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.

This document is part of 2 collections

Part 2: External Wall Systems

2.1 Introduction

An assessment of the fire risk posed by external wall systems should form part of any fire risk assessment. The cladding assessment is only one aspect to be considered as part of the overall assessment of risk. Where external wall systems are deemed to pose a risk to life on any building, reasonable steps must be taken to reduce the risk to an acceptable level. See Part 3 for Interim Measures.

For the purposes of sections 2.2 and 2.3 below, MCM panels means Category 3 MCM with an unmodified polyethylene (PE) core/filler constructed from aluminium, zinc or copper. The guidance in those sections apply regardless of building height.

2.2 MCM Category 3 cladding: extensively clad buildings (regardless of height)

In light of the Grenfell Tower tragedy and considering the evidence from subsequent Ministry for Housing Communities and Local Government fire tests, it is strongly recommended that any extensively clad external wall system incorporating Category 3 MCM should be removed from all residential buildings without delay.

2.3 MCM Category 3 cladding: partially clad buildings (regardless of height)

The risk posed by Category 3 MCM partial cladding on buildings should be assessed. Where a simultaneous evacuation plan has been put in place instead of the usual ‘stay put’ strategy which is common in blocks of flats, a change to simultaneous evacuation should only be temporary until the risk which caused the change of policy has been removed.

The following scenarios are examples that should be considered as part of the fire risk assessment:

a. The MCM cladding crosses any vertical or horizontal fire separation/compartmentation lines or cavity barriers:

  • Where MCM cladding is present on the exterior wall of the building, fire separation may be breached if the cladding crosses these lines, enabling a fire to spread.
  • MCM crossing a cavity barrier could enable a fire to spread.

Note that a vertically aligned partial band of MCM creates a greater risk of rapid fire spread vertically up the building than a partial horizontal band.

b. The MCM is located around entrances, exits (including fire exits), means of escape and other apertures in the building envelope which would pose a risk from falling debris:

  • In the event of a fire, occupants need to be able to exit the building safely, and fire fighters may need to enter the building. If there is MCM cladding around entrances, exits and fire escapes this could limits the scope to successfully evacuate the building and fight the fire.
  • Other apertures in the building envelope which may pose risk include areas around windows, balconies and other features such as solar shading and shutters as well as service penetrations such as vents, cowls, ducts etc.

c. The MCM is located at or near to ground level and could therefore be vulnerable to accidental or deliberate exposure to fire:

  • it should be removed or protected against ignition if it could be vulnerable to either accidental or deliberate ignition which could compromise safe access to and exit from the building.

d. The location of the MCM could enable a fire to spread to a neighbouring building:

  • it may require to be removed if it could enable fire to spread to a neighbouring building e.g. presenting a radiative hazard.

A competent professional (see section 1.8) will be able to identify if these circumstances exist in individual buildings on a case by case basis.

2.3.1 Other factors to consider for buildings partially clad with MCM

In addition to those listed above there are other factors that competent professional advisors should consider when advising whether it is safe to leave MCM cladding systems in place. Although this list is not exhaustive, competent professional advisers should consider all of the following factors and engage competent specialists where required:

a. The distance between MCM panels:

  • If the MCM does not itself cross any lines of separation or compartmentation could the fire spread to the nearest next panel and beyond in any circumstances? A competent specialist should be able to calculate the likely radiant heat flux, size of any flame, as well as how it might behave in differing weather conditions, and whether it could ignite another panel even if they are not directly located adjacent to each other.

b. The position of the MCM:

  • The position of the MCM on the building will determine the potential for it to be involved in a fire. Fire can arise internally and break out of the building envelope via unprotected openings (e.g. windows).
  • External fires can arise from combustible material located around the base of the building, e.g. vehicles, waste storage areas.
  • MCM should be removed if there is any possibility it could enable a fire to spread and compromise life safety measures such as vents at the top of staircases on roofs for example.

c. Whether a fire could spread down the building:

  • There is potential for debris from panels to fall downwards and cause fire to spread to other combustible items on buildings, including other cladding panels and any items on balconies.

d. Evidence that the cladding system has been installed correctly:

  • This may require intrusive inspections where there is doubt about the presence of components such as cavity barriers.

e. Indicators of diligent management and maintenance of the buildings, for example:

  • The general state or repair of the building structure as well as fixtures and fittings.
  • Evidence that the building, including the cladding system, is being properly maintained.

f. Whether or not the building has an up-to-date fire risk assessment and external wall systems appraisal:

  • building owners may be required to undertake an intrusive external wall system appraisal if they intend to leave MCM panels in situ (see 1.5).

g. Any considerations relating to how the fire and rescue service will tackle the fire, for example:

  • The operational plan to tackle a fire – i.e. would fighting the fire put the fire-fighters at risk? Even if residents could be evacuated would the risk to firefighters increase?
  • The presence and operability of fire safety installations in the building, including sprinklers and smoke alarms etc. These should be considered alongside the evacuation strategy and location of MCM externally – internal measures would not by themselves prevent an envelope fire having consequences on the occupants of a building.
  • The presence and operability of fire-fighting equipment in the building, including dry or wet risers, hoses and smoke ventilation systems etc.
  • The number and safety of evacuation routes, including staircases.
  • The difficulty of putting out a fire with MCM cladding shielding water jets from reaching the flames effectively.

h. Where there are residents who require extra assistance to evacuate:

  • There is a greater risk to life in high rise buildings which are, or could be in the future, occupied by people who require extra assistance to evacuate.

