What this calculator models
Whole-home retrofit is the most economically misunderstood domain in UK housing. Done badly — single-measure work without sequencing, ignoring ventilation, ignoring fabric-first principles — it produces homes that are no warmer and significantly more expensive to run. Done well, under PAS 2035 with a proper retrofit assessment, it produces homes that pay back the entire investment over the property's expected occupancy and dramatically reduce operating costs through to 2050. This calculator models the full picture so you see the system-level economics rather than the measure-level economics that drive most installer quotes.
Inputs
- Property type, age band, and floor area
- Current SAP / EPC band (or proxy from fuel bills)
- Wall, roof, floor, glazing construction
- Existing heating system
- Current annual fuel spend (gas, electricity, oil)
- Occupancy pattern
- Likely grant eligibility (ECO4, HUG, LA Flex)
- Phased vs single-pass approach preference
Outputs
- Recommended measure sequence (PAS 2035 fabric-first)
- Phase-by-phase capital budget
- Phase-by-phase grant contribution where eligible
- Phase-by-phase annual saving
- Total private-pay cost
- Total grant-adjusted cost
- Projected SAP / EPC band post-retrofit
- 25-year total-cost-of-ownership: do-nothing vs phased vs single-pass
- Carbon trajectory (annual tCO2e to 2050)
Typical payback band: Whole-home retrofit rarely 'pays back' on private-pay terms over typical owner-occupier residence; it does pay back across 25-40 years on TCO basis. Grant-funded retrofit (ECO4 / HUG full eligibility) can produce payback inside 8-15 years.
Best for: Homeowners planning to remain in the property 10+ years, landlords needing to reach EPC band C by 2030 (commercial PRS) / 2028 (residential PRS proposed), and self-builders or major-renovators sequencing the retrofit alongside other building work.