Low energy extension
Green Building Company has just completed the construction of a single storey extension to a Victorian family house in West Yorkshire. The project created a new sun room/lounge, bedroom and shower-room using many of the Passivhaus principles the firm has developed at its pioneering Denby Dale Passivhaus project.
The extension is the second construction job undertaken by GBC for the family. About 7 years ago Green Building Company helped undertake a renovation of the house itself – involving extensive gutting of previous structure and replacement of services etc. Insulation was also carefully applied to roof and loft during the initial renovation.
Green Building Store’s Ecoplus high performance windows & doors had been installed in the existing home, with new Ecoplus3 triple glazed windows (Uw = 0.86 W/m2K) and French doors installed in the new extension. Owner William Young said of the Ecoplus3 window & doors: "We chose Ecoplus3 windows & doors to avoid PVC, for their thermal performance and to fit in with the old house features. They look fantastic and after our first winter frost this morning, they kept us nice and warm even though we have large floor to ceiling windows and french doors".
As the house is situated within a conservation area, there were a number of constraints in terms of shape and appearance of the new extension, such as requirement for a pyramid roof shape, limitations on the footprint of the extension and need for the extension to appear separate from the main building. Green Building Company Director Bill Butcher was keen to apply Passivhaus principles to the build, as far as possible, and worked with the project’s architect to change some of the detailing to reduce thermal bridging and improve airtightness of the project.
Green Building Company modelled the extension within Passivhaus Planning Package (PHPP) and, although the project did not quite reach Passivhaus levels of thermal performance,` did include detailing inspired by GBC’s experiences at Denby Dale Passivhaus. Detailing included: stringent airtightness detailing using Pro Clima products; positioning of windows within plywood boxes to improve the airtightness detailing; use of 200mm thick mineral wool wall batts in the masonry cavity walls; and use of Teplo Tie basalt cavity wall ties to minimise thermal bridging.
The project also featured an improvement to the ground floor to wall junction that had featured at Denby Dale – resulting in a completely thermal bridge free junction as well as offering excellent airtightness detailing. This was achieved by positioning the reinforced and edged thickened concrete floor slab on top of structurally-appropriate polyurethane underfloor insulation. As with Denby Dale the inner leaf concrete block wall was built off the slab. This approach thus avoided the need to take insulation down to the foundation footings and achieved a thermal bridge free tea-cosy effect ensuring continual insulation from floor to wall. The detailing was developed in conjunction with the structural engineers and was made easier as a result of being a single storey building. Bill Butcher commented: “We were pleased to be able to develop a thermal bridge free detail for the ground floor/ wall detail, improving upon the detailing at the Denby Dale Passivhaus. We would hope to develop the use of this detailing in other low energy masonry cavity wall projects in the future”.
Sketch of floor/ wall detailing - download pdf
Owner William Young said: “I undertake academic research on environmental businesses and as a family we are really committed to environmental issues so we were keen to support a local ethical business. Green Building Company’s workmanship has always been excellent and we have also really valued the company’s proactive approach. Bill, Jude and the team always try to actively solve problems and improve detailing – something that has not been my experience with other builders.
We are really happy with the new extension, which is really cosy and looks lovely - it is performing really well in this cold weather and has dramatically improved the quality of family life. Although it has used Passivhaus detailing, in appearance there is nothing unusual or untoward about it, which is also a bonus.”
Completed 2011
