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The definition of an external wall in the Building (Amendment) Regulations 2018 (England) and the Building (amendment) (Wales) Regulations 2019, changed to include ‘any decorative or other finish applied to an external wall’.
Approved Document B defines a cavity barrier as, “A construction within a cavity, other than a smoke curtain, to perform either of the following functions.
Therefore, to satisfy Building Regulations there should be cavity barriers installed in the cavity formed behind a ‘decorative cladding’ (such as timber boarding, hung slates or tiles etc. or any other finish) which is constructed onto the outside of an external wall masonry wall.
This will include concealed spaces behind cladding on detached houses as well as semi-detached and apartments/flats.
Cavity barriers to concealed spaces behind external decorative claddings should be located in the following locations:
The following should be adhered to when specifying cavity barriers:
In England, Wales and Northern Ireland, cavity barriers should, meet the following performance requirements, 30 minutes for Integrity (E30) and 15 minutes for insulation (I 15).
In Scotland, Technical Handbook – Domestic confirms horizontal and vertical cavity barriers should achieve short fire duration (30 minutes integrity – E 30).
Proprietary cavity barriers must be supported with suitable third party test evidence to show that the minimum periods of fire resistance are achieved in accordance with the regional Building Regulations.
Decorative cladding on the external face of a masonry substrate should always have a drained and vented cavity behind. The following sections will discuss one way of maintaining the drained and vented cavity behind whilst meeting the requirements of Approved Document B for fire safety.
Fibre cement and timber cladding boards
Fibre cement and timber cladding boards are traditionally fixed to ‘vertical’ support battens in order to provide a drained and vented cavity. The use of ‘open state’ or intumescent variety as mentioned above can help maintain the drained and vented cavity whilst closing the cavity in the event of a fire.
Hung tiles are traditionally fixed onto horizontal support battens. Where hung tiles are used in small areas (e.g. between windows or as a gable feature), the horizontal battens limit the spread of smoke and fire and in these situations, no additional barriers are required, however the following conditions should still be satisfied:
This technical document has highlighted the requirement for cavity barriers to conceal spaces behind external cladding on masonry external walls. People responsible for building work (designer, builder, site manager, installer etc.) must ensure that the work complies with all relevant requirements of the Building Regulations.
Please note: approval from both your Warranty Provider and Building Control Provider would need to be gained individually. Approval of a product from either party does not automatically guarantee approval from the other. Engagement with both parties is recommended as early as possible.
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Every care was taken to ensure the information in this article was correct at the time of publication (April 2022). Guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. For the most up to date Premier Guarantee technical guidance please refer to your Risk Management Surveyor and the latest version of the Premier Guarantee Technical Manual.