 1.3 on whole-window U-value, and Band B against Band A. The GGF states the point plainly: there is no benefit in triple glazing, subject to cavity width, unless two panes of low-E glass are used, and the coatings need to be on surface 3 for a double unit and surfaces 3 and 5 for a triple.10

That is the most expensive mistake in this entire topic. Homeowners pay a 25–50% premium for triple glazing, receive a thin unit with one coating because the frame will not accept a deeper one, and end up with a window that is worse than the double glazing they could have bought instead. The fix is simple: ask for the number of low-E coatings, the overall unit thickness, the cavity gas and the whole-window Uw in writing, and refuse any quote that only offers a centre-pane figure.

Window U-values explains how Low-E coatings, argon fills and warm-edge spacers work. Double vs triple glazing compares the two panel by panel, and triple glazing goes further into payback. Where a unit has failed rather than underperformed, replacing misted double glazing units and blown window repair are usually far cheaper than a whole window, and double glazing repairs covers what else can be fixed rather than replaced. If noise rather than heat is the problem, a wider cavity and asymmetric glass thicknesses matter more than the U-value, which is why soundproof windows are specified differently.

Sash and Heritage Windows

Period properties bring their own rules, and Part L bends for them. Where windows or fully glazed external pedestrian doors cannot meet Table 4.2 because of the need to maintain the character of the building, paragraph 4.10 allows either a centre-pane U-value not exceeding 1.2 W/(m²·K), or single glazing supplemented with low-emissivity secondary glazing.1 That second route is the one most conservation officers prefer, because it leaves the original joinery untouched.

Sash windows sets out when a £150–£600 repair beats a £900–£2,500 replacement, often the deciding factor in a conservation area where matching the original profile is a planning condition rather than a preference. Secondary glazing runs £150–£500 per window and is the compliant route for a listed building where new frames are not an option. Where the glazing itself is the historic feature, leaded window repair cost covers re-leading and cracked-pane repair, from £80 for a small panel to £2,500+ for a full re-lead. Cheaper interim measures are covered in how to insulate windows.

Skylights, Roof Windows and Conservatories

Rooflights get their own limiting U-value of 2.2 W/(m²·K), which is much more forgiving than the 1.4 required of a vertical window, for the good reason that they perform worse in the horizontal plane. Two details in Approved Document L are easy to miss: rooflight U-values are based on the outer developed surface area, which is often greater than the area of the roof opening, and an upstand built on site must itself achieve a maximum U-value of 0.35 W/(m²·K).1 A well-specified rooflight sitting on an uninsulated timber kerb is a compliance failure and a condensation problem.

Overhead glazing also has a glass specification of its own. Laminated safety glass to BS EN ISO 12543-2:2021 retains a broken pane on its interlayer rather than letting it fall, which is why laminate rather than toughened glass is specified for the inner pane of overhead units.11 Toughened glass fragments instead, and fragments fall.

Roof lantern cost covers the raised, pitched-profile glazing that suits kitchen-diners and orangeries, from £1,500 to £8,000+. Our wider rooflight types comparison lines up flat rooflights, lanterns and pitched roof windows on cost and U-value, and roof window sizes explains the sizing codes before you order. If you already have roof windows fitted, Velux window servicing cost explains why an £80–£180 service every 2–3 years is cheaper than the repairs that follow neglect. Where you want a fully glazed room rather than a single window, conservatory cost breaks down lean-to, Victorian and Edwardian styles from £8,000 to £35,000, and orangery vs conservatory vs extension is the decision to make before you price any of them.

External Doors and Security

A new front door is as much a security decision as a design one, and the standard to ask about is PAS 24. Approved Document Q requires secure doorsets tested to PAS 24, caps a letter plate aperture at 260 mm × 40 mm, requires a door viewer on the main entrance door unless clear glass or an adjacent window serves the purpose, plus a door chain or limiter, and requires ground floor, basement and other easily accessible windows and rooflights to be tested to the same standard with frames mechanically fixed to the structure.12 PAS 24 itself sets the test methods and acceptance criteria for doorsets and windows meant to resist the attacks of a casual or opportunistic burglar, and it tests the manufactured product before installation rather than the installation itself.13 That distinction is worth holding on to: a certified doorset fixed badly into a weak opening is not a secure door.

