Clapham Retrofit | Residential Building of the Year (2016)

This project is a deep retrofit of a 170-year-old Grade II listed Victorian townhouse, demonstrating how rigorous low-energy design can be successfully integrated within highly sensitive historic fabric. It is the first listed building in England to achieve the AECB Silver Performance Standard and was awarded CIBSE Building Performance Award – Residential Building of the Year (2016) in recognition of its exceptional energy performance alongside conservation excellence.

Using Passivhaus methodology, the retrofit reduces the building’s space heating demand by over 75%, from 180kWh/m²/yr (5,631 kgCO₂e) to 40kWh/m²/yr (1,251 kgCO₂e), while improving airtightness from 9.6 ACH to 1.8 ACH. The result is a significantly enhanced thermal performance achieved without compromising the architectural integrity of the listed structure.

The solid brick townhouse was internally upgraded using a highly tailored fabric-first approach, incorporating nine different insulation systems, each carefully specified to respond to localised thermal and moisture conditions. Existing sash windows and doors were retained and improved through the introduction of discreet secondary glazing, maintaining original character while improving thermal performance.

Advanced airtightness detailing and thermal bridge mitigation were combined with high-performance insulation strategies to transform the building into a comfortable, low-energy home. Prior to insulation works, wireless moisture sensors were embedded within the historic fabric to monitor hygrothermal behaviour, ensuring long-term building safety and performance. This monitoring research was later presented at the 18th International Passivhaus Conference.

Awards:

• CIBSE Building Performance Award - Residential Building of the Year 2016.

• AJ Retrofit Awards 2014 (Nominated)

Location: South London, Clapham

Property type: Grade II listed Victorian townhouse

Scope of work:
Arboreal Architecture led the full design and delivery of a deep retrofit to a Grade II listed Victorian townhouse, including heritage-led fabric upgrades, Passivhaus-informed energy strategy, internal insulation design, airtightness and thermal bridge detailing, window and envelope upgrades, and integration of real-time moisture monitoring systems. The practice coordinated conservation approvals, specialist detailing, and performance verification to achieve one of the UK’s most advanced listed building retrofits.

Key Features:

• Deep retrofit of 170-year-old Grade II listed Victorian townhouse

• Passivhaus-informed retrofit methodology

• Over 75% reduction in space heating demand

• Airtightness improved from 9.6 ACH to 1.8 ACH

• Nine bespoke insulation systems tailored to historic fabric conditions

• Retention and upgrade of original sash windows with secondary glazing

• Continuous airtightness and thermal bridge detailing strategy

• Embedded wireless moisture monitoring of historic masonry

• Fabric-first approach preserving architectural heritage

Project Achievements:

• award winning project: CIBSE Building Performance Award – Residential Building of the Year 2016

• First listed building in England to achieve AECB Silver Standard

• Demonstrates successful integration of deep energy retrofit within Grade II listed context

• Significant operational carbon reduction while preserving historic character

• International recognition through Passivhaus Conference research presentation