External Wall Cladding Fire Safety: What London Homeowners and Landlords Need to Know

**What changed after Grenfell**:

The Grenfell Tower fire in June 2017 (72 lives lost) was caused by the rapid external spread of fire through ACM (aluminium composite material) rainscreen cladding panels with a polyethylene core — classified as highly combustible. The fire was fuelled by the combustible insulation behind the cladding and the cavity between the cladding and the building structure.

The legislative and regulatory response has been significant:

• **Building Safety Act 2022**:
• •Created the Building Safety Regulator (BSR) — a new regulatory body within the Health and Safety Executive with oversight of buildings in scope (initially higher-risk residential buildings of 18m+ or 7+ storeys)
• •Established new dutyholder roles (Principal Designer and Principal Contractor for higher-risk buildings) and a stronger regime of Gateway Approvals (planning, building regulations design stage, building regulations completion stage) for higher-risk buildings
• •Extended the limitation period for latent defect claims under the Defective Premises Act 1972 (retrospective to June 1992 for new claims) — meaning residents can now claim against negligent building developers and their advisers for defective cladding systems installed decades ago
• •Created the Responsible Person framework for occupied buildings — the building owner/freeholder must identify a Responsible Person who manages ongoing fire safety

**Building Regulations Approved Document B (Fire Safety) — revisions from 2018–2021**:

The key changes to Approved Document B relevant to cladding:

• *For buildings over 18m (from 21 June 2018):*
• •External wall systems on residential buildings over 18m must be of limited combustibility throughout — the entire wall system (cladding panels, insulation, fixings, membranes) must achieve Class A1 or A2-s1, d0 or better under the European classification system
• •This effectively prohibits the use of combustible materials (including timber, many common insulation types without specific fire treatment, and standard HPL panels) in the external wall of any residential building over 18m

• *For buildings 11–18m (from 1 December 2018 to present):*
• •ACM cladding with a polyethylene core is prohibited on residential buildings 11–18m
• •The requirement for A1/A2 limited combustibility materials throughout the wall system does NOT apply to the same extent as for 18m+ buildings
• •However, the entire external wall system must still achieve BS 8414 large-scale fire test performance or meet the requirements of BR 135 (the guidance document for checking compliance with Part B for tall buildings)

• *For residential buildings under 11m and domestic extensions:*
• •The BS 8414 test and limited combustibility requirements for the whole wall system do NOT apply
• •Standard Part B requirements apply — the external surface of the wall must achieve Class B-s3, d2 or better (corresponding to the UK national class 'Class 3' or better under legacy fire classifications)
• •Timber cladding, HPL cladding, and fibre cement cladding are all acceptable on residential buildings (including extensions) under 11m provided the external surface achieves at least Class B-s3, d2 fire performance

**What this means in practice for London extensions and residential renovations**:

For the vast majority of London residential extension and renovation projects — houses, flats in two-to-three-storey Victorian terraces, four-storey blocks — the building height is well under 11m. The enhanced cladding fire safety regulations for tall buildings do NOT apply.

• For these properties, the relevant Part B requirements for external wall cladding are:
• •The external cladding surface must achieve at least Class B-s3, d2 fire performance
• •The cavity within the external wall must be closed at all floor levels with cavity barriers (to prevent fire spreading through the cavity — this applies regardless of building height)
• •Fire stopping must be maintained at the junction between the external wall and any compartment wall, compartment floor, or party wall

• Common cladding materials for domestic extensions and their fire performance:
• •*Timber cladding (larch, cedar, Douglas fir, Accoya)*: Typically Class C-s2, d0 or Class D-s2, d0 untreated; can achieve Class B-s3, d2 with fire-retardant treatment (surface or impregnation treatment); check the manufacturer's fire classification certificate for the specific product
• •*Fibre cement cladding (James Hardie, Cedral, Equitone)*: Typically Class A1 or A2 — no fire performance issues
• •*HPL (high pressure laminate) cladding*: Typically Class B or C depending on the product; check manufacturer's certificate
• •*Brick slips on extension external walls*: Class A1 — no fire performance issues

**What is an EWS1 form?**

EWS1 (External Wall System 1) is a standard form developed by RICS (Royal Institution of Chartered Surveyors) in conjunction with lenders to provide a consistent method for assessing the fire safety of the external wall of a residential building for mortgage lending purposes.

An EWS1 form is completed by a qualified fire safety professional (a chartered fire engineer or a fire risk assessor with relevant qualifications) who physically inspects the external wall system of the building, reviews available documentation (as-built drawings, material specifications, fire test certificates), and reaches one of two outcomes:

• •**EWS1 Form — Outcome A** (the external wall system has no ACM cladding with unmodified polyethylene filler, no other metallic composite panel with combustible filler, no MCM with combustible filler, and no HPL panels): subdivided into A1 (no combustible materials in the external wall system — no further action needed) and A2 (combustible materials present but the risk has been assessed and remediation is not necessary).

• •**EWS1 Form — Outcome B** (combustible materials are present in the external wall system and remediation may be required): subdivided into B1 (works may be required — specific fire safety measures are outstanding) and B2 (essential remediation works are required).

*An EWS1 A1 or A2 form*: the lender is satisfied that the external wall is of acceptable fire safety for mortgage lending purposes. *An EWS1 B1 or B2 form*: the lender may refuse to lend, or may lend subject to conditions, until the identified works are completed.