The limitation to understand is that Part Q applies only to new dwellings, including those formed by a material change of use.12 Replacing the front door of an existing house triggers Part L and Part K but not Part Q, so PAS 24 certification on a replacement door is a specification you choose rather than one you are given. It is worth choosing: the security hardware is where cheap doors are cheap.

Version matters too. Secured by Design accepts PAS 24:2022+A1:2024 and PAS 24:2022 for residential doorsets, and accepted the older PAS 24:2016 only until 31 December 2025.14 A certificate quoting the 2016 version is out of date, so ask which version and year the paperwork names.

Front doors compares styles and security ratings across composite, timber, uPVC and aluminium, with composite the most common choice at £1,000–£3,000 fitted, and composite doors goes deeper on that material against uPVC and timber. For locks, the insurance benchmark on a single-point mortice lock is BS 3621:2017+A1:2024, which specifies a thief-resistant lock assembly lockable from both sides so that only key egress is possible; the earlier editions it supersedes are no longer the live specification.15 Window and door lock upgrades and smart locks cover the alternatives.

For the back or side of the house, bifold doors cost £2,000–£10,000 supply and fit depending on width, while french doors are the simpler, cheaper option for openings under 1.8 m at £800–£5,000. Wider still, sliding patio doors compares the two head-to-head and usually wins on price and thermal performance above 4 m, because a slider has fewer frames interrupting the glass and fewer opening joints to leak air. Away from the house itself, garage doors covers up-and-over, roller and sectional types from £500–£3,500. Internally, fire doors explains where an FD30 doorset is actually required.

ElementTypical Installed Cost (2026)Notes
uPVC window£300–£800 per window16U-value 1.2–1.6 W/m²K
Aluminium window£600–£1,800 per windowSlimmest sightlines
Timber sash window (like-for-like)£900–£2,500 per window17Standard in conservation areas
Secondary glazing£150–£500 per window18Part L heritage route for listed buildings
Composite front door£1,000–£3,00019PAS 24 security as standard
Bifold doors (per set)£2,000–£10,00020Width and material dependent
French doors£800–£5,000uPVC through to timber
Roof lantern£1,500–£8,000+Suits flat-roof extensions
Conservatory£8,000–£35,000Lean-to through to Victorian/Edwardian

The cited prices in this table were published in 2016 and 2023 and brought to 2026. What that means.

Check Part F Before You Sign Off Replacement Windows

3 Building Regs Part F requires background ventilation in every room where windows are replaced. If your installer doesn’t mention trickle vents or an equivalent ventilation strategy, ask, a FENSA certificate can still be issued without it, and retrofitting vents afterwards means drilling into frames you’ve just paid to install.3

Repairs and Upgrades

Not every problem needs a new door or window, and the cheapest compliant answer is often a component. Change a uPVC door lock is a 20–30 minute DIY job costing £10–£50 for a euro cylinder, or £80–£200 for a locksmith if the multipoint mechanism itself has failed. A failed sealed unit can be swapped without touching the frame. A dropped or sticking door is usually a hinge adjustment. The rule of thumb is that frames outlive glazing units and glazing units outlive hardware, so before accepting a quote for whole-window replacement, establish which of the three has actually failed.

Where to Start

If you’re planning a full replacement, start with replacement windows to understand FENSA and realistic per-window costs, then use uPVC vs timber vs aluminium windows to settle on a frame material and the GGF table above to settle on a glazing spec before you take a single quote. If a period property is involved, sash windows is the place to check whether repair beats replacement before you commit to either.

The rules in this note are those that apply in England. Scotland, Wales and Northern Ireland have their own building standards and permitted development rights.

References (20)

Figures in this note were checked against the sources below on 14 September 2026. Superscript numbers in the text point to them. Every source the site cites, by topic.

