Regulations & Compliance5 min

External Wall Cladding Regulations in London: Post-Grenfell Rules, Combustible Materials Ban, and EWS1

The Grenfell Tower fire on 14 June 2017 — in which the rapid fire spread up the external wall of the tower was attributed in large part to the aluminium composite material (ACM) cladding system installed during a 2016 refurbishment — fundamentally changed the regulatory framework for external wall materials in England. The Government's response included a ban on the use of combustible materials in the external wall construction of certain categories of building, a comprehensive inspection programme for existing high-rise residential buildings with suspected unsafe cladding, and the introduction of the EWS1 (External Wall Survey) process for mortgage lending purposes. For London homeowners, landlords, leaseholders, and developers, understanding the current regulatory framework for external wall cladding — what materials are permitted, what buildings are affected, what the EWS1 process involves, and how the regulations interact with planning and Building Regulations approval — is essential for any project involving external wall construction or cladding installation.

Key Takeaways

✓The Grenfell Tower fire led to a series of regulatory changes in England that significantly restrict the use of combustible materials in the external walls of certain building types. The primary regulatory change is the amendment to Approved Document B (Fire Safety — ADB) of the Building Regulations 2010 — specifically, the 2018 amendment that came into force on 21 December 2018, which prohibits the use of combustible materials in the external walls (including the cladding system, thermal insulation, and supporting structure) of: purpose-built blocks of flats above 18 metres in height; hotels, hospitals, and schools above 18 metres in height; student accommodation and care homes above 18 metres in height. The 18-metre height threshold was subsequently lowered to 11 metres by the Building Safety Act 2022, which extended the prohibition to more buildings and strengthened the regulatory framework for building safety more broadly. The prohibition on combustible materials in ADB is given effect by the Building Regulations 2010 (as amended), specifically Regulation 7(2), which requires that materials used in or as external walls of a building to which the prohibition applies shall be of European Classification A1 or A2-s1,d0 or better (i.e., non-combustible or limited combustibility materials). Class A1 is the highest non-combustibility classification — stone, brick, concrete, glass, and steel are all A1. Class A2-s1,d0 (limited combustibility with minimal smoke production and no flaming droplets) covers materials such as some mineral-fibre insulation systems and calcium silicate boards
✓The types of materials commonly used in external wall cladding systems that may or may not comply with the post-Grenfell regulations are: Aluminium Composite Material (ACM) panels — the material used on Grenfell Tower. ACM panels consist of two thin aluminium faces bonded to a core — the fire performance of the panel depends critically on the core material. ACM with a polyethylene (PE) core (Category 3 ACM, classified as Class B or C for fire reaction) is the most hazardous type — it was the type used at Grenfell and is now prohibited in the external walls of the relevant building categories. ACM with a limited combustibility core (mineral-filled polyethylene — Category 2, Class B-s1,d0) is also prohibited in relevant buildings. ACM with a Class A2-s1,d0 or A1 (non-combustible) core is generally compliant with the current regulations. High Pressure Laminate (HPL) panels — a composite panel made from layers of fibres (typically paper and/or glass-fibre) impregnated with thermosetting resin and cured at high temperature. HPL panels used in cladding systems are of varying fire performance — HPL panels of Class A2-s1,d0 may be used in compliant external wall systems; Class B or C HPL panels are prohibited in the external walls of relevant buildings. Timber cladding — all natural timber and most engineered timber products (including thermally modified wood, larch, cedar, and composite wood/plastic cladding boards) are classified as Class D or worse (combustible) under the European reaction-to-fire classification and are therefore prohibited in the external walls of buildings over 11m to which the regulation applies. However, timber cladding is permitted in the external walls of lower-rise buildings (under 11m) subject to normal Building Regulations fire spread requirements (an adequate cavity barrier system to prevent fire spread via the cavity is required regardless of the cladding height). Insulation materials — the fire performance of the insulation within the external wall system is as important as the cladding material. Expanded polystyrene (EPS) insulation boards, polyisocyanurate (PIR) insulation (such as Kingspan K15 or similar), and polyurethane foam insulation are all combustible materials and are prohibited as insulation in the external walls of relevant buildings. Mineral wool (rock wool or glass wool) insulation is Class A1 non-combustible and is the preferred insulation type for external wall systems on relevant buildings
