Now the UK is experiencing more extreme weather events and with the implementation of more stringent building regulations - specifying the right building board system for the job is vital. Even where specialist advice is available, a working knowledge of regulations and performance is crucial to making the right design and specification decisions.
Ian Quinton, Managing Director of RCM - suppliers of building boards and facade solutions to such high profile developments as the University of Hertfordshire – outlines some considerations when specifically looking at the design requirements for structural timber buildings.
Structural Strength and Stability
A significant consideration when assessing building boards is to ensure the optimum racking performance to enhance structural strength. The load bearing capacity of wooden shear walls loaded by wind and seismic forces can be evaluated using different testing procedures. European Norm – BS EN 594:2011 is the recognised testing protocol for testing racking strength and stiffness of timber frame wall panels. Building boards and cladding systems with BS EN 594:2011 certification have been rigorously tested and offer good racking, performance, structural strength and stability.
Another factor to consider for stability is moisture movement. When evaluating a solution, consider a system that offers a high level of dimensional stability with limited moisture movement. Building boards can be specified with as little as 0.06% moisture movement.
Resistance to Moisture and Durability
By specifying a building board that is fully tested to BS EN 1062-1, it ensures the boards have adequate moisture resistance and durability and will have a life equal to that of the building.
Selecting a building board with good external performance and durability is important, particularly through the build phase, as the product may be left exposed for several months prior to a secondary facade being installed over the top of the system.
Certification to BS EN 12467:2012 offers confidence of the building board’s durability requirement and that it can withstand the exposure cycle of freeze and thaw, heat and rain. Testing to BS EN 12467:2012 is also covered in BBA certification.
Behaviour in Relation to Fire
The Building Regulations for England and Wales set out the legal obligations for building designers. These functional requirements outline what must be done, but do not address how to achieve this. An example of a functional requirement that covers structural stability in a fire is that, ‘the building shall be designed and constructed so that, in the event of a fire, its stability will be maintained for a reasonable period.’
Robust timber structures perform well in relation to fire by slowly forming a char layer and in the case of cross laminated timber, can remain structurally stable for up to 90 minutes. However, slender timber is generally protected by fire-rated boards and great care needs to be taken on the detailing of this.
Recognised certified products generally make technical information readily available. Provided by the supplier and frequently available on websites, the material safety data sheet for building boards and external cladding systems, is a good starting point.
Fire Rating A1 and A2 - refers to reaction-to-fire classifications for contribution to fire growth in accordance with – BS EN 13501-1. A1 utilises BS EN ISO 1182 and BS EN ISO 1716 tests and is typically non-combustible rating referenced as ‘Non-Combustible’. A2 utilises BS EN ISO 1716 and BS EN 13823 testing and is referenced to typically as ‘Limited Combustible.’
Which BS and BS EN standards apply to material testing?
BS EN ISO 1716:2010 and BS EN ISO 1182:2010 are the most relevant, together with BS EN 476-21 and BS EN 476-22 and BS EN 1365-1:2012 for non-loadbearing and loadbearing fire rated wall applications. Check the material safety data sheet to ensure the product is compliant.
Site Safe Compliant - Paper 4
Produced by the Structural Timber Frame Association (STA), Site Safe Compliant - Paper 4 is a design guide to separating distances during construction - compiled and researched by the STA specifically for timber frame buildings in excess of 600m2 total floor areas.
It is recommended that timber frame design teams provide confirmation, as part of their CDM Regulation duties, that the appropriate assembly in the design submission complies with the category of timber frame required in the procurement documents, and that this is carried through to production drawings. Paper 4 provides a ‘proforma’ for self-certification on the assembly selection process and shows a diagrammatic flow chart of the steps in the process - from concept to the project starting on site. Section 4.3.2 Wall Assemblies – makes recommendations when specifying buildings boards.
CE Marking
A European Certification, CE Marking is a manufacturer's declaration that the product meets the requirements of the applicable EC directives in terms of safety, health and environmental requirements. CE Marked buildings boards appear under the harmonised standard of BS EN 12467:2012 – demonstrating that the manufacturer has checked that these products meet EU safety, health and environmental requirements is a key indicator of a products compliance with EU legislations and allows the free movement of products within the European market.
BBA Approval
And finally and most importantly - BBA Approval - which offers full technical approval for construction products, systems and is recognised by building control, government departments, architects, local authorities, specifiers and building insurers. BBA Approval provides reassurance to architects, designers and contractors when specifying or installing building board products.
APPROVAL INCLUDES:
• Factors relating to compliance with Building Regulations
• Factors relating to additional non-regulatory information
• Independently verified technical specification
• Assessment criteria and technical investigations
• Design considerations
• Installation guidance
• Regular surveillance of production
• Formal three-yearly review
Informative CPD Events
For those interested in finding out more, RCM provide informative CPD sessions including: a guide to materials, applications and specification considerations for building boards, internal and external linings and rainscreen facades, covering:
• What a specifier needs to consider
• Board materials and benefits
• Board applications
• Work on site
RCM’s BBA Approved Y-wall building board is a high performance calcium silicate based fibre cement solution. Y-wall meets all the criteria outlined in this article and offers excellent fire properties, as well as high strength levels and superior dimensional stability.
Y-wall is also widely used onto SFS framing to create load bearing and non-loadbearing fire walls – on all elevations and especially for buildings over 18 metres, where A1 non-combustible boards are becoming increasingly required.
For more details call 0845 1303725 or visit www.buildingboards.co.uk
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