Insulating a Victorian terrace in London: a practical guide
If you live in a Victorian terrace in London, you may notice a familiar pattern. The house feels lovely in summer evenings but cold in winter mornings. Some rooms warm up quickly, others never feel quite right. You may have considered new insulation, a heat pump or even a ventilation system, but it can feel overwhelming to know where to start.
This guide walks you through the essentials in a calm, step-by-step way. Victorian terraces have their own characteristic strengths and weaknesses. When you understand them, you will find that creating a warmer, more efficient home is much easier than you expect. The key is to work with the original brick and timber, not against it, and to think of insulation as one part of a well-balanced upgrade.
This article takes you from an early understanding of building science to a point where you feel ready to make confident decisions for your own home.
Why Victorian terraces lose so much heat
Victorian terraces are charming, solid and generous in detail, but their construction was never designed with modern comfort in mind.
Solid brick walls
These walls have no cavity. A cavity is the gap between two brick layers that allows for easy insulation. Solid brick means the wall absorbs rain, stores moisture and loses heat quickly.
Leaky junctions
Window frames, suspended floors, chimney surrounds and roof voids often have gaps that allow cold air to move freely. This uncontrolled air leakage is what makes a room feel draughty even when the heating is on.
Chimneys acting as open vents
Unused chimneys continuously pull warm air up the stack. It is a constant extraction system that you do not control.
Moisture in the walls
This is one of the most misunderstood issues. When the wall fabric is damp, the insulation value collapses because water conducts heat roughly twenty-two times faster than air. It is the same effect as wearing a wet jacket. You feel much colder because the soaked fabric cannot trap warm air.
A successful retrofit keeps the fabric dry, reduces unintended air movement and improves ventilation in a controlled way. Insulation is important, but it is only effective when the house can breathe.
Three principles for insulating a Victorian terrace well
1. Keep the building fabric dry
Breathability refers to the ability of a wall or floor to allow moisture vapour to travel through it. Victorian brick loves to breathe. If it becomes trapped between a non-breathable layer inside and a modern paint outside, moisture can accumulate. This increases heat loss and raises the risk of mould.
We use natural materials where possible because they allow the fabric to dry out while still offering good insulation. Wood fibre boards, calcium silicate panels and lime plasters are typical examples.
2. Reduce uncontrolled air leakage
Airtightness means controlling where air comes in and out, rather than letting it move through cracks. Leaky homes feel colder because warm air escapes quickly and cold air enters through gaps.
This does not mean sealing the house shut. It means creating a continuous layer that stops unwanted draughts while allowing managed ventilation. Your airtightness and ventilation article will sit perfectly alongside this topic for anyone who wants to explore the detail.
3. Balance insulation with ventilation
When insulation is added without considering ventilation, condensation becomes a real risk. Modern ventilation systems, such as MVHR (mechanical ventilation with heat recovery), bring in fresh air while retaining warmth. They do this by passing outgoing stale air across a heat exchanger. In simple terms, you keep the warmth while removing the moisture and pollutants.
This balance is what makes a well-insulated Victorian terrace feel calm, healthy and comfortable.
Where to insulate in a Victorian terrace
Victorian terraces follow a very consistent pattern: a narrow plan, party walls to each side, a front elevation facing the street and a rear elevation facing the garden. This makes the insulation strategy relatively predictable.
External walls
Front and rear walls can often be insulated in two different ways.
Internal wall insulation (IWI)
This means adding insulation on the inside face of the wall. It reduces room size slightly but allows breathability if the right material is used. It is often the preferred option on the front elevation, especially in conservation areas where changing the external appearance is prohibited.
External wall insulation (EWI)
This means placing insulation on the outside face of the wall. It keeps the brick warm and dry, which significantly improves performance. At the rear of a terrace, planning constraints are usually lower, which allows a breathable EWI system to be used.
A London terrace might use IWI at the front and EWI at the back. This combined approach manages moisture sensibly and keeps costs under control.
Wood fibre internal wall insulation being fitted to a Victorian terrace. This breathable build-up keeps the brick dry, reduces heat loss and prepares the room for a warmer, more comfortable finish.
Roof and loft
The loft is usually the largest source of heat loss.
Cold roof insulation places insulation at ceiling level.
Warm roof insulation places it at rafter level.
Cold roofs are simpler but need the ceiling below to act as a proper fire barrier. Any holes from recessed lights should be protected. Warm roofs are excellent when a loft conversion is planned, because the insulation becomes part of the new roof build-up.
A loft extension in a Victorian terrace during installation. Wood fibre insulation creates a warm, breathable roof build-up that supports a comfortable, energy-efficient home.
Floors
Victorian terraces almost always have suspended timber floors at the front and rear. These can be insulated by lifting the boards and placing breathable insulation between the joists. Mineral wool or wood fibre is ideal.
If a ground floor extension sits on a slab, a different insulation strategy is used, usually rigid insulation above or below the slab depending on the age and construction.
