CPD: Facing up to fire regs on cladding projects
Barnsley College features more than 5,000 sq m of Kingspan Kooltherm K15 Rainscreen Board
Rainscreen cladding is subject to stringent fire regulations, especially on buildings higher than 18m. Adrian Pargeter, head of technical, Kingspan Insulation, explains what the regulations are and the routes to ensure compliance.
Anybody involved in construction management should ensure that the buildings they are responsible for achieve the designed levels of fire safety. This means having a good understanding, both of the potential issues and of the possible solutions.
This CPD sets out the regulatory requirements and the different routes to compliance for rainscreen clad buildings, in particular those with habitable storeys above 18m.
The benefits of facades and rainscreen cladding
The use of facades and rainscreen cladding is increasing, as they provide multiple benefits, including:
- Wide range of colours and finishes for design flexibility, and to suit all locales;
- Off-the-shelf engineered systems incorporating ready-made warranties;
- Fast-track construction can assist in reducing project scheduling periods;
- Easy integration with insulation to achieve energy efficient building envelopes;
- Facilitates refurbishment, for example overcladding on regeneration projects;
- Can provide lightweight external leaf for high-rise applications.
To take full advantage of these benefits, it is also important to make sure that the design, specification and build all meet the regulatory requirements governing fire safety, and to know what is deemed acceptable by fire safety engineers, building control bodies and warranty and insurance providers for achieving compliance.
What are the regulations?
In England and Wales, the requirements are set out in Part B, Fire Safety, of Schedule 1 to the Building Regulations 2010. The sections relevant to facades are:
- External Fire Spread B4-1 – 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.
- Internal Fire Spread B3-4 – The building shall be designed and constructed so that the unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited.
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For Scotland refer to Regulation 9 of Schedule 5 Section 2 Fire to the Building Standards 2015, sections:
- Cavities 2.4 – Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited.
- Spread to neighbouring buildings 2.6 – Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the spread of fire to neighbouring buildings is inhibited.
- Spread on external walls 2.7 – Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, or from an external source, the spread of fire on the external walls of the building is inhibited.
- Spread from neighbouring buildings 2.8 – Every building must be designed and constructed in such a way that in the event of an outbreak of fire in a neighbouring building, the spread of fire to the building is inhibited.
Tier 1 guidance on how to comply with the regulations is given in Approved Document B Vol.1 and Vol. 2 (ADB1 and ADB2), with separate editions for England and Wales, and in Technical Handbooks Section 2 Domestic and Non-domestic 2015 for Scotland (THB2).
Tier 2 guidance can be found in BCA Technical Guidance Note 18, Issue 1 June 2015 (BCA TGN18). Independent technical guidance issued by an authorising body, such as a warranty provider, is also available to aid compliance across the UK.
Below 18m – Boundaries, classes and cavities
There are some restrictions that apply to all buildings, whatever their height, taking into account their construction, proximity to other buildings, occupancy and use. These restrictions are detailed below.
External surfaces or walls:
- Where the distance to one or more boundary is less than 1m the products must be rated Class 0, or Euroclass B-s3-d2 or better when installed on buildings in England or Wales;
- In Scotland, the facade material must be non-combustible.
Assembly or recreation buildings where the distance to all boundaries is greater than 1m:
- In England & Wales, the products installed on assembly or recreation buildings above 1 storey must be rated Euroclass C-s3, d2, or have an index no greater than 20 when tested to BS 476 Part 6 (Fire tests on building materials and structures. Method of test for fire propagation for products);
- In Scotland, the facade material of assembly or recreation buildings less than 10m above ground must be rated “low risk” (at least B-s3, d2 or Class 0);
- There is no specific requirement for buildings between 10m and 18m.
All other buildings under 18m where the distance to all boundaries is greater than 1m:
- There is no specific boundary provision but the wall construction must meet the minimum period of fire resistance.
- The maximum dimension of cavity spaces between barriers should be no greater than 20m.
- This distance is reduced to 10m if the fire rating of the material facing into the cavity is lower than Low Risk in Scotland, or lower than Class 1 in England and Wales.
Why 18 metres?