✓The EWS1 (External Wall Survey 1) form was introduced in December 2019 by UK Finance (the trade body for mortgage lenders) in response to the Grenfell Tower aftermath and the widespread concern among mortgage lenders about the fire safety of external wall systems on residential blocks. The EWS1 form is not a regulatory document (it is not required by the Building Regulations or by any Act of Parliament) — it is a mortgage lending tool used by lenders to assess the fire safety of the external wall system before making a lending decision on a flat in a residential block. The EWS1 form requires a qualified professional (a fire engineer, building surveyor, or structural engineer with fire safety expertise) to inspect the external wall system of the building and certify one of two outcomes: EWS1 Option A — the external wall system has no materials presenting a fire risk (i.e., all materials in the external wall system are A1 or A2-s1,d0 or the materials that are present are in locations that do not affect the overall fire performance of the system) — indicating the building passes the EWS1 assessment and the lender can proceed with the mortgage application. EWS1 Option B — combustible materials are present in the external wall system, but remediation work is required or underway, or the risk has been assessed as acceptable on the basis of compensating measures (such as a waking watch, enhanced fire detection, or a sprinkler system). Option B may prevent mortgage lending or make it more difficult until remediation is complete. The EWS1 process has been controversial — it caused significant disruption to the mortgage market for flats in multi-storey residential blocks (even lower-rise blocks that were not within the original 18m threshold) and led to many owners of flats in affected buildings being unable to sell or remortgage. Government guidance has been revised several times since 2020 to narrow the scope of buildings for which EWS1 is required — and since January 2023, EWS1 is formally only required for buildings of 6 storeys (approximately 18m) or above, or for buildings of 5 storeys or below where there are specific concerns about the external wall system. For flat owners who are unsure whether their building requires an EWS1 form, the Leasehold Advisory Service (LEASE) and RICS guidance documents provide the most current position
✓The Building Safety Act 2022 (which received Royal Assent on 28 April 2022) introduced a comprehensive new legislative framework for building safety in England, including: the establishment of the Building Safety Regulator (BSR) — hosted by the Health and Safety Executive (HSE) — to oversee the safety and performance of all buildings and to directly regulate the design and construction of "higher-risk buildings" (buildings that are at least 7 storeys or 18m in height, and that contain at least 2 residential units or are a hospital or care home); a new gateway process for higher-risk buildings, requiring design and specification review at three stages (Gateway 1 at planning application, Gateway 2 at Building Regulations full plans approval, and Gateway 3 before the building is occupied); mandatory registration of existing higher-risk occupied buildings with the BSR by April 2024; the creation of a Building Safety Fund and a Developer Remediation Contract to fund the remediation of existing unsafe cladding on higher-rise buildings; and the extension of the limitation period for defective building work claims under the Defective Premises Act 1972 from 6 years to 30 years retrospectively (allowing claims for past defective building work to be brought for up to 30 years after the work was completed). For London homeowners and developers working on residential buildings below 7 storeys, the Building Safety Act 2022's new gateway process does not directly apply — but the wider regulatory changes (including the combustible materials ban and the strengthened Building Regulations inspection regime) do affect all residential building work
✓For London homeowners extending or cladding a residential house (not a block of flats), the post-Grenfell regulatory changes are relevant in the following specific circumstances: external cladding on a single house above 11m in height (a relatively rare scenario in the London terrace context but applicable to 4–5 storey townhouses in central London) — combustible cladding materials are prohibited in the external walls above 11m; cavity barriers and fire stops within external wall systems (applicable to all houses where an external wall system has a cavity — including insulated render systems, ventilated cladding systems, and timber frame walls) — adequate cavity barriers at every floor level and at fire compartment boundaries are required by ADB to prevent fire spread within the cavity regardless of the cladding height; render and insulation systems (External Wall Insulation — EWI — systems that use a combustible insulation such as EPS or PIR board below an acrylic or silicone render coat) — these are permitted on single houses below 11m, but the system must be designed with appropriate cavity barriers if a ventilated cavity is present. For the vast majority of London Victorian terraces (typically 2–3 storeys, below 11m), the combustible materials ban does not apply to the external wall cladding — the choice of cladding material (including timber weatherboarding, renders, and composite cladding panels) is governed by normal Building Regulations requirements for fire spread rather than the specific prohibition in Regulation 7(2). A single house is not required to use A1 or A2 materials throughout its external walls below 11m

1. Safe External Cladding Options for London Houses
2. The Developer Remediation Contract and Building Safety Fund
3. What Homeowners Should Check Before Installing External Cladding
4. Frequently Asked Questions

Safe External Cladding Options for London Houses

For London houses below 11m in height, the post-Grenfell combustible materials ban does not restrict the external cladding options — the normal Building Regulations fire spread requirements of ADB Section B4 apply. The following cladding systems are commonly used on London Victorian terrace extensions and rear additions:

Brick and blockwork (traditional masonry): The default cladding for London Victorian terrace extensions is London stock brick (or a stock-brick-compatible facing brick) to match the existing elevation. Brick is an A1 non-combustible material and has no fire safety restrictions. The cost of brick-faced external walls is relatively high (facing brickwork in London: £60–£120/m² supply and lay for standard stock brick, more for premium handmade or reclaimed brick) but produces a durable, low-maintenance finish that integrates well with the existing Victorian terrace appearance.