  1. 1technicalvery 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.
  2. 2technicalvery strongThe National Archives, legislation.RN-ZCMRHVRegulation 3 of the Building Regulations 2010, the meaning of building work. Lists what counts: erecting or extending a building, providing or extending a controlled service or fitting, material alteration, work required by a material change of use, and inserting insulation into a cavity wall. If a job is not on this list it is not building work, so this is the first place to check whether approval is needed at all.
  3. 3technicalvery 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.
  4. 4technicalvery strongMinistry of Housing, Communities and Local Government.RN-XH6E39The standard that decides whether a loft ladder is legal and when a raised deck needs a balustrade. Published 3 January 2013, it covers protection from falling, collision and impact including stairs, ladders, ramps, guarding and vehicle barriers. Paragraph 1.31 states that retractable ladders must not be used as a means of escape. Paragraph 1.32 permits a fixed ladder, with fixed handrails on both sides, only for access in a loft conversion containing one habitable room, and only where there is not enough space without altering the existing space for a compliant stair, which is the rule that catches most loft ladder installations. Paragraph 1.29 restricts alternating tread stairs to loft conversions. For a private stair the maximum pitch is 42 degrees (Table 1.1 note 1), the normal relationship between rise and going is twice the rise plus the going between 550mm and 700mm, and for dwellings external tapered steps forming part of the building need a going of at least 280mm. Paragraph 3.1 requires guarding wherever it is reasonably necessary for safety at the edge of a floor, gallery, balcony, roof, light well, basement or similar sunken area. Paragraph 3.2 requires guarding to be at least the height in Diagram 3.1, allows any wall, parapet or balustrade to serve as guarding, and requires it to resist the loads in BS EN 1991-1-1 with its UK National Annex and PD 6688-1-1, with BS 6180 for barrier and infill panel design. Handrails should be positioned 900mm to 1000mm from the pitch line or floor.
  5. 5technicalstrongBSI Knowledge, a standard.RN-1HQ2DHPublished 31 October 2018 and current. This is the code of practice Approved Document K leans on for safety glazing. It gives safety recommendations for glass and plastics glazing sheet materials in locations likely to be subject to accidental human impact, covering both vertical and sloping overhead glazing, with the stated aim of reducing impact related injuries and in particular the risk of cutting and piercing injuries. It carries the guidance on general safety considerations, design considerations, impact performance, marking of safety glazing, critical locations, permanent screen protection, manifestation and specialist glazing products. It excludes glazing for furniture and fittings and for commercial and domestic greenhouses. Cite it for why glass below 800 mm in a window, or below 1500 mm in or beside a door, has to be toughened or laminated and permanently marked.
  6. 6technicalstrongBSI (British Standards Institution), a standard.RN-OPTOJCSTATUS: CURRENT. BS EN 12600:2002 was published 9 January 2003 and is the pendulum impact test that classifies flat glass products into three principal classes by performance under impact and by mode of breakage, the classification that Approved Document K uses for critical locations in glazing. The class code is a three part designation of the form Class 1(B)1 or 2(B)2, where the first figure is the drop height passed, the letter the mode of breakage and the last figure the highest class achieved. The stated purpose is increasing personal safety by reducing cutting and piercing injuries and by assessing containment. It does not cover application requirements or durability, and it superseded the old British test BS 6206:1981, which used classes A, B and C, so a note quoting BS 6206 class A glass is quoting a superseded classification. Catalogue page confirms number, title, date, status and scope; the test detail is paywalled.
  7. 7technicalvery strongMinistry of Housing, Communities and Local Government.RN-BUE914Approved Document B Volume 1, fire safety in dwellings, 2019 edition with the 2020, 2022 and 2025 amendments and the forthcoming 2026 and 2029 changes collated in. Covers means of warning and escape, internal fire spread through linings and structure, external fire spread and access for the fire service. This is the document behind escape window sizes, protected stairways, the 4.5 metre rule and the fire doors a loft conversion needs.
