FREE Quote




Products you are interested in:

Double Glazing Frequently Asked Questions

If you’re thinking of purchasing double glazing, it is always useful to know something about the product. I have listed some FAQ’s on double glazing together with some unbiased answers.

Double glazing frequently asked questions 

Q. Do I have to clean my replacement windows as I have been told they are maintenance free?

A. Providing the uPVC used to make the double glazing profile is of good quality you should not encounter any discolouration and all of our products are guaranteed against profile discoloration.

Clyde Promise.

We promise to manufacture all windows and doors from 100% virgin UPVC that has no recycled or reground upvc within any door or window.

Check out the video our videos page for more information about the UPVC used in our manufacturing process for all our UPVC windows.

Q. What is the U value?

A. Double glazing can be measured on its energy efficiency whilst comparing it to other windows, by using a calculation system known as the U value (or U factor).
The U value can be adopted for any kind of home construction and measures how effective that component is at retaining heat. Importantly, the lower the U value, the more proficient the window is at saving energy.

Clyde Promise

We will produce a window witha minimum U-Value of 1.6 Wm2K or a maximum higher value of 1.2 Wm2k depending on your choice of energy efficient glass.


Q. What are the benefits of measuring double glazing with the U-value?

A. Above all, installing new windows that are fitted with double glazing reduces heat loss, which in turn leaves a smaller carbon footprint as carbon dioxide emissions are cut by up to 50%.


Q. What are the standard U value measurements?

A. The nationally recognised rating method for double glazed panels is for the whole window, including the glass, frame and spacers. However, sometimes a centre-of-glass U Value is given, which simply measures the performance of the glazing alone.

Clyde Promise

We will always give you a U-Value of your complete window rather than just the glass unit U-Value.


Q. I am thinking of replacing a window to the back of my house which is south facing with a double glazed patio door will this make the room hot if so will I need some form of shading?

A. Yes this will make the room a bit warmer on a sunny day, I would suggest that you have window blinds fitted that will protect your furniture and keep the room cooler or most energy efficient double glazing will protect you from the UV Heat in the summer as well as the cold in the winter.

Clyde Promise

We will also offer you Glazing options to counter act the effects of heat through your windows for both incoming heat in the summer months and losinh heat in the winter months.


Q. I am considering having double glazing fitted to my house I live near to a busy road that runs down the side of my property will this help to sound proof my property?

 A. Yes, by fitting double glazing to your property will certainly improve the sound proofing. I would suggest that you have double glazing sealed units with a gap of a minimum of 20 mm.

Clyde Promise

We will advise you on sound proofing accoustic glass which is very expensive, however tests have shown that by manufacturing the glass unit with two different  thicknesses of glass ( ie 4mm and 6mm)  is nearly as efficient as accoustic glass but at a fraction of the price.

Q. I am thinking of having double glazed sash windows installed in an old terraced property, which currently has sliding box sash windows. Having received three quotes, I have also received three views on whether the whole sash box should be removed or the new units simply fitted within the existing sash box, leaving the internal wood in place. One double glazing window company said. The whole box sash should be completely removed to ensure a good job, the second said there was no need as the wood was original and was in good condition, the third said it doesn't matter, but fitting within the sash box will be cheaper. Please could you tell me who’s right?

A. When replacing box sash windows both methods can be used, some companies believe leaving the original 'box' in place and fitting the new double glazed sash windows within the existing box sash should be perfectly acceptable providing the timber is in good condition and without major timber rot showing plus it will have all the original moldings as finishes. Complete replacement is best if the old timber is rotten, If you would like more information on double glazed sash windows pop over this page with me to...double glazed sash windows

Clyde Promise

Our surveyor on site will show you how we propose to install each individual job and also explain as to whether we think boxes should be removed , partially removed or completely removed depending on current condition of windows and box sashes.


Q. I live in a conservation area, and I am considering having uPVC double glazed sash windows fitted to replace my old timber windows  would there be any restrictions?

 A. Yes there could be restrictions. As this looks like you could live in a conservation area or a listed building. My experience has found it is best to discuss this with the conservation officer or your local planning officer. To find out more please go to as the criteria may differ from one area to another. From the picture above I would imagine that uPVC double glazing would not be permitted but timber would planning permission for double glazing

Clyde Problem

We have never found any council in scotland who will accept UPVC windows in a conservation area and in these instances the only optiuon we have is to install timber frames.

Q. We suffer from bad condensation; will double glazing help prevent this?

 A. Condensation is not caused by windows or doors it purely shows up here due to internal and external temperatures and atmospheric conditions, When water vapour from the air comes into contact with cold surfaces, the vapour condenses on the cooler surface of the glass forming a foggy effect. However, by replacing your old windows with new, this may help as the sealed unit will be a warm surface which can only help.

Clydes Advice

While this condensation is annoying, it also indicates excessive humidity inside the room which should be reduced. We would suggest that the cause of high humidity is tackled first which could be as simple as additional ventilation e.g. extractor fans in the kitchen and bathrooms to remove excessive humidity.

A higher specification of insulating glass such as Vista-Therm may also help this problem as it will always keep the inner pane of glass better protected therefore not as cold a surface internally.

Check out our videos page for more information about the UPVC used in our manufacturing process for all our UPVC windows.