Why do I have condensation on my double glazed windows?
Condensation on your double-glazing windows. General The phenomenon of surface condensation on double-glazed units occurs in three forms: • On the external face (face 1) • On the inner surfaces 2 and 3 of the double-glazed unit • On the internal face or face 4.
- Condensation on the internal face (4)
The phenomenon of surface condensation on face 4 of a double glazed unit is mainly linked to the following factors:
-The external climate
-The internal air temperature
-Humidity within the building
-The ventilation flow rate
-The surface temperature of the glass To limit condensation, it is advisable to control each of the above parameters, with the exception of
the external climate, which is ever-changing.
The best way to reduce surface condensation on the internal face is to collect the water vapour at source (for example in the kitchen or bathroom) and evacuate it straight outside. It is also advisable to heat and ventilate the premises adequately.
It is also possible to reduce the risk of condensation by using a "warm-edge" spacerbar such as SGG SWISSPACER.
- Condensation on the external face (1)
Surface condensation will appear on face 1 of the insulating glazing if the temperature on this face of the glazing is significantly lower than the external air temperature and if the dew point
(i.e. temperature at which water vapour becomes liquid) of the external air is higher than the temperature of the glass.
The surface temperature on the outside of glazing is dependent on:
-The heat flow from the interior passing through the glass. This depends on the difference in temperature between the internal surface and the external surface of the glazing and the U-value of the glass
-The heat exchange by convection with the external air
-Heat loss by radiation mainly to the sky.
Various studies and measurements carried out by the CSTC have shown that heat exchange by radiation is relatively limited in overcast weather. However, when the sky is clear at night, there are significant heat losses to the sky.
The effect of radiation from a glazed surface to the sky can be compared with a car parked outdoors at night in clear (cloudless) weather: in the morning, some parts of its outer surface are wet, or even covered in frost, even if it has not rained. When the car is parked alongside a building, the windows on the building side are never wet, because the building significantly reduces the heat exchange by radiation between the car windows and the sky.
This table shows that:
-The surface temperature of single-glazing is almost never lower than the external air temperature, so condensation
rarely occurs on the external face
-Improving the thermal insulation (lower U-value) reduces the transfer of heat to the external surface: the external glazed surface is therefore colder, increasing the risk of condensation.
- When there is a high wind speed, the temperature of the glass tends to be similar to that of the external air
-The cooler the external air, the less likely the glazing is to have a significantly lower temperature than that of the external air.
- Condensation on inner faces 2 and 3
The formation of condensation on the inner faces of the double-glazed unit is an indication that the air or gas cavity is no longer completely sealed. The desiccant will rapidly become saturated and any damp air penetrating via the seal around the perimeter will reduce visibility by forming condensation on faces 2 and 3. The double-glazed unit must therefore be replaced as this cannot be reversed.
This double-glazed unit must be replaced in accordance with the terms and conditions of the warranty.
- Temporary condensation occurring:
- Is normal. This condensation should not be permanent.
- Large amounts of water are required when using building materials such as concrete, plaster, grouting and tiles during the renovation or construction of a building. As these materials dry, temporary abnormally damp climates are created inside buildings (occasionally lasting more than a year) during which time the risk of condensation is abnormally high.
- Using an aluminium spacerbar in a double-glazed unit can cause a thermal bridge effect. The unfavourable effect of this thermal bridge will be even greater the higher the degree of insulation of the insulating glazing in the central part (low central U [W/m2K]) and the higher the thermal performance of the frame in which it is inserted (low Uf [W/m2K]). SGG SWISSPACER which significantly reduces this edge effect.
- Confined spaces: Even in well-ventilated and/or heated premises, the confined spaces can be created, causing localised abnormally humid climates (e.g. the space between an external frame and a curtain, decorations or furniture near windows etc). The risk of condensation in this instance can be abnormally high.
- When does condensation occur?
Condensation on the external surfaces of an insulating glass unit can form in a wide variety of circumstances and on either the inside or the outside of a building.
The principal cause of condensation on glass on the inside of a building is a high internal humidity level coupled with a low outside temperature which cools the inside surface to below the dew point. Bathrooms, kitchens and other areas where humidity levels are high are particularly susceptible to this problem.
