Designed by Francesco Pierazzi Architects, Sawtooth House transforms an ageing rear extension to a Victorian property in Kingston upon Thames, south-west London, into a more energy-efficient and adaptable family home. Rather than pursuing substantial additional floor area, the project adds only 15 square metres to the existing building while undertaking a broader retrofit of the original house. The resulting 180-square-metre residence demonstrates how targeted additions can be combined with improvements to the existing building fabric to reduce operational energy demand and extend the useful life of established housing.
The architecture also draws on Kingston’s industrial history: its distinctive double sawtooth roof references Kingston’s former manufacturing buildings, including nearby Middle Mill, while bringing controlled natural light into the interior.
Retrofitting the existing house
Retention of the Victorian property forms the starting point of the environmental strategy. Instead of replacing the existing building, the project upgrades its performance while concentrating new construction where it delivers the greatest functional benefit. The thermal envelope is upgraded with insulation, reducing heat transfer and lowering space-heating demand. Improvements to the fabric are supported by high-performance glazing, including aluminium windows and sliding doors, alongside bespoke roof windows.
The sawtooth roof helps bring daylight into the depth of the plan. Its north-facing rooflights provide relatively even illumination while limiting the direct solar exposure associated with other orientations. Together with strategically positioned windows, this reduces dependence on artificial lighting and establishes visual connections with the garden and mature vegetation.
An all-electric energy strategy
Mechanical systems were selected to complement the improved envelope. A Mitsubishi Electric Hydrolution air-source heat pump supplies heating and domestic hot water, replacing fossil-fuel-based systems with an all-electric alternative. A mechanical ventilation with heat recovery system provides controlled fresh air while recovering heat from outgoing air. This combination supports indoor air quality without compromising the energy savings achieved through improved airtightness and insulation.
The house uses renewable electricity. According to the project figures, operational carbon emissions were reduced from approximately 30.09 kg CO₂e/m²/year before renovation to 13.63 kg CO₂e/m²/year after completion. With electricity supplied from renewable sources, the project reports effectively zero operational emissions.
Managing water and landscape
Water conservation forms another component of the retrofit. A 7,500-litre GRAF Platin underground rainwater harvesting tank collects runoff for garden irrigation, reducing demand for mains water during drier periods. This strategy also supports the retention of the established garden, which is integral to the spatial experience of the house. New openings frame existing vegetation, including a mature maple and yucca, rather than treating the landscape as a secondary element of the extension.
Materials with a long service life
Externally, Wienerberger Smeed Dean Weathered Yellow Stock bricks are laid in varying bonds, relating the addition to both the Victorian house and the area's industrial architecture. The use of brick provides a robust, low-maintenance envelope intended for long-term exposure.
Inside, oak joinery, timber flooring, and terrazzo surfaces establish a similarly durable material palette. Bespoke storage is integrated into the architecture, allowing the relatively modest increase in floor area to accommodate changing family requirements efficiently.
Material impacts have also been quantified. The renovation has an estimated embodied carbon footprint of 20.51 tonnes CO₂e, or approximately 114 kgCO₂e/m². Based on the project's calculations, this initial carbon investment is expected to be recovered through operational carbon savings in less than seven years.
