Where the moisture appears matters: room-side surface condensation, exterior surface condensation and moisture inside a sealed glazing cavity do not share one diagnosis or remedy.
A photograph labelled ‘window condensation’ may show three different conditions. Moisture on the room-side glass can reflect indoor humidity and a cold surface. Moisture on the exterior face can occur under outdoor cooling conditions. Moisture within a nominally sealed insulating-glass cavity points to a different evidence route. First locate the wet surface; only then discuss cause.
Health and building boundary: Persistent moisture can damage finishes and support microbial growth. Electrical, façade-access and concealed-moisture risks require competent personnel. This guide is not a building-science diagnosis or a warranty determination.
1. Locate the moisture surface
Confirm whether moisture is on surface #1 outside, the room-side exposed surface, or within the glazing cavity. Wipe accessible surfaces separately and observe whether the moisture returns. Do not dismantle sealed units or access unsafe elevations for this check.
Record whether moisture occurs at the centre, edge, spacer line, frame, sill or adjacent wall. A cold edge pattern, isolated cavity haze and water entering from above are different observations.
| Observation | Record |
|---|---|
| Wet surface | Exterior / room side / between panes / uncertain |
| Pattern | Centre / edge / frame / sill / wall |
| Timing | Morning, weather event, occupancy event, continuous |
| Extent | One unit, elevation, room type or repeated configuration |
| Other signs | Staining, corrosion, sealant change, odour or drainage water |
2. Understand surface condensation without oversimplifying it
Condensation can occur when a surface temperature is below the dew-point condition of adjacent air. FGIA notes that interior surface condensation commonly appears when indoor relative humidity is high, particularly in cold climates. That statement is a starting principle, not proof that occupants caused a particular event.
Record indoor and outdoor temperature and humidity using identified instruments and times; also note blinds, curtains, air supply, room use and recent moisture generation. Surface temperature, local air movement, edge-of-glass conditions, frame conductivity and installation interfaces may all matter.
- Room use and occupancy
- Indoor/outdoor temperature and humidity
- Glass/frame surface temperatures where competently measured
- Blinds, curtains and furniture position
- Heating/cooling supply and return paths
- Perimeter air leakage or cold-bridge indicators
- Frequency, duration and affected elevations
3. Treat exterior condensation as a separate condition
Exterior glass may cool below the outdoor air’s dew point under clear-sky radiation and suitable humidity/wind conditions. Improved insulating performance can reduce heat flow from indoors that might otherwise warm the exterior pane. The occurrence therefore does not by itself prove a defective window.
Document the face, time, sky exposure, shading, wind and whether neighbouring glass constructions behave differently. Do not promise that a coating or product will always prevent exterior condensation without project-specific evidence.
Diagnostic rule: Exterior moisture, room-side moisture and cavity moisture must never be grouped into one defect count without identifying the surface.
4. Investigate moisture between panes through the IGU record
Haze, droplets or deposits inside a nominally sealed cavity require confirmation that the observation is truly inaccessible from both exposed faces. Identify the IGU, manufacture/date code where available, glass make-up, spacer, seal system, drainage and installation history.
Do not state ‘argon escaped’ or ‘seal failed’ merely because glass looks cloudy; coatings, surface contamination, reflections or deposits can be misread. Obtain consistent views, inspection and the supplier/fabricator review route.
| Field | What to capture |
|---|---|
| Unit identity | Opening mark, pane and IGU marking |
| Visual condition | Both faces cleaned/checked; lighting and angle |
| Pattern/history | Edge/centre, intermittent/persistent, first observed |
| Exposure | Elevation, drainage, sealant and edge condition |
| Configuration | Glass, coating surfaces, spacer and gas specification |
| Disposition route | Inspection, warranty notice and retained evidence |
5. Review edge and frame conditions
Condensation often begins near a colder glass edge or conductive frame zone. Compare the installed frame, spacer, thermal break, glazing bite, perimeter insulation and interior air seal with the approved details. This is an interface review, not a conclusion that one component caused the condition.
Water in a track may also be managed rainwater rather than condensation. FGIA explains that many systems temporarily collect water and drain it through weep paths. Keep drainage holes clear and distinguish rainfall timing from moisture generated without rain.
