Householders FAQs - Windows and Conservatories

1 Why have I got external condensation on my windows?

We receive a lot of enquiries about the appearance of external condensation particularly in the Spring and Autumn.

Fitting modern low-emissivity glazing does increase the chances of external condensation but this is not a fault in the glass or the windows. The phenomenon is a natural and predictable event caused by the outer pane of the glazing being colder that the glass that it replaced. With single glazing and older style double glazing a larger proportion of heat was lost to the outside through the glass.  With modern low-e glazed windows more of the heat is kept inside and the outer pane is not heated as much. Moisture condenses out of the air onto a cold surface that is said to be below the dew point. The dew point varies with the air temperature and the amount of moisture it contains. In Spring and Autumn in particular the glass temperature can fall to a low level during the night and the dew point can be comparatively high in these seasons. The glass is more often likely to be below the dew point in these conditions and the moisture condenses onto the surface. 

We are all obliged to fit more thermally efficient windows in our homes to comply with the latest Building Regulations. There are only a few exceptions to the regulations and they tend to apply to unheated spaces that would suffer external condensation to the same extent anyway. The trend is to use glass that has lower U-values in future providing better thermal insulation and, the lower the U-value, the lower the outer pane temperature is likely to be and the bigger the risk of condensation on the external surface. In northern European countries where they use triple glazing with very low U-values the phenomenon is understood and accepted. The householders are focused on saving energy and maintaining a comfortable internal environment.

There is not much that can be done to avoid the risk of condensation to the outside. Heating the room more would have an effect but this understandably is not a good option. In many cases the condensation does not last long. A little heat from the sun warms the outer glass enough to evaporate the moisture and a gentle breeze or wind will do the same job. 

Those people who have fitted Pilkington Activ™ may also notice that they get fewer occurrences. Pilkington Activ™ self cleaning glass is as prone to condensation as any other glass but the properties of this product means it doesn’t allow the water to form beads on the surface of the glass and so you don’t see the effect to the same degree.

You may notice that not all of the panes are affected by early morning condensation even in the same window.  Even subtle differences in orientation and the position of objects outside the window can change the surface temperature of the glass to the point that one pane suffers and another does not.  Any object (be it an overhang, canopy, tree etc.) blocking off the window to a clear night sky may also have the effect reducing the occurences.

A plus point is the knowledge that your windows are keeping the heat in as they are designed to do thus proving that you have a superior insulating glass product. The presence of external condensation in a particular season does not mean that the glass will suffer the same throughout the year. Any occurrence is beyond the control of the window supplier and is a natural result of the environmental conditions. 

If you are experiencing condensation to the inside of the room or there is condensation between the panes of glass then that is a different problem. Misting between the panes indicates a seal failure and the glass should be replaced. Misting inside the room may be as a result of a failed unit seal but is more likely to be the humidity or moisture content of the air in the room being very high eg. from a bathroom or kitchen. Bottled gas and paraffin heaters produce a lot of moisture and even breathing expels enough moisture in an unventilated space to cause the formation of condensation. Increasing the ventilation to such spaces helps control the problem.

For more information on external condensation, please refer to our Technical Bulletin which can be obtained by completing our contact form.

We offer a glass product called Pilkington Anti-condensation Glass. This is used on the outer pane of the double glazed unit. It provides a second low-emissivity glass which is designed to delay the onset of external condensation and hence improve the view through the window. For more information visit our product page.

2

Is it true that using Pilkington K Glass™ in my conservatory will turn it into a greenhouse?

Double glazing incorporating low-emissivity glass such as Pilkington K Glass™ does not lead to significantly greater overheating problems in summer than does single glazing, or ordinary double glazing. With any type of clear glass in a conservatory it is essential to have adequate means of ventilation to reduce the possibility of high temperatures.

People sometimes think that Pilkington K Glass™, because it keeps heat in so much better, will cause extra overheating problems in Summer.  However, this is not the case.

In Winter, with cold outside temperatures, the prime concern is to retain heat within the building, in order to keep the interior temperature at a comfortable level without excessive heating cost.  The advantage of Pilkington K Glass™ in this respect can be explained technically by looking at the U value.  This indicates the amount of heat flowing out through it.

With a U value of 1.9 W/m2K, Pilkington K Glass™ double glazing lets out only about ⅓ of the heat that escapes through single glass (U value = 5.6 W/m2K) and about ⅔ of that which escapes through ordinary double glazing (U value = 2.8 W/m2K).  Any of the sun's heat which enters through a window is a bonus, reducing the amount of heating required in the building.

