Insulation & Membranes
347 sources in the library on insulation & membranes, 40 on this page cited in a published note. Each one says what the document covers and what it is good for. Name a source to see which document it is and where to read it. One at a time. Page 1 of 9.
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Building Control Northern Ireland
The index of Northern Ireland's Technical Booklets, the devolved equivalent of England's Approved Documents, and the place to check which NI booklet answers a question. The booklets run B materials and workmanship, C site preparation and resistance to contaminants and moisture, D structure, E fire safety, F1 conservation of fuel and power in dwellings (2022 edition) and F2 for buildings other than dwellings, G sound, H stairs ramps and guarding, J solid waste, K ventilation, L combustion appliances and fuel storage, M physical infrastructure for high speed electronic communications networks, N drainage, P sanitary appliances and unvented hot water storage, R access to and use of buildings, and V glazing. Amendment booklets AMD7 (amends B, C and E), AMD8 (amends R) and AMD9 (amends E and R) carry the live changes, so the base 2012 booklets must be read with them.
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Building Safety Regulator (GOV.UK)
GOV.UK publication page for the Building Safety Regulator's 28 March 2024 research on moisture risk of spray foam in timber pitched roofs, summarising low and high risk scenarios.
Cited in Spray Foam Insulation: Costs, Risks & Mortgage Issues.
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Department for Energy Security and Net Zero
The official ECO statistics explain ECO4's Solid Wall Minimum Requirement, which suppliers can meet only by installing internal or external solid wall insulation, confirming ECO4 funds both types.
Cited in Insulation Grants 2026: ECO4, GBIS & What You Can Get, Solid Wall Insulation: IWI vs EWI.
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Department for Energy Security and Net Zero
The official GB statistics estimate 8.5 million homes with solid walls and 21.6 million with cavity walls, so solid-wall homes are about 28% of the stock, not one third.
Cited in Solid Wall Insulation: IWI vs EWI.
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Department for Energy Security and Net Zero
Published 21 January 2026 and last updated 18 March 2026. It commits £15 billion of public investment over this Parliament, 2025/26 to 2029/30, to upgrade up to 5 million homes by 2030, targeting over 450,000 heat pump installations a year by 2030 and solar panels on up to 3 million additional homes. The Boiler Upgrade Scheme gets £2.7 billion to 2030, keeping the £7,500 grant for hydronic heat pumps, adding new £2,500 grants for air-to-air heat pumps and heat batteries used for central heating, and £5,000 for biomass boilers in rural areas. A Warm Homes Fund provides a £5 billion financial transactions facility including £1.7 billion for low and zero-interest consumer loans, rolling out in phases from 2026, and the Warm Homes Social Housing Fund and Local Grant merge into a single low-income scheme from 2027/28. Private rented sector properties must meet EPC Band C across two metrics by October 2030, subject to a £10,000 spending cap, and an EPC C standard is introduced for the social rented sector for the first time. Future Homes Standard regulations were to be laid in Q1 2026.
Cited in Combi vs System vs Regular Boilers.
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Department for Energy Security and Net Zero
GOV.UK's publication page for the Warm Homes Plan, published 21 January 2026 by DESNZ, describes it as the plan for cutting energy bills and upgrading homes.
Cited in Solid Wall Insulation: IWI vs EWI.
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Department of Finance (Northern Ireland)
Northern Ireland's equivalent of Approved Document L Volume 1. This edition came into effect on 30 June 2022 and gives guidance on regulations 39 to 47 of the Building Regulations (Northern Ireland) 2012, which set the requirements for conservation of fuel and power in dwellings, including the limiting U-values a replacement window or door must meet in Northern Ireland. It replaced the 2012 version, and the Department publishes an awareness briefing and FAQ setting out the differences. The full text is at https://www.finance-ni.gov.uk/sites/default/files/publications/dfp/TB%20Part%20F1%202022_On-Line%20Publication.pdf. Cite this rather than Approved Document L whenever a note gives a window U-value for a reader in Northern Ireland.
Cited in Industrial Style Windows: Cheaper Alternatives, 2026 Costs, Insulation: The Complete Guide.
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GOV.UK
The England-only successor to the Home Upgrade Grant, delivered by local councils. Eligibility: household income of £36,000 a year or less (with postcode and benefit-based exceptions), privately owned home, EPC rating D to G. Funds wall, loft and underfloor insulation, air source heat pumps, smart controls and solar panels, with the council organising and paying for the work. Explicitly 'only available in England'. Use this whenever a note says HUG closed and a successor is awaited: it is live and taking applications.
