Cameron Close is a Passivhaus development of 16 semi-detached houses and 12 sheltered accommodation apartments for Southern Housing Group in the rural village of Freshwater, Isle of Wight.
Southern Housing Group did not initially set out to develop a Passivhaus scheme. The low energy development replaces a sheltered housing scheme that had previously occupied the site, but which had reached the end of its life. For its replacement Southern Housing wanted to meet the higher levels of the Code for Sustainable Homes without having to rely on micro-renewable technologies so it looked at a fabric first approach embraced by Passivhaus. “This wasn’t innovation for innovation’s sake – it was a means to an end,” says Andrew Hulmes, Area Development Manager, Southern Housing Group.
A Passivhaus must be built according to principles developed by the Passivhaus Institute in Germany. These seek to minimise the need for space heating on the principle that reducing heat losses to a minimum is the most cost-effective and most robust way of achieving a low carbon building.
The low energy scheme has been constructed using H+H’s Thin-Joint system of aircrete blocks and Celfix Mortar. The blocks were laid by two gangs of four bricklayers. “We had not used Thin-Joint before but that did not pose any problems” says David Harris, director of Stoneham Construction. He estimates the Thin-Joint system was 20% faster to install than traditional blockwork.
The external solid walls are constructed from 200mm-thick aircrete blocks.
The separating walls were of twin leaf construction using 100mm-wide Thin Joint aircrete blocks separated by a 100mm cavity filled with insulation. This form of construction gives an average airborne sound insulation level of 57dB D DnT,w +Ctr.
“In our view Passivhaus is made simpler when constructed from masonry rather than timber frame,” says David Harris, Director of contractor Stoneham Construction
All units achieved an airtightness level of less than 0.6 air changes per hour at 50 Pascals. The homes are currently being certified to Passivhaus standard and so far all have complied with the strict airtightness levels demanded by the standard.
“Passivhaus is all about air tightness so if you can reduce the gap between blocks to 2mm instead of 10mm it makes life a lot easier,” he adds.
Graham Keenor, H+H Development Management said: “Not only did Stoneham have to understand Passivhaus in great detail; the Thin-Joint building system was also new to them. I made many visits with our demonstrator and trainer to provide support and guidance. “Achieving Passivhaus requires an exacting and meticulous approach but the use of a solid aircrete frame using Thin-Joint meant at least the construction process itself was simplified. The external and separating walls were installed straight to storey height and were immediately stable allowing early installation of retrofitted hangers and joists for the houses and precast concrete planks for the apartments”.