Research and analysis

Fire safety: Balconies, spandrels and laminated glass report (excluding appendices)

Published 22 December 2025

Applies to England

Background

This project was initiated by the Ministry for Housing and Communities and Local Government (MHCLG) and then completed and published by Health and Safety Executive (HSE) as the Building Safety Regulator (BSR). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect MHCLG or HSE policy.

1. Introduction

1.1 Background

In June 2017, the Grenfell Tower fire resulted in the death of 72 residents, many others becoming homeless and a wider impact on the local community and the UK housing sector more broadly. The incident also posed a significant challenge to the operational capabilities of the London Fire Brigade. In response to the Grenfell Tower fire, Dame Judith Hackitt conducted an independent review of Building Regulations and fire safety in England where she supported the recommendation to carry out “…further research with the construction industry to understand who uses Approved Documents, how they are used and where they are used to influence how they should be developed in the future…”. Soon after, the Government through the then Ministry of Housing, Communities & Local Government (MHCLG) introduced an effective ban on combustible materials to the external walls of relevant buildings through changes to Regulation 7 to the Building Regulations in England.

This report contributes to research that forms part of the recommended technical review by the Building Safety Regulator (BSR) at the Health and Safety Executive (HSE). The research was originally commissioned by the MHCLG, which subsequently became the Department for Levelling Up, Housing and Communities (DLUHC), which then transferred its role to develop and maintain Approved Document B to the HSE of the Building Regulations and statutory guidance given by Approved Document B (AD B) for fire safety in buildings in England.

The research investigates the mechanisms of fire spread between balconies that might be located on the external walls of multi-storey residential buildings. Particular focus is made on the impact of having laminated glass as the balustrade of balconies as the introduction to the changes to Regulation 7 resulted this product not being permitted for this use on relevant buildings (as defined in Regulation 7). The research also examined several other factors of relevance regarding the fire safety of balconies which are summarised in this report and discussed in more detail in the accompanying appendices.

‘Building work’ is a legal definition for work covered by the Building Regulations in England. Although the guidance given by AD B is generally applied to building work associated with new construction it is important to note that “Building work and material changes of use subject to requirement B1 [of the Building Regulations] include both new and existing buildings.” As such, although most of the study is assumed to be applicable to new buildings, the work also examined elements related to existing buildings, particularly where AD B gives guidance on the use of a non-combustible soffit to the underside of balcony decks that are made of a combustible material. The application of a soffit may be used as a retrofitting solution to existing buildings.

1.2 Work programme

At the start of the project the work programme associated was broken into three broad objectives. Objective A was to carry out a review of the then current research literature, standards and codes, incidents and history of balconies, spandrels and laminated glass. Objective B was to examine the current guidance associated with the three topics and Objective C was to then generate further knowledge. As the work proceeded it was clear that the three topics had several overlaps and also impacted on other research that was being carried out on behalf of the HSE. In discussion with the HSE during the progress of the work the work programme was modified to the following objectives:

• Objectives A and B: Review of the use of balconies, spandrels and laminated glass in construction (Appendix A/B)
• Objective C1: Balcony fuel load survey (Appendix C1)
• Objective C2: Small-scale laminated glass experiments (Appendix C2)
• Objective C3: Balcony fire demonstration test methodology and matrix (Appendix C3)
• Objective C4: Full-scale balcony fire demonstration tests (Appendix C4)
• Objective C5: Preliminary findings from computational fluid dynamics simulations (Appendix C5)
• Objective C6: Spandrel zone demonstration test methodology (Appendix C6)

These objectives broadly followed the initial plan of work. However, the research on spandrels was not progressed as first envisaged, partly because the work would overlap with the separate project on external wall systems (CPD 004/121/108, of which OFR is also the lead partner), and partly to allow this project to have greater focus on the balcony and laminated glass topics.

1.3 Reporting

This study has been carried out by a consortium of partners that has been led by OFR. The majority of the work has been jointly undertaken by members of OFR and Efectis. The responsibility of the members from University of Edinburgh and University College London (UCL) has been to provide internal review and critique of the work. These internal reviews have provided an important role in improving and 3 clarifying key elements. The contributors and their organisations are identified within the reports contained within each appendix, relevant to the time of writing of the reports. External oversight of the project has been provided by an Expert Review Panel (ERP) consisting of stakeholders from various public and private organisations.

