Your Home Climate
Air Quality · The problem library

Why are my windows wet every morning, and what does that actually mean?

Recently reviewed·Reviewed June 2026, next review December 2026

Condensation on glass is almost always a ventilation problem before it is a window problem. The air in the house holds moisture from cooking, washing, drying clothes and breathing, and the coldest surfaces in the room are usually the windows. Reducing the moisture in the air, or removing it before it reaches the glass, is the lasting fix. Replacing windows alone tends to move the condensation somewhere worse.

Editorial confidence
High confidence. Multiple regulator, government or academic sources agree.
Evidence status
Recently reviewed · reviewed June 2026 · next review December 2026
Monitoring
Every six months, plus whenever Approved Document F or the BSRIA domestic-ventilation guidance is updated.
Evidence drawn fromBuilding standards: ADF, CIBSEProfessional bodies: EST, Loughborough DEFACTOIndustry evidence: BSRIA
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Condensation on windows every morning; November, with morning mist. The kettle has just been on; condensation is sitting along the bottom of the kitchen window.
A Victorian terrace on an overcast November morning. The kettle has just been on; condensation is sitting along the bottom of the kitchen window.

Indoor relative humidity threshold

60% RH

Source: Building Regulations; Approved Document F · Above roughly 60% relative humidity, surface condensation and mould risk rise sharply; Approved Document F's continuous ventilation rates are designed to keep typical homes below this.

Whole-dwelling continuous ventilation rate

0.3 l/s per m² of floor area

Source: Building Regulations; Approved Document F · Approved Document F sets the minimum whole-dwelling continuous ventilation rate; many older homes deliver substantially less, especially with trickle vents closed.

Who this advice is for

Applies to

  • Houses and flats heated to typical UK winter setpoints
  • Properties with modern double or triple glazing and visible morning condensation
  • Bedrooms, kitchens and bathrooms where moisture is generated
  • Homes with trickle vents or background ventilation

Not intended for

  • Penetrating damp or rising damp diagnosis
  • Listed buildings where window or vent alterations are restricted
  • Buildings with confirmed structural water ingress
  • Commercial premises governed by workplace ventilation rules

What it usually looks like

These are the symptoms readers describe most often. None of them alone is diagnostic, but together they build a picture.

  • Streaming water on glass every morning in winter
  • Damp curtains and wet sills
  • Black spotting starting to appear in corners
  • Worse in bedrooms than in living rooms

Most common in: Victorian terrace · Edwardian semi-detached · Interwar semi (1920s–1930s) · New-build flat

Before you buy anything

Watch the house respond as you scroll.

These checks are listed in the order we would work through them. The illustration on the left changes with each one, so you can see what each check is actually addressing before deciding whether it is worth doing.

Warm wet air meets the coldest surface in the room overnight, which is almost always the window. By morning it is running.

01

Buy a cheap hygrometer and read it for a week

Above sixty per cent relative humidity is the threshold where condensation and mould risk start. Knowing the actual number tells you what kind of intervention you need.

02

Check where moisture is being created

Drying clothes indoors without ventilation can add ten litres of water to the air per week. Moving drying to a vented utility, or using a dehumidifier in the same room, makes a measurable difference.

03

Confirm the extractor fans actually work

A bathroom extractor that takes ten minutes to clear a steamy mirror is doing very little. Run-on timers and humidistat switches are inexpensive upgrades.

04

Check the trickle vents on the windows

Many homes have trickle vents that have been taped shut or painted over. Opening them is free and often resolves persistent morning condensation.

05

Measure surface temperatures in the worst rooms

A cold spot in a corner that sits below the dew point will always condense. Adding insulation to the cold surface is the real fix, not a dehumidifier.

Before you spend money

The cheapest answer is usually the one nobody sold you.

  1. 01

    Buy a £15 hygrometer and log indoor humidity for a week

    Condensation is a humidity problem dressed up as a window problem. The number tells you whether the air, the glass or both need attention.

    £15
  2. 02

    Run the extractor fan for the full shower plus fifteen minutes

    Most kitchen and bathroom fans are switched off too soon. An extra fifteen minutes after the source stops costs pennies and often removes the morning streaks entirely.

    Free
  3. 03

    Lift bedding off external walls and pull furniture an inch clear

    Trapped air against a cold surface is where mould begins. Moving a wardrobe two centimetres is free and frequently solves the entire problem.

    Free
  4. 04

    Use trickle vents or crack a window overnight

    A small continuous air change at night clears the morning streaks for free; sealing every window tighter without adding ventilation makes the problem worse, not better.