- Glass edge/spacer pattern
- Frame and thermal-break continuity
- Glazing and setting condition
- Interior air-seal continuity
- Perimeter insulation and substrate
- Track/weep cleanliness and discharge
- Rainfall correlation
6. Match the action to the supported condition
Room-side surface condensation may lead to review of moisture generation, ventilation, air distribution, surface temperatures and envelope interfaces. Exterior condensation may call for expectation management or project-specific surface/exposure review. Confirmed cavity moisture follows the IGU identification, notice, inspection and replacement/warranty route.
Avoid one-size remedies such as adding sealant, drilling a unit or lowering humidity without competent review. An action can hide evidence or create new safety, air-quality or warranty problems.
| Supported condition | Next review | Do not assume |
|---|---|---|
| Room-side surface moisture | Humidity, temperature, airflow and interface review | Product defect or occupant fault |
| Exterior surface moisture | Weather/exposure and glass comparison | IGU seal failure |
| Cavity moisture confirmed | IGU identity, inspection and claim route | Cause and warranty entitlement |
| Rainwater/track water | Drainage and leakage investigation | Condensation |
7. Verify after correction across comparable conditions
Record the intervention and repeat observations under comparable weather and occupancy conditions. A dry hour after wiping is not closure. For repeated buildings, compare affected and unaffected units while controlling for orientation, room use and configuration.
Close the issue with the supported condition, measurements, action, remaining uncertainty and monitoring period. Feed recurring configuration findings into future glass, frame and installation reviews.
Compare a wet bathroom window with a dry neighbouring room carefully
Suppose a bathroom window is wet after bathing while a bedroom window appears dry. First record the wet surface and location. Then compare room use, time, ventilation operation, blinds and the glass/frame configuration. Different room conditions mean the bedroom is not automatically a control specimen that proves the bathroom window is defective.
In the reverse situation, several windows with the same configuration may show different observations because exposure and use differ. Group observations by opening mark and room, keeping the recorded conditions alongside the images. Do not turn a count of wet windows into a count of failed insulating-glass units.
This hypothetical comparison is a way to improve the enquiry, not a diagnosis. It does not justify changing ventilation settings, replacing glazing or blaming occupants without the responsible investigation.
Send observations that a reviewer can compare
For each reported event, provide the opening identity, date/time, room use, affected face if known, and whole-opening plus detail photographs taken safely. Record whether it followed bathing, cooking, rain or another event. Include any temperature or humidity readings with instrument identity, location and time rather than an unexplained number.
Keep observations separate from interpretations. For example, write room-side lower-edge droplets observed after bathing rather than failed glass. If the face is uncertain, say so; do not dismantle the window or attempt unsafe exterior access to resolve that uncertainty.
Retain a short sequence of comparable observations if requested by the investigator. A photograph before and after wiping records an intervention, not a verified cure. Any agreed change should be documented with its review basis before the result is compared.
Feed supported findings back into the next room layout
Once the responsible team has identified the supported condition, connect the finding to future room planning where relevant. A reach problem, inaccessible screen or blind arrangement may need coordination even if it did not cause the moisture. Keep those practical improvements distinct from the technical cause and warranty decision.
Review bathroom window planning for privacy and operation, or kitchen window planning for counter and tap coordination. Send the affected opening details with the observation record when seeking help.
FAQ
Does room-side condensation prove the window is defective?
No. Indoor moisture, surface temperature, air movement, edge/frame and installation conditions all require review.
Is exterior condensation a sign of failed insulating glass?
Not by itself. Exterior surface cooling can create condensation under suitable weather conditions.
Does haze between panes prove argon loss?
No. First confirm the surface and IGU identity; specialist review is needed before cause or gas-retention conclusions.
Is water in a window track always leakage?
No. Some systems temporarily collect and drain water, but blocked or overwhelmed drainage and other leakage paths still require review.
Can one humidity target prevent all condensation?
No universal target covers every climate, surface temperature, occupancy and building condition.
Continue the project review
Connect this guide with the proposed window and door systems, then review how Cavorlen approaches manufacturing and quality control. When your schedule is ready, send it through the project review form.
Official sources used
FGIA — Caring for Windows, Doors and Skylights ↗NGA — GANA Glazing Manual ↗ASTM — Building Standards Index ↗Related buyer guides
This guide does not diagnose mould, certify an IGU seal failure, set a safe indoor humidity level or determine warranty responsibility from photographs.