The 18m limit came about because of the reach capability of fire and rescue service equipment in the past, such as wheeled escape ladders (now obsolete) and fire hoses.
The logistics of managing a fire and safely evacuating occupants in tall buildings is more challenging, and so measures are taken to reduce the risk of fire spreading.
The routes to compliance
There are three clearly defined routes to compliance (Note that the performance based route has two options):
- Performance-based — Exact system test data and Desktop study reports;
- Fire safety engineering.
The linear route
A linear approach to compliance allows the use of an insulant that is of Limited Combustibility (England & Wales) or
Non-combustible (Scotland) on all storeys of the building .
This approach relies on the fire ratings of individual elements, quite often based on the material’s ability to meet basic performance criteria when subjected to small-scale fire tests.
In practice it is possible to specify a component that is, to all intents and purposes, compliant with the requirements of ADB2 and THB2, but which, when built into a system, would fail the rigours of the large-scale tests, because of the complexity of the interactions between the various components.
This could potentially lead to a gap between the design and the actual fire safety performance. As such, the linear route may not automatically deliver the best fire safety solution.
The performance route – Exact system test data
BR 135 (Fire performance of external thermal insulation for walls of multi-storey buildings ), is directly referred to in both ADB2, THB2 and BCA TGN18, and sets out the performance criteria for the allowable large-scale tests. The large-scale testing option of the performance-based route provides data that is more reliable than that of small-scale tests, solving many of the potential issues of the linear approach.
Above: Kingspan Kooltherm K15 Rainscreen Board was installed at Kingswood Academy in Hull. Below right: Fire performance was a central design focus for a retrofit scheme involving nine 1970s residential blocks in Salford.
The relevant testing for external walls cited by BR 135 is BS 8414 – Fire performance of external cladding systems, Part 1 (Test methods for non-loadbearing external cladding systems applied to the face of a building), or Part 2 (Test method for non-load bearing external cladding systems fixed to and supported by a structural steel frame).
According to the guidance documents, and supported by BCA TGN18, products successfully tested to these standards as part of a complete external cladding system can be deemed compliant for the applications they have been tested in. The important aspect with this route is that the entire facade build-up is tested, rather than relying on the standalone performance of individual components.
However, the test result only applies to the specific build up tested, and therefore has some limitations.
The performance route – Desktop study report
Since the sheer range of possible build-ups and material combinations makes it unrealistic to expect every permutation to be tested, BCA TGN18 advises that a desktop study report can be submitted from a suitably qualified fire specialist as a practical alternative. Within the report, specialists are asked to use their professional experience and knowledge to determine whether a particular system will meet the acceptance criteria within BR 135.
The report must be backed with the results of testing by a suitable UKAS accredited testing body, and should make specific reference to any actual tests that have been carried out on the product. In addition to fire test data, the specialist will also typically require further information including plans, elevations, section and fire barrier details. Note that the specialist does not have to be UKAS accredited.
As the studies are project specific, it should not be assumed that those build-ups are automatically compliant for other projects. However, where more than one test has been carried out for similar build ups, approval can be gained for a range of insulation thicknesses based on the two most recent tests.
House builders and warranty providers can also supply pre-defined minimum specifications for common build-ups. These specifications are developed from pre-existing BS 8414 large-scale fire tests and desktop studies and, when followed precisely, should ensure constructions automatically achieve compliance. This can streamline the fire safety compliance process when using top-performing insulants such as rigid phenolic boards.
Still based upon empirical test data, the desktop study approach therefore provides a sensible route to determining compliance without having to test for every possible combination and scenario, and is now becoming commonplace.
In terms of straightforward compliance, it is always worth checking with the warranty provider for the property, as the specified construction may already meet the requirements in many applications, whichever route is being considered.
The fire safety engineering route
A “whole building” fire safety engineering approach uses the application of scientific and engineering principles to provide a holistic solution within the building design. Not only does it consider the performance of structures, systems, products and materials when exposed to fire, it also looks at fire prevention as well as active and passive fire protection measures. These might include effective means of egress, compartmentalisation with intumescent fire barriers, and adequate measures for alarm, detection, control and extinguishment.