Cited in Insulation Grants 2026: ECO4, GBIS & What You Can Get, LPG Conversion Cost: 2026 UK Price Guide.
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Historic England
Historic England's guidance that works altering a listed building in a way that affects its character or appearance need listed building consent.
Cited in Insulating & Repairing a Bay Window Roof.
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HM Revenue & Customs
Section 2.1 sets a zero rate of VAT on the installation of energy-saving materials in residential accommodation from 1 May 2023 to 31 March 2027, after which the rate reverts to the 5% reduced rate; section 2.22 extended it to buildings used solely for relevant charitable purposes from 1 February 2024. Section 2.7 lists the qualifying materials: central heating and hot water controls, draught stripping, insulation to walls, floors, ceilings, roofs, lofts and pipes, solar panels, wind turbines, water turbines, ground source heat pumps, air source heat pumps, micro combined heat and power units and wood-fuelled boilers, with water source heat pumps, batteries for energy storage and smart diverters added on 1 February 2024. Section 2.3 is the critical rule for a renovation note: relief applies to an installation service, or materials supplied and installed together, but materials bought without installation stay standard-rated at 20%.
Cited in Air Source Heat Pumps: Cost, Grants & Is It Worth It, Builders' Merchants: The Complete UK Guide (2026), Builders' Merchants Explained: How They Work & How to Buy, Cost of a New Bathroom (Full Breakdown) and 8 more.
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House of Commons Library
A House of Commons Library briefing on spray foam insulation and mortgages in England. It summarises lender refusals, surveyors' inspection difficulties and the industry guidance issued since 2023.
Cited in How to Insulate A Vaulted Ceiling In 5 Steps, How to Insulate Garage, Spray Foam Insulation: Costs, Risks & Mortgage Issues.
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LABC Warranty
LABC Warranty's breather membrane guide requires membranes on framed walls to have vapour resistance under 0.6 MNs/g, be at least Class W2 to BS EN 13859-2, and Class W1 in very severe exposure.
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LABC Warranty
LABC Warranty's technical manual section on timber-frame external walls asks for a 500 gauge polyethylene sheet, vapour control plasterboard or an accredited membrane near the warm side of the insulation unless calculation shows otherwise.
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Ministry of Housing, Communities and Local Government
The statutory figures behind a damp diagnosis, and the numbers to quote when a note explains why ground levels or a bridged damp proof course cause rising damp. Paragraph 5.2 requires that in an external wall the damp-proof course should be at least 150mm above the level of the adjoining ground (Diagram 8) unless part of the building protects the wall, and that in an external cavity wall the cavity should be taken down at least 225mm below the level of the lowest damp-proof course, or a damp-proof tray provided (Diagram 9a). For suspended timber ground floors it requires a ventilated air space of at least 75mm from the ground covering to the underside of any wall-plates and at least 150mm to the underside of the suspended timber floor or insulation, with ventilation openings on two opposing external walls of not less than 1,500mm2 per metre run of external wall or 500mm2 per square metre of floor area, whichever is greater; for suspended concrete floors the clear ventilated space is at least 150mm with the same opening sizes. Section 2.39 onwards covers radon, referring to BRE Report BR 211 for protective measures. The 2013 edition was published on 3 September 2013 with changes in effect from 1 October 2013.
Cited in Barge Boards, Fascias & Soffits: Cost & Replacement, Breathable Membranes for Roofs & Walls, Brick Slips & Brick Cladding Systems, Build Basement Cost: 2026 UK Price Guide and 46 more.
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Ministry of Housing, Communities and Local Government
Table 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.
Cited in Adding an Ensuite: Cost, Layout & Plumbing, All You Need To Know About Double Glazing Repairs, Annexe & Granny Flat: Cost, Planning & Rules, Basement & Cellar Conversions: Cost and 57 more.
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Ministry of Housing, Communities and Local Government
The 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.
Cited in Adding an Ensuite: Cost, Layout & Plumbing, Adding Porch, All You Need To Know About Double Glazing Repairs, Annexe & Granny Flat: Cost, Planning & Rules and 169 more.
