Retrofit and Low-Energy Architecture with James Rixon

In this episode of the Architecture Social podcast, Stephen Drew is joined by James Rixon, founder of Rixon Architects, a small Cambridge-based practice specialising in retrofit and low-energy design. Over roughly 43 minutes they unpack what retrofit really means, how to reframe client conversations around sustainability, and how small practices can lead on decarbonising the existing building stock. Listen to the full conversation below.

Who this is for

• Architects, architectural assistants and designers curious about retrofit and low-energy design
• Small-practice owners thinking about how to position their services
• Students and early-career professionals wanting to upskill in sustainability
• Anyone working with existing, older or historic buildings

Learning outcomes

By the end of this lesson you will be able to:

1. Explain what retrofit means and how it differs from new-build sustainability.
2. Describe practical interventions that make existing homes and offices lower carbon and more comfortable.
3. Reframe client conversations so low-energy design is the starting point rather than an optional extra.
4. Identify upskilling routes and standards relevant to retrofit, including Passive House principles and PAS 2035 roles.
5. Recognise how networks such as ACAN and place-based retrofit hubs help deliver retrofit at scale.
6. Consider how a small practice can build a viable business around retrofit and low-energy work.

What retrofit actually means

James defines retrofit as taking existing buildings and planning a series of interventions, as many or as few as needed, to make them fit for the future. It is about upgrading what we already have, rather than the "retro" styling the word sometimes suggests.

Changing the client conversation

Rather than offering sustainability as an add-on (a question that often ends with "how much does it cost?"), the practice leads with low-energy and retrofit as its core offer. Setting the agenda early makes the conversation simpler and attracts the right clients.

Retrofit for homes and for offices

Post-pandemic, many offices are being reworked, which creates a natural opportunity to make them sustainable at the same time. Homes are different: they remain in constant use, so change tends to be incremental and planned around how people actually live.

A phased, future-focused approach

Good retrofit looks forward. James describes working back from a building's long-term future to decide what to do first, taking steps now that lower carbon and improve comfort without precluding later changes such as extensions or a loft conversion.

Greenwashing and a genuine community

Any sustainability claim carries a risk of greenwashing. James finds the retrofit community unusually genuine and quick to call out claims that do not stand up, which keeps the focus on substance rather than labels.

Upskilling for retrofit

Retrofit is technical because it depends on understanding how walls, roofs and floors work together. James points to Certified Passive House Designer training and resources from the AECB (the sustainable building association) for building-physics knowledge, and to PAS 2035, the publicly available specification used on government-funded retrofit, which defines roles such as retrofit assessor, designer and coordinator. There is significant crossover with training on historic buildings.

Where AI helps, and where it does not

James finds AI useful for drafting text and potentially for the modelling "middle" of a project, but less useful for the assessment, strategy and hands-on implementation that retrofit depends on. As he notes, no chatbot can install external wall insulation.

Building a place-based retrofit hub

James is a co-founder of the Cambridge Retrofit Hub, set up as a community benefit society to act as a trusted local point for retrofit assessment, design and coordination. Inspired by examples such as People Powered Retrofit and Cosy Homes Oxford, the aim is to galvanise local trades and homeowners and to deliver retrofit at scale.

Advice for early-career architects

For those starting out, James suggests joining the Architects Climate Action Network (ACAN) and the AECB, then steadily filling the gaps in building-physics and retrofit knowledge through their courses and networks.

Key terms

• Retrofit: improving an existing building so it performs better and is fit for the future.
• Operational carbon: the carbon associated with the energy a building uses in day-to-day operation.
• Embodied carbon: the carbon associated with materials and construction.
• Passive House (Passivhaus): a low-energy building standard; the Certified Passive House Designer course covers the underlying building physics.
• PAS 2035: the publicly available specification for retrofitting dwellings, mandatory on government-funded projects, defining retrofit assessor, designer and coordinator roles.
• ACAN: the Architects Climate Action Network, a volunteer network campaigning and educating on climate action in the built environment.
• AECB: the sustainable building association, offering guidance and training on low-energy building.
• RIBA 2030 Climate Challenge: the RIBA framework of stepped targets for operational energy, embodied carbon and water use.

Reflective prompts for your CPD record

1. Which of your current or recent projects could have begun as a retrofit conversation, and what would you change about how you framed it?
2. Where are the gaps in your own building-physics or retrofit knowledge, and which training or network could help you close them?
3. How could your practice make low-energy and retrofit advice more accessible and affordable to clients without undervaluing the work?

About the guest

James Rixon is the founder of Rixon Architects, a small Cambridge-based practice specialising in retrofit and low-energy design (the practice relocated from South London to Cambridge). James has completed Certified Passive House Designer training, is involved in the Architects Climate Action Network (ACAN), and is a co-founder of the Cambridge Retrofit Hub. Find out more at the Rixon Architects website.