Prior to the latest revision of Part L, heat loss through party walls had not been considered as it was thought that the loss would be insignificant. However, research on completed homes showed that the heat loss was in fact the equivalent of having a wall U-value of 0.5W/m2K.
Approved document L1A gave guidance on how to design for this aspect: edge sealing combined with fully filled cavities will have a U-value of zero. Cavity fill materials such as blown fibre or mineral batts provide an adequate solution.
A question mark remained, however, over the acoustic performance of such structures. The aircrete industry has been researching the issue and third party verification has now been obtained, with the results incorporated into the existing Robust Details.
Following this process, the aircrete Robust Detail constructions for all traditional and thin joint construction can incorporate mineral insulation with a maximum density of 40kg/m3; this may be in the form of blown fibre, batts or rolls such as Isover Rolls. The revised Robust Details were published in October 2011.
With the introduction of more stringent requirements for the assessment of energy loss at junctions, the benefits of H+H party walls can be used to significantly reduce energy and carbon emissions from the head and base of the wall over other forms of construction. Our technical department can carry out these assessments and provide clients and designers with the information.