External wall systems: draft advice note

We are seeking your views on this draft Scottish Advice Note (version 3.0), which provides guidance to assist in determining the fire risk posed by external wall systems in existing multi-storey residential buildings. This will inform the publication of the final Advice Note later in 2020.

Part 1: Introduction

1.1 Purpose

This Advice Note provides guidance for building owners / managers to assist in determining the fire risk posed by external wall systems. It will also be of interest to fire risk assessors and specialist wall appraisal experts.

For the purposes of this Advice Note, external wall systems are cladding systems (including cavity barriers and any insulation material exposed in the cavity behind the cladding), spandrel panels, window infill panels, balconies, solar shading and any other architectural feature or attachment to the external building structure.

The aim of the fire safety risk assessment and any supporting appraisal exercise should be to provide assurance that building occupants are not placed at undue risk of harm as a result of fire spread via the external wall system.

1.2 Scope

This advice note applies to existing multi-storey residential buildings of two or more storeys, including:

  • Blocks of domestic flats (including sheltered, extra-care and supported flats);
  • Student accommodation (including halls of residence);
  • Hospitals or other premises with overnight patient accommodation;
  • Care homes;
  • Hotels;
  • Hostels

This Advice Note is concerned with the life safety of occupants only. More stringent measures may be considered necessary for property protection or business continuity purposes but the management of such concerns are outwith the scope of this guidance.

1.3 Fire Safety legislation

Although not a legal requirement in Scotland, a fire safety risk assessment for domestic blocks of flats is recommended as best practice. Guidance on home fire safety including fire safety in high rise flats is available at https://www.gov.scot/policies/fire-and-rescue/home-fire-safety/.

Non-domestic residential premises are classed as “relevant premises” under Part 3 of the Fire (Scotland) Act 2005, as amended. A fire safety risk assessment is a legal requirement for all “relevant premises” and must “identify any risks to the safety of relevant persons in respect of harm caused by fire”.

Further information on the fire safety risk assessment process and how it applies more generally to a building can be found at https://www.gov.scot/policies/fire-and-rescue/non-domestic-fire-safety/.

1.4 The Building Standards system

The building standards system in Scotland is established by The Building (Scotland) Act 2003 (the Act). The thirty two local authorities in Scotland are appointed by Scottish Ministers as verifiers to administer the building standards system. Each local authority is responsible for their own geographic area. Guidance on the building standards system is published in a Procedural Handbook.

The building standards system is pre-emptive and is designed to check that proposals meet building regulations. The main principles of the system are:

  • that a building warrant must be obtained before work starts on site and
  • prior to a building being occupied, a completion certificate must be accepted by a verifier if, after undertaking reasonable inquiry, they are satisfied with the declaration by the ‘relevant person’ that the work meets the building regulations.

The purpose of the building standards system is to protect the public interest. It is not intended to provide protection to a client in a contract with a builder. The system is intended to ensure that building work on both new and existing buildings results in buildings that meet reasonable standards.

The standards are set out in the Building (Scotland) Regulations 2004, as amended. The building regulations apply to the design, construction or demolition of a building the provisions of services, fittings or equipment in or in connection with a building, and the conversion of a building. The regulations do not generally apply to existing buildings unless the owner intends to carry out a type of work that must meet building regulations. In general terms, work must be carried out in a technically proper and workmanlike manner, and the materials used must be durable and fit for their intended purpose.

A building warrant application will be granted by a local authority verifier where it is shown to meet building regulations at the time of application. The warrant is valid for a period of three years from the date is granted, and can be further extended by application made to the verifier before the warrant expires.

Once the building warrant has been granted it is the responsibility of the “relevant person” to ensure that the construction work meets the building regulations and is built in accordance with the building warrant. The ‘relevant person’ is the building owner or developer in most cases. In the case of changes made on site to the approved specification e.g. product substitution, an amendment to the building warrant should be submitted to the verifier covering the changes.

The relevant person can appoint an agent to act on their behalf if they are unsure of their responsibilities. It is recommended that this person is a suitably qualified and experienced building professional, for example an architect, building surveyor or structural engineer. Similarly, it is the responsibility of the relevant person to make sure that design or construction work is carried out by qualified and experienced building professionals, ideally registered with a reputable trade or professional body.

Once the work has been completed the ‘relevant person’ must submit a completion certificate to the local authority. The ‘relevant person’ signs the certificate which confirms that the work has been completed in accordance with both the building regulations and the granted building warrant.

