Pilgrim’s Barn
Pilgrim’s Barn is an exceptionally energy efficient CLASS Q [i] residential development offering the best in passive solar building design.
The former chicken shed benefitted from Permitted Development Rights (Class Q) allowing a change of use (Planning Ref: DC/21/01912) to a 465m2 five-bedroom residential dwelling.
In October 2022, Pilgrim’s Barn in Suffolk achieved an exceptionally high SAP Rating of 134A, surpassing the average UK new dwelling SAP Rating of 83B according to the English Housing Survey. The SAP, or Standard Assessment Procedure, is the UK’s method for predicting a home’s energy efficiency and carbon mitigation, with the Energy Performance Certificate (EPC) as its output. To illustrate, a higher SAP Rating indicates greater energy efficiency and generally lower CO2 emissions during occupation. The main focus of this barn conversion was to achieve optimal energy efficiency through passive solar building design.
Another outstanding performance characteristic of Pilgrim’s Barn is its remarkably low Air Pressure Test (APT) of 1.9m3/h.m2 @ 50Pascals. In comparison, the UK average APT for new homes is 5m3/h.m2, which is required for compliance with Building Regulations under Approved Document Part L1A in England and Wales. To provide further clarity, the APT measures the air permeability of a building’s fabric, with higher air leakage leading to potential heat loss.
PASSIVE SOLAR BUILDING DESIGN
The home owners, Nick and Saffy Woolley, engaged design consultants Hockerton Housing Project (HHP) to assist in the detailed design of Pilgrim’s conversion. The HHP design team have a collective experience and knowledge from self-building HHP and twenty-seven years of living a near autonomous lifestyle in the UK’s largest collection of earth-sheltered dwellings. For this reason they were thought to be best placed for assisting with this project.
The design principles used at Pilgrim’s Barn are the same design principles applied at HHP by its Architects, Professor’s Brenda and Robert Vale, The Vale’s. The Vales work was first published in their 1975 book, ‘The Autonomous House’ and later implemented at their former Nottinghamshire home, ‘The New Autonomous House’
The building places passive solar building design at the heart of it strategy to achieve the very best in energy efficiency using green energy. In order to do this it captures the sun’s heat within the the dwellings elements and then releases the heat during times when the sun isn’t present. It does this whilst also maintaining a comfortable room temperature. As a result the building can rely entirely on green energy. The dwelling has several key features that allow for this, including the following.
- Southerly orientated glazing – triple glazing 8W/m2K
- Thermal mass superstructure – concrete floor and block walls
- Super-insulated envelope – better than Part L minimum requirements
- Renewable energy – 27KWpeak Roof Mounted (75no. panels) pv’s
- Energy Storage – Tesla Powerwall2 batteries
Triple Glazing
ENHANCED FABRIC INSULATION LEVELS
Enhanced fabric insulation levels are a key characteristic of Pilgrim’s Barn performance in reducing heating demand and tempering internal air temperature variation. Allied with roof mounted photovoltaics (pv’s) and energy storage (batteries), energy consumption for the 12months May 2023 to April 2024 were 10,800KWhrs (home) and 7,000KWhrs (EV cars).
Pilgrim’s building fabric comprises;
Floor – 300mm Jablite, 300mm reinforced concrete slab, resin bonded laminate floor finish.
Wall – Black painted vertical timber cladding, 100mm thermalite, 300mm Rockwall cavity fill, 100mm dense concrete, sand/cement render & skim.
Roof – Profile steel roof cladding, 440mm Celotex, plasterboard & skim ceilings.
Windows – Rationale external doors and windows, triple glazed 0.8 U-Value.
Space heating is provided by two sources but;
Space Heating
- Electric underfloor heating &
- MVHR Vent Axia 190W rating
Renewable Energy:
- 27KWpeak Roof Mounted (75no. panels) PV’s [58W/m2 Gross Floor Area]
- Tesla Powerwall2 Batteries,
- 8KW SolarEdge Invertors
- Zappy EV Chargers
Essential Resources
Pilgrim’s utility connections include, the National Grid and mains water supply.
Additional on-site resources include, rainwater harvesting and grey water harvesting. Waste water from Pilgrim’s is managed by an on-site Sewerage Treatment Plant, with filtering via a reedbed pond.
NOTIONAL BUILDING COMPARISONS
Pilgrim’s building element specification significantly out performs the UK Building Regulations ‘Notional Building’ (See Table 1).
Favourable comparisons in fabric heat transmittance (U-Values) to the Notional Building are up by 40% for its walls (0.1W/m2K). They are also up 30% for its floors (0.09W/m2K) and up 35% for the roof (0.06W/m2K).
The most significant improvement against the Notional Building is Pilgrim’s Air Pressure Test (APT), which recorded 1.9m3@50Pascals. Therefore this is a 62% reduced fabric air infiltration rate.
CONSTRUCTION COST FOR PILGRIM’S BARN
The reported build cost by the owners is £1,650 m² excluding the reedbed pond and wider landscape environs. This compares favourably with £2,000 m² for a conventional dwelling and £2,200m² for a Passive House.
BUILDING PERFORMANCE STATISTICS FOR 2023
Total solar pv generation for the 12months of 2023 was 26MWhr, the equivalent of 963KWhrs/KW/year, an exceptionally high annually pv generation rate for the UK.
The total home (including two EV cars) energy consumption was 18.5MWhr, circa 40KWhrs/m2 across gross building floor area.
The total energy imported during 2023 from the Grid was 8MWhr. This is the equivalent of 17KWhrs/m2, nearly double the total export to the Grid at 15.5MWhr.
The balance of energy exchange with the Grid was a surplus exported of 7.5MWhr, enough to power another similar home.
PROJECT SUMMARY
Pilgrim’s Barn offers a valuable insight in to how existing buildings can be upgraded to exceptional levels of energy efficiency at a commensurate cost to more conventional building specifications. Essential to that performance is an understanding of passive solar design techniques, the role of thermal mass and fenestration arrangements. Solar gains are encouraged in to the home. This therefore provides the means to conduct and store that ubiquitous heat source. This results in reducing the requirement for primary heating systems.
Pilgrim’s design solution was informed by over three decades of Hockerton Housing Project’s first hand experience, building and living a near autonomous lifestyle. Such is the legacy of its Architects, the Vales, a growing number of new and existing homes are now adopting the virtues of passive solar design principles.
[i] UK Government. 2015. The Town and Country Planning (General Permitted Development) (England) Order 2015.