Innovative methods and systems can bring benefits in construction efficiency and the sustainability of buildings, but relatively little is known about their performance in fires. Ron Alalouff examines a report into the potential safety issues surrounding them.
This article is based on a study examining a range of issues concerning innovative construction products and techniques (ICPT), particularly the fire safety and robustness of new and emerging products and systems. The study – commissioned by the Communities and Local Government department and carried out by BRE – is the first part of a wider project to help ensure that innovation in construction is embraced and encouraged in a way that maintains fire safety and structural integrity. The study aims to give an understanding of the range of issues associated with these methods, and to provide recommendations and priorities for further work that might be needed.
The report asserts that many of the issues are about quality of workmanship and attention to detail – rather than about these innovative methods per se – so can equally apply to other forms of construction. The specific objectives of the study were:
– to consider innovative construction products and techniques in the context of cavity barriers, fire compartmentation/separation and, where relevant, their respective inter-relationships
– to produce a prioritised programme of further work needed on the issues raised above. This should include the possible development of suitable methods of test and assessment that cover all forms of construction – with particular emphasis on innovative methods of construction – where a database of performance in real fires does not exist.
Issues of concern
A number of initiatives have already been taken to address key concerns about some of these methods of construction. In general, these have concentrated mainly on the housing sector; examples include LPS 2020, a certification scheme for innovative housing systems.
Mortgage lenders, for example, may be less willing to lend against properties built by non-traditional forms of construction with which they are unfamiliar and which, to them, may appear to be similar to systems with which they have had problems in the past. A number of housing systems were designated as defective under the 1984 housing defects legislation. Problems were also identified with Large Panel System (LPS) buildings used to construct many of the high-rise towers built during the 1950s and 1960s. Although the vast majority of these systems were originally built as public sector dwellings, many subsequently entered the private housing market through the right-to-buy legislation.
The insurance industry has concerns about the lack of information on these types of construction to provide a suitable ‘risk profile’ needed to underwrite the risk. The industry would like to see how they would perform against conventional building methods in a range of common risks. For fire risks, insurers have indentified the case of a fire in a single room breaking out through a window and damaging the internal linings and external cladding above the window.
A recent technical claims forum held by the Chartered Institute of Loss Adjusters identified fire and flood as areas of specific concern, and highlighted the issue of disproportionate damage in buildings using innovative construction products and techniques. Composite panel systems used in inappropriate environments were cited as a specific example where the costs of repair were significantly higher compared to those for alternative traditional materials.
Fire and rescue concerns
One of the main concerns of the fire and rescue service is that when attending a fire, they may not be aware of the nature of the building and its key structural elements. What are termed ‘cultural and ‘aesthetic’ considerations mean that innovative structural forms can mimic traditional forms of construction, which can lead to mistaken assumptions when committing firefighters into a building.
The fire and rescue service has also expressed concern over the increasing use of polymeric materials in construction. The study says that from fire investigation reports, it is clear that a number of serious fires have occurred from a small ignition source, leading to extensive fire spread within concealed cavities. Many modern building systems contain polymeric insulation sheets to reduce thermal loss and, in general, this insulation is protected from the effects of a fully developed fire by fire-resistant plasterboard. The concern arises when the ignition source is in the cavity itself where there is no intrinsic fire resistance. Melting of the thermal insulation can also provide an effective route for fire to spread, bypassing any cavity barriers or fire stopping. This issue applies to external walls, cladding systems, internal walls and cavities between floors. It is particularly significant with multi-occupancy residential buildings, where phased evacuation would be the normal procedure.
There have been a number of serious fires during the construction of buildings using innovative products and techniques. There is some concern that light framing systems – which rely on sheathing boards for their protection from fire – are especially vulnerable. These are often not fixed until the entire superstructure has been erected, so large building frames are often completely unprotected, albeit for a short time. Recent fires – such as that at the Beaufort Park development in Colindale in July 2006 – have also brought into question the practice of allowing partial occupation of a partially completed building, in order to provide the income streams required to complete the project.
Many of the concerns expressed about the performance of individual products mirror those discussed in relation to system performance. One particular aspect relates to the anticipated larger deformations associated with long span engineered floor joists. This has implications for firefighters, who may rely on experience with traditional flooring systems to decide when structural stability is a problem for access to floors above the fire floor.
Building Regulations
Parts A and B of the Building Regulations are limited in scope to ensuring the safety and health of people (including the fire and rescue service) in and around buildings – they do not concern themselves directly with the protection of property. The design and construction of a building is assessed against guidance set out in the Approved Documents, as well as associated test and design standards based on pre-existing knowledge of how construction systems tend to behave.
