How to Improve Your Property's EPC Rating — A Practical Guide for London Homeowners and Landlords

An Energy Performance Certificate is produced by a qualified Domestic Energy Assessor (DEA) who inspects the property and records a set of data points — insulation levels, heating system type, glazing, hot water system, and so on. The data is fed into the Standard Assessment Procedure (SAP) calculation, which produces a score from 1 to 100, mapped to a rating band:

• •G: 1–20
• •F: 21–38
• •E: 39–54
• •D: 55–68
• •C: 69–80
• •B: 81–91
• •A: 92–100

**The SAP score is weighted**: not all improvements are equal. Some improvements have a large impact on the SAP score; others have a smaller impact. Understanding which improvements move the score most is essential for efficient investment.

**Typical London Victorian terrace EPC position**: Most Victorian terraced houses in London without improvements typically score D to E — sometimes F where they have no insulation and an old gas boiler. The target for MEES compliance is E (39+) currently; the expected future target is C (69+).

**What the EPC measures** (and what it does not): The EPC measures the theoretical energy performance of the building envelope and fixed services (heating, hot water, ventilation). It does not measure actual energy consumption — occupant behaviour is not included. A property with a low EPC may have efficient occupants; a property with a high EPC may still have high energy bills if over-heated.

In order of typical SAP score impact:

**1. New boiler and heating controls (replacing a G-rated or old boiler)** A condensing combi boiler of at least 90% efficiency, with a programmable thermostat and TRVs on radiators, is one of the most impactful single improvements. For an old G-rated boiler (below 70% efficiency), replacing it with an A-rated condensing boiler can add 5–15 SAP points. Typical cost: £2,500–£5,000 installed

**2. Cavity wall insulation (where cavity walls exist)** Victorian terraces (pre-1919) typically have solid walls, not cavities. 1930s and later houses typically have cavity walls (two skins of brick with a gap). Cavity wall insulation fills this gap with mineral wool or polystyrene beads injected through holes drilled in the outer skin. SAP impact: 5–20 points. Cost: £500–£1,500 for a typical house (often subsidised under ECO4 for eligible households).

**3. Loft insulation (upgrading to 270mm)** If existing loft insulation is below 100mm or absent, upgrading to 270mm of mineral wool insulation is one of the most cost-effective improvements available. SAP impact: 3–10 points. Cost: £300–£500 for a typical house (often free under ECO4).

**4. Floor insulation (suspended timber floor)** Many Victorian and Edwardian houses have suspended timber ground floors with a void beneath. Adding insulation between the joists (mineral wool or rigid board from below if accessible) significantly reduces heat loss. SAP impact: 2–5 points. Cost: £1,500–£3,000.

• **5. Solid wall insulation (for pre-1919 houses)**
• Victorian solid brick walls cannot be cavity-filled. Two options:
• •**External wall insulation (EWI)**: insulation boards fixed to the outside face of the wall, then rendered or clad. SAP impact: 10–20 points. Cost: £8,000–£18,000 for a typical mid-terrace. Requires planning permission if in a Conservation Area.
• •**Internal wall insulation (IWI)**: insulation boards fixed to the inside face of external walls (reduces room size slightly). SAP impact: similar to EWI. Cost: £6,000–£14,000.

**6. Double glazing (replacing single glazing)** For properties with single-glazed windows, upgrading to double glazing has a meaningful SAP impact (3–8 points) and dramatically improves comfort and condensation levels. Cost: £3,000–£10,000 for a typical house depending on window count and specification.

**7. Solar PV panels** Solar PV panels generate on-site electricity and have a significant SAP impact — potentially moving a D-rated property to C. SAP impact: 5–20 points depending on array size. Cost: £6,000–£12,000 for a 3–4kWp array.

**8. Air source heat pump (replacing gas boiler)** Heat pumps are the government's preferred decarbonisation technology and have a large SAP impact because the SAP assessment treats electricity-derived heat favourably when compared against gas. SAP impact: potentially 10–25 points. Cost: £8,000–£15,000 (grant-subsidised under the Boiler Upgrade Scheme in England).

For landlords targeting the minimum EPC E (current requirement) or EPC C (likely future requirement), the most cost-effective improvement sequence is typically:

• **Step 1 — Free or low-cost measures first**:
• •Loft insulation upgrade (if below 270mm): often free under ECO4 or low-cost under LA Flex
• •Smart thermostat and programmer installation
• •Draught-proofing (sealant around frames, letterbox, loft hatch)

**Step 2 — Boiler replacement (if over 10 years old)**: A new boiler typically adds 5–15 SAP points and makes any further improvements more effective (a better system makes better use of insulation improvements).

**Step 3 — Cavity wall insulation (if applicable)**: For 1930s and later houses, cavity fill is highly cost-effective — low cost, high SAP impact.

**Step 4 — Solid wall insulation (if pre-1919)**: For Victorian terraces, EWI or IWI is the most impactful remaining measure — but the most disruptive and expensive. For rental properties, IWI is often more practical than EWI.

**Step 5 — Solar PV (for landlords with ownership of the roof)**: Solar PV has a large SAP impact and generates an income stream from the electricity produced (or consumed on site). Payback period 7–12 years.

**Cost cap for MEES**: landlords are only required to spend up to £3,500 on EPC improvements (the 'cost cap') to achieve compliance. If improvements costing £3,500 are insufficient to reach EPC E, the landlord can register an exemption. (The cost cap may change with future MEES updates — verify the current figure.)