In Summer, the situation is somewhat more complicated.  Double glazing lets in less of the sun's heat than does single glazing, due to the extra pane of glass, and Pilkington K Glass™ double glazing lets in less than ordinary double glazing (although it is not a solar control glass) due to the presence of the Pilkington K Glass™ coating.

In technical terms:
Single clear glass    86% of the solar radiation is transmitted
Clear double glazing    76% of the solar radiation is transmitted
Pilkington K Glass™ double glazing 72% of the solar radiation is transmitted

The reduction in solar heat transmission, through windows facing the sun, largely offsets the ability of each type of double glazing to retain this heat.  The net result is that the type of clear glass in the windows - whether single glazing, ordinary double glazing or Pilkington K Glass™ double glazing - has a limited effect on the temperature rise in an unventilated room or conservatory.

If the proportion of window area is high in relation to the size of the room, for instance as it is in a conservatory, all three types can give rise to unacceptably high temperatures, unless there is adequate ventilation.







3 What are Window Energy Ratings?

Window Energy Ratings were introduced by the Government in 2005 as a means for window companies to demonstrate compliance with Building Regulations Part L concerning energy efficiency of their windows.

The Window Energy Rating (WER) level on a scale of A+ to G, with A+ being the most energy efficient, is shown on a label attached to the window. It looks very much like the kind of label you see on domestic appliances such as fridges and washing machines.

The more energy efficient the window is, the better it is at keeping heat in your home. This means that upgrading to more energy efficient windows can save you money on your energy bills.   

For further information relating to Window Energy Ratings please click here

4 Why have I got a haze/milky appearance on my windows?

Haze is an optical phenomenon which makes the glass look like it is covered in a very fine, uniform layer of dust when viewed from an oblique angle or viewed under strong light incident on the glass at an oblique angle. Our original Pilkington K Glass™ can, under certain lighting conditions, display this phenomenon to a limited extent.

The reason for this is that the Pilkington K Glass™ coating is not as smooth as the glass surface. While this is not obvious to the eye when examining the glass, some people who regularly handle Pilkington K Glass™ can tell which side the coating is on by the feel of it.

The optical effect of the slightly rougher surface is to scatter a small proportion of the light incident on it (in exactly the same way as a thin layer of dust would, which is why it looks similar).  With Pilkington K Glass™ the amount of scattered light is generally less than half of one percent of the light coming through the window, so under most viewing conditions it is not obvious. However, when incident sunlight is at an oblique angle and the view through the glass is of a shaded area, then the scattered light can become more visible, giving rise to the appearance of haze.

Nowadays low-emissivity glass is coated using alternative technologies so that our latest low-emissivity glass products; Pilkington K Glass™ S and Pilkington Optitherm™ do not suffer from this phenomenon to such a noticeable degree.

 

5 Why do my net curtains look grey/dirty?

The benefit of improved thermal insulation offered by using the original low-emissivity coated glass, Pilkington K Glass™ is due to the presence of a special transparent metallic type coating on one of the surfaces of the double glazing unit. This ultra-thin coating is transparent but has a very small effect on white light transmission. 

Pilkington K Glass™ has high light transmission and often appears indistinguishable from clear float glass. For this reason it is recommended that the presence of the coating is confirmed by the use of a Pilkington K Glass™ detector after installation. However, the coating does have a pale straw coloured tint and when a light coloured object or material is viewed through the glazing, depending on local circumstances and conditions, occasionally a slight darkening effect may be seen. This may make net curtains or Georgian Bars look grubby or discoloured in certain situations.

Unfortunately, there is no way of overcoming this characteristic, although it does confirm the presence of Pilkington K Glass™ in the windows. Nowadays, this phenomenon is rarely present due to the technology used in producing the latest low-emissivity coated glass products such as Pilkington K Glass™ S and Pilkington Optitherm™

6 Can Pilkington K Glass™ be used in single glazing or secondary glazing?

Yes. It needs to be installed with care following the guidelines below;

Single Glazing

The coating on original (so-called hard coat) Pilkington K Glass™ is very hard and is difficult to scratch.  Unfortunately, it is slightly rough (although not in a visible sense), so it may collect marks and dirt in a way which is difficult to clean off.  It is therefore inadvisable to use it as single glazing with the Pilkington K Glass™ coating to the exterior*.

