This was phase two of a multi-staged project to build new council homes on existing council-owned land. Typical sites for the project included disused garages and areas of waste ground between developments.
The dwellings were all built to Code Level 4 of the Code for Sustainable Homes. Although in advance of the existing building regulations, this objective fitted with the government aim of encouraging government agencies to increase standards of sustainability.
To achieve this rating, the construction elements needed a high level of thermal insulation. The Rå Build method using the H+H Thin Joint masonry system was specified using Jumbo Bloks. Fully filled cavities were combined with either aircrete or brick outer leaves.
This is not only an extremely fast and efficient method of building, but also provides substantial benefits in reducing heat loss. In designing the wall structure, the use of aircrete’s very low psi values, based on Accredited Construction Details, allowed a halving of the y-value from 0.08 to 0.04 W/m2K. This is used to calculate the impact of linear thermal bridging within SAP 2005. The 0.04 y-value is achieved by virtue of the thermal efficiency of aircrete, without the need to resort to Enhanced Construction Details, and has a similar effect on all external elements.
Wherever possible the contractors used aircrete for both leaves of the external walls in order to fully capitalise on the inherent thermal efficiency of aircrete. The outer leaf was then finished with a through-colour monocouche render.
High performance full-fill cavity wall insulation manufactured by Superglass was used in the 125mm cavity. The structural width of the whole cavity wall was no more than 325mm with a U-value of 0.19W/m2K using two Thin Jointed leaves of 3.6N/mm2 aircrete. However, taking into account the 0.04 reduction in the y-value meant that the walls effectively provided a U-value of 0.15W/m2K.
To complete the energy efficiency of the build, solar PV panels were used on the roof of the dwellings. It was necessary to include some renewables in this project to achieve Code 4 level, but the contractors did note that the very thermally efficient structure significantly reduced the PV requirement.