VELUX Condensation & Ventilation Guide

Why Does Condensation Form on VELUX Windows?

Condensation on the inside of a VELUX window is a common occurrence — especially in bedrooms, bathrooms and loft conversions. It happens when warm, moist indoor air meets a cold surface, such as the glazing of a roof window.

This guide explains the causes, how to prevent it and what to do if condensation appears *between* the panes of glass.

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1. Is Condensation Normal?

Yes — internal condensation is normal and does not mean the window is faulty. It usually indicates high humidity in the room.

• Common in winter
• More likely in rooms with poor ventilation
• Often seen after showers, cooking or drying clothes

You can reduce it significantly with better airflow and temperature control.

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2. Common Causes of Condensation

Several everyday activities produce moisture in the air:

• Showering or bathing
• Cooking without extractor fans
• Drying clothes indoors
• Breathing while sleeping (especially in small loft rooms)
• Insufficient ventilation or lack of air circulation

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3. How to Reduce Condensation on VELUX Windows

These simple steps can dramatically reduce moisture build-up:

• Use the VELUX ventilation flap daily
• Open the window for a few minutes of fresh air
• Ensure extractor fans are working in bathrooms/kitchens
• Avoid drying clothes in enclosed rooms
• Maintain consistent room temperatures
• Use blinds correctly to prevent temperature differences

Modern VELUX glazing also improves insulation, helping reduce condensation.

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4. Condensation *Between* the Panes

This type of condensation is not normal. If you notice misting between glazing layers, the sealed unit may have failed.

• The window insulation is reduced
• Visibility becomes cloudy or streaked
• A permanent “fog” appears inside the glass

This is a strong sign the window may need replacing. See our VELUX Replacement Guide.

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5. Improving Ventilation in Loft Conversions

Lofts are among the most common spaces for condensation due to warm air rising and moisture collecting near the roof.

• Use windows daily for passive ventilation
• Consider installing multiple VELUX windows for cross-flow air
• Ensure trickle vents are kept open
• Check insulation around the window is fitted correctly

Proper installation reduces cold spots that can attract moisture. Learn more in our VELUX Flashing & Installation Guide.

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6. Preventing Condensation on Blinds

Blinds can trap warm air against the glazing, increasing condensation if the room is humid.

• Open blinds daily to release trapped moisture
• Choose blinds with insulating honeycomb designs for temperature control
• Use external awnings to reduce heat variation in sunny rooms

See our VELUX Blinds & Shading Guide for more options.

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7. When Is It Time to Replace the Window?

Replacement may be necessary if you notice:

• Condensation *inside* the glazing layers
• Cold draughts around the frame
• Water ingress or staining
• Worn or damaged timber surrounding the window

Newer VELUX models offer better insulation and improved ventilation features.

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8. Quick Checklist for Reducing Condensation

• Use ventilation flap daily
• Open the window briefly each morning
• Keep extractor fans maintained
• Avoid excess indoor moisture
• Keep blinds open when possible
• Upgrade glazing on older windows

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