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Ministry of Housing, Communities and Local Government
The 2026 edition takes effect on 24 March 2027 for work not connected with higher-risk building work, and 24 September 2027 where it is, with transitional arrangements in Circular Letter 01/2026. Table 3.1 sets limiting U-values for new dwellings: all roof types 0.16, wall 0.26, floor 0.18, window 1.6, rooflight 2.2, doors 1.6 W per square metre per kelvin, with air permeability 8.0 cubic metres per hour per square metre at 50Pa. Table 3.2 covers new elements in existing dwellings, that is extensions and loft conversions: roof 0.15, wall 0.18, floor 0.18, window 1.4 or Window Energy Rating Band B, rooflight 2.2. Table 3.3 covers upgrading existing elements: a roof with a U-value worse than the 0.35 threshold must be improved to 0.16, and note 2 confirms that for dormer windows the roof figure covers the roof parts and the wall figure the cheeks, while note 3 allows a higher U-value where the standard would limit head room provided the insulation plus air gap is at least the depth of the rafters.
Cited in External Wall Insulation (EWI) Systems & Finishes, Insulation: The Complete Guide, Triple Glazing: Worth the Cost?.
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Ministry of Housing, Communities and Local Government
Supports Part O of Schedule 1 to the Building Regulations 2010 (requirement O1 and regulation 40B); the 2021 edition took effect on 15 June 2022 in England, with transitional relief for work notified before that date and started before 15 June 2023. Critically, paragraph 0.3 limits the guidance to NEW residential buildings only (dwellings, residential institutional and residential other, plus shared communal rooms, common spaces and live/work units), and paragraph 0.7 applies it only to the residential parts of mixed-use buildings. Compliance is by the simplified method (Section 1) or dynamic thermal modelling to CIBSE TM59 (Section 2); the simplified method splits England into a high risk location (urban and some suburban London listed in Appendix C, with guidance for parts of central Manchester) and a moderate risk location (the rest of England). Table 1.1 (cross-ventilated) caps glazing as a percentage of floor area at north 15 high risk / 18 moderate, east 18/18, south 15/15, west 18/11, with the most glazed room capped at north 37/37, east 37/37, south 22/30, west 37/22. Table 1.2 (no cross-ventilation) caps glazing at north 15/18, east 11/18, south 11/15, west 11/11, most glazed room north 26/26, east 18/26, south 11/15, west 18/11.
Cited in Glass Box & Bifold Extensions: Cost & Ideas, Glazed Extensions: The Complete UK Guide, Glazing Explained: U-values, Low-E, Argon & Spacers, Rooflights & Skylights: Materials & Types.
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Ministry of Housing, Communities and Local Government
2024 government hygrothermal modelling assessment of sprayed foam on domestic timber roofs, and an unusually quotable secondary source for BS 5250:2021's prescriptive roof guidance. Risks are low only where an OPEN CELL, moisture permeable insulant is used with an air and vapour control layer on the warm side and a space left between insulation and underlay, ventilated from the eaves where a high resistance underlay is used. For a WARM pitched roof with a high resistance underlay such as bitumen felt: each ventilated void should be at least 25 mm deep, ventilated at high and low level, plus a 15 mm allowance for underlay drape, giving 25 + 15 = 40 mm. For a low resistance underlay, option 1 is an AVCL plus an unventilated counter batten air gap for air permeable coverings; option 2, where an AVCL is impracticable, follows the HR guidance. It also states plainly that official moisture guidance is Approved Document C, that AD C was last fully revised in 2004 with 2010 and 2013 amendments, and that AD C REFERENCES THE 2002 EDITION OF BS 5250, not the current 2021 edition. It names BS EN ISO 13788:2012 (the Glaser method) as the calculation method referenced by the 2002 edition, and notes the Glaser method may underestimate risk because it cannot simulate heat and liquid transport, unlike BS EN 15026:2007.
Cited in Internal Wall Insulation: Costs & Methods, Roof Tiles & Slates: Coverage, Fixings & Ventilation, Spray Foam Insulation: Costs, Risks & Mortgage Issues.
- very strong RN-2WZR3Y cited
Ministry of Housing, Communities and Local Government
The landing page for Approved Document F, Ventilation. Volume 1 covers dwellings and Volume 2 buildings other than dwellings; the current edition took effect 15 June 2022 and a 2026 edition is published on the same page. This is the document that sets background ventilation (trickle vent) equivalent areas and intermittent extract rates, and the reason replacement windows must not make existing ventilation worse. Volume 1 is a 859 KB PDF, Volume 2 is 662 KB.
