Typical cost of a maisonette eco upgrade starts at £3,500 for basic measures
The cost of making a maisonette more energy efficient varies significantly based on the measures you choose and your property’s construction. A full eco upgrade package for a mid-terrace maisonette — covering loft insulation, cavity wall insulation, draught-proofing, and a new heating system — averaged £8,200 in 2026, according to DESNZ’s Household Energy Efficiency Statistics (DESNZ, 2026).
Maisonette eco upgrade costs start at £3,500 for basic measures like loft insulation and draught-proofing, rising to £8,200 for a full package. Loft insulation offers the fastest payback at 2–4 years.
- A full eco upgrade for a mid-terrace maisonette averages £8,200 in 2026.
- Loft insulation top-up costs £500–£700 and saves £180–£250 per year.
- Cavity wall insulation pays back in 3–5 years at £200–£300 annual saving.
- First-floor maisonettes cost 10–15% more due to scaffolding needs.
- Draught-proofing is the cheapest measure, paying back in 1–3 years.
- Typical cost of a maisonette eco upgrade starts at £3,500 for basic measures
- Quick numbers — energy savings and payback periods for common measures
- The direct answer — the best single measure for a maisonette is loft insulation (if accessible)
- How to choose between cavity wall, solid wall, or internal wall insulation for a maisonette
- Eligibility for the 2026 Great British Insulation Scheme and other grants for maisonettes
- How to verify a certified installer for a maisonette eco upgrade
- The specific constraints of a first-floor maisonette vs a ground-floor maisonette for eco upgrades
A basic package that includes a loft insulation top-up, draught-proofing, and a smart thermostat costs between £3,500 and £4,800 (Energy Saving Trust Home Energy Scotland, 2026). First-floor maisonettes typically cost 10–15% more than ground-floor equivalents because scaffolding or external access is needed for wall insulation (MCS Installer Survey, 2026). These figures exclude any grant or subsidy, so the actual net cost is lower for eligible households.
Quick numbers — energy savings and payback periods for common measures
| Measure | Typical cost (2026) | Annual saving (£) | Payback period (years) | U-value improvement |
|---|---|---|---|---|
| Loft insulation (270mm top-up) | £500–£700 | £180–£250 | 2–4 | 0.16 to 0.11 W/m²K |
| Cavity wall insulation (CWI) | £800–£1,200 | £200–£300 | 3–5 | 1.6 to 0.35 W/m²K |
| Draught-proofing (whole home) | £200–£400 | £100–£150 | 1–3 | N/A |
| Air source heat pump (ASHP, no radiators) | £7,000–£13,000 | £400–£700 (vs old gas boiler) | 10–18 | N/A |
| Smart thermostat + heating controls | £150–£300 | £75–£120 | 1–3 | N/A |
Costs are from EST Which? Trusted Trader data for 2026 (Energy Saving Trust, 2026). Savings are DESNZ modelled averages for a typical mid-terrace maisonette (80m², EPC band D). Payback assumes gas heating at 10p/kWh under the Ofgem price cap for Q1 2026 (Ofgem, 2026) and no grant offset. U-value sources are from BRE’s U-value calculator for typical 1970s maisonette construction (BRE, 2026).
The best single measure for a maisonette is loft insulation (if accessible)
For most maisonettes, the largest heat loss is through the roof, accounting for 25–30% of total heat loss. Loft insulation reduces this to 10–15% (Energy Saving Trust Heat Loss Model, 2026). If the loft is shared — common in first-floor maisonettes — you must check ownership and access rights before insulating. If it is a private loft, you can proceed without neighbour consent (GOV.UK Loft insulation guidance, 2026).
The typical payback of 2–4 years makes loft insulation the most cost-effective single measure for any maisonette, regardless of floor level. For ground-floor maisonettes, solid floor insulation (cost £1,500–£3,000) is a close second, but loft insulation remains the priority.