A local authority must accept a completion certificate if, after reasonable inquiry, it is satisfied as to the matters certified in the certificate. Acceptance of a completion certificate cannot be, nor is it intended to be, a guarantee that all workmanship and materials are suitable. Such a guarantee would require a constant supervisory presence on site and this is a matter for the developer/owner to put in place.

Any person who submits a completion certificate containing a statement to a verifier that they know to be false or misleading, or recklessly submits a completion certificate which is false or misleading, is guilty of an offence under the Act.

The local authority has powers under the Act to serve a building warrant enforcement notice on work for which a building warrant is required which has or is being carried out:

  • without a building warrant; or
  • not in accordance with the granted building warrant.

1.5 Building Regulations

The Act is supported by the Building (Scotland) Regulations 2004, as amended. A schedule of mandatory building standards are provided in the building regulations and are expressed in terms of ‘functional standards’. These standards are simply-stated fire safety objectives that the completed building must fulfil or allow.

The principal supporting guidance documents are the Technical Handbooks for domestic and non-domestic buildings. Following the guidance in the Handbooks is the usual route to compliance and may be relied on in any legal dispute as ‘tending to negate liability’ for an alleged contravention of building regulations. Alternative means of compliance is possible and the verifier has the power to decide whether or not alternative solutions fulfil the mandatory functional standards.

1.6 Benchmarks and their relationship with Building Regulations

Fire risk assessors often use guidance from a variety of sources as a means to inform their professional judgement and assessment of the risks. Current guidance within the Technical Handbooks that support the Building Regulations is often used as a benchmark to assist with the fire safety risk assessment process for existing buildings.

Benchmarks are not prescriptive or minimum standards or even recommendations. They should be used only as comparators to assess just how far removed existing provision is from current standards. The assessor must consider whether deviations from the benchmarks result in unacceptable risk and, if so, what measures may be required to reduce that risk to an acceptable level.

1.7 Fire Safety Risk Assessment and External Wall System Appraisals

A fire safety risk assessment must give due consideration to the potential for fire spread on external walls. All available evidence should be taken into account when determining the fire risk posed by external wall systems (EWS).

A key principle of fire safety risk assessment is to take steps which are “reasonably practicable” to reduce the risk to life from fire to an acceptable level. This principle applies regardless of whether or not the EWS meets current or previous requirements under building regulations.

It is recognised that on some occasions, intrusive inspection involving testing and performance assessment of EWS may be recommended (referred to throughout this Note as external wall “appraisals”). This is a highly specialised field. Such an appraisal may be required to inform the fire safety risk assessment but this will depend on the particular circumstances. The following approach is suggested:

1. An appropriately competent fire risk assessor may be able to conclude from a review of available documentation that the EWS is unlikely to pose a significant risk to life e.g. by considering a previously undertaken external wall appraisal report or other reliable supporting documentation (such as building warrant information, photographic evidence, Operation & Maintenance manual information etc). In such cases, a full external wall appraisal may not be necessary.

2. Where a competent fire risk assessor, familiar with the building type in question, is unable to reach such a conclusion or feels unable to offer appropriate remedial advice, the building owner or manager may need to seek advice of a suitably competent specialist (see Section 1.8). If there is reason to suspect that cladding might constitute a fire hazard, a detailed appraisal involving intrusive inspection and testing of samples may be recommended. Circumstances where this may be considered appropriate include:

  • The type of cladding (or insulation exposed in the cavity behind the cladding) is unknown;
  • A lack of, or gaps in, supporting records and documentation;
  • Where there is evidence to suggest that product substitution has occurred;
  • Where there is evidence of systemic problems with a particular product/manufacturer/installer.
  • Where doubts exist as to whether the constructed system adequately reflects the system as originally designed and tested;
  • Where test evidence suggests that a system has failed to meet the performance criteria in BR 135 ‘Fire performance of external thermal insulation for walls of multistorey buildings’ when subjected to a BS 8414 test;
  • Where the test report shows an overprovision/unusual positioning of cavity barriers as tested under BS 8414 ‘Fire performance of external cladding systems’;
  • Where there are doubts over the appropriateness of accepting a BR135 system for the type of premises in question;
  • Where there are doubts regarding the independence of the testing facility e.g. not United Kingdom Accreditation Service (UKAS) Accredited fire test house.