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Office for Product Safety and Standards and Ministry of Housing, Communities and Local Government
Names the Office for Product Safety and Standards as the UK regulator for construction products and most consumer goods, a role it took on in April 2021, funded by and acting on behalf of MHCLG. Confirms the enforced legislation is the Construction Products Regulations 2013 as amended by the Construction Products (Amendment) Regulations 2022, which gave OPSS its enforcement powers. Records that the Grenfell Tower Inquiry final report was published on 4 September 2024, the Government response on 26 February 2025 accepting all 58 recommendations, and a Construction Products Reform White Paper on 25 February 2026 proposing reform of testing, certification, product information and enforcement. OPSS carries out product testing, site inspections and technical documentation reviews, responded to over 100 non-compliance allegations in 2023, and publishes construction product safety alerts, reports and recalls.
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Ofgem
Ofgem's ECO4 delivery guidance version 4.0 records that ECO4 was extended by nine months to 31 December 2026, and gives GBIS as running to 31 March 2026.
Cited in Spray Foam Insulation: Costs, Risks & Mortgage Issues.
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Ofgem
ECO4 is the fourth phase of the Energy Company Obligation across Great Britain. It applies to measures installed from 1 April 2022 and runs until 31 December 2026 following a nine-month extension; ECO3 closed on 31 March 2022 and ECO4 came into force in July 2022. The scheme places a Home Heating Cost Reduction Obligation on medium and large energy suppliers to promote measures that improve the ability of low-income, fuel-poor and vulnerable households to heat their homes, funding insulation and heating upgrades for both homeowners and tenants. Ofgem also lists the Great British Insulation Scheme as a separate obligation on this page.
Cited in All You Need To Know About Double Glazing Repairs, Best Loft Insulation: Materials Compared, Boiler Upgrade Scheme & Heating Grants 2026, Cavity Wall Insulation Materials Compared and 19 more.
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Ofgem
Ofgem's ECO4 delivery guidance for suppliers and installers. Its consumer contributions section requires the amount a household contributes towards any ECO4 measure to be recorded, so contributions do happen.
Cited in Insulation Grants 2026: ECO4, GBIS & What You Can Get.
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Ofgem
The scheme, formerly known as ECO+, ran from April 2023 to 31 March 2026 and is now closed. It obliged medium and large energy suppliers to deliver measures reducing energy use in the least energy-efficient homes in Great Britain. Eligibility was homes with an EPC rating of D to G in Council Tax bands A to D in England, or A to E in Scotland and Wales, plus low-income and vulnerable households. Unlike ECO4, which funds whole-house packages, GBIS mostly delivered a single insulation measure per home. This is the page to cite when a note has to say a grant route has closed rather than leave a reader chasing it.
Cited in Best Loft Insulation: Materials Compared, Boiler Upgrade Scheme & Heating Grants 2026, Electric Heating Options Compared, EPC Ratings Explained & How to Improve Yours and 17 more.
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Ofgem
Ofgem's homeowner page for the Great British Insulation Scheme. It lists the eligible insulation measures, including under-floor and solid floor insulation.
Cited in Underfloor Insulation: Suspended & Solid.
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Scottish Government (gov.scot)
Scotland's U-value backstops, which differ from England's Approved Document L and are the numbers to quote for a Scottish reader. Table 6.3 for new dwellings gives area-weighted average maximum U-values in W/m2K of wall 0.22, floor 0.18, roof 0.15, windows, doors and rooflights 1.6, and cavity separating wall 0.2, with individual element values of 0.70 for wall and floor, 0.35 for roof and 3.3 for windows, doors and rooflights. A cavity separating wall can be assigned 0.2 where the cavity has effective perimeter sealing around all exposed edges in line with the insulation layers of abutting elements, and 0.0 where the cavity is also fully filled with a material limiting air movement. Table 6.5 for extensions and conversions is two-column: where the existing dwelling's wall and roof U-values are poorer than 0.7 and 0.25 respectively, wall 0.17, floor 0.15, pitched roof with insulation between ceiling ties or collars 0.11, flat or pitched roof with insulation between rafters or integral 0.13 and windows, doors and rooflights 1.4; where those parameters do not apply the figures relax to 0.22, 0.18, 0.15, 0.18 and 1.6, with individual element values of 0.70, 0.70, 0.35, 0.35 and 3.3. Localised poorer areas such as a meter box must be compensated by the rest of the element and are important for condensation control, while repeating thermal bridges such as timber studs are not treated as individual elements because they are already in the BS EN ISO 6946 calculation.