2.4 Buildings of 11 m or over

On the 1 October 2019 building regulation guidance requires that external walls in taller domestic and non-domestic buildings do not contribute to the development of fire or to vertical fire spread up the facade of the building. The 11 m storey height threshold is based on the reach capability of a fire and rescue service ground mounted water jet where there is sufficient pressure and flow in the water main. In addition, external rescue by the fire and rescue service above this height would depend on the availability of specialist height appliances and adequate site access. Cavity barriers are intended to prevent unrestricted fire spread behind the external wall cladding. Panel deformation could allow fire to by-pass cavity / fire barriers but this is assessed in the BS 8414 test against the performance criteria in BR135.

The 11 m threshold recognised in the Technical Handbooks applies since 1 October 2019 to new building work. Failure to comply with current building regulations does not make the building unsafe, so there needs to be flexibility when using these benchmarks for existing buildings. Each risk assessment / appraisal must be building specific. It is therefore possible that some buildings less than 11 m may require remediation to reduce risk; equally, it is possible for lower risk buildings above 11 m to fall short of the benchmark, without it posing an unacceptable risk to life. At all times, the key question must be whether the presence of the external wall system poses a risk to life.

Where there are doubts, or minor departures from the benchmarks, a range of other factors should be considered (see section 1.7) e.g. height and use of the building; information on approval by a building control verifier; height, position and extent of cladding on the building; access for fire service vehicles and equipment; likelihood of spread from existing buildings; potential for fire-raising / bin store fires, car parking locations; internal fire protection measures including compartmentation, fire detection and warning systems, fire suppression systems, etc.

From 1 October 2019, Technical Handbook guidance for new work requires external wall cladding systems on buildings of 11 m or over to be constructed of products achieving European Classification A1 or A2 (limited combustibility). Alternatively, the guidance provided in BS 8414 and BR135 may be used, where endorsed by a suitably competent professional. BS 9414 ‘Fire performance of external cladding systems’ provides additional information on the application of results from BS 8414 tests. This guidance also applies to hospitals and care homes regardless of height. This should be used as a benchmark for the risk assessment process / external wall system appraisal.

Some products in existing residential buildings are likely to have achieved Class B-s3,d2 or Class 0. These classifications are not, on their own, evidence that a system is safe. The combustibility of the material beyond the direct surface of the product may contribute to fire spread over the external walls of buildings and therefore should be included in the assessment as a whole (such as the core/filler materials of metal composite panels or sandwich panels). It may be appropriate, subject to advice from a competent specialist and supported by test evidence, to retain cladding panels achieving class B-s3,d2 if any core/filler material within the products and any insulation material achieves Class A2-s3,d2 or better.

2.4.1 Metal Composite Material (MCM) Cladding (see 2.1/2.2 for MCM Category 3)

If it is suspected that other categories of MCM e.g. Category 2, pose a significant risk to life safety - e.g. if it is not A1/A2 or a system has failed a BS 8414 test and BR 135 assessment, or is yet to be tested - the advice of a suitably competent specialist will be required to determine what actions, if any, are necessary to reduce the risk to life to an acceptable level. The fire safety risk assessment should also be reviewed.

2.4.2 High Pressure Laminate (HPL)

Class B HPL with stone wool insulation met the BR 135 performance criteria when tested to BS 8414 and may be considered to be safe, subject to confirmation by a suitably competent specialist. Where Class C/D HPL or any HPL used in combination with combustible insulation is found on existing buildings, BS 8414 test evidence should be requested to support its use, which should also be fully justified in the fire safety risk assessment. Where this is not the case or doubts exist over safety, advice should be sought from a suitably competent specialist and the fire safety risk assessment reviewed. Remedial action may be required. The advice on building partially clad with MCM Category 3 in clause 2.3 can also be used for buildings partially clad with HPL. The research in clause 1.10 can also be used to inform the cladding assessment by a competent professional or specialist.

2.5 Buildings under 11 m

For buildings under 11 m, the fire safety risk assessment must also take into account the factors in section 1.5. Notwithstanding the earlier guidance on MCM Category 3 systems, it is recognised that there may not always be the same degree of risk to life in a building which has a storey height less than 11 m, compared to taller buildings.

