Three Passivhaus projects: Hattie Hartman on Mole Architects’ Hindolveston Road Housing
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Mole Architects’ Hindolveston Road Housing for Broadland Housing Association in Fulmodeston was developed as a prototype to test the viability of Passivhaus to deliver affordable housing. Part-funded by Norfolk County Council, a key part of the brief was to develop a housing type that could help alleviate fuel poverty in an area of northern Norfolk where the holiday letting market inflates housing prices.
A total of eight units in Fulmodeston and in another nearby village were built, with four built to Passivhaus standard (only two are certified) and four achieving Code for Sustainable Homes Level 3, with a cost premium of 24 per cent for the Passivhaus units. The scheme was Mole’s first foray into Passivhaus, as it was for the client, the contractor and the subcontractor supplying the SIPs panels.
The decision to go for Passivhaus was taken late after planning was achieved. This made it more difficult to accommodate the increased wall thickness, achieve a continuous airtightness barrier and eliminate thermal bridging, because these aspects had not been considered early on.
‘Everything worked on paper but, when you start dealing with thickness of materials and membranes, it’s not easy to achieve complete continuity,’ explains project architect Ian Bramwell.
What distinguishes Hindolveston Road Housing is creative use of local materials including naturally finished timber boards, brick, and black clay pantiles.
The houses proved so energy efficient that no central heating system was necessary. Monitoring equipment installed in December 2013 proved faulty, but has recently been corrected and monitoring is now under way.
The four houses at Fulmodeston, two certified to Passivhaus standard and two built to identical standards, were constructed from a panelised SIP system, Sigma II, manufactured by Stuart Milne. The system consists of 235mm cavity filled with EPS beads. The studwork is thermally broken and two 63x63mm studs are connected by an OSB fin with 9mm OSB sheathing lining the exterior of the panels.
Achieving a consistent air barrier was a challenge and involved considerable pre-construction analysis of the manufacturers’ drawings. Specific issues surrounded the installation of the floor cassettes, which sit upon the ground floor walls. In this area the airtightness membrane had to be installed as the cassettes were lowered into place, and the line of the airtightness barrier moves from lining the internal face of the panels to wrapping around the end of the floor cassettes externally.
Extreme care was necessary in order to avoid puncturing these barriers while the floors were installed. Frequent air tests allowed any damage to be identified and rectified prior to being concealed with further construction.
Ian Bramwell, senior sssociate, Mole Architects