It is important that the conclusions of any detailed external wall appraisal informs the fire safety risk assessment to ensure that all hazards, risks and fire safety measures are considered holistically, and not in isolation. In addition, determining the fire performance of external wall systems will not, in itself, be sufficient to determine the fire risk posed by such systems. Therefore, either the appraisal specialist should also be a competent fire risk assessor or the findings from the appraisal should be reviewed by a competent fire risk assessor who can interpret the results and use them to inform the fire safety risk assessment. Factors which need to be considered to fully determine the life safety risk posed by external wall systems include:

  • The type of evacuation strategy in use i.e. simultaneous, delayed or ‘stay put’ and the anticipated evacuation time should evacuation become necessary;
  • The vulnerability of residents;
  • The premises’ emergency plan, including an assessment of staffing levels, where required for the type of evacuation method employed;
  • The construction of the external walls, including any cladding and its method of fixing and the presence, and appropriate specification of, cavity barriers;
  • The apparent quality of construction, or presence of building defects;
  • The combustibility of other aspects of the building structure;
  • The potential for exposure of an external wall system to an external fire;
  • The height and complexity of the building;
  • Fire protection measures within the building (e.g. fire separation/ compartmentation, automatic fire suppression, automatic fire detection);
  • The location of escape routes; and
  • The suitability of facilities for firefighting, including site access and water supplies.

Where EWS is thought to pose a significant risk to life, the Scottish Fire and Rescue Service (SFRS) should be informed and interim measures put in place until such times as the situation is properly remediated (see Part 3).

1.8 Competence

The consideration of external wall systems on existing buildings should be undertaken by a suitably competent professional.

Some competent fire risk assessors may be able to review relevant documentation and evidence where available, and satisfy themselves that the relevant mandatory building standards and supporting guidance in the technical handbooks have been met e.g. the external wall system meets European Classification A1 or A2 or by classification under BR 135 on the basis of the large scale fire test specified in the relevant part of BS 8414.

The Scottish Government and SFRS recommend selecting a fire risk assessor or company that is registered with a Professional Registration Scheme or is third party certificated by a United Kingdom Accreditation Service (UKAS) accredited Certification Body. More information can be found on the SFRS website and in existing fire safety guidance.

If more detailed appraisal is required (see section 1.7), it will likely be beyond the capabilities of most fire risk assessors. A suitably competent specialist with appropriate knowledge, skills and experience in construction and fire safety who understands the BR135 performance criteria and the parameters of the BS 8414 fire tests could be a chartered or incorporated fire engineer registered with the UK Engineering Council or a chartered building surveyor. These specialists can advise on the construction of the external wall system and whether remedial action may be necessary.

To find a chartered or incorporated fire engineer visit https://www.ife.org.uk/Find-a-UK-Fire-Engineer.

To find a chartered building surveyor visit the Royal Institution of Chartered Surveyors (RICS) website here.

Although not a requirement of fire safety legislation, the Royal Institution of Chartered Surveyors (RICS), the Building Societies Association, and UK Finance have developed a cross-industry approach to enable assessments of external wall systems in high rise blocks of flats to be undertaken for mortgage lending valuation purposes (EWS1 assessment form). Further information on this approach is available on the RICS website at https://www.rics.org/uk/news-insight/latest-news/fire-safety/cladding-qa/.

1.9 External wall systems documentation / evidence

It is important to understand how the design, construction, installation and maintenance of external wall systems may affect their performance in the event of fire. Building owners/managers can obtain relevant information from “as-built” drawings or the operation and maintenance manual for the building. Advice and information should also be available from the product manufacturers and/or contractors/developers about the fire performance, installation and maintenance of external wall systems

Information on the building design may also be obtained from building warrant drawings if they are available from the local authority. A local authority maintains a building standards register that contains information in two parts, part 1 containing data and part 2 containing documents. Part 1 of the register is open for public inspection at all reasonable times, and is available electronically. Part 2 contains copies of warrants and completion certificates and the principle drawings and specifications and are available for inspection during normal office hours.

The documents in Part 2 should be kept for at least 25 years but details of complex buildings or unusual structures should be kept, ideally until the building is demolished but at least for 50 years. The description ‘complex’ is intended to cover both occupancy and construction method. The local authority archivist and the building standards manager should agree which records are to be disposed of after 25 years, 50 years or at a later date as agreed. The procedure regulations also require registers kept under previous legislation to be retained, although they will contain less detailed information. Duty holders (owners, managing agents, etc.) have fire safety responsibilities under Part 3 of the Fire (Scotland) Act 2005 and associated Regulations and may also hold records of external wall systems.

