Why Fabric First Approach is our go to solution for Retrofit Projects
August 19, 2022
At Barefoot Architects we are working on a number of refurbishment and extension projects. The current energy crisis means that the majority of our clients are seeking to improve the energy performance of their existing house. Everyone is trying to understand where their budget is best spent. Should they insulate the house and make it airtight? Should they look at on the site energy production and storage? Should they change their primary heat source from what is usually a gas boiler to electricity in the form of an Air Source Heat Pump (ASHP)?
Ideally, they would do all of the above, but the reality is that most project budgets don't allow for this! So our advice is always to focus on a 'Fabric First' Approach; to insulate the house as much as possible while also making it airtight, this is to reduce the amount of energy required for heating in the first place. Of course, ventilation has to be carefully considered when a fabric first approach is taken to mitigate condensation and mould growth – this can be done in a number of ways, including trickle vents and various forms of mechanical ventilation.
Adding on-site energy production and potentially energy storage should be the second most important improvement. In our experience the only viable system for a domestic household is the installation of Photovoltaic Panels (Pvs) for electricity generation. However the amount of energy produced from solar during the winter months is relatively low in the UK so PVs don't really help with the heating energy demand.
The graph below shows the amount of energy produced by 3kW solar panels installed on my house over the last 9 years (a Terrace house in Bristol, the roof is south facing and the panels are installed on a relatively shallow pitch, so they are less efficient in winter months).
We think that changing the primary heat source from gas to electricity should be the last course of action. This is because the energy in the national grid comes from as much wind, solar and nuclear as possible and anything more is produced from gas (gas is currently used for the production of approximately 50% of the national grid electricity https://grid.iamkate.com/ ) When a household switches from a gas boiler to a heat pump, that increases the electrical load on the national grid, which currently has to come from burning gas. This is likely to change in the future, but will still take some time.
Another aspect to consider is the efficiency of different ways of using gas/ electricity.
A gas power station is approximately 50% efficient.
A condensing boiler is approximately 90% efficient
A heat pump is approximately 300% efficient.
So per unit of heating required, the gas use is:
Gas Boiler: 1.11 units of gas
Heat pump: 0.33 units of electricity which is 0.67 units of gas.
So there is an improvement, it just isn’t massive. In addition electricity costs ~3.6x as much as gas. So one ends up paying slightly more to heat one's home. On top of the large Capital expenditure should be considered.
That is why at Barefoot architects, we encourage a Fabric First Approach, because if you insulate and reduce your heating requirement by a factor of 2x. Then your gas usage will be lower and your bills be a lot lower accordingly.