Condensation Control in North London
Streaming windows every winter morning, mould creeping across cold corners — condensation is the most common moisture problem in North London homes, and the most fixable.
How do you stop condensation in a house? Condensation stops when indoor moisture is removed faster than it's produced and surfaces stay above dew point. In practice that means: effective extraction in kitchens and bathrooms (ducted outside, humidity-controlled), adequate background ventilation (trickle vents, undercut doors, or a positive input ventilation system for the whole home), consistent low-level heating rather than short blasts, and insulating or warming the cold surfaces where moisture condenses. A typical North London condensation remedy costs £300–£1,500 — a fraction of the damp-proofing works condensation is often mistaken for.
Understanding the problem
An average household puts 10–15 litres of water vapour into the air daily — cooking, showers, laundry, breathing. Older homes shed it through draughty sashes, open flues and suspended floors. Then we sealed them: double glazing, draught-proofing, blocked chimneys. The moisture now has nowhere to go, so it finds the coldest surface and condenses there — and North London's solid-wall stock and converted flats offer plenty of cold surfaces.
The result is streaming glazing, saturated reveals, mildewed clothes in wardrobes on outside walls, and black mould. It peaks November–March and is routinely misdiagnosed as rising or penetrating damp — an expensive error our damp vs condensation page helps you avoid.
Signs and symptoms
- Water streaming or pooling on windows in the morning
- Black mould on reveals, corners, ceilings and behind furniture
- Damp bedding, mildew in wardrobes against external walls
- Persistent musty smell despite cleaning
- Condensation on toilet cisterns and cold pipework
- Worse in winter; largely absent in summer
Common causes
- Insufficient extraction where moisture is produced (kitchen, bathroom)
- Draught-proofing and glazing upgrades that removed background ventilation
- Cold surfaces: solid walls, uninsulated lintels, single-glazed or metal frames
- Intermittent heating that lets the fabric cool between bursts
- Indoor laundry drying and unvented tumble dryers
- Overcrowding relative to the dwelling's ventilation provision
Getting the diagnosis right
A condensation assessment measures the problem rather than guessing: humidity and temperature logging to establish dew-point margins, surface temperature mapping to find the cold spots, extraction flow tests against Building Regulations Part F rates, and a room-by-room ventilation audit. It also rules out fabric damp masquerading as condensation. Start with our free Condensation Risk Calculator and Ventilation Audit Checklist, then have a survey confirm the plan.
Treatment
- Extraction where moisture starts — humidity-controlled extractor fans in bathrooms, ducted cooker hoods in kitchens, both vented to outside.
- Whole-home ventilation — a positive input ventilation (PIV) unit gently pressurises the home with filtered air, displacing humid air outwards; the single most effective retrofit for persistent whole-house condensation.
- Background ventilation — trickle vents, door undercuts, and reinstated airflow where refurbishment sealed everything.
- Warm the cold spots — targeted insulation of reveals, lintels and problem walls lifts surface temperatures above dew point.
- Habits that help — lids on pans, doors closed while showering, laundry dried outside or in a vented space, low continuous heat in cold snaps.
What does it cost in North London?
| Item | Indicative range |
|---|---|
| Condensation assessment | £150 – £300 |
| Humidity-controlled extractor fan, installed | £250 – £450 |
| PIV unit, installed | £800 – £1,500 |
| Trickle vents / background ventilation | £60 – £120 per window |
| Cold-spot insulation works | £300 – £2,000 |
Most homes are fixed for £300–£1,500. Compare that with a mistakenly prescribed DPC — diagnosis pays. Figures are indicative for North London (2026) and vary with property, access and scope — written quotations follow a survey. See the North London Damp Cost Guide or try the Damp Proofing Cost Calculator.
Our process
Tell us the problem
Call or use the contact form — describe what you're seeing and where. Photos help.
Survey & diagnosis
An independent qualified surveyor inspects the property and identifies the true cause, with a written report.
Clear written quote
You receive a costed scope for exactly what the property needs — no more, no less.
Treatment & verification
Works are carried out by vetted independent specialists, with guarantees where applicable and verification that the fix worked.
Frequently asked questions
Overnight, moisture produced during the evening meets glazing that has cooled below dew point, so it condenses there first — glass is usually the coldest surface in the room. It signals that indoor humidity is running too high for the ventilation available.
A dehumidifier helps manage symptoms and dry a damp room, but it treats air, not the cause, and costs money to run continuously. Fixed ventilation — extraction plus background or PIV — removes moisture automatically and permanently. Dehumidifiers are a good stop-gap, not the solution.
Positive input ventilation is a loft- or wall-mounted unit that continuously supplies filtered air at low volume, gently displacing humid stale air out through the building's natural leakage points. For whole-home condensation and mould in typical houses and flats it has a strong track record; installed costs run £800–£1,500. Details on our ventilation solutions page.
Current Building Regulations Part F expects intermittent extraction of 30–60 l/s in kitchens and 15 l/s in bathrooms, plus background ventilation in habitable rooms. Many older North London homes, especially converted flats, fall well short — which is exactly why they suffer.
Yes: rotted window timber, ruined decorations, saturated plaster, mould-damaged possessions and, in concealed spots, wet rot in structural timber. It's not cosmetic — it's the most common moisture defect in the housing stock and worth fixing properly.
Worried about damp, mould or a wet basement?
Speak to us today or book a survey — we'll arrange the right independent specialist for your property.