  8. 8technicalvery strongMinistry of Housing, Communities and Local Government.RN-SAMO3MThe official list of competent person schemes whose members can self-certify certain building work instead of getting building regulations approval, published 4 April 2013 and last updated 12 March 2018. Named schemes with contact numbers include ATTMA, APHC, Assure Certification, Blue Flame Certification, the British Board of Agrement, BESCA, Capita Gas Registration and Ancillary Services trading as Gas Safe Register, CIGA, Certass, Certsure LLP trading as NICEIC, the Elmhurst Airtightness Scheme, Fensa Limited, HETAS Limited, NAPIT Registration Limited, the National Federation of Roofing Contractors trading as CompetentRoofer, and OFTEC. Two footnotes matter: the Gas Safe Register is not technically a competent person scheme although in practice its installers carry the same building regulations responsibilities, and Benchmark Certification Limited ceased to operate as a competent person scheme on 10 February 2017, becoming part of NAPIT Registration Limited that day. Installers joining an electrical scheme are added to the single electrical competent person register.
  9. 9technicalstrongBritish Fenestration Rating Council, a page from the body itself.RN-XMDL91The BFRC describes itself as the UK's most trusted and widely recognised rating organisation for verifying the energy performance of windows and doors. Its Window Energy Rating runs on a scale from A++ down to E and combines three measured factors rather than one: solar gain, the heat travelling in through a window, counted positive; thermal transmittance or U-value, the heat loss out of a window, counted negative; and air leakage, the uncontrolled air flow out of a window that causes heat loss, also negative. BFRC makes the point that a rating is more comprehensive proof than a single U-value. This matters because Approved Document L Table 4.2 accepts either a 1.4 W/(m2K) U-value or Window Energy Rating Band B for replacement windows, so a reader can meet the standard by either route.
  10. 10technicalgoodGlass and Glazing Federation, guidance.RN-ABUR2TThe GGF's own comparison table, and the best single answer to whether triple glazing is worth it. Table 1 gives typical values with warm edge spacer. Double glazed 28 mm 4-20-4 with one low-E coating: centre pane 1.5 W/m2K air filled or 1.2 argon filled, g-value 0.70 to 0.71, whole window Uw 1.6 giving WER -13 (band C) for air, and Uw 1.3 giving WER +7 (band A) for argon. Triple glazed in the same PVC-U frame: 28 mm 4-8-4-8-4 argon with one low-E gives Ug 1.3, Uw 1.4, WER -9 (band B), which is worse than the argon double unit; with two low-E coatings it gives Ug 1.0, Uw 1.1, WER +2 (band A). 36 mm 4-12-4-12-4 with two low-E gives Ug 0.8, Uw 1.1, WER +22 (A++); 40 mm 4-14-4-14-4 with two low-E gives Ug 0.7, Uw 1.0, WER +29; 44 mm 4-16-4-16-4 with two low-E gives Ug 0.6, Uw 0.9, WER +36 (A++). The document states plainly that with certain double glass unit specifications the whole window U-value may be better than a basic specification triple unit, and that there is no benefit in triple glazing, subject to cavity width, unless two panes of low-E glass are used, with the coatings on surface 3 for double and surfaces 3 and 5 for triple. It also sets out the definitions: Uw whole window to BS EN ISO 10077 parts 1 and 2, Ug centre pane to BS EN 673, g-value to BS EN 410, and notes DSER counts the g-value only where glazing exceeds 60 per cent of the door.
  11. 11technicalstrongBSI (British Standards Institution), a standard.RN-BI7QQGSTATUS: CURRENT. BS EN ISO 12543-2:2021 was published 28 February 2022 and is identical to ISO 12543-2 and EN ISO 12543-2; it supersedes BS EN ISO 12543-2:2011. It sets the performance requirements for laminated safety glass as defined in ISO 12543-1, covering impact behaviour, durability against humidity, high temperature and solar radiation, fire performance, appearance and dimensional specification. This is the part to cite for laminated safety glass, which matters for rooflights and overhead glazing where laminate is required so that a broken pane is retained by the interlayer rather than falling; toughened glass to BS EN 12150-1 fragments instead. The series has six parts: -1 definitions and component parts, -2 laminated safety glass, -3 laminated glass, -4 test methods for durability, -5 dimensions and edge finishing, -6 appearance. Catalogue page confirms number, title, date, status and scope; the requirements are paywalled.
  12. 12technicalvery strongMinistry of Housing, Communities and Local Government.RN-VGR6O6The security standard for doors and windows, ISBN 978 1 85946 601 8, in force from 5 March 2015 and last updated 22 November 2024. Requirement Q1 applies only to new dwellings, and to easily accessible doors and windows giving access into a dwelling from outside, into a building containing flats from outside, or into a flat from the common parts. Paragraph 1.2 requires secure doorsets tested to PAS 24:2012 or designed to Appendix B, with STS 201 Issue 5:2013, LPS 1175 Issue 7:2010 security rating 2, STS 202 Issue 3:2011 burglary rating 2 and LPS 2081 Issue 1:2015 security rating B accepted as equivalents. Paragraph 1.3 caps a letter plate aperture at 260mm x 40mm and points to DHF technical specification TS 008:2012. Paragraph 1.4 requires a door viewer on the main entrance door unless clear glass or an adjacent window serves the purpose, plus a door chain or limiter. Paragraph 2.2 requires ground floor, basement and other easily accessible windows and rooflights to be tested to PAS 24:2012, with STS 204 Issue 3:2012, LPS 1175 rating 1 and LPS 2081 rating A as equivalents, and paragraph 2.3 requires frames to be mechanically fixed to the structure. Appendix B specifies a doorset in solid or laminated timber to a minimum density.
