Working file A2
1930s semi retrofit cost (UK 2026)
1930s semi retrofit cost: working capex envelope, sequenced measure cost, PAS 2035 risk path.
Working envelope (90 m² semi-detached)
Phased deep retrofit: £35,000to£55,000(pre-grant). Net after BUS plus GBIS where eligible: £24,000to£46,000. ASHP-only route: £8,000to£14,000(after BUS).
Sequenced cost
- CWI £1,200 to £2,600 (often £0 net after GBIS).
- Loft top-up to 300mm £700 to £1,200.
- ASHP plus low-temp rads £10,500 to £18,000 plus £1,800 to £4,500.
- Glazing review later, often deferred under MTIP.
Risk path
Path A, post-1919 cavity
Surveyor's note
This is the modal case for the calculator. Most 1930s semis fall within Path A and reach a defensible EPC C inside a five-year medium-term improvement plan.
Surveyed 1 October 2026. Ofgem cap for 1 October to 31 December 2026 applied (gas 7.97p, elec 26.32p, gas standing 29.68p, elec standing 54.83p). Next scheduled review 25 November 2026 (January cap announcement). [ref A2]
By Oliver Wakefield-Smith, Founder, Digital Signet. Corrections to oliver at digitalsignet dot com.