The appendices to this final report are those documents released throughout the research project with some relatively minor editorial and formatting changes. The appendices retain the tenses as they were written at the time rather than being updated to reflect their current status. The earlier documents make reference to work that may or may not have subsequently been carried out as the result of ongoing findings, and feedback from the BSR and the ERP. The research also needed to adapt to various external factors such as newly published documents and events that have occurred over its duration.

Related to the release of the contents of the appendices, several articles have been published in the open literature. As a result of the review process, some of these articles contain updated and or additional content that has not been included in the original documents (the attached appendices). Further articles may be forthcoming which may again differ from some elements of the work presented here in response to feedback. A list of the published articles and those currently under review is provided below:

1. M. Spearpoint, I. Rickard, ‘Laminated glass in balcony balustrades’, International Fire Professional, 38, 43-51, 2021.

2. M. Spearpoint, I. Rickard, S. Lay, ‘Additional perspective on three balcony fire incidents involving glass balustrades’, Fire Technology, Jul. 2021, doi: 10.1007/s10694-021-01154-6.

3. S. Bryant, I. Rickard. M. Spearpoint. ‘A survey of fire loads on private residential balconies in England’, Fire Technology, 59, 3415–3443, 2023. 10.1007/s10694-023-01467-8

4. Bryant S, I. Rickard, M. Spearpoint, ‘Findings from a survey of fire loads on private residential balconies in England’, International Fire Professional, 48, 39–46, 2024.

5. D. Hopkin, M. Spearpoint, K. Chotzoglou, T. Fateh. ‘Analysis of fire exposure to structural elements forming and supporting balconies’, CONFAB 2024, London, England, UK, 9–10 Sept 2024.

6. M. Spearpoint, G. Remy, I. Rickard, L. Bisby. ‘Reaction-to-fire performance of vertical laminated glass panels with different inter-layer materials when exposed to an external heat flux’, submitted to Fire Safety Journal (under review)

2. Objectives A and B - Review of the use of balconies, spandrels and laminated glass in construction

Objectives A and B combined work to conduct a scoping study to identify key issues and establish the current state of knowledge on balconies, spandrels, and laminated glass with a review of the current provisions relating to balconies, spandrels and laminated glass in AD B and their effectiveness. Appendix A/B is the result of this phase of the work in which the tasks listed below were completed.

• Balconies: The work examined the evolution of balconies throughout the ages from a design and use perspective and then discussed what a modern balcony is and what it can be used for. Balconies that are used as amenity spaces (private and shared) were distinguished from those used as means of escape as they present different challenges from a fire safety perspective. The study investigated the main form of construction of modern balconies and details the main components that can be found in balconies. The work lists the different pros and cons of balconies on external fire spread. A review of the building regulations and fire safety guidance applicable across the UK and elsewhere that may have an impact on balcony design was carried out. Finally, the balcony section discussed several UK fire incidents associated with balconies and examined some of the available international research into their impact on external fire spread.

• Spandrels: The spandrel section focused on what is a spandrel, how is a spandrel zone defined and what is its role in relation to fire safety. It also provided details of the various typologies and details related to panels used in a spandrel zone.

• Laminated glass: The section on laminated glass begins with a historical account of the development of laminated glass from the early 1900s and its introduction into building construction. In the context of the use of laminated glass in buildings, a selective review of the various British Standards for its design and application is provided. A summary of the materials used to manufacture laminated glass is given along with a brief discussion on how the glass is mounted in glazing and balustrade systems.

The section included a review of the literature that has investigated the performance of glass in fire with a focus on laminated glass that aids in identifying the flammability of the product in relation to its use, the materials used to form interlayer/s, configuration.

The section described the fire safety considerations that are relevant to the use of laminated glass. These considerations include the fire separation functions of glazing systems along with reaction-to-fire performance, and the potential for vertical fire spread.

The work provided a set of recommendations for the next steps in the research that included proposals for experimental and numerical investigations. This work was caried out in Objective C as described below.

3. Objective C1 - Balcony fuel load survey

Objective C1 provided a survey of the fuel load on balconies of 1020 residential buildings in England using images sourced from Google Street View. Objective C1 also reviewed guidance produced by various organisations regarding the use of balconies and also identified some balcony fires at the time of writing. Additional balcony fire incidents were also noted as part of Objective A/B. The key findings from Objective C1 were:

• Guidance notes produced by London Fire Brigade and insurance companies consider the ideal fuel load on a private residential balcony to be zero, and that balconies should not be used for storage.

