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Extending your property or making internal alterations? Consider a retrofit at the same time.

With energy prices escalating there is no better way to reduce future heating bills than improving the thermal performance of your property. Improving levels of airtightness and insulation levels will reduce heating costs. This is known as the fabric first approach (where the performance of the building fabric is improved to reduce heat losses).

Heat losses are shown in red and yellow.
Thermal imaging of terraced property with losses shown in red showing poorly insulated areas. Note also the bonnet of the moving car.


This fabric first approach has been the doctrine of all designers of low energy building for the last 15 years. There are different degrees of retrofit, from simply taking measures to provide additional insulation in given rooms to a full low carbon retrofit, or ‘deep retrofit’.


If you are extending your property, (perhaps a small kitchen and utility extension) consider insulating other walls within these rooms, for example; it is highly likely there will be a degree of disruption to walls and floors as part of the renovation work, so providing insulation and improving airtightness at the same time should be basic common sense; there will never be a better opportunity to reduce your heating bills. Insulating walls and floors internally is generally disruptive; consideration will need to be given over to electrics, skirting boards, window reveals and of course the décor, including carpets and floor finishes.


Recent retrofit project by Carvell Associates showing extent of insulation and airtightness barrier location

Consider insulating the extension over and above the requirements of the current Building Regulations; there are some simple details that will also improve airtightness of a cavity wall, floor or roof.


On revisiting our extension projects I am struck by how many clients report that the house feels so much warmer.




Don’t forget that a new, well insulated extension will improve the overall thermal performance of the entire home, as you are effectively replacing older, poorly performing external walls with a better performing extension (by their nature home extensions are in the ‘living’ part of the house where you spend most of your waking time so it makes sense to insulate).


Extract of drawing for a home renovation including a retrofit to reduce heating costs. Insulation is shown as pink.

The Government's approach is more simplistic; by de-carbonising the grid and converting homes to electric heating (through air source heat pumps for example) they intend to address the climate crisis. But to rely on an air source heat pump alone would be foolhardy, particularly if you live in a draughty, poorly insulated property. A good heat pump installation in a poorly performing property will result in still larger heating bills as more electricity will be required to heat the property. There are stories surfacing of people reporting increased heating bills, following heat pump installation in poorly performing properties. It should be understood that even a well designed air source heat pump installation is unlikely to show significant savings over gas.


It should be understood that even a well designed air source heat pump installation is unlikely to show significant savings over a gas boiler.

Dr. Tom Cambray, founder of Greengage suggests a fabric first approach alongside a heat pump installation, if you are considering heat pump installation. He writes in Passivehouse + magazine this month; ‘When we started Gereenguage 11 years ago, typical advice was to fit a fossil boiler, and spend the money you could have dropped on a heat pump, on insulation, airtightness and ventilation-you could always opt for a heat pump when the boiler gave up. I stand by that advice of 11 years ago, but I think the calculus has changed. The climate crisis is more urgent, the UK heat pump market has matured significantly and the retrofit market is bumping along thanks to a band of dedicated individuals rather than soaring, thanks to the bold, consistent policy support needed’ (Source: Passive House+ magazine, Issue 40. pp 66).


In summary, there is no Government intervention to encourage homeowners to upgrade existing properties, although there will be help with renewable technology in the form of the The Clean Heat Grant, now known as the Boiler Upgrade Scheme.


it is good common sense to take full advantage of any building work that will provide the opportunity for you to better insulate your home, taking advantage of the significant disruption an extension or alterations bring to to the property. This approach will further protect against future energy price rises and will increase the viability of future bolt-on renewable technologies.


Further background reading on this subject:

UK edition - passivehouseplus.co.uk

Retrofitting a Home: The Definitive Guide | Homebuilding

Publications | LETI


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