The short answer
Condensation on the inside of conservatory glass is usually caused by warm, humid air meeting the cold glass surface — it is a ventilation issue rather than a structural fault. Condensation between double-glazed panes indicates a failed seal and requires unit replacement. External condensation on solar-control glass is normal and disappears as the sun rises. Damp in the frame, base or walls may indicate a leak or drainage problem. See are conservatories cold in winter for the thermal context.
Condensation is one of the most frequent sources of concern for conservatory owners, and it is important to distinguish between three different types: internal condensation (inside the room on the glass surface), interstitial condensation (between the two panes of a double-glazed unit), and external condensation (on the outer surface of the glass). Each has a different cause and a different solution. Alongside condensation, actual damp — water ingress from leaking seals, guttering, or the junction with the house — is a more serious issue that needs investigation.
Condensation and damp at a glance
- Internal condensation Normal in cold weather — improve ventilation
- Between panes Failed unit seal — replace the glazing unit
- External condensation Normal on solar-control glass — not a defect
- Damp in frames Check seals, guttering and roof junctions
- Damp on base Check drainage and base waterproofing
- Mould on walls Persistent humidity — ventilation or heating needed
Internal condensation — what causes it
Internal condensation on conservatory glass forms when warm, humid air inside the conservatory meets a cold glass surface. The glass surface is below the dew point of the air, so moisture precipitates out as condensation. In a conservatory this commonly happens in the morning, particularly in autumn and winter, because the glass has cooled overnight and the first warm air of the day (or steam from the adjoining kitchen) triggers condensation when it reaches the cold surface. This type of condensation is a ventilation and humidity issue, not a structural defect. The practical remedies are: improve ventilation (particularly night-time ventilation, which allows the glass to exchange heat more slowly), reduce humidity sources (good kitchen extraction, avoid drying clothes in the conservatory), and consider a low-emissivity glass upgrade which keeps the inner glass surface warmer.
Interstitial condensation — failed glazing unit
Condensation or fogging between the two panes of a double-glazed unit is a definitive sign that the hermetic seal of the unit has failed. Once the seal fails, moist air enters the cavity and condenses on the inner glass surfaces, often forming a permanent internal misting or water droplets that cannot be wiped away. A failed unit cannot be repaired — it needs to be replaced. Unit replacement in a conservatory is generally possible without replacing the whole frame, provided the frame is in good structural condition. A FENSA-registered glazier can usually replace individual units. The cost of replacement varies by size and glass specification, but for a standard conservatory roof panel it typically runs £100–£300 per panel. Unit failure is more likely in older conservatories (10 years+) or where the original units were of poor quality.
| Type of condensation | Where it appears | Cause | Solution |
|---|---|---|---|
| Internal | Inside surface of glass | Warm air meets cold glass | Ventilation, heating |
| Interstitial | Between the two glass panes | Failed unit seal | Replace glazing unit |
| External | Outside surface of glass | Cold glass surface, solar-control coating | None needed |
| Structural damp | Frames, walls, floor | Water ingress | Find and fix the source |
External condensation — a sign of a good coating
External condensation — misty or dewy glass on the outer surface of the roof — is a phenomenon associated particularly with solar-control and self-cleaning glass coatings. The coating reduces the glass’s ability to re-radiate heat, so on clear nights the glass surface temperature can drop below the dew point of the outside air, causing external condensation. Counterintuitively, external condensation is actually a sign that the glass coating is working as intended: the solar-control coating is keeping the outer surface cooler. It typically clears within an hour or two of sunrise and requires no action. If a customer has been told their solar-control glass is “steaming up” and offered a replacement, be aware that external condensation is not a defect.
Damp in frames, base or walls
Damp that appears to be coming from the frame, from the floor base or from the junction with the house wall is generally a water ingress problem rather than a condensation issue. Common sources include: failed silicone sealant at the ridge, eaves or frame junctions; blocked or leaking guttering overflowing back into the frame; a cracked or deteriorated base allowing groundwater to track up; or a gap at the flashing between the conservatory roof and the house wall. Investigating the source systematically — starting with the most likely cause (guttering and ridge seals) — is more useful than applying more sealant broadly without understanding the entry point. A professional conservatory repair specialist can survey the structure and identify the source. This page is general information, not a structural or damp survey; if damp is persistent or significant, a professional inspection is recommended.
Concerned about condensation or damp?
A conservatory repair specialist can inspect and identify whether the issue is simple ventilation, a failed glazing unit, or a water ingress problem that needs structural attention.
Frequently asked questions
Why is my conservatory roof steaming up on the outside?
External condensation on the outside of solar-control or self-cleaning glass is normal and is actually a sign the coating is working correctly. It clears within a couple of hours of sunrise and is not a defect.
How do I stop condensation inside my conservatory?
Improve ventilation (particularly overnight ventilation), reduce humidity sources (kitchen extraction, avoid drying clothes in the space), and consider a low-emissivity glass upgrade which keeps the inner glass surface warmer. See our winter guide for related advice.
My conservatory glass has gone misty between the panes — what does that mean?
Misting between the panes of a double-glazed unit means the hermetic seal has failed. The unit needs replacing — it cannot be repaired. A FENSA-registered glazier can usually replace individual units without replacing the whole frame.
My conservatory floor is damp — is that normal?
No. Damp on the floor or walls indicates a water ingress problem, not normal condensation. Common sources are blocked guttering, failed sealant joints, or a crack in the base. Investigate the source — applying sealant without finding the entry point rarely fixes the problem long-term.
Sources & further reading
- Glass & Glazing Federation — conservatory condensation types, glazing unit failures and ventilation guidance
- FENSA — replacement glazing unit standards and FENSA-registered installer requirements
- GOV.UK — Building Regulations Approved Document C (resistance to moisture) as applied to conservatory junctions
- LABC — Local Authority Building Control guidance on weatherproofing and damp in conservatory structures
This is general information about conservatories and orangeries in the UK, not planning, structural, legal or financial advice. Costs are typical illustrations only and are not quotes for any specific project; actual prices vary with size, site conditions and your chosen installer.