AECB Retrofit Standard: A Practical Guide to Deep Retrofit for UK Homes

Most homes don’t need a quick fix. They need a proper upgrade.

Cold spots. Draughts. Rooms that never quite feel comfortable. Energy bills that keep climbing.

So you start looking into retrofit.

And quickly run into confusion.

There isn’t one clear path.

If you’re planning a whole house retrofit in the UK, you’re already in deep retrofit territory. The real question is:

👉 how strict do you want to be?

This is where the AECB retrofit standard sits.

Understanding the retrofit spectrum

Not all retrofit projects are the same.

They generally fall into four broad levels:

• Light retrofit approach
  Smaller upgrades like replacing windows or adding insulation in isolation

• AECB CarbonLite Retrofit
  A deep, whole-house approach designed to work in real UK homes

• EnerPHit retrofit standard
  A deep retrofit standard within the Passivhaus family, with stricter targets and certification routes

• Passive House
  The highest performance benchmark, typically used for new build

If you want a broader overview, see how much you should retrofit your home.

At this level, the choice is not whether to retrofit deeply.

👉 It is how tightly you define success.

What is the AECB retrofit standard?

In plain English:

👉 The AECB retrofit standard is a practical retrofit standard for UK homes. It improves performance significantly using the same underlying principles as Passivhaus, but with more flexibility.

It is built on:

• detailed energy modelling (using PHPP, a tool that predicts how your home will perform)

• a fabric-first approach

• careful attention to moisture, ventilation and how the building is actually constructed

• a focus on comfort and health, not just energy targets

It is designed specifically for:

• existing buildings

• UK construction methods

• real-world constraints

It can be applied as:

• a full deep retrofit

• or a phased approach over time

If you’re new to this way of thinking, start with a broader home retrofit guide.

What does this mean for your home?

AECB is not about hitting a number on a spreadsheet.

It is about how your home behaves.

In practice, a well-designed AECB-level retrofit can lead to:

• more consistent temperatures across rooms

• fewer draughts and cold surfaces

• lower and more predictable energy use

• reduced risk of condensation and mould

• fresher, more stable indoor air

Clients often tell us the biggest change is not the energy bill.

It is that they stop thinking about the heating altogether.

The house simply feels comfortable.

AECB and EnerPHit: what’s the difference?

This is where a lot of confusion arises.

Both AECB and EnerPHit are:

👉 deep retrofit approaches

Both use:

• Passive House methodology

• PHPP modelling

• a fabric-first strategy

The difference is not how “deep” they go.

👉 It is how strictly performance is defined and verified.

AECB CarbonLite Retrofit

• Designed for UK homes and constraints

• More flexibility in targets and sequencing

• Strong focus on comfort, risk management and practical buildability

• Certification is optional

👉 In simple terms:
Deep retrofit designed to work in the real world

EnerPHit

• Part of the Passivhaus family

• Stricter performance targets

• Formal certification through the Passive House Institute

• Requires tighter design control and execution

👉 In simple terms:
Deep retrofit designed to meet a stricter benchmark

Think of it this way:

👉 AECB is a well-planned route.
👉 EnerPHit is a stricter rulebook.

Both can get you to a high-performing home. One allows more flexibility in how you get there.

If you want to explore this further, see EnerPHit retrofit standard explained or Passivhaus standard explained.

When AECB is a good fit

AECB is particularly well suited when:

• you are already planning a renovation or extension

• you want a meaningful improvement in comfort and energy use

• your home has constraints, such as being a period property

• you want a coordinated whole-house retrofit approach, not isolated upgrades

• you value practical decision-making and buildable solutions

It works especially well across London’s solid-wall housing stock.

When you might consider EnerPHit instead

EnerPHit may be more appropriate if:

• you are aiming for very high performance

• you want formal certification

• you are willing to design and build to a tighter benchmark

• your project allows a high level of control and coordination

When a lighter approach might be appropriate

In some cases, a full deep retrofit may not be realistic.

You might opt for a lighter approach if:

• the budget is limited

• the scope of work is small

• the project is short-term

But this comes with a risk.

Upgrading one part of a house without considering the rest is like fixing one note in an instrument that is out of tune.

It rarely solves the underlying problem.

The real risk is not choosing a standard. It’s not having a strategy.

Most retrofit problems don’t come from choosing AECB or EnerPHit.

They come from:

• doing things in the wrong order

• upgrading one part of the house without considering the rest

• not understanding how the building works as a system

This is why having a retrofit strategy matters.

If you’re new to this idea, start with fabric first retrofit: why the building comes before the systems.

How to decide what’s right for your home

There is no one-size-fits-all answer.

The right level of retrofit depends on:

• your goals

• your budget

• your building

• your appetite for complexity

If you’re still unsure where you sit, this guide on how much you should retrofit your home breaks it down.

What matters is that the decisions are:

• coordinated

• informed

• sequenced properly

Want clarity on the right approach for your home?

We help homeowners define the right level of retrofit through two routes:

• A Retrofit Strategy, focused on performance, comfort and sequencing

• A Home Visit Appraisal, focused on feasibility, scope and early decisions

Both are designed to help you move forward with confidence.