• The survey identified the fuel load from a range of balconies throughout the year. Analysis determined an average fuel load energy density (FLED) of 64.4 MJ/m2 , and an 80th percentile of 110 MJ/m2 for a balcony. Balcony FLEDs within London are 1.6 to 1.7 times higher than the FLEDs outside of London. Comparisons on balcony fuel load were explored including the impact of building height, season, year, and balcony size. It was found that buildings between 18 m and 30 m in height have a statistically significant higher FLED than other heights, and that balconies smaller than 2.5 m2 have a statistically significant higher FLED than balconies larger than 2.5 m2 . Furthermore, it was found that Social Grade has no statistically significant impact on the average FLED.

• A ‘representative balcony’ was found to have dimensions of 2.85 m wide and of 1.3 m deep. The total fuel load of this representative balcony was 233.7 MJ, where 179.2 MJ is from plastic-based materials, and 54.5 MJ from wooden contents, the fuel composition by mass on balconies is 60% plastic and 40% wood and has a FLED of 63 MJ/m2 . The average peak heat release rate for the representative balcony was estimated as 105 kW/m2 , with an 80th percentile of 173 kW/m2 with a Medium growth rate of 0.012 kW/s2 .

Results from Objective C1 fed into the work conducted as part of Objective C3 and Objective C4.

4. Objective C2 - Small-scale laminated glass experiments

Objective C2 was an extensive series of small-scale experiments on the reaction-to-fire performance of vertical laminated glass panels with different inter-layer materials when exposed to an external heat flux. Samples of laminated glass at two sizes, three glass thicknesses, four types of inter-layer material were used in the study. The samples were exposed to three radiant heat fluxes at three exposure locations. Measurements of time to glass shatter, ignition time, and mass loss were recorded along with observations of flame behaviour and dripping inter-layer.

• For panels with PVB and EVA inter-layers the results showed that time to ignition generally increased with glass thickness and did not change significantly whether the heat exposed pane was broken or unbroken prior to heating. Furthermore, the time to ignition with the PVB inter-layer was generally unchanged when heated in one of the three locations (the top, middle or bottom of the panels). For panels with the SGP inter-layer, times to ignition showed substantial variability both with panel thickness, the initial condition of the exposed pane, and somewhat the heating location.

• Although the SGP was found to have the highest calorific value of the four inter-layer materials, the panels with the PVB inter-layer showed the highest peak heat release rate when compared to panels using the other three laminate types.

• The thickness of the panel (the thickness of panes of glass) may have had some impact on heat release rate, although the results were generally inconclusive when it came to peak values.

• Breaking the front pane of glass prior to exposure to the radiant heat flux can make a difference to the burning characteristics of a panel in terms of the peak heat release rate, although it did not necessarily result in a more severe fire when assessed in terms of time to ignition or total mass loss.

• Results both in terms of total mass loss and also peak heat release rate suggested that heating the panels in the centre would likely give the highest values when compared to heating at the bottom or at the top.

• The larger laminated glass panels with the PVB and SGP inter-layer generally resulted in a higher peak heat release rate, although the finding was not universal.

• The reaction-to-fire performance of laminated glass with an SGP inter-layer had greater variability when compared to PVB. Among the tested inter-layers, 8 the PVB inter-layer stood out as having the highest occurrence of flame spread or flame flashing at a higher location when compared to the other inter-layer types.

• Overall panels with the PVB inter-layer showed a faster time to ignition and higher peak heat release rate when compared to panels that used the other three inter-layer types.

Results from Objective C2 fed into the work conducted as part of Objective C3 and Objective C4.

5. Objective C3 - Balcony fire demonstration test methodology and matrix

Objective C3 described the development of the scenarios that led to the full-scale balcony demonstration tests to fulfil Objective C4. The scenarios considered the wide range of balcony design parameters that could be investigated but focused on the key ones that BSR had particular interest in, namely the inclusion of laminated glass in the balustrade, the use of timber as a decking material, and the presence of a moveable fuel load. The scenarios also included an assessment of the using a non-combustible soffit to the underside of balconies with combustible decking, which was not part of the scope of the original objectives. Furthermore, as discussed in Objective C4, there was a subsequent change to the balcony test programme as the result of the fire that occurred at Hallam Court, Croydon on 7 th June 2023.

