Gresford Architects Upgrades Oxfordshire Bungalow to EnerPHit Standard

Key facts

• Gresford Architects has retrofitted and extended a 1960s bungalow in West Oxfordshire to EnerPHit standards.
• The project retained the original ground-floor slab, foundations, and wall openings to reduce embodied carbon to 65 kgCO2eq/m².
• A lightweight timber first floor was added above, creating a 292-square-metre two-storey family home.
• External cladding was milled from western red cedar trees felled on site prior to construction.
• The building achieved an EPC band A rating, an airtightness of 1.14 m³/h.m², and operational energy of 77.82 kWh/m²/yr.

Gresford Architects has completed the deep retrofit and upward extension of a former bungalow in a rural hamlet in West Oxfordshire. The project transforms a neglected cruciform building into an airtight family home built to EnerPHit standards, retaining almost all of the original sub-structure and external walls.

What has been completed in West Oxfordshire

The project, known as Old Orchard, delivers 292 square metres of internal living accommodation across two storeys, expanding an original single-storey building that had stood vacant in recent years. Built under an RIBA Domestic Building Contract at a recorded construction cost of £3,092 per square metre, the scheme reached practical completion in April 2025, as first reported by Architects' Journal.

Rather than razing the building, the design team retained the original foundations, ground-floor slab, and masonry shell, using the footprint as a structural base. Above, a section of the 1960s timber roof structure was dismantled to allow for a new lightweight timber-framed first floor. This vertical volume runs along one wing of the property's original cruciform footprint, creating a two-storey house without expanding the built footprint into the surrounding garden.

On the ground floor, external structural modifications were limited to the replacement of a dilapidated conservatory. In its place, the practice introduced a contemporary glazed extension that opens onto an external timber-framed veranda facing panoramic views of the Thames Valley.

The background and retrofit strategy

The property occupies a plot in rural West Oxfordshire purchased by practice founder Tom Gresford and his wife Phoebe following the Covid-19 pandemic. The original dwelling was erected during the 1960s as a timber-framed bungalow and subsequently underwent several ad hoc extensions and alterations through the 1980s. When acquired, the layout was fragmented, but a structural appraisal verified that the underlying foundations and perimeter walls remained sound.

Choosing preservation over demolition aligned the project with the rigorous requirements of EnerPHit, the retrofit equivalent of the Passivhaus standard. In typical low-energy residential schemes across the South East, replacing post-war housing stock is often favoured for simplicity of detailing. Here, retaining the structure suppressed the scheme's actual embodied carbon to 65 kgCO2eq per square metre, substantially below standard benchmarks for modern one-off housing.

Upgrading the building envelope saw the Energy Performance Certificate rating shift from band D to band A. Operational energy performance is measured at 77.82 kWh per square metre per year, underpinned by an airtightness result of 1.14 m³/h.m² tested at 50 Pascals. The completed house has a projected design life in excess of 60 years.

The design, fabric and spatial layout

The external envelope incorporates high-performance external continuous insulation wrapped over the retained masonry and timber walls. This application produces exceptionally low area-weighted thermal transmittance values: 0.095 W/m²K on existing external ground-floor walls, 0.094 W/m²K on timber-framed ground-floor elements, and 0.097 W/m²K on the new first-floor walls. The new standing-seam powder-coated corrugated metal roof delivers a U-value of 0.067 W/m²K, while vaulted sections over retained roof rafters achieve 0.068 W/m²K.

The exterior is clad in western red cedar timber boards machined directly from trees felled on the site at the commencement of construction. Corrugated steel roofing references the vernacular palette of nearby agricultural barns, a technique also seen in other rural interventions such as a Studio Weave conversion on the Isle of Wight. Ground-floor window apertures were retained in their original positions, fitted with high-specification triple-glazed units. Southern and western windows incorporate integrated solar blinds within the glazing units to manage summertime heat gain.

Internally, non-loadbearing partitions were removed to establish an open ground-floor flow organised around discrete functional zones. Sliding pocket doors and colour-coded joinery volumes differentiate utility areas from primary living spaces. Mechanical ventilation with heat recovery (MVHR) supplies filtered, conditioned fresh air continuously across both levels.

On the new upper floor, bedrooms and bathrooms radiate from a central circulation spine finished in deep green joinery. Within the children’s bedrooms, mezzanine platforms provide raised play areas with interior cut-outs looking down onto the bedrooms and borrowed-light openings linking into the corridor. A hidden door within the hallway joinery provides access to an integrated slide descending between levels.

What the project team is saying

Describing the decision to preserve rather than rebuild, practice director Tom Gresford emphasised that reusing existing building stock delivers substantial environmental advantages, even when detailed envelope upgrades present technical challenges.

Retaining the slab, shell, and foundation structure prevented significant volumes of masonry from entering waste streams, while keeping door and window openings in their original coordinates minimized the need for structural lintel replacements.

Addressing the technical balance between heritage fabric and contemporary energy performance, Gresford explained that the process aimed at "extending the lifespan of the bungalow and upgrading this into a usable, resilient and comfortable home, with minimal environmental impact."

Specialist engineering input was provided by structural engineers engineersHRW and building services consultants Williams Energy Design. Studio 31 advised on landscape integration, AVINU delivered audiovisual systems, and Kitchen Architecture handled the bespoke kitchen joinery. Cook Brown acted as approved building control inspector.

What happens next

Following handover in spring 2025, Old Orchard serves as an occupied family residence and an operational test case for Gresford Architects’ research into deep residential extend and retrofit methods. The project contributes empirical data to current UK discussions regarding whole-life carbon accounting and rural housing decarbonisation.

With domestic heating representing a primary focus of UK building regulations updates, monitored data from the property’s continuous mechanical ventilation and thermal performance will be benchmarked over multi-season cycles. Similar fabric-first philosophies continue to gain traction among self-builders and private clients pursuing low energy and Passivhaus credentials across rural England.

Timeline

1. October 2023Construction work commenced on site in West Oxfordshire.
2. April 2025Practical completion achieved on the deep retrofit and extension.
3. May 2026Technical performance details published following post-completion occupancy.

Why this matters

Old Orchard demonstrates that unlisted post-war bungalows, which are frequently demolished across England's rural settlements, can be successfully repurposed into high-performance homes. By retaining the structural slab and masonry envelope while building an upper storey within a lightweight timber frame, the scheme delivers Passivhaus-level thermal efficiency at a modest embodied carbon figure of 65 kgCO2eq/m². It establishes a viable precedent for whole-life carbon reduction in one-off residential projects.

Questions answered

what standard was the oxfordshire bungalow retrofitted to

The project was designed and built to the EnerPHit standard, the official Passivhaus certification pathway for retrofitted existing buildings.

who designed the old orchard retrofit in west oxfordshire

Gresford Architects designed the retrofit and extension as a private residence for practice founder Tom Gresford and his family.

what materials were used on the exterior of the house

The exterior features powder-coated corrugated steel roofing and timber cladding sourced from western red cedar trees felled and milled on the property.

how did the architect minimise embodied carbon during construction

The team preserved the existing foundations, concrete floor slab, and perimeter walls, avoiding wholesale demolition and limiting embodied carbon to 65 kgCO2eq/m².

what is the energy performance rating of the completed home

The property was upgraded from an Energy Performance Certificate rating of band D to band A, with an operational energy demand of 77.82 kWh/m²/yr.

did the bungalow footprint expand during the retrofit works

The ground-floor footprint remained virtually unaltered, with extra living space created by adding a timber-framed upper floor over one wing of the cruciform structure.

Source: originally reported by Architects' Journal.