1.10 Common types of external wall cladding

Metal composite material (MCM) panels typically include aluminium, zinc and copper. These are often used as “rainscreen” panels which prevent significant amounts of water from penetrating into the wall construction. Thermal insulation, airtightness and structural stability are provided by the second, inner part of the wall construction.

Aluminium Composite Material (ACM) cladding is a type of MCM, consisting typically of two skins of aluminium 0.5 mm thick bonded together using a core/filler material 3 – 4 mm thick. Three cores/fillers are available, each with different fire performance:

Category Common core/filler composition Calorific Value
MJ/Kg [1]
1 (limited combustibility) Largely of mineral composition affording a high standard of fire performance (sometimes described as A2) ≤ 3
2 (fire resistant - FR) A mixture of polyethylene and other, inorganic additives to enhance fire performance >3 and ≤ 35
3 Unmodified polyethylene (PE); > 35

[1] Screen test based on BS EN ISO 1716 ‘Reaction to fire tests for products. Determination of the gross heat of combustion (calorific value)’.

MCM panels are popular because of their precise flatness, variety of surface finishes and colours, lightweight and formability. However, fire performance varies greatly according to the composition of the core/filler and the panels can melt, warp, disband or delaminate in a fire.

Where MCM cladding with an unknown core/filler material is identified, high rise domestic building owners are encouraged to make use of the government’s free screening programme to confirm the category of the core/filler material.

High Pressure Laminate (HPL) panels are usually made by taking sheets of wood or paper fibre, layering them with a resin and bonding them under heat and pressure. The fire classification can vary significantly depending on its material properties, thickness and whether or not it incorporates fire retardant additives. HPL panels with fire retardant chemicals added are sometimes referred to as “FR grade” and may achieve Class B-s1,d0 in accordance with BS EN 13501-1 ‘Fire classification of construction products and building elements. Classification using data from reaction to fire tests’. Panels manufactured without fire retardant can be Class C, D or even lower depending on the thickness and make-up of the panel (e.g. fibre and resin used).

On 2 April 2020, the UK Government published the test and analysis report ‘Fire performance of cladding materials research’. The aim was to identify if there were other types of cladding that burn like the type of metal composite material which was present on the Grenfell Tower i.e. aluminium composite material (ACM) with an unmodified polyethylene core, ACM (PE), or ‘ACM category 3’.

The tests were undertaken by the Building Research Establishment (BRE), on advice from the UK Government Independent Expert Advisory Panel. The research showed that none of the materials tested (including HPL), performed in the same or even similarly to the type of cladding believed to be on Grenfell tower, ACM (PE).

1.11 BS 8414 Fire Tests and BR 135

Following the outbreak of a fire inside the building, if no intervention occurs, the fire may develop to flashover and break out from the room of origin through a window opening or doorway. Flames breaking out of a building from a post-flashover fire will typically extend 2 m above the top of the opening. The BS 8414 large scale façade tests are based on this principle i.e. a post flashover compartment fire emanating from a window or door opening. The test has been designed to allow the external fire performance of both applied and supported non-loadbearing external wall cladding systems to be determined.

The BS 8414 fire test is read in conjunction with BR 135 which assesses the performance of the cladding system from the outbreak of fire inside or outside the building and spreading onto the cladding. The test facility allows cladding systems to be installed as close to typical end-use conditions as possible including the provision of fire barriers behind the cladding. The test faces consist of a vertical main test face, into which the combustion chamber is located, and a vertical return wall or wing, set at 90° to the main test face. The test specimen should be installed with all the relevant components, and should be assembled in accordance with the manufacturer’s instructions. The main test face is at least 8 m high and 2.6 m wide, with the return wing being 8 m high and 1.5 m wide. BS 8414-1 is constructed from masonry and BS 8414-2 constructed using steel frame.

The test standard provides thermal performance criteria to permit the use of alternative heat sources. A wooden crib is typically used as the heat source for this test, although a gas burner can be used as an alternative. The combustion characteristics of the crib give a total nominal heat output of 4500 MJ over a 30 min period at a peak heat release rate of 3 ± 0.5 MW. The test is terminated early if sustained flaming extends above the height of the test rig. The cladding system fails the performance criteria in BR 135 where the any of the thermocouples at level 2 (5 m above the combustion chamber) exceeds 600 ºC for a period of at least 30 seconds, within 15 min of the start time of the test. The fire test and reporting of the test results require a competent professional to assess the extent to which the system tested is applicable to the real building.

