What kWh per m² per year targets apply?

EnerPHit targets 25 kWh/m²/yr space heating; AECB Retrofit Standard targets 50 kWh/m²/yr; the Building Regulations baseline for new build is around 30 to 45 kWh/m²/yr. A deep retrofit aims for the EnerPHit or AECB band, not just for an EPC C uplift.

What does it include beyond a heat pump?

Fabric improvements (walls, loft, floor, glazing), a deliberate ventilation strategy (MVHR or PIV), the heat pump itself plus low-temperature emitter design, solar PV plus battery, and intelligent controls with weather compensation.

Cost envelope in 2026?

£35,000 to £70,000 pre-grant for a phased deep retrofit on a 90 m² semi; £42,000 to £75,000 on a Victorian solid-wall terrace where IWI plus heritage glazing is required.

Working file Q2

What is a deep retrofit

Direct-answer page: What is a deep retrofit. Ofgem Q4 2026 cap anchors applied.

Direct answer

A deep retrofit is one that addresses all five PAS 2035 measure strata (fabric, ventilation, heating, renewables, controls) and reduces space-heating demand to a level approaching EnerPHit (the Passivhaus retrofit standard, around 25 kWh per m² per year) or AECB Retrofit Standard.

Further questions

What kWh per m² per year targets apply?: EnerPHit targets 25 kWh/m²/yr space heating; AECB Retrofit Standard targets 50 kWh/m²/yr; the Building Regulations baseline for new build is around 30 to 45 kWh/m²/yr. A deep retrofit aims for the EnerPHit or AECB band, not just for an EPC C uplift.
What does it include beyond a heat pump?: Fabric improvements (walls, loft, floor, glazing), a deliberate ventilation strategy (MVHR or PIV), the heat pump itself plus low-temperature emitter design, solar PV plus battery, and intelligent controls with weather compensation.
Cost envelope in 2026?: £35,000 to £70,000 pre-grant for a phased deep retrofit on a 90 m² semi; £42,000 to £75,000 on a Victorian solid-wall terrace where IWI plus heritage glazing is required.

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 Q2]

By Oliver Wakefield-Smith, Founder, Digital Signet. Corrections to oliver at digitalsignet dot com.