New London Architecture

Building sustainable housing affordably: NLA Expert Panel on Housing

Thursday 01 April 2021

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Linda Thiel

Director of London Studio
White Arkitekter

Jo McCafferty

Director
Levitt Bernstein

Marion Baeli

Partner
PDP London

Following our response to the Mayor’s ‘Good Quality Homes for All Londoners’ SPG, the theme of the third meeting of the NLA Expert Panel on Housing was to prompt a discussion on the design and technical aspects of building sustainable housing affordably.

The focus was not only net zero carbon new build homes, but also retrofit, which holds significant potential, as the vast proportion of existing stock within London requires extensive upgrading to improve environmental performance, and therefore forms an important component to meet the capital’s sustainable goals.

The debate circled on how to make Passivhaus a viable, affordable housing model and the key priorities when minimising embodied carbon. The panel also discussed rethinking procurement to unlock the quality and delivery, and barriers to retrofitting existing homes. A recurring theme was the importance of measuring data and meaningful POE, where this has demonstrated the importance of early investment in constructing energy efficient, high quality homes to create long-term benefits for residents and custodians of housing. 

The panel was joined by Annalie Riches, Founding Partner of Mikhail Riches and Marion Baeli, Partner at PDP and a member of the Net Zero Expert Panel, who shared their experiences of designing sustainable affordable housing – both through new build and retrofit models.

Annalie Riches highlighted lessons learnt from their Passivhaus project at Clayfield and Goldsmith Street. In the Clayfield project in Suffolk, a low carbon housing project delivered 10 years ago, one of the design drivers was to harness the winter sun to heat the new homes. On this relatively small site Mikhail Riches carefully designed houses with a 15 degree roof pitch, the angle of winter sun, and a staggered configuration, to achieve the required density.

POE, led by Buro Happold, demonstrated that some residents were very focussed on energy usage and living zero carbon lifestyles and some were less energy conscious, illustrating, despite the thermal performance of the new homes and efficient design, human behaviour also plays a significant role in the long-term operational carbon levels of the buildings themselves.

Goldsmith Street, the award-winning social housing project in Norfolk, was adapted from a passive solar project to full Passivhaus, led by the Norwich City Council client. As with Clayfield, the masterplan was derived using winter sun as one key design driver. The site was well suited for this and was able to accommodate four rows of terraces, developing the typologies and roof form first tested in Clayfield. The masterplan challenged planning policy norms regarding streets widths and prioritised pedestrian movement and fostering neighbourliness through the integrated design of expanded rear ginnels, giving space for families to socialise and children to play safely. 

This case study clearly demonstrates that the investment in a high quality and efficient fabric, and careful detailing to minimise cold bridging, creates significant operational benefits over the long term. The use of a traditional contract to ensure the architects were at the centre of the design and decision-making process and site supervision was also cited as fundamental to the quality and success of the project.

Reflections from the panel included the translation of these ideas into urban, denser development in London and a discussion concerning the frequent conflict between planning requirements, overheating, optimal orientation, building layout efficiency and BRE guidance. 

Marion Baeli’s presentation focused on understanding the retrofit components in making housing more affordable to run and maintain. With 3 million households living in fuel poverty in England, there is clearly vast potential in retrofit, with many registered providers driven by their climate change commitments to reduce CO2 emissions from buildings in use.

Two strands of retrofit were discussed: light vs deep and the balance of focus on embodied versus operational carbon. Strategically if the overriding goal is overall to reduce carbon, then should we focus on completely decarbonising the grid rather than deep retrofit to radically improve the built fabric? 

Marion also illustrated that retrofitting is not only about energy use or carbon reduction, but also the multitude of associated benefits such as improved health for occupants (comfort in winter and summer), stable internal temperatures, improved relative humidity and CO2 concentration conditions and an overall aim for durability – a target to only retrofit once. 

The main challenges in retrofitting highlighted were:

  • Cost for registered providers, circa £20k – 50k per property (rough average estimate for light retrofit + electrical services)
  • The lack of policies and finance mechanisms
  • The technical and legal tenure aspects to enable retrofitting
  • Conflicting Building Regulations in Part L & F (between making a building more airtight and ventilating it sufficiently)
  • Planning consensus on the replacement of windows in conservation areas
  • More practical aspects of upgrading an existing building fabric eg. installing internal or external insulation, addressing airtightness and thermal bridges, installation new windows and services systems (air source heat pumps). 
  • Understanding moisture behaviour in the building fabric, which is paramount to achieving a good retrofit.
  • Education in operation:  easy guides and training for residents are crucial to ensure environmental control measures are understood and correctly used.
  • Skills shortages in retrofit trades have resulted in a need for training programmes, supported by the industry to ensure we have the workforce to implement retrofits en masse. 

Despite all these barriers, there are several potential incentives and initiatives, including VAT at 0 per cent for properly defined retrofits (still at 20 per cent), more subsidies and grants that are robustly put together and implemented, PAS 2035 is now in place and a very helpful guidance, the Retrofit for the Future programme delivered 100 case studies to illustrate how to complete these projects (now 10 years old with a wealth of data attached: Residential Retrofits, 20 case studies - RIBA publication by Marion Baeli), various campaigns (such as the AJ Retrofirst), and soon to be a Retrofit Guide to be published by LETI in the Spring.

As buildings in use still represent close to 40 per cent of the UK total CO2 emissions, there is a demonstrable need in addressing emissions in existing housing, to also secure its durability and comfort for the future. Now there is greater interest and expertise in this field, and empirical evidence to support its benefit, we all need to explore retrofit opportunities in our own work, to tip the retrofit balance from the exceptional pilot project into the mainstream.

SIGN UP TO OUR WEEKLY NEWSLETTER

Linda Thiel

Director of London Studio
White Arkitekter

Jo McCafferty

Director
Levitt Bernstein

Marion Baeli

Partner
PDP London


Housing

#NLAHousing

Programme Champion

Transport for London

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