If Pilkington K Glass™ is used in single glazing with the coating facing the room, it may also promote the formation of condensation. This is because the coating acts as a barrier to heat, keeping the glass colder than ordinary single glazing. Because the surface is colder, condensation will form more readily and in larger quantities than on uncoated single glazing. 

The only circumstances where Pilkington K Glass™ would not generally promote condensation on the room surface is when the external temperature is always higher then the room temperature. This can occur if the room is a cold store, or if the building is in the tropics.

*Note: Some manufacturers of proprietary systems are using Pilkington K Glass™ in situations where the coating is on the external surface, apparently without significant problems of dirt and marks over several years of use.  However, we do not take any responsibility for the durability and performance of Pilkington K Glass™ when used in this manner.

Secondary Glazing

Pilkington K Glass™ can be used in secondary glazing with the Pilkington K Glass™ as the inner pane and the coating facing the air gap between the two panes. Although the coated surface will have to be cleaned occasionally, it is generally protected by being in the cavity and washing with clean soapy water or a clear window cleaning solution should maintain it in good condition. 

There is a risk of the coating being marked by the sliding sashes when used in secondary sliding glazing systems.

As with any secondary glazing, there is a risk of condensation on the inner surface of the outer pane, unless the air gap has some ventilation to the outside, possibly just through gaps in the existing window.

A secondary glazed window using Pilkington K Glass™ does not give sufficient insulation to meet the current Building Regulations concerning energy efficiency.

Pilkington Spacia™

Pilkington Spacia™, our ultra thin vacuum glazing achieving excellent thermal insulation of U-value 1.1 can be used in situations where there is only sufficient space for single glazing. Find out more.

7 What is the U-value of my windows?

The U-value is one measure of how well your windows are keeping your heat in. So called Low-emissivity coatings on glass which offer heat insulation normally define their efficiency using the U-value. The lower the U-value the better the insulation.

There is also a measure of the overall energy efficiency of your windows called the Window Energy Rating (WER). Measured on an A+ to G scale (with A+ being the best) and using the labelling system we are all used to seeing on fridges and washing machines, the WER takes account of how well the window utilises free heat energy from the sun as well. 

A window with a rating from C up to the top level which is A+, meets the latest Government regulations concerning the energy efficiency of homes. All the products from our low-emissivity glass range, including Pilkington K Glass™, the UK's most well known low-emissivity coated glass, will help a window to achieve these high levels. Ask your window installer for more details.

8 My double glazing units have failed, who will repair them?

You need to refer in the first instance to your window supplier who will inspect the units and then take up the matter with the unit supplier if appropriate. This is not something that we are able to assist with directly since your contract is with you installer. If our own units are installed and considered to be at fault your window installer will take up the matter with us directly.

9 My window supplier says he has installed a Pilkington patterned glass but it doesn't look right, can you help?

We can't help directly since your contract is with your installer. However, in order to help please browse through our range of Pilkington Texture Glass and the Pilkington Oriel Collection patterns to compare or request a sample directly using our contact form.

10 Where should the Pilkington K Glass™ pane be positioned in my double glazing containing patterned glass?

Normally the low-emissivity glass, such as Pilkington K Glass™, would be on surface 3 of the double glazed unit counting from the outside ie. the surface on the inside of the unit on the pane which faces the interior of the house.

 

However, patterned glass such as Pilkington Texture Glass is normally positioned on the inside since the surface is not flat.

 

So, in this case, the low-emissivity glass can be positioned on surface 2 ie. the inner surface of the external pane where thermal efficiency is effected to a negligible degree.

11 The labels that were on my windows have left marks can you advise on cleaning them off?

Cleaning of Glass
 
Glass should normally be cleaned with a clean cloth and a clear non-abrasive cleaner, such as clean soapy water or a proprietary window cleaner.  For glass with a patterned, etched or sandblasted surface, a stiff bristle or nylon brush can be used to remove dirt from the recesses in the surface.
 
If the glass does not become clean using the above methods the following can be tried:-
 
Use a mild acid (e.g. vinegar) or a mild solvent (e.g. methylated spirit), taking care not to spill any of these on other surfaces or materials.
 
If neither treatment works then the glass will need to be abraded and re-polished.  this is likely to be expensive and should be left to experts.  The process may result in some optical distortion where the glass surface has been removed.
 
Special Notes on Cleaning
 
Organic solvent cleaners should be avoided on mirrors since they may attack the backing paint.
 
Leaded Glass should only be cleaned with a clear non-abrasive cleaner.  The cleaner should be of a type that does not remove the patina (aged surface finish) of the lead.
 