**When is an EWS1 form required?**

EWS1 forms were originally required by most mortgage lenders for all residential buildings with a storey at 18m or above with cladding. Following RICS guidance updates in 2021 and 2022, the position is:

• •Mandatory for mortgage lending: buildings of 11m+ with cladding that is NOT brick, stone, or concrete (i.e., buildings with ACM, HPL, timber, or other non-masonry external wall systems)
• •Not typically required: buildings entirely of brick, stone, or concrete external wall construction at any height; buildings under 11m regardless of cladding type; buildings where the only external wall material above ground is brick, stone, glass, or concrete (even if there is a small amount of cladding around windows or ground-floor areas)

• In practice in London:
• •A Victorian terraced house (brick external walls): **EWS1 not required**
• •A 1960s/70s concrete-frame residential block with original concrete external walls: **EWS1 not required**
• •A converted Victorian warehouse with timber-frame external walls and cladding: **EWS1 may be required if 11m+**
• •A modern residential apartment building 11m+ with composite cladding panels: **EWS1 required**
• •A 3-storey flat converted from a Victorian house with masonry external walls and a new extension with timber cladding: **EWS1 depends on the proportion and type of cladding — seek specialist advice**

**The practical impact on flat sales, purchases, and remortgages**:

If an EWS1 form is required and cannot be obtained (because no qualified assessor can be found, because the assessment is pending, or because the building owner has not commissioned one), the mortgage lender will decline to lend. This freezes the flat's salability and remortgageability until the EWS1 issue is resolved.

• For flat owners in buildings that require an EWS1:
• •Check whether the building's freeholder, management company, or building's Responsible Person has commissioned an EWS1 assessment
• •If not, the flat owners' management company or residents' association should push the freeholder to commission the assessment (the building owner/freeholder/Responsible Person has obligations under the Building Safety Act 2022)
• •If the EWS1 assessment finds that remediation is required (Outcome B2), the costs of remediation fall on the building owner for qualifying leaseholders under the Building Safety Act's Leaseholder Protections (freeholders and developers cannot pass remediation costs to qualifying leaseholders in buildings over 11m for cladding defects in buildings completed before 5 April 2022)

**Cladding for domestic extensions — practical guidance**:

For the vast majority of London extension projects (rear extensions, side returns, loft dormer cladding, ground floor extensions), the building is a two-to-three-storey terraced or semi-detached house well under 11m in height. The high-rise cladding regulations do not apply.

The relevant questions for choosing cladding for a domestic extension are:

**1. Fire performance — Part B Class B-s3, d2 minimum**:

For extensions to houses and small residential buildings (under 11m), the external surface of the cladding must achieve at least Class B-s3, d2 (where the European classification system applies). Most common cladding materials used in London for domestic extensions comply:

• •Brick or stone (masonry): Class A1 — no fire performance issues; appropriate for extensions matching the host building
• •Fibre cement or cement board (Cedral, Hardie, Eternit): Class A1 or A2 — no fire performance issues; popular for contemporary extension cladding
• •Timber cladding: Class C-D untreated; achieves Class B with fire-retardant treatment — timber cladding for domestic extensions is acceptable and widely used in London with fire-treated timber
• •Powder-coated aluminium panels: typically Class A1 — no fire performance issues
• •Glass fibre reinforced concrete (GFRC): Class A1 — no fire performance issues

**2. Cavity barriers**:

Regardless of the building height, Part B requires that cavities in external wall construction are fitted with cavity barriers at: all floor levels; all junctions between external walls and compartment walls or floors; around all openings (windows, doors) where the opening is adjacent to a cavity; at maximum 20m spacings vertically and 20m spacings horizontally.

For a domestic extension with a timber-frame external wall and cladding on battens (a rainscreen configuration), cavity barriers must be installed in the cavity behind the cladding at the floor level, at the eaves/roof junction, and around all windows and doors. This is a first-fix construction detail that the Building Control officer will want to see on the drawings before issuing a Building Regulations approval.

**3. Planning and conservation considerations**:

• Beyond fire safety, cladding choices for London extensions are also governed by:
• •*Planning policy*: Many London boroughs have design guidance strongly preferring natural materials (brick, stone, timber) for extensions to Victorian and Edwardian properties; contemporary extensions in innovative materials (zinc, Corten steel, polished concrete) are generally acceptable for contemporary new-build extensions but may require planning permission in Conservation Areas
• •*Conservation Area Article 4 Directions*: Some London Conservation Areas restrict the materials that can be used for extensions (requiring brick to match the host building); check with the borough's planning department
• •*Listed Building Consent*: Any external alteration to a listed building requires Listed Building Consent — the choice of cladding material will be scrutinised by the heritage officer

**Common cladding specifications for London extensions**:

| Cladding material | Fire class | Planning reception | Typical cost supply only | |---|---|---|---| | Brick (stock, London yellow stock) | A1 | Excellent | £40–£80/m² | | Fibre cement (Cedral, Hardie) | A1–A2 | Good | £30–£60/m² | | Timber (cedar, larch, Accoya, treated softwood) | B (treated) | Good–excellent for contemporary | £40–£100/m² | | Zinc standing seam | A1 | Good for contemporary | £80–£150/m² | | Powder-coated aluminium | A1 | Good for contemporary | £60–£120/m² |