As noted above, the 11 m storey height used by the Technical Handbooks is based on the reach capability of a fire and rescue service ground mounted water jet where there is sufficient pressure and flow in the water main. As a result, Class B, C, D or E is generally allowed for external wall systems if the building is more than 1 m from the boundary of an adjacent building and has a maximum storey height <11 m. In many cases, this will not pose an unacceptable risk to life and is likely to be acceptable. That said, it should be remembered that fire service vehicular access and mains water pressure may be inadequate in existing buildings and potential detrimental changes in the future could further impact on risk. To guard against this, it should be a guiding principle of the fire safety risk assessment process to ensure that occupants can escape safely without an over-reliance on fire service intervention.

Some buildings are considered higher risk, regardless of height due to the vulnerability of occupants and other factors. Consequently, all new hospitals, care homes, places of entertainment and assembly buildings must generally comply with the benchmark for buildings over 11 m, regardless of height i.e. achieve Class A1/2 or BS 8414/BR 135 compliant. In existing buildings under 11 m, remediation, if required, may only be necessary for buildings which are considered higher risk e.g. hospitals, care homes and other premises with delayed evacuation.

2.6 Spandrel panels

Spandrel panels (including window panels, infill panels, etc.) are part of the external wall of the building and are provided for both aesthetic and functional purposes. Like the rest of the external wall, the panels are generally required to meet acoustic, thermal, moisture, and fire performance requirements. They are not normally loadbearing but are often designed to account for wind loading.

The design and materials of panels varies between buildings; some are made of singular components such as cement particle board, other panels are composite products comprising outer facing materials bonded to an inner core/filler which may include combustible insulation.

Building owners should check the materials and products used to ensure that they do not present a risk of fire spread over the wall to an extent which could endanger life. It may not be readily apparent what materials are present, particularly for composite products which can include inner combustible insulating cores/fillers. Where sampling of the panel has been carried out, care should be taken to remediate any damage to the panels which would otherwise increase the fire risk (e.g. by exposing a combustible core/filler).

Note that vertically aligned spandrel panels or window infill panels create a greater risk of rapid fire spread vertically up the building than a horizontal band.

2.7 Balconies

The design and construction of balconies should not facilitate fire spread over the external wall to an extent that would pose a risk to life. There are indications that fires on balconies are becoming more common. The most common causes of such fires are wilful fire raising, careless disposal of smoking material and misuse of barbeques. Often, the severity of these fires is increased by combustible materials, such as furnishings or discarded materials stored, or used, on the balconies.

Balcony fires have occurred which have led to rapid external fire spread. BRE Global published examples in their 2016 report “Fire safety issues with balconies” which can be accessed at: www.bre.co.uk/filelibrary/Fire and Security/FI---Fire-safety-and-balconies-July-16.pdf. The report identifies additional risks from insulation materials used to prevent heat loss that may increase fire spread. It concludes “…the potential remains for a fire in a balcony…to pose a significant life safety issue”. The risk is clearly exacerbated if there are significant areas of combustible cladding in close proximity to a balcony.

Building owners/managers should be aware of the materials used in the construction of balconies. This will enable them, or their fire risk assessor, to better understand the risk of external fire spread so they can decide whether further action is required to manage this risk. Particular attention should be given to wooden balconies. Also, where balconies have been infilled and incorporated into flats, fire separation and fire stopping between flats should be checked.

Where there is doubt over the materials used, or risk presented, building owners should seek professional advice. Where it is assessed that there is a likelihood that rapid fire spread could pose a risk to life, building owners should seek professional advice and take appropriate action to address that risk.

Fire risk is increased when balconies are used as storage areas. Building owners may have policies on balcony use and storage and should review these to take account of the findings of the fire safety risk assessment. They should also engage with residents to develop their understanding of these risks and to share the significant findings of the fire safety risk assessment.

In order to comply with current building regulations guidance, where the building has a storey at a height of more than 11 m above the ground balconies should be constructed of products achieving European Classification A1 or A2. Where this benchmark is not possible, the advice of a competent professional should be sought.

2.8 Other attachments

There is a risk of vertical fire spread from other attachments to an external wall including solar panels and solar shading. Solar shading are devices attached to an external wall to reduce heat gain within a building by deflecting sunlight. Fire-fighters may not be able to apply a water jet from a fire-fighting hose directly onto a fire that has spread onto specified attachments high above the ground.

Where the building has a storey at a height of more than 11 m above the ground, specified attachments should be constructed of products achieving European Classification A1 or A2. Where this benchmark is not possible, the advice of a competent specialist should be sought.

2.9 Green Walls

Green walls (also called living walls) have become popular in recent years. Best practice guidance can be found in ‘Fire Performance of Green Roofs and Walls’ published by the Department of Communities and Local Government.


Email: buildingstandards@gov.scot

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