FIS-BP-Guide-Through-Wall-SFS

DESIGN PROCESS

Other materials used in conjunction with through- wall may have an impact on compliance with Building Regulations and guidance.: • An air and vapour control layer (AVCL) may not be required as part of the test evidence for the through-wall but may be a requirement for the performance of the external wall system. Where installed, it should be B-s3, d0 or better when in a relevant building. • A breather membrane may not be required as part of the test evidence for the through-wall but may be a requirement for the performance for the cladding system. Where installed, it should be B-s3, d0 or better when in a relevant building. Note: the warranty provider may have different minimum requirements for AVCL and breather membranes. • Flexible seals used between windows and the external wall construction – EPDM (ethylene- propylene diene monomer rubber) seals do not satisfy Regulation 7 (2), which requires materials that become part of an external wall to achieve a fire classification of A2-s1, d0 minimum. (2) 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 BS EN 13501-1:2007+A1:2009 entitled “Fire classification of construction products and building

(3) Paragraph (2) does not apply to – (a) cavity trays when used between two leaves of masonry; (b) any part of a roof (other than any part of a roof which falls with paragraph (iv)

of regulation 2(6)) if that part is connected to an external wall;

materials used below ground level;

(f) intumescent and fire stopping materials where the inclusion of the materials is necessary to meet the requirements of Part B of Schedule 1; (g) membranes; (h) seals, gaskets, fixings, sealants and backer rods;

Extract from Regulation 7 (3)

The government approved guidance below confirms that the membranes exemption in paragraph (3) means that membranes are only excluded or exempt from the A2-s2, d0 requirement and not exempt altogether. Membranes are required to achieve B-s2, d0 minimum.

10.15 Particular attention is drawn to the following points.

a. Membranes used as part of the external wall construction above

ground level should achieve a minimum of class B-s3, d0.

elements. Classification using test data from reaction to fire tests” (ISBN 978 0 580 59861 6) published by the British Standards Institution on 30th March 2007 and amended in November 2009.

Extract from Approved Document B Volume 1– B4 Clause 10.15

Designers might consider using point (g) in paragraph (3) to re-classify membranes that create a seal as ‘seals’. The regulations should be followed and not interpreted, so that a specific component is not re-classified when mentioned within the regs – for example, ‘defining an EPDM membrane as a seal’ or ‘classifying the membranes as part of the window’ – in order to circumvent the regulations.

Extract from Regulation 7 (2)

Regulation 7 Paragraph (3) lists the exemptions from paragraph (2) for the A2-s1, d0 requirement. Point (g) specifically refers to membranes. However, this does not mean that membranes are entirely exempt – for clarification, we need to go to AD B point 10.15.