Objective C3 provided preliminary calculations for the specification of the moveable fire load. The work considered what combustible materials should be used for the decking, and the design of the laminated glass balustrade. An initial design of the test rig and its associated instrumentation was proposed which were subsequently refined as part of Objective C4.

6. Objective C4 - Full-scale balcony fire demonstration test

Objective C4 described a series of eight full-scale balcony fire demonstration tests that were carried out by Efectis under their calorimeter in their Belfast laboratory facility. The test series resulted from the work carried out as part of Objective C3, and further discussion with BSR and specific members of the ERP associated with glazing specifications and balcony design.

Measurements of heat release rate, gas temperatures and heat fluxes were used to quantify balcony-to-balcony fire spread and compare the eight different balcony configurations. Findings from the tests examine the impact on balcony fire spread of a range of factors including:

• the presence of a moveable fuel load
• where a balcony has an exposed timber deck
• having laminated glass balustrades
• the use of a non-combustible soffit on the underside of balconies with a timber deck
• the likely performance of non-combustible balconies
• where combustible balustrades, in particular a HPL panel system, has been used
• the implications on lateral fire spread to neighbouring balconies

In addition to considering fire spread, results from the tests were used to assess the stability of balcony structures under thermal exposure conditions. The findings from the tests were:

• Moveable fire load: The presence of moveable combustible items on balconies can influence fire behaviour, modifying airflow, contributing to heat release, and impacting flame dynamics. These items can enhance upward or downward fire spread through burning or falling materials. Non-combustible items, though not directly involved in combustion, may also affect fire spread by modifying airflow and shielding combustible materials.

• Exposed timber deck: Balconies with non-fire retardant treated exposed timber decks demonstrated poor fire performance. Tests showed rapid fire spread within minutes. Timber decking was identified as the dominant factor in fire spread, more so than the type of balustrade. Smaller gaps between 11 decking planks might influence fire behaviour, but this aspect was not investigated.

• Laminated glass balustrades: Tests using laminated glass balustrades suggested they do not significantly influence upward fire spread in the early phases of a fire. Laminated glass contributes a small fuel load in comparison to other potential combustibles. The presence of glass can slow the ignition of moveable fuels by separating them from flames extending to the edges of a balcony. The tests represented a worst case in which the bottom edge of the glass was exposed. Dripping, burning laminate could ignite other materials although observations in tests showed that when this occurred the pool fires were small. Placing the laminated glass within a channel may reduce the likelihood of dripping laminate, although this was not examined in the tests. Glass panels could fail and fall, potentially spreading fire downward.

• Non-combustible soffit: Tests of non-combustible soffits showed improved fire performance compared to balconies with exposed timber decks. However, while upward fire spread was slowed, it was not completely prevented.

• Non-combustible balconies: Balconies with non-combustible decks and balustrades are likely to perform better in fire scenarios when compared to those with combustible decks and/or balustrades. Solid balustrades can reduce heat flux to the façade (in a similar way as shown by the laminated glass balustrade tests), lowering the likelihood of igniting the moveable fuel load. The study indicated that solid balustrades may not have a significant impact on flame height but could alter airflow and flame dynamics.

• Combustible balustrades: Combustible balustrades add energy to a fire and increase the likelihood of both upward and downward fire spread. Tests with combustible HPL balustrades showed burning material falling away and contributing to fire spread. The specific behaviour of larger HPL panels or other combustible materials remains uncertain, and further investigation would be needed.

• Lateral fire spread: Lateral fire spread on the same balcony level can occur when flames exit a building’s exterior opening and combustible items are nearby. While upward fire spread is generally more influential, lateral spread could be significant for certain balcony configurations with timber decks.

• Stability of balcony structures in fire: The tests revealed that unprotected steel used in balcony structures could reach temperatures associated with structural failure. It is recommended that balconies should either align with the fire resistance period for the building, or achieve 60 min. This will mitigate premature failure in low-rise buildings and enhance the likelihood of structural survival in medium- and high-rise buildings during a fire.