  13. 13technicalstrongBSI Knowledge, a standard.RN-LUDU9FThe current version of PAS 24, published 30 September 2024, superseding PAS 24:2022. It specifies test methods and acceptance criteria for doorsets and windows intended to resist the attacks associated with a casual or opportunistic burglar, covering hinged, sliding, pivot and folding windows and single and double leaf hinged, sliding, pivot and folding doorsets. The A1:2024 amendment was made to keep pace with the changing modus operandi of criminals and to update referenced industry documents. It tests the manufactured product before installation and does not specify materials or installation methods. PAS 24 is the specification behind Approved Document Q in England and Wales, appears at clause 4.13 of the Scottish building standards, and certification to it is one route to meeting the police Secured by Design scheme.
  14. 14technicalstrongSecured by Design (UK Police Service).RN-F8DIKQThe police list of security standards accepted for residential doorsets under Police Preferred Specification. It names PAS 24:2022+A1:2024 as the newest accepted version, with PAS 24:2022 still accepted and PAS 24:2016 accepted only until 31 December 2025, so a door certified to the 2016 version is no longer current. Other accepted routes are STS 201 Issue 14:2021, STS 202 Issue 10:2021 and STS 222 Issue 2:2021 from Warringtonfire, and LPS 1175 Issue 8.2, LPS 1673 Issue 1 and LPS 2081 Issue 1.1 from the LPCB. Useful for dating a supplier's security claim: ask which PAS 24 version and year the certificate quotes.
  15. 15technicalstrongBSI (British Standards Institution), a standard.RN-PSAEIMSTATUS: CURRENT. The live edition is BS 3621:2017+A1:2024, published 26 September 2024, superseding BS 3621:2017, BS 3621:2007+A2:2012, BS 3621:2004, BS 3621:1998 and BS 3621:1980. It specifies performance requirements and test methods for a thief resistant, mechanically operated single point lock assembly (including locking plates, fixing screws, fitting instructions, cylinders and protective furniture) incorporating a lock conforming to BS EN 12209:2016, lockable from both sides by key so that only key egress is possible, for doors, window doors and entrance doors. It explicitly excludes keyless egress assemblies, which are covered by BS 8621, and secure no egress modes, covered by BS 10621. Notes that quote BS 3621 as the insurance benchmark for a front door lock should cite the 2017+A1:2024 edition, not the 2007 one. The BSI catalogue page confirms number, title, date, status and scope; the full requirements are paywalled.
  16. 16costvery strongCambridge Architectural Research for the Department of Energy and Climate Change.RN-SW1L3OA price, true at 2016, brought forward on the Construction Output Price Index. The summary tables behind the government's domestic retrofit cost assumptions, published as a spreadsheet by Cambridge Architectural Research in July 2016. The per-measure installed costs used in national energy modelling, by house type and measure. A 2016 price base: the structure is still useful, the numbers need bringing forward.
  17. 17coststrong locallyRoyal Borough of Greenwich, Housing and Safer Communities, a government page.RN-SXB1KMA price, true at 2025-03. The priced schedules from a London borough's capital programme delivery contract with its contractor, published as a spreadsheet. Genuine competitively tendered rates for housing works at real scale, which is rare to see in public. Read them as contract rates for volume work under a framework, which is a different market from a homeowner buying one job.
  18. 18costsupplier figureSecondary Glazing Specialist.RN-42XJW4A price, true at 2026. Secondary Glazing Specialist publishing its own price guidance for this work. A trade supplier writing about what it charges is evidence of the market rate and not a quotation, and the cost book treats it as one figure among several rather than on its own
  19. 19coststrong locallyWelwyn Hatfield Borough Council, a government page.RN-CVCUIVA price, true at 2023-06, brought forward on the Construction Output Price Index. Appendix B of a council's repairs and maintenance policy, the rechargeable repairs price list, with the useful note that prices were correct at February 2025 and are uplifted by September CPI each year. A dated and openly indexed schedule, which is better documented than most. Still a landlord recharge including administration, so it reads above a bare trade rate.
  20. 20costsupplier figureVufold.RN-6A2ZVLA price, true at 2026-09. a Vufold category listing for Aluminium bifolding doors, recorded as the page a price was read from. A listing changes as the range changes, so it evidences the retailer and the range rather than a price a reader can confirm today. Flagged for re-sourcing to the product page