Suspended floor insulation in progress. Mineral wool between the joists and a continuous airtightness layer help reduce draughts and create a warmer ground floor in a Victorian terrace.
Windows and doors
New sash windows with good airtight seals can transform comfort levels. Secondary glazing is often the best solution in conservation areas because it retains the original timber frame while improving thermal performance.
Airtightness tapes at the junction between the frame and the wall are important. These are flexible membranes that seal the perimeter and prevent draughts.
Choosing materials that suit a Victorian home
Natural, vapour-open materials help the house manage moisture naturally.
Good choices include:
Wood fibre insulation
Calcium silicate boards
Vapour open plasters
Lime-based paints
These materials allow the wall to breathe, which keeps it dry and efficient. They pair well with the existing brick and timber because both were originally designed to move small amounts of moisture.
Modern materials can also work well when used with care. Rigid PIR boards, for example, are useful in roof spaces where moisture levels are controlled.
Sequencing the works in a logical order
Budget constraints mean most London homeowners complete their retrofit in stages.
A good sequence looks like this:
Loft or roof insulation
Airtightness improvements and ventilation planning
Wall insulation (internal at front, external at rear if appropriate)
Suspended floor insulation
Window upgrades
Heating system improvements, such as a heat pump
Each step prepares the house for the next. The wrong order increases risk and cost. For example, a heat pump only performs well once insulation and airtightness have been improved.
Budget guidance for London Victorian terraces
Costs vary depending on the age and condition of the home, planning constraints and material choices. Typical London ranges in 2025 are:
Internal wall insulation: £180 to £250 per square metre
External wall insulation: £260 to £350 per square metre
Loft or roof insulation: £45 to £75 per square metre for ceiling level insulation
Warm roof upgrade: £180 to £260 per square metre
Suspended floor insulation: £80 to £120 per square metre
New high-performance windows: £1,200 to £2,000 per unit depending on size
MVHR: £8,000 to £15,000 for a typical terrace
Light retrofit package: £25,000 to £45,000
Deep retrofit package: £65,000 to £110,000 and above
These are starting points. Prices move with inflation, access constraints and detailing complexity. London projects typically demand a fifteen to twenty five percent uplift over national averages.
Common mistakes we fix when other builders get it wrong
Many builders are excellent at general construction but are unfamiliar with the specific needs of period homes.
The most common issues we resolve include:
Using impermeable foams that trap moisture in solid brick walls
Blocking suspended floor ventilation, which leads to decay in timber joists
Insulating one room in isolation, creating cold bridges that encourage condensation
Mixing internal and external insulation without a moisture plan
Installing insulation without upgrading airtightness, which reduces performance
Adding insulation to ceilings without protecting fire compartmentation
Using the wrong plaster types, which can blister or peel on traditional substrates
Over-skimming damp walls, hiding the symptom rather than solving the cause
These are small details, but they have a significant effect on comfort, longevity and safety. This is where a carefully considered approach adds value.
Case study: the Victorian Terrace
Many of our projects involve Victorian terraces in London, each with its own constraints and opportunities. A common pattern is a conservation-area front elevation with original brick detailing and a rear elevation that has more freedom.
A typical project might use:
Internal wall insulation at the front, preserving the façade
Breathable external wall insulation at the rear, improving performance
A suspended floor upgrade to remove draughts
A loft ceiling or warm roof upgrade, depending on future loft plans
In one recent project, the homeowner noticed that the front reception room was always colder than the kitchen. Internal wall insulation reduced heat loss, while external wall insulation at the rear created a stable thermal environment. The difference in comfort was immediate. Rooms felt calmer, warmer and quieter. A future heat pump is now a realistic option.
A Victorian terrace in Hackney with an upgraded exterior. The retrofit includes wood fibre insulation, new triple-glazed Passivhaus windows and a warm roof extension that improves comfort throughout the home.
The new loft bedroom and ensuite. Natural materials, a warm roof build-up and triple-glazed windows create a calm, comfortable space with excellent thermal performance.
Next steps and how we can help
A Victorian terrace becomes a very different home once insulation, airtightness and ventilation are working in harmony. Rooms warm evenly, surfaces stay dry and the whole house feels calmer. The challenge is knowing where to start and how to make improvements in a sensible order.
If you would like a clear route forward, our Home Visit and Appraisal is the simplest first step. We walk through the house with you, listen to your priorities and explain where the largest gains sit. You will understand whether to begin with the loft, the walls, the floors or the ventilation, and how each decision affects the next.
From there, our Retrofit Strategy becomes your roadmap. It sets out two upgrade pathways, outlines budget ranges, highlights moisture risks and shows you how to phase the work without wasting money. Homeowners find that this early clarity removes stress and makes every later decision easier.
Whenever you feel ready to explore what is possible for your own terrace, we would be delighted to help you plan the next stage.
You may also find it helpful to read our in-depth guide on airtightness and ventilation as well as our broader article on how to insulate a London home.