Cement render (external wall insulation with render finish): Reinforced mineral or silicone render systems over external insulation (EWI) are widely used on London extensions and whole-house overcladding projects. The insulation is typically EPS (expanded polystyrene) below 11m (on houses where the combustible materials ban does not apply) or mineral wool above 11m (where the ban applies). The render finish provides a smooth or textured external face in any colour. Render over EWI provides excellent thermal performance (U-values of 0.15–0.25 W/m²K are achievable) and transforms the appearance of a previously uninsulated solid brick wall.

Timber weatherboarding and composite cladding: Timber cladding (larch, cedar, oak, thermally modified wood, or composite wood-effect boards) provides a contemporary architectural appearance and is permitted on houses below 11m. The design of the cavity drainage and cavity barriers within a timber cladding system is important — the cavity behind the cladding boards must be adequately closed at every floor level and at the top and bottom of the wall by fire-stopped cavity barriers, regardless of the building height. Untreated softwood cladding will require staining or oiling maintenance every 3–5 years; thermally modified timber (such as Accoya or Kebony) or high-quality composite boards have significantly lower maintenance requirements.

Zinc and aluminium panels: Zinc and aluminium standing seam or flat-lock panel cladding systems are widely used for contemporary extension and alteration projects in London. Both materials are non-combustible (Class A1) and require no maintenance painting. The initial cost is higher than timber or render (typically £150–£250/m² supply and install for a standing seam zinc or aluminium system) but the long service life (50+ years) makes the whole-life cost competitive.

The Developer Remediation Contract and Building Safety Fund

The cost of remediating unsafe cladding on existing residential blocks in London is one of the most significant financial and social issues in the UK housing market. Two principal mechanisms have been established to fund or secure remediation:

Developer Remediation Contract: The Government established a Developer Remediation Contract under which the largest residential developers agreed (under threat of legislation and regulatory intervention) to fund the remediation of unsafe cladding on residential buildings they developed or refurbished that are between 11m and 18m in height. By signing the Developer Remediation Contract, a developer commits to funding the remediation of eligible buildings at its own cost, without passing costs to leaseholders. Developers who have signed the contract include most of the major UK housebuilders (Persimmon, Barratt, Taylor Wimpey, Bellway, Berkeley Group, and others).

Building Safety Fund: The Building Safety Fund (BSF) was established to fund the remediation of unsafe cladding on buildings above 18m in height where the original developer cannot be identified, has become insolvent, or has not signed the Developer Remediation Contract. The BSF was initially set at £5.1 billion (in the 2021 Budget) and was subsequently increased. The BSF covers the cost of remediation of the external cladding system and related fire safety works.

Practical implications for London leaseholders: For leaseholders in buildings with identified unsafe cladding, the Building Safety Act 2022 provides legal protections — "qualifying leaseholders" (those who occupied their flat as their main residence at the time the Act came into force, or who are not property developers or significant landlords) are protected from being charged for the cost of remediating cladding defects under their leases. If your building has unsafe cladding and you are a qualifying leaseholder, you should seek specialist legal advice from a solicitor experienced in building safety and leasehold law to confirm your rights under the Act.

What Homeowners Should Check Before Installing External Cladding

For London homeowners planning to install external cladding (as part of an extension, a whole-house renovation, or an external insulation system), the following checks should be carried out before proceeding:

Planning permission: External cladding that materially alters the appearance of a house may require planning permission — particularly in conservation areas (where any change to the external appearance of the front elevation is likely to require planning permission, and materials must typically match the original Victorian brick, render, or stucco construction). Even where planning permission is not required for the cladding works themselves, the choice of materials may be restricted by any design guide or supplementary planning document applicable to the area.

Building Regulations: All cladding works to an existing house that involve adding insulation or changing the thermal properties of the external wall require a Building Regulations application (under Part L — conservation of fuel and power) and notification to Building Control. The Building Regulations application should be submitted before work starts. For cladding systems that include a ventilated cavity, the cavity barrier design must be submitted to and approved by Building Control. A completion certificate should be obtained after the works are inspected.

