A priority for James and Debbie was that the building should be low energy and include natural materials, with minimal embodied energy, where possible.

Firstly, we decided that the structure should be timber frame. We looked at a number of different timber frame systems but decided that an I-beam was the best solution as it has less timber than a standard timber stud. The structural timber parts are smaller, and the thin web of the beam reduces the thermal bridge from outside to inside. James and Debbie visited the PYC Construction factory in Mid Wales and saw how the insulated panels are constructed. They then visited the BUILD-A-KIT factory in Nelson, Lancashire, where Bill Richardson has developed a panel system for low-energy and Passivhaus buildings, using mineral wool insulation between 300mm deep timber I-beams. 

The advantage of using a natural material like Rockwool mineral wool is that it creates a breathable construction. It has great thermally insulating properties, it is inherently fire resistant, it is an acoustic insulation, but it is also vapour permeable. The BUILD-A-KIT panels have factory fitted Pro Clima Intello Plus vapour control membrane on the inside of both the wall and roof panels.

Intello Plus vapour control membrane is a climate-controlled membrane. The fleece membrane provides a seal against moisture in winter, but in summer, the molecular structure becomes more open to allow drying to the inside. This protects the timber structure from moisture damage or mould growth within the panels.

The outside of the BUILD-A-KIT panels are clad with Panelvent board and covered with a breathable membrane. Panelvent is a structural fibreboard, used as a sheathing board, which is also vapour permeable. The boards have a natural wax additive so, in certain circumstances an additional breather membrane is not required. As James and Debbie wanted timber cladding as an external finish, which will act as a rainscreen, the additional breather membrane was required.

Preferring to use natural materials as much as possible, James and Debbie looked at different timbers for the external cladding. After seeing a timber clad house, they decided on Cedar. The natural oils in Cedar make it resistant to rot and insect damage. It is low maintenance and will shrink and swell less than other timbers. When left untreated, Cedar will gradually weather to a silver grey colour.

The windows and doors are all timber. After visiting a house building exhibition, James and Debbie met Mike Shufflebotham from 21 degrees, formally Green Building Store. 21 degrees manufacture a range of triple glazed, air tight windows for Passivhaus projects. Timber windows have a lower carbon footprint than alu-clad windows. They can last for decades when properly maintained. They can be easily refurbished or repaired to extend their lifespan and reduce the need for replacement. Lancaster Passive House windows are finished in a mid grey colour which will sit well with the Cedar cladding as it weathers.

As this is a low energy house, James and Debbie wanted to include Photovoltaic (PV) panels on the roof. James didn't want just a patch of PV panels surrounded by slate. The roof had to look uniform, so it was decided to cover the the south facing roof with as many panels as possible. The panels sit within a perimeter metal edge, which is powder coated to match the ridge capping and the gutter.

The rear, north facing roof is cover by a blanket of Sedum.  The "Riefa Green Roofing" system was provided by Paul Gilby from nearby Halton. Sedum requires very little maintenance but as the roof slope is 30 degrees, the water tends to run off quite quickly. A water irrigation system under the Sedum makes sure it can be evenly watered after a long dry spell.

Inside, James and Debbie have continued to use natural materials. The majority of the ground floor has engineered Oak flooring over insulated underfloor heating boards. The stair and balustrading, manufactured and fitted by Mike Jackson of MDJ Staircases Ltd, are solid Oak.