The Cowshed

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Address: The Cowshed, Ashurst Lane, Plumpton, East Sussex, BN7 3AP. 
Owners: Ruth and Mark Segal
Type: New build
Age: under construction
Walls: I-beam timber construction

Opening Times

Sunday 16th October
Sunday 23rd October


Airtight construction
Natural materials
Solar PV (4kWp)
Superinsulation (woodfibre)
Timber construction
Ground Source Heat Pump (Boreholes)
High performance double glazing
Underfloor heating
Woodburning stove


Ruth and Mark bought this site in 2013, with existing permission to convert the cowshed and outbuildings to residential. However, the design was ugly and unworkable, so they collaborated with local architect Sally Williams to produce a design for a far more practical and handsome new build timber building to the highest standards of sustainability. Despite oppostion from the planners, support from neighbours and the inspirational design won over the planning committee and building eventually began in March 2016.

The site is just south of Plumpton racecourse overlooking the South Downs and the house has been designed to be very low energy, both in the energy needed to run it and embodied in its construction. The building uses mainly natural materials and has a 500mm thick heavily insulated walls with an I-beam structure, which is infilled with loose woodfibre insulation and clad externally with woodfibre board insulation beneath the attractive oak finish. Even the roof uses natural materials, with its cedar tiling.

Heating also uses natural resoures, being supplied by a ground source heat pump extracting heat from two deep boreholes. The electricity used to run this is largely offset by the 4kW of solar panels on the roof, which generate over 4000kWh pa.

Eventually the house will switch to its own well water which can be easily treated to meet all needs.

Construction:- The walls are 500mm thick clad in green oak shiplap. To minimise thermal conduction through the timber frames, 300mm "I" beams are used, the 50mm square plywood ends to the beam providing the strength and the thin MDF sheet between them providing stiffness needed without giving much of a thermal path through the wall. As a result, at least between the plywood ends, the loose wood fibre insulation occupies nearly all of the wall area. Even the minimal thermal path through the “I” beams is reduced by an external cladding of 60 mm Stieco compressed wood fibre cladding under the shiplab. The result is a remarkably low value U value for the walls of 0.111 W/m²K   compared to the maximum allowed by the building regulations for new buildings 0.3 W/m²K  

The roof is covered in cedar shingles above 300 mm of Stieco insulation and achieves a U value of 0.127 W/m²K, again way below the regulation maximum

The floor has 150 mm of polyisocyanurate foam under a reinforced 65 mm concrete screed with the underfloor heating pipes embedded in it and an aluminium spreader plate between the pipes. This is covered with oak laminate flooring or ceramic tiles in wet areas.

The windows are  double glazing with e-coated glass  with a 20 mm argon filled gap. This should give a U value of 1.1 W/m²K at the centre of the pane. Aluminium frames are used for the glazing units but to stop this causing thermal leaks at the edges the metal frames are set against deep wooden frames.

Heating uses an  A+++ rated 8 kW Nibe F1145 ground source heat pump. The land area of the site is  limited which made it difficult to get good performance from ground pipes near the surface. Instead pipes in vertically drilled holes were used. Two 100 m deep vertical boreholes each containing a single loop of 40 mm polythene pipe with the borehole backfilled with bentonite clay thermally enhanced with graphite.  Vertical pipes achieve better performance than near surface ones as they stay warmer especially when heating is needed most. The water returned from them will stay warm even in the deepest and most prolonged frost. They are however more expensive.

The combination of deep vertical pipes, an extremely efficient heat pump and a high specification underfloor heating system should result in a average coefficient of performance of 5. That is 5 kW of heating for every 1 kW of electricity used to drive the system. The house is heated on both floors by the underfloor heating. A wood burning stove provides back up heating. The heat pump also heats the domestic hot water tank which has a back-up immersion heater.

Electricity is generated by 16 all black monocrystalline photovoltaic panels of 250 W rating, Intenergy type INE-250MB-60, these provide a 4 kW system which is expected to generate 4400 kWh a year of electricity. This is equivalent to the average domestic consumption of electricity in this area and is about a third of the estimated annual energy consumption of 13,200 kWh per year.

This annual energy consumption of 13,200 kWh is about 83% of maximum that the building regulations  mandate for a building this size.

The photovoltaic panels are set into the south facing side of the roof and form the roof here rather than sit on the roof. A trough mounting system made by the French company GSE

LED lighting is used throughout.

There is a pond in the garden of about 80m² that the owners have made watertight and hope to improve to be an ecological haven.

Getting there: The postal address is Ashurst Lane, but this is shown as Streat Forge on some maps. This runs westard from Plumpton Lane, just south of Plumpton racecourse and is not signposted, but is just marked "Plumpton Racecourse". Follow the road, ignoring the turning to the racecourse, until it narrows and the Cowshed is on the left.


Architect: Sally Williams, Ditchling.
Builder: Dermot Burton, Westmeston.
Heat Pump: A Greener Alternative, Shoreham.
Boreholes: Nicholls Boreholes Ltd.
PV Solar: Clear Sky Energy, West Sussex.