The SD Foundation published a news item titled "Retrofit at scale" on 31 July 20241. The item is listed among the Passivhaus Trust's references on its Passivhaus retrofit pages, which set out how existing buildings can be upgraded to use very little energy1.
The Trust states that retrofit projects can be delivered by meeting the full Passivhaus Classic standard or, more commonly, through the specialist retrofit standard EnerPHit, and that works may be completed in a single phase or planned in stages over time1. It says the Passivhaus standard includes EnerPHit because an existing building's orientation, structure, shape and amount of glazing cannot be changed, and that some criteria are relaxed to reflect this, though it remains "a very demanding standard" that will typically produce a building outperforming a new-build property on energy and comfort1.
On savings, the Trust is explicit about the limit of the claim:
"Passivhaus alone cannot guarentee a 'house with no bills', it does give proven reductions in heating demand by up to 80%"
The Trust describes itself as an independent, non-profit organisation providing evidence-based guidance rather than commercial retrofit services1. It says high-quality Passivhaus retrofit is cost-comparable with other deep retrofit standards, and that modelling, testing and independent certification reduce performance gaps and delivery risk compared with approaches based on specification or assumptions alone1. It also states that UK homes are among the oldest and least efficient in Europe1.
| Item | Detail as given |
|---|---|
| Retrofit standards named | Passivhaus Classic, or EnerPHit (more common)1 |
| Phasing | Single phase or staged over time1 |
| Heating demand reduction | Up to 80%1 |
| Cost position | Cost-comparable with other deep retrofit standards1 |
| Verification | Modelling, testing and independent certification1 |
The Trust's guidance lists five steps for affordable Passivhaus retrofit: working with an experienced Passivhaus Designer or Consultant and an independent Certifier; getting the retrofit modelled in PHPP (Passivhaus Planning Package); developing a whole-house plan even if measures cannot all be done at once; considering a component-based route; and considering a step-by-step approach alongside other home improvements1. It notes that a whole-house retrofit is often staged over several years and that sequencing decisions early avoid "carbon lock-in"1.
Why it matters for households
For a household, the practical content here is about what a deep retrofit is claimed to deliver and how it is checked. The Trust's figure of up to 80% reduction in heating demand is a reduction in demand, not a promise of no bills, and it says so directly1. That distinction matters for anyone weighing up insulation and glazing work against expected running costs.
The Trust's position is that performance should be measured rather than assumed, with modelling before work and testing afterwards, and that this reduces the gap between designed and actual performance1. It also states that a retrofit to an existing home can make it more comfortable and energy efficient than a new home built to current standards1. On standards and trust, it says: "PAS2035 as a compulsory retrofit requirement will result in better standards and hopefully a greater degree of trust from homeowners"1.
What happens next
The Trust lists training and events, including a 2026 Passivhaus retrofit Masterclass series of six expert-led sessions, an online training course delivered by PHT Patron Coaction on delivering deep fabric retrofits, and an on-demand series of eight webinars organised jointly with RIBA1. It also refers to the ERFIT Programme, which "aims to deliver trained practitioners with the technical knowledge and expert skills to install, advise and troubleshoot existing and new retrofit projects"1. A business case page is marked "coming soon", and the Trust's recommendations on assessing whether Passivhaus retrofit is right for a household are described as "coming soon"1. No further detail on the SD Foundation item itself has been reported in these pages beyond its title and date1.
Sources2 cited
- Passivhaus Retrofit, passivhaustrust.org.uk
- Passivhaus Retrofit, passivhaustrust.org.uk