• Fire development: Those balcony configurations in which the heat release rate exhibited a significant increase beyond the contribution of the BS 8414 12 crib showed an approximately linear growth. Balcony fires differ from enclosure fires since there are not the same heat feedback and ventilation effects taking place. Fires in room-scale enclosures often exhibit an accelerating fire growth and a transition to a fully developed regime following flashover. However, fires on balconies are likely subject to external wind conditions which could change the burning characteristics when compared to typical enclosure fires. The influence of wind was not investigated in this study.

7. Objective C5 - Preliminary findings from computational fluid dynamics simulations

The principal aim of Objective C5 has been to investigate the possibility of benchmarking computational fluid dynamics (CFD) simulations against the results from the full-scale balcony fire demonstration tests in Objective C4. The findings from this phase of the research followed on from the completion of the tests and analysis of the results.

The work assessed whether the Fire Dynamics Simulator (FDS) computational fire dynamics (CFD) model could reliably replicate the thermal conditions observed in the full-scale balcony fire tests. The assessment process involved:

• simulating the same balcony fire conditions in FDS
• comparing key outputs such as gas temperatures and radiant heat flux between the FDS simulations and the test data
• considering how refining the simulation parameters might improve the agreement between the FDS predictions and test results

The work focused on Test A as detailed in Objective C4, which served as the baseline scenario with non-combustible balcony floors, open balustrades, and no additional fuel targets. This test was designed to characterise heat fluxes and other fire-related parameters under a simple configuration. The benchmarking of FDS against Test A was important as it will serve as the foundation for any future work on a comparison with the more complex scenarios undertaken in Objective C4.

The study highlighted the challenges and implications of simulating the relatively simple balcony fire scenario using FDS. Representing the burning of the BS 8414 wood crib was not a straight-forward process. While the simulations adequately represented certain aspects, such as the heat release rate (HRR), the comparative analysis between the test measurements and simulated data revealed several discrepancies in gas temperature and heat flux predictions. OFR plan to carry on with investigating the performance of FDS outside the BSR project and will look to report its findings through a different means.

8. Objective C6 - Spandrel demonstration test methodology

The purpose of Objective C6 was to propose an experimental programme for the assessment of the spandrel zone, as detailed in Objective A and Objective B. The work examined options for the design of a test rig, the type of instrumentation that would likely be required, and the configuration of representative façade systems. However, ultimately the work proposed in Objective C6 did not go ahead as the scope of the balcony demonstration tests expanded through the project timeline and the resources needed to build a specific rig and complete the spandrel zone tests was not available. Furthermore, the proposed tests have the potential to overlap with a separate project being carried out on behalf of BSR on external wall systems (EWS) and it is possible the EWS research will be able to address aspects of spandrel zone performance.

9. Implications

9.1 Introduction

The findings from this research project have potential implications on three key aspects of the fire safety regulatory system in England, namely the functional requirements, Regulation 7, and the statutory guidance given in Approved Document B (AD B). Each of these are discussed in more detail below.

9.2 Functional requirements of the Building Regulations

Given that the Building Regulations in England for building work are expressed in the functional requirements B1 to B5, it is appropriate to consider the findings of this research project in their context. The discussion below suggests that consideration of the functional requirements from the perspective of balconies on the outside of buildings needs a nuanced approach. In addition, it is important to note that balconies have a complicating factor in that they may also have moveable fuel load present which cannot be directly addressed by building work requirements of the regulations as this will be introduced by building users once a building has been completed. The presence of moveable fuel loads is likely to be more relevant to private balconies but cannot be ruled out from access balconies.

9.2.1 Fire spread

The primary requirement that this work relates to is the fire spread associated with balconies. Fire spread can be both external and internal to the building, and also between buildings. Functional requirement ‘B4(1): External fire spread’ states that:

The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another having regard to the height, use and position of the building.

