A high performance retrofit project utilising natural materials (where possible) typically costs between £900-1500 per meter squared. So for an average 3 bedroom home of 100m2, this would be between £90-150k depending on how complicated the design & scope of works is.

For a full house deep retrofit of a typical 3-bed detached house, it normally takes 2-3 months for everything.

1.      A high-performance retrofit upgrades an existing building to dramatically improve its energy efficiency, comfort, and indoor air quality. It typically involves the following:

a.       insulating the building fabric,

b.      improving airtightness,

c.      upgrading windows,

d.      installing efficient ventilation and heating systems.

The goal is to reduce energy demand, carbon emissions, and running costs—often to near new-build standards. Upgrades are measurable, and there are two main building standards to aim for, these are Enerphit and AECB Carbonlite.

a.      Both AECB and Enerphit revolve around the same fundementals….. but with differing levels of performance, as outlined below:

Metric

EnerPHit Requirements

Space Heating Demand

≤ 25 kWh/m²/yr (alternatively: peak heat load ≤ 10 W/m²)

Primary Energy Demand (PER)

≤ 120 kWh/m²/yr (for all uses: heating, hot water, appliances, lighting)

Airtightness

≤ 1.0 air changes/hour @ 50 Pa (n50)

Thermal Bridge Free Design

Required – All thermal bridges must be minimized and assessed

Ventilation

Mechanical ventilation with heat recovery (MVHR) required; ≥ 75% heat recovery

U-values (Components)

Windows: typically ≤ 0.85 W/m²K; Opaque elements: ~0.15–0.25 W/m²K

Moisture Control

Must ensure no risk of condensation or mould (e.g., surface temps ≥ 17°C)

Certification Options

EnerPHit Standard or EnerPHit Component Method (if some existing elements are retained)

Metric

AECB CLR Requirements

Space Heating Demand

~40 kWh/m²/yr (may vary depending on location and strategy)

Primary Energy Demand

≤ 120 kWh/m²/yr (aligned with EnerPHit, but can vary slightly)

Airtightness

≤ 1.0–2.0 air changes/hour @ 50 Pa (depending on tier of CLR)

Thermal Bridge Free Design

Encouraged but not always required

Ventilation

MVHR strongly encouraged but not strictly mandatory

U-values (Components)

Typically: Windows ≤ 1.2 W/m²K; Walls ≤ 0.2–0.3 W/m²K

Moisture Control

Condensation and moisture risks must be managed

Certification Options

CLR performance tiers (e.g., CLR Silver, Gold) offer flexibility

Yes, this is the perfect time to retrofit your home. Complement the decorative, aesthetic, or functional alterations you wish to make whilst improving the energy efficiency of your home.

Yes. Research conducted by the RIBA showed that for every EPC your home improves by, the sale price of the home increases by approximately 2%.

Yes, you can finance a retrofit through various options, including government grants, low-interest green loans, or energy-efficient mortgage top-ups. Contact us if you want help exploring your options.

Natural materials such as wood fibre insulation, lime plaster, hemp, and cork are highly compatible with high-performance goals. They offer good thermal performance, excellent moisture regulation, low embodied carbon, and are particularly well-suited for breathable and traditional buildings.