MIMA, the Mineral Wool Insulation Manufacturers Association, has launched a design guide on how to eliminate thermal bypassing in party cavity walls, utilising mineral wool insulation solutions. The guide has been produced in response to the October changes to Part L of England and Wales’s Building Regulations and Section 6 of Scotland’s Building Standards. The guide details the construction of party cavity walls (referred to as separating walls in Section 6) to achieve an effective U-value of zero without compromising the acoustic performance.
The revisions to Part L and Section 6, for the first time recognise that where party cavity walls between connected buildings are untreated, considerable heat can escape through them. As a result, in order to achieve a U-value of zero, new requirements call for new-build party cavity walls to be built with an effective combination of full fill insulation material and edge sealing. For this to be fully effective, the insulation material must be in full contact with both leaves of the party wall as built.
The heat lost from party cavity walls was previously thought to be zero. However, extensive research conducted by the Centre for the Built Environment at Leeds Metropolitan University on both masonry and timber framed construction has identified that heat is drawn from the habitable space and dissipated through an empty party wall cavity primarily into the roof space, but also into external wall cavities and voids below suspended floors and out of the building. Developers will clearly require solutions that provide a robustly proven zero U-value solution to Party Wall Bypass, that also meet the requirements of Part E1: Protection against sound from other parts of the building and adjoining buildings.
Independent tests have shown that if the cavity is completely filled with mineral wool insulation combined with sleeved, flexible mineral wool cavity barriers at the edges of the cavity (edge sealing), a U-value of zero is achieved without compromising acoustic performance. A number of the solutions in the guide have been approved as Robust Details and can therefore be used to comply with the requirements of Part E1 in England and Wales.
Providing comprehensive constructional diagrams for both timber frame and masonry cavity wall constructions, MIMA’s guide clearly and effectively sets out the thermal and acoustic requirements - and mineral wool solutions to them - for specifiers and developers alike.
Crispin Dunn-Meynell, General Secretary at MIMA comments: “At a time when it is becoming increasingly important for specifiers, developers and contractors to fully understand and adhere to the new Regulations for the UK, the technical guide is an invaluable tool.
“MIMA has been instrumental in bringing to the fore the significant effect thermal bypasses can have on the energy efficiency of buildings separated by cavity party walls through the numerous independent site trials conducted. The publication of this guide continues MIMA’s commitment to improving the built environment, in this instance by providing clear ‘how to comply’ guidance, supported by practical and cost-effective solutions.”