Sefton Retrofit

Design Approach

The project adopts a context-led and performance-driven methodology, shaped by both the client brief and the inherent qualities of the existing building. Detailed analysis of orientation, historic fabric, and the relationship between the house and its garden informed a series of measured interventions. Rather than imposing a singular formal gesture, the design evolves from the constraints and opportunities of the site, with an emphasis on environmental responsibility, long-term durability, and reduced operational demand.

Thermal Retrofit

Constructed over 130 years ago, the building retains solid masonry walls, single-glazed windows, and open fireplaces - features that contribute to its character but fall short of contemporary thermal performance standards. The retrofit strategy therefore prioritises a fabric-first approach, recognising that the reduction of heat demand is fundamental to lowering operational energy use.

Thermal upgrades were implemented through a combination of internal and external insulation, carefully calibrated to balance performance with conservation. External insulation was applied to less sensitive rear elevations to improve overall envelope efficiency, while internal insulation to the principal façade allowed the retention of its historic appearance. These measures were complemented by improvements to airtightness and the introduction of high-performance windows and doors, significantly reducing uncontrolled heat loss and enhancing internal comfort.

Connection to Landscape

The original layout offered limited engagement with the garden, both visually and spatially. The reconfiguration establishes a more direct and continuous relationship between inside and outside, enabling the landscape to become an active component of daily occupation. Enlarged openings and glazed doors frame views and provide access, while roof overhangs mediate the threshold between interior and exterior. These elements provide shelter from rainfall and act as passive shading devices, limiting solar gains during the summer months.

Light and Solar Response

Natural light is treated as a primary design material, with interventions aimed at maximising daylight penetration while carefully managing solar gain. During winter, low-angle sunlight is allowed to extend deep into the plan, contributing to passive heating. In contrast, summer conditions are moderated through fixed shading elements that reduce the risk of overheating, ensuring a more stable internal environment throughout the year.

Natural Ventilation

The environmental strategy relies on passive systems wherever possible. Natural ventilation is facilitated through the careful positioning of operable openings, enabling cross-ventilation across the plan. In addition, the vertical organisation of spaces supports stack-driven airflow, drawing cooler air from the garden level through the building and exhausting warm air at higher levels. This approach is particularly effective in dissipating heat during summer evenings, reducing the need for mechanical cooling.

Operational Carbon

The transition to low-carbon energy systems is integral to the project’s long-term performance. With the continued decarbonisation of the UK electricity grid, the building is designed to operate without reliance on fossil fuels. An air-source heat pump provides space heating and hot water, supported by energy-efficient appliances and reduced overall demand through passive design measures. Together, these strategies substantially lower operational carbon emissions.

Embodied Carbon

In parallel with operational considerations, the project addresses embodied carbon through careful material selection and construction methods. Preference is given to renewable and low-impact materials, including timber and bio-based insulation, while the use of carbon-intensive materials such as steel and concrete is minimised. Where possible, reclaimed and reused elements are incorporated. These decisions are informed by whole-life carbon assessment, ensuring that environmental impact is evaluated across all stages of the building’s lifecycle.

Circularity and Waste

The design also engages with principles of circular construction, responding to the high levels of waste associated with the building industry. Components are selected and detailed for durability, repairability, and eventual disassembly. Mechanical fixings are favoured over adhesives to allow for future recovery and reuse, while modular coordination reduces material waste during construction. The result is a building that is not only efficient in its current state but also adaptable over time.

Biodiversity

The landscape strategy extends beyond visual amenity to support local ecosystems. Planting is selected to encourage pollinators and provide habitat, while features such as integrated bird and bat boxes are incorporated into the building fabric. A small water source introduces additional ecological value, supporting a range of species and contributing to a more diverse and resilient garden environment.

Location: South - west London

Property type: Victorian end-of-terrace

Scope of work: The project involved the retrofit and extension of a late 19th-century dwelling, combining fabric-first upgrades to improve thermal performance with a reconfiguration of internal spaces and the addition of a rear extension to enhance daylight and strengthen the relationship to the garden. The scope integrated passive environmental strategies, natural ventilation, and low-carbon building systems, alongside the careful selection of materials to reduce embodied carbon, and included landscape interventions to support biodiversity, with coordination across architectural, structural, and environmental design from concept through to construction.

Key Features:

• EnerPHit-informed deep retrofit strategy

• Fabric-first envelope upgrade

• Hybrid insulation system (internal + external)

• Airtightness enhancement to Passivhaus levels

• High-performance triple glazing and doors (Uw ≤ 0.8 W/m²K)

• Thermal bridge minimisation strategy

• Passive solar design with external shading devices

• Natural ventilation strategy (cross + stack-driven airflow)

• Air-source heat pump for space heating and DHW

• Photovoltaic renewable energy generation

• Low embodied carbon material specification

• Rear extension with improved spatial efficiency

• Biodiversity-led landscape integration

Project Results:

• Space heating demand reduced by ~75% (≈293 → 75 kWh/m²/yr)

• Airtightness improved to ≤1.0 ACH@50Pa (Passivhaus-aligned)

• Operational carbon reduced by approximately 60–70%

• Elimination of gas use through full electrification

• Stable internal temperatures maintained within 20–25°C band (95% of year)

• Overheating risk reduced to <10% annual hours (CIBSE TM59-aligned)

• Daylight levels increased, achieving higher daylight autonomy across key spaces

• Thermal bridging reduced, approaching Passivhaus thresholds

• Renewable energy generation via PV offsets a significant portion of annual electricity demand

• Whole-life carbon reduced through material and construction strategy