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retrofit briefing Technologhy4Change

Published by BRE Trust

Retrofit for the future: early learning


Think about insulation thickness, detail with care and treat windows with respect. These are some of the many points emerging from a research programme to retrofit 119 homes.

Retrofit for the future has been one of the most keenly followed research programmes in UK construction, as its innovations, experience and lessons could have an impact on both industry and all of our homes. The Technology Strategy Board (TSB) backed research programme to demonstrate ways of retrofitting affordable homes is still in progress, but significant lessons for industry are already emerging.

The programme involves the application of a wide range of approaches and technologies, from super-thin Aerogel-based insulation to energy monitoring systems. Across the programme specific learning is resulting from the application of new and unfamiliar products.

The second phase of the programme comprises 86 live projects to carry out retrofits on 119 homes, and all works are scheduled for completion in May. The projects shared £17 million of government funding to demonstrate how 80 per cent carbon emission reductions could be delivered in existing housing stock. They also provided lessons for construction-related businesses in the UK in helping them develop their own strategies. Following completion of the build works, home performance is being monitored for two years. 

Air leakage of homes was assessed pre-retrofit, and that provided one early lesson on the airtightness of the traditional home. Ian Meikle, innovation platform leader with TSB explains: "Around two thirds of the homes performed pretty well on air leakage. That was a surprise for the project teams involved."

The full projects database will be available in summer, initially to project participants only. The research programme has its own website, www.retrofitforthefuture.org.

Routes to the 80 per cent reduction

The 80 per cent reduction in carbon emissions is being achieved through a range of measures, including:

  • external and internal insulation of around 150mm plus
  • triple glazing
  • airtight barriers
  • high efficiency heating and hot water, some of it quite innovative
  • mechanical ventilation and heat recovery
  • renewable energy technology.

Learning so far

Paul Ruyssevelt is working with TSB on the Retrofit for the future programme and outlined some of the early learning at Inside Housing magazine's Sustainable social housing conference in London last month.

Some of Ruyssevelt's conclusions from the programme to date are:

  • "We're starting to learn things about junctions between wall and floor insulation. We've not had this package of measures before. It's the same with services in that we've got a number of technologies being brought together. Some make sense, but some may be fighting one another."
  • "The high levels of insulation typically mean thick walls, so novel materials like Aerogel are being used. It is very important to think about detailing in key areas, such as wrapping around intermediate floor joists"
  • "We got to the point where the number of projects specifying Aerogel was such that the supply wasn't there, so teams had to change specification to thicker insulation. That highlights the need to think about the supply chain."
  • "Vacuum glazing was used for some projects, but some had issues with planners."
  • "Whole house mechanical ventilation and heat recovery (MVHR) is complex and has significant space requirements, so typically can only be used in extensive refurbishments in decanted properties."
  • "42 of the homes in the programme had both PV and solar. Given the size of the homes, it is a challenge in roof area availability."
  • "CHP produces a relatively small amount of electricity for heat, so you need heat/hot water demand and these properties are trying to reduce that demand, so it is not necessarily the best solution."
  • "There aren't many controllers that operate at a domestic scale. There were a couple in the programme, and the dominant one was the Wattbox [heating controller]. This will provide useful information. One piece of early information is that some of the systems haven't been commissioned properly and have air source heat pumps working 24/7."

Top tips

Based on the experience from the Retrofit for the future projects, Ruyssevelt gave a list of eight points to consider in retrofit projects:

  1. Have a plan
  2. Think thick - think of the space available for insulation. You may want to mix and match thick and thin insulation options for different locations within a house to produce the solution that is most cost effective, space efficient and aesthetically suitable
  3. Airtightness and ventilation are critical
  4. Detailing is key - a lot of work in these deep retrofits has caused challenges and required good detailing
  5. Look for ways to minimise waste and save time. There is a need for systems that can be manufactured offsite to minimise time spent in a property, for example United House's Whiscers cut-to-fit approach to wall insulation
  6. Treat windows with respect - remember the old adage of measure twice and cut once
  7. Consider the available space - this level of carbon reduction requires a large amount of insulation and technologies like bigger boilers. It's an issue for social housing and also for private housing where space standards have been driven down
  8. Keep controls simple. Ruyssevelt said that if the control technologies being trialled perform well in the programme, "they'll begin to revolutionise the way we use controls in our homes".

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