How to choose between cavity wall, solid wall, or internal wall insulation for a maisonette
Cavity wall insulation (CWI) is only suitable if your maisonette has unfilled cavity walls. Check with a surveyor or your EPC. Cost is £800–£1,200 with a payback of 3–5 years (Energy Saving Trust Cavity Wall Insulation guide, 2026).
Solid wall insulation — external or internal — is needed for pre-1930s maisonettes. External costs £8,000–£14,000 plus scaffolding, while internal costs £4,000–£8,000 (DESNZ Solid Wall Insulation cost data, 2026). Internal wall insulation reduces room size by 50–100mm per wall and requires redecoration. External insulation is more disruptive but does not shrink living space.
For first-floor maisonettes with a shared wall, internal insulation is often the only option unless both neighbours agree to external work. Read more about internal wall insulation cost breakdown
Eligibility for the 2026 Great British Insulation Scheme and other grants for maisonettes
The Great British Insulation Scheme (GBIS) covers loft and cavity wall insulation for households with an EPC rating of D or below and a total household income under £31,000 (GOV.UK GBIS eligibility, updated Jan 2026). The Boiler Upgrade Scheme (BUS) offers £7,500 off an air source heat pump installation for any home in England and Wales, with no income cap, but the home must have a valid EPC and no outstanding insulation recommendations (DESNZ BUS guidance, 2026).
The Energy Company Obligation (ECO4) is available for low-income households — income under £31,000 or on certain benefits — and covers full insulation packages plus heating upgrades (Ofgem ECO4 guidance, 2026). Maisonettes in Scotland can access Warmer Homes Scotland, offering up to £7,500 grant, with an income threshold of £20,000 (Home Energy Scotland, 2026).
How to verify a certified installer for a maisonette eco upgrade
For insulation — loft, cavity, or solid wall — installers must be registered with the National Insulation Association (NIA) and hold a valid MCS certificate for the relevant measure (MCS Installers Directory, 2026). For heat pumps, installers must be MCS-certified and registered with the Microgeneration Certification Scheme to qualify for BUS grants (MCS Heat Pump Standard, 2026).
For gas boilers, installers must be Gas Safe registered (Gas Safe Register, 2026). For electrical work — smart thermostats, heat pump wiring — use an NICEIC or NAPIT registered electrician (NICEIC, 2026). Always check the installer’s certification number on the relevant register before paying a deposit. Ask for a copy of their MCS or Gas Safe card.
The specific constraints of a first-floor maisonette vs a ground-floor maisonette for eco upgrades
First-floor maisonettes present unique challenges. Loft insulation requires access through the top-floor flat unless you own the loft. You must get written permission from the neighbour or landlord (GOV.UK Party Wall Act guidance, 2026). Ground-floor maisonettes can have solid floor insulation installed, costing £1,500–£3,000, but this requires lifting floorboards or concrete slab and may need temporary rehousing for 2–3 days (Energy Saving Trust Floor Insulation guide, 2026).
First-floor maisonettes often have no cavity walls if built as a block. Internal wall insulation is then the only option, reducing room size and requiring new skirting boards and window reveals. Ground-floor maisonettes can typically have cavity wall insulation installed from outside without internal disruption, though scaffolding may be needed for upper floors (MCS Installation Best Practice, 2026). Learn more about floor insulation options for maisonettes
Frequently Asked Questions
A basic package costs £3,500–£4,800, while a full upgrade covering loft insulation, CWI, draught-proofing, and a new heating system averages £8,200 (DESNZ, 2026).
Loft insulation is the best single measure for most maisonettes, costing £500–£700 and saving £180–£250 per year with a payback of 2–4 years (Energy Saving Trust, 2026).
Yes, first-floor maisonettes typically cost 10–15% more than ground-floor equivalents because scaffolding or external access is needed for wall insulation (MCS Installer Survey, 2026).
Cavity wall insulation saves £200–£300 per year on energy bills for a typical mid-terrace maisonette, with a payback period of 3–5 years (DESNZ, 2026).
An ASHP costs £7,000–£13,000 and saves £400–£700 per year versus an old gas boiler, but payback is 10–18 years without grants (Energy Saving Trust, 2026).