In order to control this form of condensation, consideration should be given to improving the heating and ventilation in these areas. However, another way to reduce the problem is to use high performance windows containing an enhanced thermally insulating glass.
Thermally insulating glass
Windows manufactured using insulating glass units containing an energy efficient "low-emissivity (low-E) coating" such as, SGG PLANITHERM TOTAL actually restricts heat exchange across the airspace between the two panes of glass keeping the inner pane of glass warmer and so reducing the instances when condensation can form.
Condensation forms on the outdoor surface of glass when its temperature drops below the outdoor dew point temperature.
Insulating units containing an energy efficient, low-emissivity glass such as SGG PLANITHERM TOTAL, have enhanced thermal insulation properties thanks to a high performance transparent coating that reflects heat back into the room. As a result the outer pane of glass does not get warmed by heat escaping from inside the building through the glass and remains cooler in comparison to less thermally efficient windows.
External condensation only occurs in certain climatic conditions with high humidity levels and/or particularly cold weather. It is possible that, external condensation will appear on some windows but not on others. This is due to localised atmospheric conditions such as shelter from nearby trees or buildings, variable air currents and wind speeds and varying levels of nearby vegetation.
- Please note:
Condensation on the outdoor surface of such high performance windows is in no way an indication of a defective unit. Indeed, this can be seen as a positive indication that the enhanced thermally insulating units are actively reducing heat loss through the glass.
Secure By Design – What Is It All About?
Secure By Design, or SBD, is an industry standard which many will have heard of. But for those not so familiar, or if you’re wanting to scrub up on the whole subject, this is the post for you.
Secure By Design is a police backed standard which promotes products which are designed in such a way to make life more difficult for would-be burglars. Well that’s my paraphrasing. This is the definition of SBD by the Police themselves:
Secured by Design focuses on crime prevention of homes and commercial premises and promotes the use of security standards for a wide range of applications and products.
The principles have been proven to achieve a reduction of crime risk by up to 75%, by combining minimum standards of physical security and well-tested principles of natural surveillance and defensible space.
Our objective is to reduce burglary and crime in the UK by designing out crime through physical security and processes.
Secure By Design was established in 1989 and is owned by ACPO (Association of Chief Police Officers). They are dedicated on the design and security for new & refurbished homes, commercial premises and car parks as well as the acknowledgement of quality security products and crime prevention projects. Since 1989, companies in the window industry have been striving to design products which meet the SBD standard. Companies that do reach those standards are able to use this logo on their products and literature:
How to Toe and Heel
Toeing and Heeling
UPVc doors and opening windows (sash) are heavy, and although the dead weight is supported on the hinge side when it is opened, there is nothing on the lock side to support the weight , and without the procedure of toeing and heeling the door will “drop” on the handle side. To prevent a door or sash dropping the glass or door panel has to be braced diagonally corner to corner (See Diagram) by the insertion of plastic packers slipped in the gap between the glass or panel and frame.
The door or sash on the lock side should be raised to the desired height and squared up with the door frame. On the hinge side place the packers at the bottom corner, whilst on the lock side, the packers go at the top (opposite) corner – place a dab of silicone under the packers on the door sides to stop the packers dropping. It is advisable to use a glazing shovel when lifting the glass or panel. The packers should be placed approximately 150mm from the edge of the frame.
Why does double glazing mist up?
Double glazing is formed from two panes of glass sealed together, with a gap left between them, to form a double glazed unit. The air trapped inside the window (or gas depending on the rating of double glazing you have fitted), creates an insulating barrier that keeps heat in. It is only when the seal on the glass breaks, or fails as is known in the industry that condensation gets into the window, resulting in a misted up window. The seal can break for a number of reasons, but is mainly due to the age of the window and how it was manufactured (the seals don’t last forever), how it was originally fitted and any chemical cleaning material used on the window overtime that might have damaged the seal. To resolve the problem a new glass pane needs to be fitted by a qualified installer. Pro-Fit can advise you on the best way to sort this type of problem out whilst keeping costs at a minimum. So get in contact with us today to get that annoying window sorted out.