Why your home feels draughty — even with the heating on
A draught is not a mystery. It is air moving through your home along a path you cannot see. Warm air rises and escapes through gaps high up — around loft hatches, ceiling light fittings, the tops of walls and chimney flues. As it leaves, it pulls cold air in low down — under skirting boards, through floorboards, around window and door frames, and even through electrical sockets on external walls. This constant exchange is called air leakage, and in a typical London home it can account for a large share of wasted heat.
The frustrating part is that air leakage is invisible. You feel the symptom — a cold draught across the floor, a room that never quite warms up — but you cannot see the cause. That is why so many homeowners spend money on new radiators, thicker curtains or extra insulation and still feel cold. They have treated the symptom without ever locating the leak.
Where draughts and air leaks really come from
Most homeowners assume draughts come from obvious places — an ill-fitting front door, or a rattly sash window. Those are real, but they are rarely the whole story. In our investigations across London properties, the largest leakage paths are almost always hidden inside the building fabric, where you would never think to look.
Windows and doors
Gaps around the frame — not just the opening light — are a common culprit, especially where a window has been replaced without properly sealing the reveal behind the plaster. Old sash windows, worn seals and unfilled gaps beneath thresholds all allow a steady flow of cold air.
Floors and skirting boards
Suspended timber ground floors are ventilated underneath by design, and the gaps between floorboards and at the skirting-board junction let that cold air straight into the room. This is why floors and skirting boards so often feel cold even in an otherwise well-heated home.
Sockets, switches and service penetrations
Every electrical socket, switch, pipe and cable that passes through an external wall or ceiling is a potential leak. Individually they are small; together, across a whole house, they add up to a surprisingly large opening — the equivalent of leaving a window ajar.
Loft hatches, downlights and the ceiling line
Warm air collects at ceiling level and escapes through unsealed loft hatches, recessed downlighters and gaps where walls meet the ceiling. Because warm air is buoyant, these high-level leaks drive the whole air-exchange process — sealing them often has the biggest single effect.
Chimneys and flues
An open, unused chimney is effectively a permanent hole in the top of your house. It creates a powerful upward draught (the stack effect) that pulls cold air in everywhere else. Managing it correctly — without trapping moisture — is part of a proper investigation.
Why ordinary draught-proofing often fails
Draught-proofing strips, silicone and expanding foam all have their place. But sealing the gaps you can see, without testing, misses the gaps you cannot. Worse, sealing the wrong things can cause new problems: block off ventilation carelessly and you can trap moisture, leading to condensation and mould.
There is a crucial balance in every home between airtightness and ventilation. A building should be sealed against uncontrolled leakage but ventilated deliberately, so that stale, moist air is removed in a controlled way. Random DIY draught-proofing upsets that balance. A measured investigation protects it.
How Retrofit IQ investigates air leakage
A Draughts & Air Leakage Investigation is a measured, whole-building process — not a quick look round with a hand held to the window. We combine several diagnostic methods so that we can both quantify the leakage and pinpoint exactly where it is.
Blower door testing
A calibrated fan is fitted to an external doorway and used to pressurise or depressurise the whole house. This lets us measure your home's air-leakage rate to a recognised standard — turning an invisible problem into a hard number we can track and improve. It also exaggerates every leak, making the next steps far easier to find.
Smoke tracing
With the house under pressure, we introduce controlled smoke at suspect points. The smoke shows, visibly and in real time, exactly where air is moving — around a frame, through a socket, under a skirting board. There is no more powerful way to see a leakage path with your own eyes.
Thermal imaging
A calibrated thermal camera reveals the temperature patterns cold air creates as it tracks through the fabric. Used alongside the blower door, thermal imaging distinguishes an air leak from missing insulation — two very different problems that need two very different fixes.
Visual inspection and void checks
We inspect the loft and, where accessible, floor voids, checking insulation continuity, service penetrations and the condition of any existing air barrier. Windows, doors and their reveals are examined, along with every significant service penetration through the external envelope.
The stack effect: why draughts get worse in winter
One of the most useful things to understand about draughts is why they feel so much stronger on a cold, windy day. It comes down to a simple piece of physics called the stack effect. Warm air inside your home is more buoyant than the cold air outside, so it rises and pushes out through any gaps high up in the building — the loft hatch, ceiling downlights, the tops of walls. As that warm air escapes, it creates a slight negative pressure lower down, which sucks cold air in through gaps around skirting boards, floors, doors and windows.
The bigger the temperature difference between inside and out, the stronger this effect becomes — which is exactly why your home feels draughtiest in the depths of winter, when you most want it to be warm. Wind makes it worse still, driving air in on the windward side and pulling it out on the sheltered side. This is why a draught you barely notice in October can feel like a howling gale in January.