Party wall: Where the cladding is to be applied to an external wall that is a party wall or adjacent to a neighbouring property, the Party Wall etc. Act 1996 may apply — particularly where the thickness of the new cladding system reduces the gap between the house and any right of way or drainage easement.

Fire safety of the proposed system: Before specifying a cladding system, confirm with the manufacturer that the system (including the cladding board, the insulation, the adhesive or mechanical fixing, and the cavity barrier design) has been tested as a system for fire performance and meets the applicable Building Regulations requirements. Ask for the product's European reaction-to-fire classification (A1, A2, B, C, D, or E — with full subclassifications for smoke and flaming droplet production) and confirm with your architect or Building Control officer that the proposed system is appropriate for the building height and type.

Frequently Asked Questions

Can I put timber cladding on a London Victorian terrace extension?▼

Yes — timber cladding is generally permitted on the external walls of a single house below 11m in height in London. The combustible materials ban (Regulation 7(2) of the Building Regulations) that was introduced after Grenfell applies to certain higher-risk buildings (blocks of flats, hotels, hospitals, and certain other building types above 11m) but does not apply to single dwellinghouses below 11m. For a standard 2–3 storey London Victorian terrace rear extension (well below 11m), timber cladding (larch, cedar, thermally modified wood, or composite boards) is a commonly used, Building Regulations-compliant material choice. However, you will need to check: whether the design includes adequate cavity barriers within the ventilated cavity behind the cladding boards (required by ADB at every floor level and at the top and bottom of the wall to prevent fire spread via the cavity); whether the specific wall height or position triggers any additional fire spread requirements under ADB B4; and whether planning permission is required for the cladding (particularly in conservation areas where external material changes may require planning approval and where the LPA's design guidance may express a preference for traditional brick or render rather than timber cladding).

I own a flat in a London block. How do I find out if my building has an EWS1 form?▼

The EWS1 form is obtained by the building owner or freeholder (or their managing agent) — not by individual leaseholders. If you are buying or selling a flat in a multi-storey residential block and your mortgage lender requires an EWS1 form, the first step is to contact your building's freeholder or managing agent to ask whether an EWS1 assessment has been carried out and whether an EWS1 form is available. If an EWS1 form has not been obtained, the building's freeholder or managing agent is responsible for commissioning one (from a suitably qualified fire engineer or EWS1-qualified building surveyor). The RICS maintains a list of professionals qualified to sign EWS1 forms. If the freeholder is unresponsive or refuses to commission an EWS1 form, you can escalate to the First-tier Tribunal (Property Chamber) — which has jurisdiction over leasehold disputes — or seek legal advice from a solicitor specialising in building safety. The Leasehold Advisory Service (LEASE) provides free advice to leaseholders about their rights in EWS1 and building safety disputes.

Does the combustible materials ban affect insulation on London house extensions?▼

The combustible materials ban (Regulation 7(2)) affects insulation materials in the external walls of buildings within its scope — blocks of flats and other higher-risk buildings above 11m. For a single-dwellinghouse below 11m (which covers virtually all London Victorian terrace extensions), the combustible materials ban does not apply — PIR (polyisocyanurate) insulation boards (such as Kingspan Kooltherm or Celotex GA4000) and EPS (expanded polystyrene) insulation are permitted in the external wall of a house extension below 11m and are compliant with normal Building Regulations requirements. These materials are combustible (Class D or worse on the European reaction-to-fire classification) but their use in the external walls of low-rise houses is not prohibited by the current regulations. However, where an EWI (External Wall Insulation) system with combustible insulation is installed on a house and the system includes a ventilated cavity (for example, a rendered insulation system with a drained render finish), cavity barriers must be installed at every floor level and at the roof line to prevent fire spread via the cavity — this requirement applies regardless of the building height or the combustibility of the insulation. If you are in any doubt about the fire performance requirements for a specific cladding or insulation system on a house extension, discuss the specification with your architect and Building Control officer before ordering materials.

Important Note

This guide is for general information only. Building regulations, planning rules, and legal requirements change regularly and vary by local authority. Always seek professional advice specific to your project and location. RCB Design & Build offers free initial consultations — book your free survey.

Was this guide helpful? Share it:

WhatsApp Facebook Share on X

Have a question about your project?

Chat with us on WhatsApp — Faith usually replies within the hour.

Chat with us Book free review