Cited in Insulation: The Complete Guide.
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The National Archives (legislation.gov.uk)
Section 65 of the Building Safety Act 2022 defines a higher-risk building in England as one at least 18 m high or with at least 7 storeys that contains at least 2 residential units.
Cited in PIR vs Mineral Wool Insulation Compared.
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The National Archives (legislation.gov.uk)
Article 4(1) of the retained Construction Products Regulation requires a manufacturer to draw up a declaration of performance when a product covered by a designated standard, or conforming to a UK Technical Assessment, is placed on the market. Article 4(2) makes the declaration the only permitted route for stating performance against essential characteristics, so a performance claim outside the declaration is not valid. Article 4(3) provides that by drawing up the declaration the manufacturer assumes responsibility for the product's conformity with the declared performance, and that in the absence of objective indications to the contrary the declaration is presumed accurate and reliable. The words designated standard and UK Technical Assessment were substituted for harmonised standard and European Technical Assessment on 31 December 2020 by the Construction Products (Amendment etc) (EU Exit) Regulations 2019 (S.I. 2019/465), Schedule 1 paragraph 6.
Cited in PIR vs Mineral Wool Insulation Compared.
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The National Archives (legislation.gov.uk)
Annex III of the retained F-gas Regulation lists products banned from the market. Item 16 bans XPS foams containing HFCs with a GWP of 150 or more from 1 January 2020.
Cited in EPS vs XPS Insulation: Which & Where.
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The National Archives (legislation.gov.uk)
The regulation behind the combustible cladding ban. Regulation 7(2) requires materials in the external walls or specified attachments of a relevant building to achieve European Classification A2-s1, d0 or A1 for reaction to fire, and regulation 7(1A) prohibits relevant metal composite materials in external walls. Regulation 7(4) defines a relevant building as one with a storey at least 18 metres above ground level, excluding roof-top plant areas and storeys consisting only of plant rooms, containing one or more dwellings, an institution, or a room for residential purposes. Regulation 7(3) lists the exempt components: cavity trays between masonry leaves, parts of roofs connected to external walls, door frames and doors, electrical installations, fibre optic cables, insulation and waterproofing below ground or up to 300mm above it, intumescent and fire-stopping materials, membranes, seals, gaskets, fixings, sealants and backer rods, solar shading device components other than the primary shade element, thermal break materials used for Part L compliance, window frames and glass, and balcony floor layers classified A1fl or A2fl-s1 over an imperforate substrate.
Cited in Builders' Merchant vs DIY Store: Which Is Cheaper?, Cladding and Render: The Complete UK Guide (2026), External Wall Insulation (EWI) Systems & Finishes, Fibre Cement Cladding & Boards Explained and 4 more.
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The National Archives (legislation.gov.uk), Northern Ireland Statutory Rules
NORTHERN IRELAND, and the part letters mean different things from England, so quoting an England part letter into an NI note is a straight error. The parts are A interpretation and general, B materials and workmanship, C site preparation and resistance to contaminants and moisture, D structure, E fire safety, F conservation of fuel and power, G resistance to the passage of sound, H stairs, ramps, guarding and protection from impact, J solid waste, K ventilation, L combustion appliances and fuel storage systems, N drainage, P sanitary appliances, unvented hot water storage systems and reducing the risk of scalding, R access to and use of buildings, and V glazing. So NI Part D is England's Part A, NI Part E is England's Part B, NI Part F is England's Part L, NI Part K is England's Part F, NI Part L is England's Part J, NI Part N is England's Part H, NI Part P is England's Part G and emphatically NOT electrical safety, NI Part R is England's Part M, and NI Part V is glazing. There is NO part covering electrical safety anywhere in these regulations, so domestic electrical work in Northern Ireland is not notifiable building work as it is under England's and Wales's Part P. Regulation 41 imposes consequential improvements, regulation 42 change of energy status and regulation 43 renovation of thermal elements.
