We are trying to keep away from heat pumps for as long as we can but trying to make homes as low carbon as possible... focussing on fabric.

The first principle for low energy homes is to reduce the energy demand by making sure all the fabric elements are achieving the highest standards – fabric first.

Once these passive measures are in place then the heating and ventilation technology can be considered. 

We will soon be switching to low carbon technologies mandated from 2025 through legislation in the building regulations. There will be some reluctance to change, not because the technology is flawed but because of the perceived maintenance costs, and the uncertainty of whether there are enough qualified suppliers and installer and, for housing associations, the re-training of staff. 

In the past, housing associations have been forerunners, implementing new technology to qualify for public funding and to achieve higher levels of the Code for Sustainable Homes, often before the essential demand reduction had been achieved.

The fabric or passive measures need to be executed correctly to prevent energy from being wasted and to help ensure good ventilation and comfort in summer. When the passive measures are built correctly there can be some confidence that the active heating and ventilation will work also efficiently. However, things can go wrong with the fabric too if there is poor detailing of junctions and if the implications of wider cavities and thicker wall constructions have not been fully understood.

Things that can go wrong

  • Heating and ventilation inadequate due to poor fabric specification and/or poor installation;
  • Poor detailing at junctions;
  • Building walls with larger cavities, without consideration to wall ties, cavity trays, structure. 

Future-proofing recommendations

  • DESIGN: Design the passive measures first to reduce energy demand (‘fabric first’);
  • INSTALL: Pay attention to gaps and discontinuities in insulation. Fit air-barriers and membranes carefully to control unwanted air or moisture movement;
  • COMMISSION: Ensure all construction details are built to drawings and record critical details ‘as-built’ especially at the interfaces and junctions of different elements.

Further Reading

  • Passivhaus Trust

    Demand reduction should be the first priority for reducing bills and carbon emissions. Passivhaus Trust suggests the UK is unlikely to meet zero carbon targets without very high levels of fabric efficiency. (Passivhaus Trust, Passivhaus: the route to zero carbon? March 2019, p2)

    Demand reduction should be first priority
  • Climate Emergency Design Guide

    Independent research determined an average performance gap of 40% between the overall energy usage of a newbuild house compared to its EPC modelling. (LETI, Climate Emergency Design Guide, January 2020, p122)

    Demand reduction should be first priority
  • Institute for Government, Decarbonising heating at home

    Domestic heating accounts for around 14% of UK emissions. (Institute for Government, Decarbonising heating at home home, April 2021, p4)

    Demand reduction should be first priority

Find below relevant NHBC standards/reports for further reading:

NHBC UK - Points to Watch when Constructing Wider Wall Cavities

Next Chapter 2. Cost Implications

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