In the case of innovative construction products and systems, tests and standards that have been developed with experience of conventional construction may not be appropriate. In theory, building control bodies could reject a proposed design – even if it meets the guidance in the relevant approved documents – if they consider that the nature of the construction means that functional requirements would not be met. In practice, however, the study says that building control bodies would be hard pressed to do this without considerable resources.
In most situations, guidance to Approved Document B has provided acceptable levels of safety for the performance of fire construction products and systems. There is evidence, however, that these assessment methods may not always take into account key performance criteria for modern building systems and modular construction. A number of products, systems and techniques apparently capable of meeting Building Regulations through small-scale or isolated testing, may still be inappropriate when used with other elements in a building.
Under Approved Document B, materials chosen to minimise the environmental impact of the building “must not have any adverse implications for the health and safety standards of the building work”. But measures to enhance the thermal performance of buildings, for example, have led to the creation of voids and cavities, which can be difficult to fire stop adequately.
So a number of initiatives are underway to develop test and assessment methods which more accurately reflect real fire scenarios. This performance testing involves a trend towards larger-scale system tests, but imposing this approach on all innovative systems and sub-assemblies would be difficult, and potentially costly. What can be concluded is that:
– there is a gap between procedures used under Building Regulations to demonstrate the safety of buildings, and the requirements of sustainable buildings in the longer term
– the development of industry standards may help to bridge this gap and offer an alternative approach to compliance
– in some instances, the inappropriate use of materials intended to minimise the environmental impact of building work has compromised fire performance
– the involvement of key stakeholders – including product manufacturers – will be essential in developing future research and development strategies for innovative products and techniques.
Building lifetime
‘Second generation’ lightweight construction systems – such as structural insulated panels (SIPs) which exploit new manufacturing techniques and material technology – are increasingly being used because of their ease and speed of construction and their energy efficiency. But there are several issues relating to their construction on-site, and to their subsequent alteration and maintenance. While most systems for residential use have been certified by bodies such as the British Board of Agrement for, among other criteria, fire resistance, the effect of any subsequent damage is not taken into account. But damage to SIPs can occur during construction, maintenance or change of use, especially when the system design relies on load-sharing between the cladding and the frame. When wiring is recessed into the facing materials, for example, it destroys the continuity of the face layers and impacts on the load-bearing and fire performance of the panels. Likewise, the post-fire structural stability of SIPs cannot be assumed, as the load-bearing mechanisms are fundamentally different to those of conventional construction methods.
Many of these potential problems are not insurmountable. The adoption of standards such as LPS 2020 is one way forward. Another is a change in the approach to regulations, to ensure that someone with sufficient knowledge and experience is consulted when making decisions on alterations or repairs.
The bigger picture
The study highlights a number of specific topics as warranting further research or testing. The first is the performance of innovative building products and systems in use, taking into account potential damage from specific events. A useful staring point may be the database of real fire events held by the London Fire Brigade.
Another issue highlighted is the interaction between construction members and the ability of connections to withstand large forces and deformations during and immediately after a fire. For many large framed systems, the benefits of structural continuity can lead to load redistribution from heated areas to cooler undamaged areas. However, these features do not necessarily apply to light framed systems, where connections are principally designed to resist shear force. These brittle connections may not be able to transmit the large tensile and prying forces generated during a fire, and premature failure of the connections would prevent the individual members attaining their anticipated fire resistance period. Large-scale fire testing – such as that outlined in emerging national, international and industry standards – would allow a proper evaluation of system performance.
For cavity barriers and fire stopping, existing requirements assume a fire on the (protected) inner face of panel systems. The study says this should be reviewed to also take into account the effect of an ignition source in the cavity itself. The vulnerability of certain design solutions to poor workmanship or poor site supervision could also be investigated, as there is evidence that critical fire barriers are not always correctly installed, or indeed are always present.
Facade performance is another area worth further investigation. Small-scale reaction-to-fire tests deal principally with the surface spread of flame. As well as vertical flame spread, with modern systems there is a possibility of burning through the cladding to provide a route back into the building. So consideration needs to be given to encouraging the greater use of the large-scale test method available.
The study also proposes a research project to investigate the potential disproportionate collapse following a fire, as well as a need to evaluate the performance of engineered floor joists relating to loading and clear span under realistic fire conditions. Information on deflection under fire conditions and residual load-bearing capacity would also be helpful.
Finally, although concrete is considered inherently fire-resistant, conventional test data may not be applicable to modern cement replacement materials and fillers which are used to improve lifetime performance.
The principal objective of the study was to develop and prioritise a programme of further work examining innovative construction products and techniques. Specific actions have been prioritised according to the volume of use, likely impact and scale of any study required.