This approach requires every factor of a building to be fully considered, from general aspects such as building type, location and occupancy level, to specific details such as how different cladding or roofing materials combine.
Both ADB2 and THB2 agree that a fire engineering approach is the only practical route for more complex projects, regardless of height. By making fire engineers a key part of every stage, and maintaining full collaboration with all interested parties, it should be possible to achieve effective fire performance; both in the initial design and in the finished building.
A recent survey shows that more than 88% of FSF members and 42% of CIC members feel ADB does not reflect today’s construction methods, design and usage, while research from the Association of British Insurers suggests the inclusion of fire safety engineering in ADB would prevent £1bn worth of fire-related damage over 25 years . Compliance with regulations/standards for energy and CO2 in the UK is already achieved through adoption of a “whole building” approach. So why not fire safety?
Design & build quality
It is important to remember that whichever route is taken, a strong facade specification and installation alone is not enough to guarantee a high level of fire safety. A good fire stopping and cavity barrier strategy is essential. This means pairing robust, high-quality fire barriers with proper, detail-oriented workmanship.
Critically, both building control and installers expect fire safety measures to be installed precisely to the original building specifications. Any deviations should therefore be agreed in advance with relevant parties within the project team to ensure the design fire performance level is met.
Furthermore, achieving excellent fire performance should not mean having to compromise other key areas such as aesthetics or energy performance. By carefully assessing the available routes it should be possible to meet all project requirements to a high standard using the best-quality construction materials.
Desktop study clears student digs design
Kingspan Kooltherm K15 Rainscreen Board was specified as part of a new £42m purpose-built student accommodation project in Portsmouth.
The Unite Students development will provide accommodation for 836 students. Cooley Architects’ design uses coloured Alpolic ACM cladding to form an eye-catching cube at the top of the building.
A desktop study was carried out to ascertain whether the specification would be compliant with the stringent fire performance requirements for the project, as Marvin Village, managing director of Metclad Contracts, explains: “We chose to take the Desktop Study route to compliance as this would allow us to use a premium performing insulation, a fundamental component in achieving the energy efficient design requirements, whilst also demonstrating compliance with fire safety regulations.
A fully qualified fire specialist was asked to draw up a report, specific to this project, on the facade system. The specialist was supplied with specifically referenced test data for the rainscreen components and planning documents including cross-sections, elevations and fire-stop details.
Based on this information, they gave their approval that the entire rainscreen solution would meet the performance requirements of BR 135.
Kingspan Kooltherm K15 Rainscreen Board has been successfully tested in differing thicknesses with a range of cladding materials to BS 8414-1 and BS 8414-2, in accordance with the performance criteria set out in BR 135. The product is Class 0 as defined by the Building Regulations and delivers excellent thermal performance with thermal conductivities as low as 0.020W/mK. It is also the first insulation board to receive LABC System Approval.
Woodberry Down’s face of the future
Woodberry Down, once heralded as the “estate of the future”, had suffered from an increasing number of issues including subsidence, asbestos, damp, and poor insulation. An eight-phase regeneration project carried out by Berkeley homes, Hackney Council, Genesis Housing Association and residents’ group Woodberry Down Community Organisation will now replace outdated concrete tower blocks with more than 5,500 new homes over the next 20 years.
Architect Hawkins/Brown specified Kingspan Kooltherm K12 Framing Board and K15 Rainscreen Board for Kick Start Sites 2 and 5 within the masterplan.
Kingspan Kooltherm K15 Rainscreen Board was installed as part of the anodised rainscreen cladding used on the top storeys of many of the blocks. These sections extend beyond 18m and it was, therefore, essential that the product offered excellent fire performance. The board has been tested to BS 8414-1 and BS 8414-2, and successfully assessed in accordance performance criteria set out in BR 135, in a range of insulation thicknesses with a variety of cladding finishes. It is, therefore, acceptable for use above 18m in accordance with the Building Regulations.
Kingspan Kooltherm K12 Framing Board was also installed within a steel framing system behind the main brickwork facade elements. The lightweight boards are easy to install and can be used with timber or steel frame constructions. Both products deliver premium levels of thermal performance and have been assigned 2008 Green Guide Summary Ratings of A+ by the BRE.
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