Condensation on the inside of windows

Do this first

Your safe boundary

You may record the pattern and use existing occupant controls, but do not wipe, dry or clean condensate or alter glazing or ventilation.

Water on room-facing glass may be surface condensation, but repeated wetting, mould or damaged finishes needs investigation.

No verified cost range is available for this page.

Safety warnings

Warning

Damp needs a diagnosis

Do not buy an invasive damp treatment from a label, photograph or meter reading alone. Condensation, leaks, penetrating damp and rising damp need different remedies; get the cause inspected first.

Visible damp, mould, mould odour or water damage requires prompt action, but it does not by itself identify the cause. Several causes may coexist. Rising damp is often misdiagnosed and may need chemical testing to confirm. An appropriately qualified inspection should assess severity, location, moisture sources and health risk before remedial work is chosen.

Do now

Report damp, mould, mould odour or water damage promptly to the landlord or property manager; owner-occupiers should arrange an appropriately qualified inspection.
Record the location, extent, timing, odour and visible water damage, but do not delay urgent reporting or repairs while collecting evidence.
Ask for the inspection to identify all likely moisture sources and the underlying cause before treatment is specified.
Seek healthcare advice if damp or mould may be affecting someone's health; call 999 for a medical emergency.

Do not

Do not assume rising damp from a photograph, surface mark or simple moisture-meter reading alone.
Do not commission an injected damp-proof course, tanking, sealing or another invasive treatment before the cause is competently assessed.
Do not treat surface mould removal or repainting as proof that the moisture source has been fixed.
Do not blame occupant behaviour, close the report or delay property action while waiting for medical evidence.

Get help

For a rented home, notify the landlord or property manager and request an in-person inspection by an appropriately qualified contractor.
In England, if a landlord does not address the problem, contact the local council's housing or environmental health team for advice and possible inspection.
Escalate promptly where there is extensive mould, an active leak, vulnerable occupants or reported health effects.
Where water is near electrical equipment or wiring, keep away and treat it as an electrical danger.

Caution

Stay at ground level

This check is ground-level only. Do not climb a ladder, roof, wall or platform to improve the view. If the area cannot be seen safely from the ground, record it as unknown and use a competent contractor.

Ground-only observation can help identify whether professional inspection is needed, but it does not confirm condition or make access safe. The moment the task needs ascent or exposure to a fall, this warning no longer applies and W-HEIGHT is required.

Do now

Remain on stable ground and keep the observation non-invasive.
Record anything that cannot be seen safely as unknown rather than moving to a higher position.
Use a competent contractor if a closer or elevated inspection is needed.

Do not

Do not climb a ladder, roof, wall, tree, vehicle or improvised platform.
Do not lean from a window or cross a barrier to improve the view.
Do not convert a ground-only check into work at height.

Get help

Use a competent contractor for elevated access or inspection.
Resolve W-HEIGHT if the task requires ascent or exposes anyone to a fall.
Call 999 if someone falls or is in immediate danger.

What is known — and what is not

What is known

Only the page's recorded observations, documents and stated scope are treated as known.

What remains uncertain

Wet room-facing glass cannot identify whether indoor moisture, cold fabric, heating, ventilation or water ingress is responsible. [1][2]

Possible explanations

surface condensation on a cold pane [1][2]
insufficient moisture removal from the room [1][2]
a rain-related frame or surrounding-wall defect [1][2]
a wider dwelling moisture problem [1][2]

What the pattern may mean

Water that appears on the room-facing pane after sleep, cooking or bathing may fit surface condensation, but it does not identify the underlying reason. [1]
Clouding enclosed between panes is outside this condensation page and may indicate a sealed glazing-unit issue.
Wetness that starts at one frame edge during rain, or local wet plaster around the opening, may indicate an external water path. [1]
The same morning pattern in several rooms may indicate a dwelling-wide moisture, temperature or ventilation issue. [1][2]

What you can check safely

Photograph the glass, frame and nearby finish without touching, wiping or drying the condensate. [1]
Log which exposed pane face is wet, the time, recent room activity and weather. [1]
Use an installed background ventilator only through its normal occupant control and leave it unobstructed. [2]
Operate an extract fan only through its normal user control and record sound, indicator or apparent failure without removing a cover. [2]

When to stop and escalate

Stop at observation if access is awkward, mould is extensive, finishes are failing or water is near electrical equipment. [1]
Do not remove glazing beads, seals, vents, fan covers or electrical enclosures. [2]
Do not treat between-pane moisture as room-side condensation or select replacement glazing from this symptom alone.
Do not paint over mould or commission invasive damp treatment before the moisture source is assessed. [1]

Diagnosis before remedial decisions

Ask an independent building or damp professional to separate room-side condensation, water ingress and cold-building details where the pattern persists. [1]
Use a competent ventilation professional if a fan, background ventilator or whole-dwelling air path may be defective. [2]
Use the written diagnosis to define the responsible system and scope before any remedial decision.

Property, sale and letting implications

Repeated standing water may damage frame-adjacent finishes and support mould if the underlying conditions remain. [1]
For sale preparation, retain dated evidence, the diagnosis and completed-work records rather than relying on cosmetic covering.
In an English rented home, report recurring condensation, mould or a suspected repair need to the landlord or agent. [3]

Frequently asked questions

Does this prove the window has failed? No; room-side water may be surface condensation, while enclosed between-pane moisture is a separate glazing symptom.
Should the windows be replaced first? No; moisture sources, ventilation, heating, cold surfaces and possible ingress should be separated before a product is chosen. [1][2]
What should a tenant do? Keep dated evidence and report recurrence or mould to the landlord or agent rather than arranging unauthorised building work. [3]

Review triggers

Review this page if H3 changes any linked safety row or warning reference.
Review after a change to Approved Document F or national damp and mould guidance.

Evidence checkpoints

The exposed face on which water forms is a diagnostic clue, but it does not by itself identify the moisture source. [1]
Evidence date: 2026-08-12
Approved Document F addresses extraction at moisture sources and ventilation for the whole dwelling. [2]
Evidence date: 2026-08-12
GOV.UK tells tenants in England to contact their landlord if the property needs repairs or has mould. [3]
Evidence date: 2026-08-12

Scope and safety review

This guidance applies to homes in England.

Jurisdiction: England
Who this covers: adult resident
Tenure: owner-occupied, private rented, social rented
Reviewed: 2026-08-13

Sources

Understanding and addressing the health risks of damp and mould in the homeMinistry of Housing, Communities and Local Government; Department of Health and Social Care; UK Health Security Agency. Accessed 2026-08-12.
Ventilation: Approved Document FMinistry of Housing, Communities and Local Government. Accessed 2026-08-12.
Private renting: RepairsGOV.UK. Accessed 2026-08-12.