Understanding the stack effect also explains why sealing high-level leaks — the loft hatch, the downlights, the ceiling line — often has a bigger effect than sealing the obvious gap under the front door. Stop the warm air escaping at the top, and you reduce the suction pulling cold air in everywhere else. This is the kind of insight a measured investigation gives you, and the reason the order of sealing matters as much as the sealing itself.
How draughts affect comfort, health and running costs
Draughts are not simply an annoyance. They have three real consequences that most homeowners underestimate. The first is comfort: moving air feels much colder than still air at the same temperature, which is why a draughty room never feels warm no matter how high you turn the thermostat. You end up heating the whole house harder to compensate for a localised problem.
The second is cost. Every cubic metre of warm air that leaks out has to be replaced and reheated. In a leaky home, your boiler or heat pump is effectively heating the street. Reducing uncontrolled air leakage is one of the most cost-effective improvements you can make, precisely because it tackles heat that is being thrown away rather than heat that is being used.
The third, and least obvious, is moisture and air quality. The same gaps that let cold air in can, in the wrong conditions, let warm moist air into cold parts of the structure where it condenses — contributing to damp and mould inside walls and lofts. This is why we always assess airtightness and ventilation together: the goal is never simply to seal everything, but to control where air moves.
Draught-proofing done properly: the right order of works
Once an investigation has located and measured your leakage, effective draught-proofing follows a logical order — and it is very different from working through the house sealing whatever looks gappy. We prioritise by impact, which usually means starting at the top of the building and working down, because that is where the stack effect does most of its damage.
- Seal high-level leaks first — loft hatches, ceiling downlights, service penetrations into the loft and the wall-to-ceiling junction — where warm air escapes and drives the whole process.
- Address the ground floor and skirting-board junction next, since ventilated timber floors are often the single largest low-level source of cold air.
- Seal around window and door reveals, not just the opening lights, because leakage often bypasses the frame through the plaster behind it.
- Deal with sockets, switches and pipe runs on external walls, which are small individually but significant across a whole house.
- Manage unused chimneys and flues carefully, sealing them in a way that still allows a little background ventilation to prevent trapped moisture.
- Re-test with the blower door afterwards, so the improvement is measured and proven rather than assumed.
Doing the work in this order means each step builds on the last, and you can see — and measure — the improvement as you go. It also protects the balance between airtightness and ventilation, so you never trade a draught problem for a condensation problem.
Why choose Retrofit IQ for your air leakage investigation
Almost anyone can buy a blower door or a thermal camera. Far fewer are qualified to interpret what they reveal. Your investigation is led by a Certified Passive House Designer — someone who works to the most demanding airtightness standard in the world and understands how air, heat and moisture move through a building as one connected system.
That means you are not paying for a test and a number. You are paying for a diagnosis: an explanation of why your home behaves the way it does, a prioritised plan of what to seal and in what order, and honest advice about what is worth doing and what is not. Whether you carry out the work yourself, use your own builder, or ask us to deliver and verify it, you leave with clarity rather than a list of readings.
Air leakage is part of a bigger picture
Air leakage rarely acts alone. It interacts with insulation, thermal bridging, moisture and ventilation. That is why an air-leakage investigation is most valuable as part of a full Building Performance Investigation — a whole-building diagnosis that looks at how every element performs together, rather than in isolation.
If your only concern is draughts, we can scope the investigation tightly to air leakage. But if you also have cold rooms, high bills or condensation, a Building Performance Investigation gives you a single, coherent picture and one prioritised plan — instead of a series of disconnected fixes.
What you receive
You finish the process understanding your home and knowing exactly what to do next — and in what order — before you spend a penny on remedial works.
- Clear findings, explained in plain English
- Photographic evidence of every significant leakage path
- Thermal images showing where cold air is tracking
- A measured air-leakage result where blower door testing is carried out
- A prioritised plan — what to seal first, and why
- A practical remedial strategy any competent contractor can follow
A real-world investigation example
A homeowner in a Victorian London terrace had already fitted draught excluders to every door and new seals to the sash windows, yet the living room still felt draughty and cold. Under blower door depressurisation, smoke tracing told the real story: most of the cold air was arriving through the gaps between the suspended timber floorboards and at the skirting junction, while warm air escaped through an unsealed loft hatch and a row of recessed downlights. The visible doors and windows were only a minor part of the total. Sealing the floor perimeter and the high-level leaks, then re-testing with the blower door, cut the measured air-leakage rate substantially — and the draughts the owner had chased for years finally stopped.
Common homeowner mistakes
The most common mistake is sealing only the gaps you can see — the front door, a rattly window — while the largest leaks hide in the floor, loft hatch and ceiling. The second is over-sealing without thinking about ventilation, blocking trickle vents or airbricks and swapping a draught problem for a condensation and mould one. Homeowners also reach for expanding foam everywhere, which can trap moisture and is impossible to reverse. Without a blower door test there is no way to know which leaks actually matter, or to prove the sealing has worked.