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Cavity trays and the ban on combustible materials in relevant buildings


BKE 3


BUILD ING KNOWLEDGE EX C HANG E


NonCom Cavitray with NonCom Weepvent


NonCom Weepvent -


one of four types of NonCom Weepvent manufactured by Cavity Trays


New construction projects in England with a storey 18 metres or more above ground level must now comply with new regulations. Subject to certain exclusions, materials or products used in the external walls plus any specified attachments must now be non-combustible when assessed under the European fire classification system. The regulation applies to ‘relevant buildings’, principally those containing one or more dwellings, a room for residential purposes, or an institution. The 18-metre rule currently applies in England, whilst in Scotland the figure is 11 metres or more above ground level.


WHAT CONSTITUTES AN EXTERNAL WALL?


Any reference to an external wall includes anything located within any part or any space within the wall.


Any decoration or finish applied to the external surface. Windows and doors in the wall.


Any part of a pitched roof (at an angle of 70 degrees to the horizontal) where the roof adjoins a space which persons can enter (but excluding spaces providing access for repairs etc only).


WHAT CONSTITUTES AN ATTACHMENT?


A balcony attached to an external wall. A solar panel attached to an external wall.


Any device for reducing heat gain (by deflection or shading) within a building which is attached to an external wall.


CAN ELEMENTS NOT FORM PART OF AN EXTERNAL WALL?


Despite the above qualifications of what constitutes an ‘external wall’ of a ‘relevant building’, there are some elements of an ‘external wall’ or ‘specified attachment’ that are excluded from the ban: A principal example is a cavity tray when used between two leaves of masonry. Conditional that both skins of the cavity wall are of masonry in the form of either brickwork, blockwork or concrete, cavity trays may be used in their usual form. Where both skins of a relevant building’ fall outside of this qualification, non-combustible trays must be used.


A spokesperson for Cavity Trays Ltd commented, “We have manufactured cavity trays that are non-combustible since the 1950’s, it is not a new phenomenon. In the 1970’s the Greater London Council (GLC) issued to Cavity Trays of Yeovil an Approval Bulletin - the first for cavity trays ever issued by the GLC - approving our cavity trays for use within the London Boroughs. Non-combustibility was one of the key considerations, recognising the proximity of buildings as well as the height necessitates caution and appropriateness of material choices at all times.”


Non-combustible trays are prefixed NonCom for easy identification, and manufactured from approved Class A1 and Class A2 non-combustible metals instead of conventional DPC material. A1 and A2 classifications are the highest material specifications available and comply with the requirements of The Building (Amendment) Regulations 2018. (materials which become part of an external wall are of European Classification “A2-s1, d0” or “A1”. (BS EN 13501-1:2007 +A1:2009 - fire classification of construction products and building elements).


Metal NonCom trays have the advantage of being robust and holding to shape. They are difficult to damage and importantly, they will not ‘feed’ a fire. They can fulfil the criteria demanded by the new regulations. Metal trays can also self-support, meaning trays can terminate in the cavity adjacent to the inner leaf, rather than having to enter into it or fix to it. Heat loss through thermal conductivity can thus be avoided.


Metal trays might not be appropriate in some construction configurations and/ or might be subject to manufacturing restraints.


Suitability with adjacent materials must always be established in terms of compatibility, analytic behaviour and structural integrity. Projects should be individually assessed.


Cavity Trays Ltd is the longest-established company within its’ specialised cavity tray field and will be releasing further NonCom solutions and product types during 2020.


CAVITY TRAYS OF YEOVIL


TEL: 01935 474769 13


(Our thanks to John Shillabeer, Cavity Trays of Yeovil, for this BKE article) WWW.CAVITYTRAYS.CO.UK


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