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Guidance on Building Regulations - amendments to Approved Document B

Amendment to Approved Document B: November 2018

Guidance on how external walls can meet the Building Regulations requirement for resisting fire spread is set out in Approved Document B. Following the Independent Review of Building Regulations and Fire Safety, and subsequent Interim Report by Dame Judith Hackitt, the Government has introduced an amendment to the Approved Document B: Fire safety, which has a significant impact on the design and construction of buildings above 18 metres. Published in November 2018, the new regulations came into force on 21 December 2018.

Materials and workmanship

Regulation 7 of the Building Regulations relates to materials and workmanship and reads as follows:

  • 7. (1) Building work shall be carried out—
  • (a) with adequate and proper materials which—
  • are appropriate for the circumstances in which they are used.
  • (ii) are adequately mixed or prepared, and
  • (iii) are applied, used or fixed so as adequately to perform the functions for which they are designed; and
  • (b) in a workmanlike manner.

(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 Class A1, classified in accordance with BS EN 13501-1:2007+A1:2009 entitled “Fire classification of construction products and building 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.

Use of membranes as part of the external wall construction

It is important to note that with specific reference to membranes the Regulation provides an exemption and further clarification is found within Regulation 7, as stated below: 12.14 Particular attention is drawn to the following points. a. Membranes used as part of the external wall construction should achieve a minimum classification of European Class B-s3, d0

In summary, the amendment stipulates significant changes to which membranes can now be used and limits these to a rating of Class B,s3,d0.

The reason for this clarification is due to the complexity of manufacturing a non-combustible membrane which is still breathable to BS5250 standard, which cannot be achieved. Some European membrane products whilst quoting A2 ratings do not breathe or comply with BS5250, meaning using these membranes in the UK climate would make the building unhealthy and result in a much greater risk of condensation issues and mould growth.

Therefore Wraptite offers a safer and simplified membrane system, not only because Wraptite conforms with the required Class B rating, but also because it provides a lower calorific value being a fully adhered membrane, which bonds back to the substrate, making the calorific value significantly lower than standard mechanical/tape fixed membranes, and ensures a simplified design to airtightness and simple installation method.

High-performance off-site solutions

  • • Complies with use on buildings of high rise and over 18m under Part B amendments made in November 2018, Membranes need to be Class B,s3,d0 or better, with Wraptite at Class B,s1,d0*.
  • Included within BS8414 testing with cladding manufacturers.
  • EPDM not needed to the frame of the building as Wraptite is self-adhesive and continues across the whole envelope of the building against the sheathing board and the frame of the building.
  • Less EPDM around window details due to Wraptite lapping into the building at junctions
  • Corner detailing for opening and movement joint interfaces are easily treated.
  • Improved airtightness and may negate the use of a VCL totally from the design internally, meaning easier a quicker install of dry lining package
  • Hydro-Thermal Modelling (WUFI) showing the difference of not using a VCL within some constructions benefits the building further.
  • Improving airtightness may allow you to change thickness or type of insulation used when modelled through SAP or SBEM.
  • No need to tape sheathing boards as Wraptite is positioned across the whole board.
  • Testing has seen results as low as 0.5 m3 /(h.m2) @ 50PA carried out at Windtech on a window façade panel.
  • By using Wraptite on the external, this may show you an improvement on making the building watertight, allowing your cladding package to come off the critical path and internal works to start earlier, and also internal works may not be installing a VCL so the site program is potentially quicker
*tested over 12mm calcium silicate board / fibre cement board as per BS EN 13238:2010. All tests carried out to EN 13859-2 standard.

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