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TRADA Technology Ltd has warned that the thermal performance of party walls will have to be considered for the first time when the revised version of Approved Document L (ADL) of the Building Regulations England & Wales (Conservation of fuel and power) is released later this year.
Lewis Taylor of the company’s Building Performance Division, said: ‘To date, the thermal performance of party walls has been deemed to be “perfect”, that is with a U-value of 0W/m2K. In reality, this is far from true. Movement of air within the party wall cavity can transport heat away from the structure, leading to far greater energy use than anticipated or desired.’ If the proposed inclusion of party wall thermal performance in ADL goes ahead, building designers and fabricators will have to review their approach, he believes. ‘It will encourage the use either of solid party walls or cavity party walls with thermal insulation fully filling the cavity.’ Both options will eliminate the movement of air within the party wall structure and so reduce heat loss. He added, ‘If a non-insulated cavity party wall is used, whether timber, masonry or steel, with no perimeter sealing and a free flow of air in and out of the cavity, an assumed U-value of 0.5 W/m2K will need to be applied. This will have a massive effect on the calculated thermal performance of, for instance, terraced houses, where more heat could be lost through the party walls than through external walls.’ Timber frame buildings typically use cavity party walls. At present, most of these walls will contain some acoustic insulation between the studs. ‘In future, we may see the inclusion of full-fill thermal insulation to party wall stud voids and cavity. Edge-sealing is achieved at present with the use of cavity barriers for fire. The use of these cavity barriers and any additional sealing measures required, as well as additional insulation, should ensure that timber frame buildings can continue to assume a party wall U-value of 0 W/m2k. |
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