    Free

What we recommend, and why

Every recommendation explains why it comes first, the evidence behind it, how confident we are, and when it would not apply.

01

Measure indoor humidity for a week before doing anything

Why this comes first

Condensation is the visible symptom of an invisible variable, so changing kit before you know the actual humidity is guesswork. A ten-pound hygrometer logged for a week tells you whether the room sits at 50%, 65% or 80% relative humidity, and that number determines whether the right answer is ventilation, dehumidification or fabric.

Evidence

Approved Document F frames continuous ventilation in terms of moisture loads; BSRIA's domestic-ventilation guidance and EST advice recommend a hygrometer-first diagnosis before any system change.

ADF · BSRIA · EST

Confidence

High confidence. Multiple independent sources agree on the direction and the order.

Exceptions
  • Homes with installed humidity-aware ventilation already reporting data
  • Visible water ingress that requires a building survey first
Next step
Open the MVHR assessor
02

Open the trickle vents and run the extractors properly

Why this comes first

A surprising share of morning condensation in UK homes comes from trickle vents that have been closed, taped or painted shut, and from extractor fans that run only briefly during a shower. Restoring background ventilation usually resolves morning condensation within a week and has no capital cost.

Evidence

Approved Document F treats trickle ventilation and continuous extract as the baseline strategy; EST guidance documents real-world reductions in surface condensation from restoring background ventilation.

ADF · EST

Confidence

High confidence.

Exceptions
  • Properties with confirmed whole-house mechanical ventilation systems
  • Homes on noise-exposed elevations where trickle vents are demonstrably unusable
Next step
Open the ventilation overview
03

Move to a continuous ventilation strategy if the house is permanently damp

Why this comes first

A house that sits above 60% relative humidity all winter is producing more moisture than its current ventilation can remove. Positive input or mechanical extract with heat recovery moves the dwelling onto a continuous rather than intermittent strategy, which is what modern UK guidance now expects of tighter buildings.

Evidence

Approved Document F, BSRIA BG 58 and CIBSE design guidance all support a continuous ventilation strategy for tighter modern homes; intermittent extract alone is not sufficient when air change is low.

ADF · BSRIA · CIBSE

Confidence

Reasonable confidence.

Exceptions
  • Leaky pre-1919 homes where uncontrolled infiltration already provides high air change
  • Properties where fabric and shading should be addressed before ventilation plant
Next step
Open the MVHR hub

The trade-offs

Every choice gives you something and asks for something back.

  • Behavioural and ventilation fixes only

    You get

    The morning condensation gone for the price of a hygrometer and a habit change, and no risk of over-engineering.

    You give up

    Reliance on remembering to vent, which is not realistic in every household.

  • Continuous extract or positive input ventilation (PIV)

    You get

    A measurable, automatic drop in indoor humidity and a much wider margin against future mould.

    You give up

    £400-£1,500 plus install, a unit in the loft or hallway and the slight running cost of a low-wattage fan.

  • Upgrade windows to better double or triple glazing

    You get

    A warmer inner pane that condensation forms on less often, plus better acoustic and thermal comfort.

    You give up

    Several thousand pounds, disruption and the truth that windows alone will not fix the underlying humidity.

Real homes that faced this

Publicly documented UK projects that ran into the same problem and reported what happened.

We did not run these projects. Each links back to the original publisher so you can read the figures in context and judge for yourself what carries over to your home.

How we'd approach this

Fix the air before you blame the glass.

If this were happening on our own windows we would buy a hygrometer before doing anything else. Condensation is humidity meeting a cold surface; the surface is half the story. Treating it as a window problem is how people spend ten thousand pounds and still have damp curtains in January.

We would change the cheapest things first: extractor run times, trickle vents, the gap behind furniture, the lid on the saucepan. These adjustments are unglamorous and almost always sufficient in a typical UK home; the kit only earns its place when the habits have been tried and the numbers still sit above 60% for weeks.

When ventilation kit is the right answer, we would lean toward continuous extract or PIV rather than another bathroom fan, because the problem is the whole-house air balance rather than one wet room. Windows we would treat last, and only as part of a wider fabric upgrade rather than as a moisture cure.

Evidence behind this page

Every recommendation on this page is traceable to its source. Click a publication to read the original.

Products that may help

Only consider these once the checks above have been ruled out. A product fitted into the wrong cause is rarely satisfying.

House Summary

The cheapest answer to condensation on windows every morning is usually the one that addresses the cause rather than the symptom. The list above is in the order we would work through it, because the checks at the top tend to rule out the most expensive mistakes further down.

Related decisions
Next Best Step

Ventilation; what your home actually needs

Take the next step