Innovative Construction Products and Techniques (BD 2503) is published by the Communities and Local Government department and is available at www.communities.gov.uk
Innovative methods and systems can bring benefits in construction efficiency and the sustainability of buildings, but relatively little is known about their performance in fires. Ron Alalouff examines a report into the potential safety issues surrounding them.
This article is based on a study examining a range of issues concerning innovative construction products and techniques (ICPT), particularly the fire safety and robustness of new and emerging products and systems. The study – commissioned by the Communities and Local Government department and carried out by BRE – is the first part of a wider project to help ensure that innovation in construction is embraced and encouraged in a way that maintains fire safety and structural integrity. The study aims to give an understanding of the range of issues associated with these methods, and to provide recommendations and priorities for further work that might be needed.
The report asserts that many of the issues are about quality of workmanship and attention to detail – rather than about these innovative methods per se – so can equally apply to other forms of construction. The specific objectives of the study were:
– to consider innovative construction products and techniques in the context of cavity barriers, fire compartmentation/separation and, where relevant, their respective inter-relationships
– to produce a prioritised programme of further work needed on the issues raised above. This should include the possible development of suitable methods of test and assessment that cover all forms of construction – with particular emphasis on innovative methods of construction – where a database of performance in real fires does not exist.
Issues of concern
A number of initiatives have already been taken to address key concerns about some of these methods of construction. In general, these have concentrated mainly on the housing sector; examples include LPS 2020, a certification scheme for innovative housing systems.
Mortgage lenders, for example, may be less willing to lend against properties built by non-traditional forms of construction with which they are unfamiliar and which, to them, may appear to be similar to systems with which they have had problems in the past. A number of housing systems were designated as defective under the 1984 housing defects legislation. Problems were also identified with Large Panel System (LPS) buildings used to construct many of the high-rise towers built during the 1950s and 1960s. Although the vast majority of these systems were originally built as public sector dwellings, many subsequently entered the private housing market through the right-to-buy legislation.
The insurance industry has concerns about the lack of information on these types of construction to provide a suitable ‘risk profile’ needed to underwrite the risk. The industry would like to see how they would perform against conventional building methods in a range of common risks. For fire risks, insurers have indentified the case of a fire in a single room breaking out through a window and damaging the internal linings and external cladding above the window.
A recent technical claims forum held by the Chartered Institute of Loss Adjusters identified fire and flood as areas of specific concern, and highlighted the issue of disproportionate damage in buildings using innovative construction products and techniques. Composite panel systems used in inappropriate environments were cited as a specific example where the costs of repair were significantly higher compared to those for alternative traditional materials.
Fire and rescue concerns
One of the main concerns of the fire and rescue service is that when attending a fire, they may not be aware of the nature of the building and its key structural elements. What are termed ‘cultural and ‘aesthetic’ considerations mean that innovative structural forms can mimic traditional forms of construction, which can lead to mistaken assumptions when committing firefighters into a building.
The fire and rescue service has also expressed concern over the increasing use of polymeric materials in construction. The study says that from fire investigation reports, it is clear that a number of serious fires have occurred from a small ignition source, leading to extensive fire spread within concealed cavities. Many modern building systems contain polymeric insulation sheets to reduce thermal loss and, in general, this insulation is protected from the effects of a fully developed fire by fire-resistant plasterboard. The concern arises when the ignition source is in the cavity itself where there is no intrinsic fire resistance. Melting of the thermal insulation can also provide an effective route for fire to spread, bypassing any cavity barriers or fire stopping. This issue applies to external walls, cladding systems, internal walls and cavities between floors. It is particularly significant with multi-occupancy residential buildings, where phased evacuation would be the normal procedure.
There have been a number of serious fires during the construction of buildings using innovative products and techniques. There is some concern that light framing systems – which rely on sheathing boards for their protection from fire – are especially vulnerable. These are often not fixed until the entire superstructure has been erected, so large building frames are often completely unprotected, albeit for a short time. Recent fires – such as that at the Beaufort Park development in Colindale in July 2006 – have also brought into question the practice of allowing partial occupation of a partially completed building, in order to provide the income streams required to complete the project.
Many of the concerns expressed about the performance of individual products mirror those discussed in relation to system performance. One particular aspect relates to the anticipated larger deformations associated with long span engineered floor joists. This has implications for firefighters, who may rely on experience with traditional flooring systems to decide when structural stability is a problem for access to floors above the fire floor.
Building Regulations
Parts A and B of the Building Regulations are limited in scope to ensuring the safety and health of people (including the fire and rescue service) in and around buildings – they do not concern themselves directly with the protection of property. The design and construction of a building is assessed against guidance set out in the Approved Documents, as well as associated test and design standards based on pre-existing knowledge of how construction systems tend to behave.