The UK government initially commissioned six tests, testing three types of Aluminium Composite Material (ACM) cladding with two commonly used types of insulation, polyisocyanurate (PIR) foam and stone wool; and published the accompanying explanatory note on 20 July 2017. A seventh test was subsequently commissioned, to test ACM (FR) with phenolic foam insulation.

Results of the seven tests, and accompanying advice for building owners, are available on the Building Safety Programme webpage and are summarised in the table below.

Aluminimum Composite Material (ACM) with… Insulation
PIR Foam Phenolic Foam Stone Wool
Unmodified polyethylene filler
(Category 3 in screening tests)
Test 1 failed
N/A Test 2 failed
Fire retardant polyethylene filler
(Category 2 in screening tests)
Test 3 failed
Test 7 failed
Test 4 passed
Limited combustibility filler
(Category 1 in screening tests)
Test 5 passed
N/A Test 6 passed

It is important to note that there are many different combinations of cladding and insulation and it is likely that products from different manufacturers will behave differently in a fire. The composition of ACM panels with fire retardant polyethylene core/filler varies between manufacturers. The average of the calorific values of the fire retardant panels (Category 2) used in the test were 13.6 MJ/kg. Building owners with this combination of materials should consult their screening tests to establish the calorific value.

Fire safety risk assessment does not routinely involve opening up construction. However, an external wall system appraisal will normally involve a degree of intrusive inspection on a sample basis to identify the type and thickness of materials used or where serious issues in structural fire protection are suspected, such as inadequate provision of cavity barriers or fire stopping. The longer rainscreen cladding remains in place the more effective the cavity barriers will perform to inhibit fire growth. Intrusive inspection is usually a one-off exercise which requires a contractor to open up construction and make good after the inspection. Materials may have been fitted or maintained differently to how the tests were specified and constructed, which can affect the fire performance of the cladding system. Where doubts exist, building owners/managers must seek advice from competent specialists that can examine the specific circumstances of their building.

Tests 4, 5 and 6 wall systems passed, which means they resisted the spread of fire over the wall to the standard set out in BR 135. These results show ways in which compliance could be achieved and offer an indication of how remedial works could be specified for those buildings that have been found to have problems.

HPL (FR) panels (Class B-s1,d0) with stone wool insulation, in the specific configuration tested, also successfully achieved the performance criteria set out in BR135, and these test results are available on the government website.

Some external wall systems may incorporate insulation products, combustible core/filler material, etc. which do not meet Class A2-s3,d2 or better (previously referred to as ‘limited combustibility’) and has achieved the BR 135 performance criteria following a BS 8414 test. External wall systems rely upon correct design detailing and construction of cavity barriers, fire stopping and in some cases external renders to inhibit fire spread. Building owners should seek professional advice on whether the external wall has been installed correctly, as per the BS 8414 test, and that the BS 8414 result is fully applicable to the building in question. It should be subject to maintenance in line with manufacturer/supplier recommendations.

The BRE maintain a list of external wall cladding systems which achieve the BR 135 criteria when tested to BS 8414, but the list is not comprehensive http://www.bre.co.uk/regulatory-testing. Cladding systems not on the list, but tested to BS 8414, may or may not satisfy BR 135 performance criteria. Reports from other UKAS accredited test laboratories may be considered, where available, relevant and appropriate. It is important to understand that the test results are highly sensitive to minor variations in design, construction and parameters used in the test. These minor variations can lead to different fire performance outcomes from materials which are of a broadly similar product description e.g. ACM Category 2. It is essential that cladding system installed accurately reflect the system as tested, for the data to be meaningful. It is also essential that a suitably competent professional confirm that the BS 8414 result is applicable to the particular circumstances, geometry, and make-up of building in question.

1.12 Fire statistics

Fire related deaths and injuries in Scotland have declined significantly in the last 20 years. In 2001 there were more than 8000 accidental dwelling fires per year in Scotland resulting in 88 fatalities and more than 2000 injuries. Since then, there has been a downward trend on accidental dwelling fires to approximately 5000 resulting in 40 fatalities and 900 injuries. Less than 1% of accidental dwelling fires in multi-storey residential buildings spread beyond the floor of fire origin. Most fires are contained to the item first ignited and to the room of origin.

There have been no fire related deaths beyond the dwelling of fire origin since statistics were transferred in 2009 to the Scottish Fire and Rescue Service from the Home Office.


Email: buildingstandards@gov.scot

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