Balconies are not specifically ‘external walls’ but, where present, are part of the external envelope of the building and therefore it is appropriate to expect them to also ‘adequately resist the spread of fire’ both over the external envelope and between buildings. On first inspection one could interpret that functional requirement ‘B2: Internal fire spread (linings)’ and functional requirement ‘B3: Internal fire spread (structure)’ are not directly relevant to balconies as these requirements addresses internal fire spread and a balcony that is on the outside of a building is not ‘internal’. Functional requirement B3(3) states that:

Where reasonably necessary to inhibit the spread of fire within the building, measures shall be taken, to an extent appropriate to the size and intended use of the building, comprising either or both of the following:

(a) sub-division of the building with fire-resisting construction (b) installation of suitable automatic fire suppression systems

and functional requirement B2(1) states:

To inhibit the spread of fire within the building, the internal linings shall:

(a) adequately resist the spread of flame over their surfaces; and (b) have, if ignited, either a rate of heat release or a rate of fire growth, which is reasonable in the circumstances.

Depending how ‘within a building’ is interpreted in the context of balconies then B3(3) might be relevant particularly where private balconies are connected across a compartment line between separate properties. If the application of B3(3) leads to balconies as being within a building then B2(1) also becomes relevant, although it can be argued that B4(1) already addresses the same requirement.

However, the key point is that balconies provide a potential means of storey-to-storey or compartment-to-compartment fire spread, thus potentially affecting compliance with B3(3) and B4(1). A fire could start in a compartment on a storey and then spread to other compartments above, below and/or laterally via balconies as the result of the structure and/or contents associated with those balconies. Similarly, a fire could start on a balcony and spread in a comparable manner. Fires associated with balconies may also provide a mechanism for building-to-building fire spread.

9.2.2 Stability

Functional requirement B3(1) states that:

The building shall be designed and constructed so that, in the event of fire, its stability will be maintained for a reasonable period.

Where a balcony is on the outside of a building, its stability can be integral to other building functions and their associated functional requirements, for example B1 and B5(1), as discussed below. Similar to some façade systems, the mechanical failure of balcony components could present a hazard to those below, for example, evacuating occupants and FRS.

9.2.3 Means of escape

Functional requirement ‘B1: Means of warning and escape’ states that:

The building shall be designed and constructed so that there are … appropriate means of escape in case of fire from the building to a place of safety outside the building capable of being safely and effectively used at all material times.

Therefore, where a balcony is used for access then functional requirement B1 is of relevance. The structural stability and any hazard posed by the flammability of materials used to form the balcony need to be addressed to ensure appropriate means of escape remains available. This would include considerations of falling debris and its potential impacts on egress routes.

It is reasonable to conclude that in the case of private balconies, requirement B1 is less significant other than such balconies form an ‘inner room’ when considering means of escape.

9.2.4 Fire service access

Functional requirement ‘B5(1): Access and facilities for the fire service’ states that:

The building shall be designed and constructed so as to provide reasonable facilities to assist fire fighters in the protection of life.

The observations regarding functional requirements B1 and B3(1) for balcony access apply to this requirement, as does the more general comment regarding mechanical failure and considerations of falling debris.

9.3 Regulation 7

In addition to the functional requirements of the building regulations, this work also has implications for Regulation 7(2) as it is applied to ‘relevant buildings’. More details of this regulation are covered in Objectives A and B (see Appendix A/B-4) however the key component is that Regulation 7(2) currently states:

Subject to paragraph (3), building work shall be carried out so that materials which become part of an external wall, or specified attachment, of a relevant building are of European Classification A2-s1, d0 or A1 (classified in accordance with the reaction to fire classification).

Where Class A1 or Class A2-s1, d0 products do not exist and there are no suitable alternatives, the Regulation includes a list of exemptions, given in Regulation 7(3). Thus, this regulation achieves an in-effect ban on the use of materials and hence products (in and on the external wall zone) that do not meet the reaction-to-fire requirements as set out by the Government.

The exemptions given in Regulation 7(3) do not include where a balcony balustrade is constructed using laminated glass panels (or any other specified materials). As discussed in Objectives A and B (see Appendix A/B-28.3), the outcome from European Commission decision 96/603/EC (consolidated 2003/424/EC) and the work previously undertaken by Glass for Europe meant that all laminated glass products are considered Euroclass B when classified by BS EN 13501-1. Over the time this research has taken place at least one processor of laminated glass has released a product that does meet Regulation 7(2), but it is expensive, relatively heavy, and there is a limited capacity to supply the market.