Patterned glass, acid etched glass and sandblasted glass should only be cleaned with a clear non-abrasive cleaner.  Any insoluble material in the cleaner may deposit in the recesses of the etching or sandblasting and may be very difficult to remove.

12 Where should the Pilkington K Glass™ pane be positioned in my double glazing?

Pilkington K Glass™ is a low emissivity glass, specifically designed to enhance the thermal insulation of insulating units. It achieves this by being positioned in the insulating unit with the Pilkington K Glass™ coating on a surface facing the cavity.

In a double glazing unit, counting the surfaces from the exterior of the building, The Pilkington K Glass™ coating should be on surface 2 (the inner surface of the outer pane) or surface 3 (the cavity surface of the inner pane).

Pilkington K Glass™ performs the function of enhancing the thermal insulation (reducing the U value) equally well whether it is positioned on surface 2 or surface 3. However, with any coated glass, there may be slight optical effects when the coating is present. These optical effects are reduced when Pilkington K Glass™ is used with the coating on surface 3, rather than surface 2.

General advice is that the preferred location of the Pilkington K Glass™ coating is on surface 3 of the unit, but if the glass types used in the unit make it difficult to assemble the unit with the Pilkington K Glass™ coating on surface 3, then no loss of thermal performance is obtained by using it on surface 2. In particular, when Pilkington K Glass™ is combined with Pilkington Texture Glass, where the Pilkington Texture glass is normally installed as the inner pane of a double glazing unit, the Pilkington K Glass™ should be installed with its coating on surface 2. Any slight optical effects will be masked by the presence of the Pilkington Texture Glass. 

13 How can I tell whether I have got Pilkington K Glass™ in my windows?

When the installation is complete, your window company should demonstrate this to you using a detector which will light up in the presence of Pilkington K Glass™ (or an other low-emissivity glass from our range) within the double glazed unit.

14 How can my windows help to reduce the noise level in my home?

There are a number of ways that sound reduction can be achieved. These include;

- using double glazed units which have uneven thicknesses of glass in the front and back panes

- using regular laminated glass in one of the panes

However for the best reduction, use our special acoustic laminated glass, Pilkington Optiphon™.

Windows incorporating Pilkington Optiphon™ are accredited by Quiet Mark (see www.quietmark.com

Ask your window company for advice.

15 Can you provide advice on how to clean my windows?

Cleaning of Glass
 
Glass should normally be cleaned with a clean cloth and a clear non-abrasive cleaner, such as clean soapy water or a proprietary window cleaner.  For glass with a patterned, etched or sandblasted surface, a stiff bristle or nylon brush can be used to remove dirt from the recesses in the surface.
 
If the glass does not become clean using the above methods the following can be tried:
 
Use a mild acid (e.g. vinegar) or a mild solvent (e.g. methylated spirit), taking care not to spill any of these on other surfaces or materials.
 
If neither treatment works then the glass will need to be abraded and re-polished.  this is likely to be expensive and should be left to experts.  The process may result in some optical distortion where the glass surface has been removed.
 
Special Notes on Cleaning
 
Organic solvent cleaners should be avoided on mirrors since they may attack the backing paint.
 
Leaded Glass should only be cleaned with a clear non-abrasive cleaner.  The cleaner should be of a type that does not remove the patina (aged surface finish) of the lead.
 
Patterned glass, acid etched glass and sandblasted glass should only be cleaned with a clear non-abrasive cleaner.  Any insoluble material in the cleaner may deposit in the recesses of the etching or sandblasting and may be very difficult to remove.

 

Alternatively, have Pilkington Activ™ installed in your replacement windows or conservatory. This revolutionary coated glass which goes on the external surface of windows or conservatories has a unique dual action. When exposed to daylight the coating breaks down any organic dirt deposits such as bird droppings and tree sap and then when it rains the rain water washes the loosened dirt away leaving the windows streak free. It is available from window companies nationwide for all external glass areas of your home but is especially beneficial in hard to reach areas such as conservatory roofs, rooflights, inaccessible windows or just to save time and keep the large expanses of glass we love in our homes looking clean. For more information, click through to more information about Self cleaning Glass

16 Who is my nearest installer for windows incorporating products from the Pilkington glass range?

Customers who supply windows incorporating products from our range in their double glazed units are registered with us. They provide information about the products and services they offer through our on-line supplier finder. 

Please click here to find a supplier near you.