- very strong RN-03F4DZ cited
The National Archives (legislation.gov.uk), UK Statutory Instrument 2022/603
The amendment that tightened the England combustible cladding ban, made under sections 1 and Schedule 1 of the Building Act 1984 and in force on 1 December 2022, extending to England and Wales but expressly not applying to any building in Wales. It inserts the definitions that decide the ban's reach. Reaction to fire classification is fixed as BS EN 13501-1:2018 published by BSI in 2019. Relevant metal composite material means any panel or sheet no more than 10 mm thick comprised of layers, two or more of metal, alloy or metal compound, and one or more substantial layer of a material with a gross calorific value of more than 35 MJ/kg tested to BS EN ISO 1716:2018, with a substantial layer defined as at least 1 mm thick or at least 1 kg per square metre. Specified attachment means a balcony attached to an external wall, a solar shading device other than one attached at a height of no more than 4.5 metres above ground level, or a solar panel attached to an external wall. It also lowers the material change of use trigger in regulation 6(1)(c) from fifteen to eleven metres, and substitutes regulation 6(3) so that on a material change of use under regulation 5(k) the external wall and specified attachments must contain only Class A2-s1, d0 or A1 materials. Regulation 7(2) is substituted in the same terms.
- very strong RN-KXCXCY cited
Welsh Government (gov.wales)
WALES. First published 3 April 2017, last updated 7 April 2026. Wales publishes its own Approved Document F, and the page carries the current volume 1 for dwellings (910 KB PDF) and volume 2 for buildings other than dwellings, plus replacement volumes that TAKE EFFECT ON 4 MARCH 2027, the same changeover date as the Welsh Approved Document L and distinct from England's 24 March 2027. Welsh Part F diverged from England's when England issued its 2021 edition alongside Part L and Part O, so extract rates and background ventilator provisions for a Welsh bathroom, kitchen or loft conversion should be taken from this document rather than from England's Approved Document F.
Cited in Trickle Vents & Background Ventilation.
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Welsh Government (gov.wales)
WALES. The Welsh Government publishes its own Approved Documents, and this collection page, last updated 19 June 2025, lists them with their current dates so the right edition can be cited: A structure 3 April 2017, B fire safety 19 June 2025, C site preparation and resistance to contaminants and moisture 3 April 2017, D toxic substances 3 April 2017, E resistance to the passage of sound 13 April 2022, F ventilation 7 April 2026, G sanitation, hot water safety and water efficiency 10 May 2023, H drainage and waste disposal 3 April 2017, J combustion appliances 6 January 2025, K protection from falling 19 March 2025, L conservation of fuel and power 7 April 2026, M access 20 March 2025, N glazing 5 April 2017, O overheating, P electrical safety, Q security and R volumes 1 and 2. Wales still has a live Approved Document N on glazing safety, opening and cleaning, which England withdrew in 2013 when its content moved into Part K, so an England-based note that says Part N no longer exists is wrong for Wales.
- very strong RN-CY8PF5 cited
Welsh Government (gov.wales)
WALES. Loft insulation must meet the minimum energy efficiency values in the Welsh Approved Documents, and where that upgrade is not technically or functionally feasible the element must instead be upgraded to the best standard achievable within a simple payback of no greater than 15 years. Installing loft insulation as part of a roof renovation where MORE THAN 25 PER CENT OF THE ROOF is being renewed triggers the full Approved Document standard, the Welsh version of the renovation of a thermal element trigger. The guidance warns against blocking ventilation at the eaves. Read alongside Table 4.1 of the Welsh Approved Document L Volume 1, which sets 0.13 W/m2K for roofs in both new and existing dwellings.
Cited in Insulation: The Complete Guide.
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Hertfordshire Building Control (published by Harrow Council)
Building control guidance with insulation thickness tables by perimeter/area ratio. For suspended timber floors at P/A 0.5 it gives 110 mm (Kingspan TF70) to 140 mm (Celotex XR4000) of PIR between joists for 0.18 W/m2K.
Cited in Underfloor Insulation: Suspended & Solid.
- strong locally RN-CARE2F cited
Wealden District Council
Council energy advice page giving the typical heat loss breakdown of an uninsulated home, including 15% through floors, which is the share the sentence states.
Cited in Triple Glazing: Worth the Cost?, Underfloor Insulation: Suspended & Solid.
- strong RN-KVNMZY cited
BRE
BRE's conventions for U-value calculations (BR 443, 2019). Its multifoil section rests on a BRE study and on Building Control Alliance guidance on multifoil and Part L compliance.
- strong RN-PY45YZ cited
BSI
BSI listing for BS 5617:1985, showing it specified urea-formaldehyde foam cavity fill (not polyurethane) and was withdrawn on 2 January 2024.
Cited in Cavity Wall Insulation Materials Compared, Rockwool vs Other Mineral Wool: Which to Use.