How Much Should You Retrofit Your Home?
If you’re planning a home retrofit, the hardest question is not what to install, but how far to go.
Get this wrong, and you can spend a lot of money without really fixing how your home feels.
Most homeowners get conflicting advice.
Some are told to “just insulate and add a heat pump.”
Others are pointed toward complex standards.
And somewhere in the middle, you’re left wondering:
👉 How much should I actually retrofit my home?
Before you decide what to install, you need to decide how far you are trying to go.
Most people start in the wrong place
Most homeowners start with a solution.
A heat pump.
New windows.
Insulation.
Each one sounds sensible.
But without a plan, they often work against each other.
It’s a bit like putting a powerful new engine into an old car without fixing the rest of it. You’ve upgraded one part, but the system still doesn’t work properly.
We regularly see homes where money has been spent, but the house is still cold, uneven, or expensive to run.
This is why retrofit projects go wrong.
Not because the ideas are bad.
Because the sequence is wrong.
👉 The problem is rarely the technology. It’s the lack of a plan.
The real decision: how far should you retrofit your home?
Retrofit is not one thing.
It’s a spectrum.
At one end, you make small, practical improvements.
At the other, you fundamentally change how the house performs.
Both can be right, but they suit very different homes, budgets, and levels of ambition.
The key is choosing the level that matches your priorities.
The four levels of home retrofit (light to deep)
These levels are not rigid rules. Think of them as a way to understand what’s possible.
Light retrofit is one path.
AECB and EnerPHit are different ways of approaching a much deeper, whole-house upgrade.
Light Retrofit
This is the most common starting point and is explored in more detail in our light retrofit approach.
You improve what you can, where you can.
That might include:
Loft insulation
Draught-proofing
Upgrading windows
Improving heating controls
It’s relatively low disruption and lower cost.
It can make your home feel less draughty and slightly warmer, and it can reduce energy bills.
But it has limits.
You’re not fundamentally changing how the building works. So improvements are often modest, and issues like cold spots or uneven temperatures may remain.
AECB CarbonLite Retrofit
This is where you move into what’s often called a deep retrofit.
The AECB CarbonLite Retrofit standard is a UK-developed approach that uses Passive House methods, but applies them in a more flexible and practical way for existing homes.
You can read a full breakdown in our guide to the AECB CarbonLite Retrofit standard.
In simple terms, it means:
Improving insulation across the whole house
Reducing unwanted draughts through airtightness
Designing a proper ventilation approach, so fresh air is controlled rather than accidental
This is where the fabric first approach to retrofit becomes important. In other words, improving the building itself before relying on technology.
Think of it as wrapping the house in a well-fitted thermal coat, then controlling how fresh air comes in.
The result is a home that feels evenly warm, quieter, and much more stable throughout the day, without constantly adjusting the heating.
It requires careful coordination, because more elements need to work together, but it is often a practical balance between performance, cost, and disruption.
👉 This sits firmly in the category of whole-house retrofit, rather than isolated upgrades.
EnerPHit
EnerPHit sits in the same category of deep retrofit, but follows the stricter Passivhaus-family criteria set by the Passive House Institute.
We explain this in more detail in our article on the EnerPHit retrofit standard.
This is where you start to seriously transform the building.
Typical characteristics:
Very high levels of insulation
Extremely airtight construction
Mechanical ventilation with heat recovery, meaning fresh air is supplied while keeping heat inside
In simple terms, both AECB and EnerPHit aim to transform how the building performs. The difference is that EnerPHit follows a tighter, more formalised standard, often with certification, while AECB allows more flexibility to respond to real-world constraints.
This is where you start to feel a real shift in how the house behaves day to day.
But this is also where projects can go wrong if not properly designed.
It is more complex.
More disruptive.
And usually more expensive, with more at stake if decisions are made in the wrong order.
Without careful design and delivery, the benefits can quickly be lost.
Passivhaus
Above both of these sits full Passive House, which is typically associated with new buildings and represents an even higher performance benchmark.
The goal is simple:
A home that requires very little energy to heat or cool.
In practice, this means extremely high levels of insulation, airtightness, and ventilation working together as one system.
If you want a clear explanation, see our guide to the Passive House standard.
For most existing homes in London, Passivhaus is not always practical. But it provides a useful benchmark for what the highest level of performance looks like.
What changes between light and deep retrofit?
As you move from light to deep retrofit, several things change. Not just energy use, but how your home feels day to day.
Comfort
Rooms feel evenly warm, even on cold mornings. Fewer cold spots. No more moving from one uncomfortable room to another.
Energy use
Heating demand drops. In deeper retrofits, it can fall dramatically.
Running costs
Bills become more predictable and often lower, depending on how well the system is designed.
Air quality
With the right ventilation strategy for period homes, the air becomes fresher and healthier, by design rather than by accident.
Complexity and disruption
This is the trade-off. The deeper you go, the more coordination is required, and the more the house may need to be opened up.
👉 Most homes in London sit somewhere between light retrofit and a carefully planned deep retrofit. The right answer is rarely at the extremes. Most homes sit where performance, cost, and disruption are properly balanced.
👉 The end result, when done properly, is a home that feels warmer, quieter, calmer, and far more predictable day to day.
Why a deeper retrofit is not always better
It’s easy to assume that the highest standard is always the best choice.
In reality, it rarely is.
Every home has constraints:
Planning restrictions, especially in conservation areas
Structural limitations
Budget
How long you can live with disruption
There are also diminishing returns.
The first improvements often deliver the biggest gains. Beyond that, each step becomes harder, more expensive, and more dependent on getting the details right.
👉 Retrofit is not about doing everything. It’s about doing the right things, in the right order.
So how far should you retrofit your house?
Most people try to choose a standard.
Light. AECB. EnerPHit.
But that’s not really the decision.
You are not choosing a label.
You are choosing a strategy, whether you realise it or not.
A way of improving your home that:
Fits your budget
Works with your building
Can be delivered in the right sequence
Often, the best approach is phased, especially in period homes where everything cannot be done at once.
You do not need to decide everything at once, but you do need a plan for how it fits together.
You might start with a light retrofit.
Then move toward a deeper upgrade over time.
Or you might take the opportunity during a major renovation to go further in one go.
There is no single correct answer.
But there is a correct way to decide.
Start with a Retrofit Strategy
If you’re unsure how far to go, the best place to start is not with a product, but with a plan.
A retrofit strategy helps you:
Understand how your home currently performs
Define the right level of ambition
Plan improvements in the right order
Avoid costly mistakes
It brings everything together into one clear direction.
It also connects back to the wider home retrofit process, so each decision supports the next.
If you are planning a renovation, extension, or energy upgrade, this is where you start.
Where to go next
To go deeper into specific parts of your retrofit, you can explore:
Or, if you want help defining the right level for your home, we can work with you to build a clear, step-by-step retrofit strategy.