  1. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments, Ministry of Housing, Communities and Local Government, accessed 7 September 2026. assets.publishing.service.gov.uk

  2. The Building Regulations 2010, regulation 3: Meaning of building work, The National Archives, accessed 14 September 2026. legislation.gov.uk

  3. Approved Document F, Ventilation, Volume 1: Dwellings, 2021 edition, Ministry of Housing, Communities and Local Government, accessed 7 September 2026. assets.publishing.service.gov.uk

  4. Approved Document K, Protection from falling, collision and impact, 2013 edition, Ministry of Housing, Communities and Local Government, accessed 7 September 2026. assets.publishing.service.gov.uk

  5. BS 6262-4:2018 Glazing for buildings. Code of practice for safety related to human impact, BSI, accessed 7 September 2026. knowledge.bsigroup.com

  6. BS EN 12600:2002 Glass in building. Pendulum test. Impact test method and classification for flat glass, BSI, accessed 7 September 2026. knowledge.bsigroup.com

  7. Approved Document B (fire safety) volume 1: Dwellings, 2019 edition incorporating 2020, 2022 and 2025 amendments, HM Government (GOV.UK), accessed 7 September 2026. assets.publishing.service.gov.uk

  8. Competent person scheme: current schemes and how schemes are authorised, Ministry of Housing, Communities and Local Government, accessed 7 September 2026. gov.uk

  9. BFRC energy performance ratings for windows and doors, British Fenestration Rating Council, accessed 7 September 2026. bfrc.org

  10. GGF Triple Glazing Guidance (Advice to Trade, reference 4.2.2, April 2016), Glass and Glazing Federation, accessed 7 September 2026. ggf.org.uk

  11. BS EN ISO 12543-2:2021 Glass in building. Laminated glass and laminated safety glass. Laminated safety glass, BSI, accessed 7 September 2026. knowledge.bsigroup.com

  12. Approved Document Q, Security, dwellings, 2015 edition, Ministry of Housing, Communities and Local Government, accessed 7 September 2026. assets.publishing.service.gov.uk

  13. PAS 24:2022+A1:2024 Enhanced security performance requirements for doorsets and windows in the UK, BSI Knowledge, accessed 7 September 2026. knowledge.bsigroup.com

  14. Secured by Design: Doors standards, Secured by Design (UK Police Service), accessed 7 September 2026. securedbydesign.com

  15. BS 3621:2017+A1:2024 Lock assemblies operated by key from both the inside and outside of the door. Thief resistant lock assembly. Key egress. Specification, BSI, accessed 7 September 2026. knowledge.bsigroup.com

  16. Domestic Cost Assumptions: Summary Tables, Cambridge Architectural Research for the Department of Energy and Climate Change, accessed 21 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

  17. Equans pricing schedules, contract SPS-2686, Timber Windows schedule ref W1895, Royal Borough of Greenwich, Housing and Safer Communities, accessed 15 September 2026. Priced at 2025-03, so no calibration is needed. royalgreenwich.gov.uk

  18. Secondary Glazing Cost: 2026 Price Guide, Secondary Glazing Specialist, accessed 15 September 2026. Priced at 2026, so no calibration is needed. secondaryglazingspecialist.co.uk

  19. Rechargeable repairs price list 2025, Welwyn Hatfield Borough Council, accessed 21 September 2026. Priced at 2023-06; brought to 2026 on the Construction Output Price Index, housing repair and maintenance (Great Britain), published by Office for National Statistics, a factor of 1.0358. welhat.gov.uk

  20. Aluminium Bifolding Doors, Vufold, accessed 15 September 2026. Priced at 2026-09, so no calibration is needed. vufold.co.uk