Condensation and Conservation Rooflights

Condensation and Conservation Rooflights

Almost every activity that we do within the home produces water vapour. Whether it is cooking, washing or simply breathing we all add moisture to the atmosphere around us. Under normal circumstances the air within your home is able to support or absorb this moisture and hold it in suspension.

Moisture rich air circulates around the house and is changed as it travels out of windows and doors. This happens most months without any problems and you never notice any visible signs. That is until the balance shifts and gap between internal and external temperatures increases.

One particular activity that likely to increase water vapour in the air is drying laundry indoors. Yes your clothes will dry quicker in the house but where does that water from your clothes go? It does not simply dry up and disappear but is absorbed into the air within the home.

When the summer months draw to a close, we start to keep the windows and doors shut for longer as the evening temperatures drop off. Our activities of cooking, washing and breathing continue unchanged but in the colder conditions and with windows closed, there are fewer air changes in the home. The air continues to circulate picking up more and more moisture as we go about our normal lives.

The amount of moisture or water vapour that can be held is increased by putting on the heating but there is still a limit to how much water the air can hold. In todays’ world of high energy prices more and more of us are holding off that decision until absolutely necessary but the heating does much more than just warm us.

A good example of the air reaching saturation point is when we emerge from a bath or shower and see steam floating around in the bathroom. The air has absorbed as much as it can and you can suddenly see all this moisture before your eyes. We accept this as the norm and in most cases the water vapour will deposit itself on your mirror or tiled surfaces before clearing through into another room or out of the window.

Condensation and Conservation Rooflights

Although not so exaggerated as in the bathroom scenario, our normal living activities produce large amounts of moisture which for certain months of the year start to manifest as condensation.

Condensation is the result of moisture saturated air coming into contact with a cold surface and then shedding its water onto that surface. Traditionally condensation would form on window frames and the glass as this would have been the point where the colder temperature of outside had the best opportunity to pass through into the warmer house.

Years on from the old metal frame windows, most modern homes now have energy efficient glass in thermally broken frames, problem solved? Unfortunately not; in fact modern construction methods actually make the incidence of condensation more likely as the airtight designs reduce the opportunity for air to flow and change within the homes. Years ago most homes had a chimney and ill-fitting windows and doors which allowed the air to flow. Condensation appeared on the windows and that was widely accepted.

Modern windows and skylights do not suffer as much from condensation but modern living and home design actually increases the moisture within the air. This is not a problem when the heating is cranked up but without it you are more likely to see mould growth in the backs of wardrobes, the hall and in bedrooms than you are condensation on your windows.

Condensation and Conservation Rooflights

Condensation and Conservation Rooflights

Two sleeping adults produce around 1 ½ pints of moisture in 8 hours which is absorbed as water vapour into the atmosphere. If you turn off your heating at night as the temperature drops, the air cannot hold as much moisture and it will deposit that when it comes into contact with a colder surface.

A new 3 bedroom house will absorb around 1500 gallons of water during the construction, much of which is dissipated into the indoor atmosphere during the drying out period. Adding heating and carpet will help but that is still a large amount of moisture being added to the air which is likely to be seen as condensation somewhere in the property.

Condensation and Conservation Rooflights

The architects and product manufacturers continue to try and design out condensation from our homes but our very way of life still remains the biggest problem. Cooking, showers & baths, drying clothes, better fitting windows and doors, no chimney all add to the problem and increase the risk of condensation.

Condensation is not caused by products but merely reflects the atmospheric conditions that we as occupants create. As such, we also have a responsibility to manage both the risk and the water when it does occur. Simply ignoring those beads of water on the glass in the morning will ultimately result in the discolouration of your window frames, silicone and rubbers. Ignore the water in your bathroom and the grout and silicone will go black and you may suffer from mould growth in corners and on the ceiling.

Unchecked, condensation will damage paintwork, curtains, wall coverings and fittings. Over time it will damage items beyond repair and could be costly. It is natural to regularly vacuum the carpets or dust the furniture, whereas maintaining our windows and rooflights seems less of a priority. Most view windows and skylights as unimportant or even products that do not require regular care, which is far from the truth.

All products require some maintenance, particularly those in coastal or high pollution environments. Why then should it not be as natural to clear away the water from the bedroom windows in the morning or wipe down the tiles in the bathroom after use and check the walls for any spots of damp or mould each month.

Despite the introduction of modern glazing, genuine steel framed windows and conservation rooflights will always have a slightly increased risk of developing condensation particularly when used in modern buildings.

The Glass & Glazing Federation (GGF) produce an information booklet about causes and advice for condensation which can be viewed on our downloads section. This guide not only explains how condensation forms but also gives practical tips about reducing the risk of it happening.

Some useful advice, taken from the GGF booklet pertaining to how to reduce condensation when formed on the room side surface of the inner glass is as follows:

– Provide natural ventilation through an opening section of the window, or through a proprietary ventilating unit, or through an airbrick.

– Where there is no open fire, or where existing flues have been blocked off (and cannot be unblocked), ensure that all vents are fitted and kept clear.

– Open at least one window in each room for some part of the day to permit a change of air.

– Ensure ventilation of all rooms where gas or oil heaters are used.

– Fix hoods over cookers and other equipment producing steam, and ventilate them to the outside air.

– Ensure that bathrooms and kitchens are ventilated in accordance with National Standards.

– Draught proof internal doors and keep them closed to prevent transfer of air with a high water vapour content from the main moisture producing rooms – kitchens, bathrooms, and drying rooms. It should be borne in mind that water vapour does not remain in the room where it is first generated, but tends to migrate all over the house because:

    1. The water vapour pressure in the original room may be higher than elsewhere, and so the moist air will be forced out into rooms with a lower pressure, and
    2. Convection currents will carry it through the house,

– Increase slightly the air temperature within the house.

– In cold weather, keep some form of heating on permanently in the house.

– Wherever practicable, fix radiators under windows to maintain the temperature of the inner glass at a reasonable level.

– Condensation can be caused by isolating the inner glass from the warm room air with heavy curtains when drawn. To allow free passage of warm air to the glass, position curtains 15cm to 20cm away from the window, and ensure there are sufficient gaps at the top and bottom to permit continuous circulation. (Holes should be drilled along the top of any box pelmet used.)

In conclusion, condensation is caused by the way we live combined with a perception that modern products are somehow maintenance free. With a better understanding of how condensation comes about we can take action to reduce the possibility of it happening and care for our products when it does.

Should your window or rooflight or ceiling suffer from condensation or mould growth it is most likely to be the reflection of the environment rather than any serious product failing. Clearing any moisture away from the affected area will extend the product life and stop unsightly mould patches spreading.

For further information or to discuss your conservation rooflight requirement contact the Stella Rooflight team on 01794 745445 or email

Stella Rooflight Launches ‘The Ultimate Guide to Conservation Rooflights’ A Groundbreaking Resource for Architects & Homeowners
Stella Rooflight Launches ‘The Ultimate Guide to Conservation Rooflights’ A Groundbreaking Resource for Architects & Homeowners