In the case of innovative construction products and systems, tests and standards that have been developed with experience of conventional construction may not be appropriate. In theory, building control bodies could reject a proposed design – even if it meets the guidance in the relevant approved documents – if they consider that the nature of the construction means that functional requirements would not be met. In practice, however, the study says that building control bodies would be hard pressed to do this without considerable resources.
In most situations, guidance to Approved Document B has provided acceptable levels of safety for the performance of fire construction products and systems. There is evidence, however, that these assessment methods may not always take into account key performance criteria for modern building systems and modular construction. A number of products, systems and techniques apparently capable of meeting Building Regulations through small-scale or isolated testing, may still be inappropriate when used with other elements in a building.
Under Approved Document B, materials chosen to minimise the environmental impact of the building "must not have any adverse implications for the health and safety standards of the building work". But measures to enhance the thermal performance of buildings, for example, have led to the creation of voids and cavities, which can be difficult to fire stop adequately.
So a number of initiatives are underway to develop test and assessment methods which more accurately reflect real fire scenarios. This performance testing involves a trend towards larger-scale system tests, but imposing this approach on all innovative systems and sub-assemblies would be difficult, and potentially costly. What can be concluded is that:
– there is a gap between procedures used under Building Regulations to demonstrate the safety of buildings, and the requirements of sustainable buildings in the longer term
– the development of industry standards may help to bridge this gap and offer an alternative approach to compliance
– in some instances, the inappropriate use of materials intended to minimise the environmental impact of building work has compromised fire performance
– the involvement of key stakeholders – including product manufacturers – will be essential in developing future research and development strategies for innovative products and techniques.
Building lifetime
‘Second generation’ lightweight construction systems – such as structural insulated panels (SIPs) which exploit new manufacturing techniques and material technology – are increasingly being used because of their ease and speed of construction and their energy efficiency. But there are several issues relating to their construction on-site, and to their subsequent alteration and maintenance. While most systems for residential use have been certified by bodies such as the British Board of Agrement for, among other criteria, fire resistance, the effect of any subsequent damage is not taken into account. But damage to SIPs can occur during construction, maintenance or change of use, especially when the system design relies on load-sharing between the cladding and the frame. When wiring is recessed into the facing materials, for example, it destroys the continuity of the face layers and impacts on the load-bearing and fire performance of the panels. Likewise, the post-fire structural stability of SIPs cannot be assumed, as the load-bearing mechanisms are fundamentally different to those of conventional construction methods.
Many of these potential problems are not insurmountable. The adoption of standards such as LPS 2020 is one way forward. Another is a change in the approach to regulations, to ensure that someone with sufficient knowledge and experience is consulted when making decisions on alterations or repairs.
The bigger picture
The study highlights a number of specific topics as warranting further research or testing. The first is the performance of innovative building products and systems in use, taking into account potential damage from specific events. A useful staring point may be the database of real fire events held by the London Fire Brigade.
Another issue highlighted is the interaction between construction members and the ability of connections to withstand large forces and deformations during and immediately after a fire. For many large framed systems, the benefits of structural continuity can lead to load redistribution from heated areas to cooler undamaged areas. However, these features do not necessarily apply to light framed systems, where connections are principally designed to resist shear force. These brittle connections may not be able to transmit the large tensile and prying forces generated during a fire, and premature failure of the connections would prevent the individual members attaining their anticipated fire resistance period. Large-scale fire testing – such as that outlined in emerging national, international and industry standards – would allow a proper evaluation of system performance.
For cavity barriers and fire stopping, existing requirements assume a fire on the (protected) inner face of panel systems. The study says this should be reviewed to also take into account the effect of an ignition source in the cavity itself. The vulnerability of certain design solutions to poor workmanship or poor site supervision could also be investigated, as there is evidence that critical fire barriers are not always correctly installed, or indeed are always present.
Facade performance is another area worth further investigation. Small-scale reaction-to-fire tests deal principally with the surface spread of flame. As well as vertical flame spread, with modern systems there is a possibility of burning through the cladding to provide a route back into the building. So consideration needs to be given to encouraging the greater use of the large-scale test method available.
The study also proposes a research project to investigate the potential disproportionate collapse following a fire, as well as a need to evaluate the performance of engineered floor joists relating to loading and clear span under realistic fire conditions. Information on deflection under fire conditions and residual load-bearing capacity would also be helpful.
Finally, although concrete is considered inherently fire-resistant, conventional test data may not be applicable to modern cement replacement materials and fillers which are used to improve lifetime performance.
The principal objective of the study was to develop and prioritise a programme of further work examining innovative construction products and techniques. Specific actions have been prioritised according to the volume of use, likely impact and scale of any study required.
Innovative Construction Products and Techniques (BD 2503) is published by the Communities and Local Government department and is available at www.communities.gov.uk
