Lucy took the plans to a meeting with the planner in late March. The parish council approved the design in April but we didn’t receive our final Notice of Decision from the planner until the middle of June 2013.
This meant it had taken 26 weeks from our initial submission for our plans to be approved.
We instructed our solicitor to purchase the plot. This was completed in late August 2013 but we had to wait until we had sold our house in Kendal before proceeding with detailed construction drawings and starting on site.
However, we were able to make progress with decisions about the build and heating strategy.
Masonry or timber frame
The 40 passive houses at Lancaster co-housing were built successfully using a masonry construction so it was tempting to go down this route.
However, Andrew had other clients, Tim and Sarah, who were building to passivhaus standards using a timber frame construction. We were able to visit their site as the frame was being assembled. We liked the idea of a frame being made in factory conditions with the insulation and airtight membranes in place before delivery to the site.
We engaged a firm of quantity surveyors to make two estimates of the building cost, one based on masonry construction and the other based on timber frame. The masonry construction was less expensive but not to the extent that it dictated the decision.
We had already talked to a local frame manufacturer, Trevor Lowis from Eden Insulation based in Appleby, about 5 miles from our site. Eden Insulation had completed two energy efficient frames utilising a ‘fabric first’ approach on the site at Crosby Ravensworth but neither home had attempted to achieve the passivhaus airtightness standard. However, Trevor was confident that the standard could be achieved and he was happy to take on the role of airtightness champion for the build.
The decision was made. Stoneworks Garth would be a timber frame construction from Eden Insulation.
Heating and ventilation strategy
We appointed Alan Clarke of Elemental Solutions to help with the heating and ventilation design and to carry out our PHPP analysis.
Stoneworks Garth is not on mains gas so heating strategy was something we were concerned about. The decision came down to a choice between LPG and an air source heat pump (ASHP). The initial costs were lower for the former while running costs are lower for the heat pump.
The predicted Coefficient of Performance (CPO) for the heat pump was at a level where the CO2/kWh for the two strategies were about the same. This would move in favour of the heat pump if, in the future, CO2/kWh for the UK grid improved. LPG also had the disadvantage of requiring regular deliveries of cylinders, estimated at 6 per year.
The south-facing roof was ideal for solar capture and we considered incorporating both solar PV and solar thermal. However, working with Alan, we decided that the simplest strategy was to install only solar PV. With the output from the PV feeding the heat pump, this was predicted to provide us with free domestic hot water (DHW) for 6 months of the year.
We decided to use a Viessmann 3kW air source heat pump with 4kW of Romag integrated solar tiles on the roof.
Firewood is readily available locally so we decided to also install a Morso S11 wood-burning stove. As well as looking cheerful, this would provide a backup in the event of power cuts. Although the S11 is not marketed as a passivhaus stove it has a suitable low output (2-4kW), the option of an external air supply and Alan had experience of using them successfully in previous projects.
A Paul Novus 300 mechanical ventilation and heat recovery unit (MVHR) was selected for the ventilation.