It is beyond the remit of this report to suggest if and how Regulation 7 might be amended. However, as demonstrated in Objective C4 (see Appendix C4), the research does suggest that the presence of laminated glass with characteristics that represent a reasonable worst case does not make a significant impact on the likelihood of fire spread during the initial phase of a fire. The fuel load introduced by a laminated glass balustrade is likely to be small when compared to the moveable fuel load, and the balustrade may increase the time to ignition of that fuel load by separating it from the flames from below the balcony floor.

As discussed in Section 9.4, there would likely need to be consideration on any impacts of any proposed changes to Regulation 7, the guidance given by AD B, and the relationship with other guidance such as that given by BS 9991 and BS 8579, where relevant.

9.4 Approved Document B (AD B)

Most of the findings from the research project do not have a direct impact on the guidance given in the current (at time of writing 2019 edition (incorporating 2020 and 2022 amendments)) of AD B since it only assigns certain fire safety features to balconies. In general, clauses address the materials and construction of balconies in relation to the functional requirements in B4, and there are a small number of clauses that address Functional Requirement B1 including a reference to clause 7.3 in BS 9991 for common/deck access balconies.

As noted in Section 6, one specific finding from Objective C4 (see Appendix C4-7.4) that the fire resistance of elements forming or supporting balconies should either align with the fire resistance period for the building or achieve 60 min, whichever is the lesser. It is recommended that a future version of AD B be updated to include this expectation. More generally it is possible to contemplate where the guidance in AD B could be amended in relation to balconies, noting that this research project does not address whether such changes are necessary, nor to what level, if such changes were believed to be necessary. Any changes would need to be cognisant of the relevant requirements specified by Regulation 7 and BS 9991 depending on if and how those are updated. Some examples are as follows:

• Moveable fire load: AD B (nor the Building Regulations) cannot directly exert influence on the moveable fire load present on a balcony after construction. Where there might be particular concern, such as on access balconies, then The Regulatory Reform (Fire Safety) Order and/or the Building Safety Act 2022 could have relevance on the control of items, or other mechanisms such as leasehold contracts. However, if the intention is to allow building occupants to use their private balconies in a reasonable manner there needs to be an acceptance that some amount of fire load will be present.

• Combustibility: Where the hazard posed by the combustibility of the materials associated with balconies other than residential buildings with a storey 11 m or more in height be of concern then clause 12.11 / clause 10.10 in the two volumes of AD B could be extended to cover other occupancy types and or building heights. It might be argued that restricting balconies on low-rise, low occupant buildings might be unnecessary as the risks may be sufficiently low.

• One of the balcony provisions in AD B (clause 10.10 b. in Volume 1 and clause 12.11 b. in Volume 2) relates to the use of a non-combustible soffit and Class B materials in the line of compartment walls to mitigate lateral fire spread. Beyond that, however, there are no limitations on either the deck or balustrade flammability. The test with the HPL balustrade presented in Objective C4 (see Appendix C4-5.8) showed that the benefit of a soffit can be undermined by a highly combustible balustrade and, therefore, some consideration could be given to prescribing some minimum reaction-to-fire classification for materials forming balustrades.

• Balcony arrangement: Should the hazard posed by fire spread vertically and/or horizontally between separated balconies be deemed to be unacceptable then AD B could present provisions to restrict the spacing between balconies. This could be in the form of minimum distances between the floors/balustrades. These distances could be dependent on the construction materials used, although that would likely introduce additional complexity. Alternatively, if separation was not an option, balconies could be separated by fire-resisting construction.

• Building separation: Similar to the issue of fire spread between balconies associated with a given building, the question of fire spread between buildings from balconies and/or external walls (balcony to balcony, wall to balcony) could be specifically accounted for in AD B by appropriately updating Section B4. Currently, guidance exists for canopies that could be extended to include specific consideration of balconies.

• BS 8579: As noted in Objectives A and B, there is no mention of BS 8579: 2020 ‘Guide to the design of balconies and terraces’ within AD B at the time that objective was completed, nor at the time of writing this final report. It is 20 beyond the scope of this discussion to fully review BS 8579, but an option exists for AD B to adopt all, or parts, of this standard (as Volume 1 of AD B has done in the case of BS 9991).

It must be noted that any changes to one part of AD B could have positive (or negative) implications to another part. For example, including minimum spacing provisions could allow balconies to be constructed with more combustible materials. However, changes to AD B would need to be considered in view of any impact they might have on the way that balconies are designed, constructed, and used, along with the many legacy buildings that already exist.