In defense of fabric

This article was originally published in issue 47 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €15, or click here to receive the next issue free of charge

It’s hard being a retrofit advocate nowadays – heatpumpification, fabric fifth, step by step… the landscape is shifting under our feet and will probably continue to do so for some time.

As I have previously pointed out, cracking on with heat pumps is a pragmatic, but not problem-free, way forward – a view reflected in the step-by-step route to achieving AECB’s CarbonLite Retrofit standard.

Heat pumps connect homes to a rapidly decarbonising source of energy and recent advances in demand side flexibility can keep price per kWh low as well as doing a great deal to keep the increased loads on infrastructure realistic. Given the struggle we face with rolling out fabric retrofit to even a basic standard, it makes sense to reassess the order of operations.

Nigel Banks has highlighted (see ‘Fabric Fifth’ via LinkedIn, as well as the Zero Ambition podcast episode) the value of managing the energy system in a more intelligent manner, matching demand to supply to facilitate the replacement of renewable energy generation – the long-awaited power of demand response and flexibility has arrived, and it’s purple. Indeed, with a large (ish) PV array and a battery (and of course a heat pump), there is the promise that only quite light-touch retrofit is necessary to achieve affordable, low-operational carbon homes.

This is a seductive vision, and to be welcomed, but as Dr Ben Goldacre once put on a T-shirt, I think you’ll find it’s a bit more complicated than that. This is a potential drop-in solution for many houses – detached and many terraces (which is a big proportion of our stock), but flats, houses in multiple occupation, and any number of odd ball conversions, extensions, sub-divisions require more holistic approaches, and that’s before we even start on the non-domestic sector.

Prioritising decarbonisation of the supply ahead of demand reduction (in the parlance of Rosenow and Hamels, 2023) does not mean never doing fabric measures, as Nigel’s work also acknowledges, but is he just saving the feelings of those of us who have dedicated decades to promoting fabric efficiency? If like me, you are conflicted, don’t hang up your PHPP just yet: envelope performance refreshes the places that tech driven approaches can’t reach.

Simply swapping a boiler for a heat pump, no matter how smart the controls or low carbon the electrons, won’t fix the surface temperatures or improve the air quality. On the other hand, it can make it easier and more economic to keep it warmer for longer, which reduces the risk of mould and adverse health effects. Cold homes are at much higher risk of mould, especially if they are under-ventilated – these effects are compounding. For those in fuel poverty, these issues go hand in hand as a response to financial duress, and switching off the heating will always be cheaper at the meter.

So heatpumpification is not guaranteed to solve these issues, but when done properly it should help. An important point here is what does ‘properly’ mean? The list must include good standards of heat pump design and installation, controls that provide demand flexibility, a proper moisture risk assessment and resultant fabric and ventilation measures, and a careful programme of engagement with the people – owner-occupiers, tenants, landlords, housing teams, maintenance teams.

There is another class of objections around resilience. What happens during power cuts, especially if we experience more of those? Fabric performance insulates literally and metaphorically against system shocks, as I found out when the relocation of my meter went wrong on the coldest day of the year. Fabric measures also present the opportunity to reduce overheating risk, but heat pumps also have a role to play here in active cooling. My instinct is to avoid getting drawn into apocalyptic planning scenarios, which tend to culminate in prepperist nuclear bunkers and a three-year supply of baked beans and, significantly, log burning stoves. Surely, it’s much better to put our energies into avoiding such scenarios by working together via good government and governance, which includes building resilient energy systems, from the turbines, via the infrastructure (hardware and software) to the homes they power.

Decarbonisation is one of the most crucial objectives of our time, but along that road also lie opportunities and threats. There is the potential to transform innumerable cold, damp, expensive homes into cosy and affordable ones – and crucially, more resilient ones.