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Is All Double Glazing The Same?

Absolutely not.

All replacement windows and doors vary significantly in their lifespan, their ability to keep in heat, their ability to keep out high winds and driving rain and their ability to keep out intruders.

If all double glazing was the same, cost would be the only issue to consider, but this is far from the case. Buying replacement windows and doors based on cost alone will seldom result in getting the best replacement windows or double glazing for your needs, or the best value for money over the lifespan of your installation.

Which is the best value for money?

A householder gets two quotes for replacement double glazing direct from two local double glazing contractors. Both sets of replacement windows look the same but one quote is £200 more than the other.

The lower quote uses cheaper materials which will start to present problems within 5 years.

The more expensive quote uses more energy efficient materials that could save an extra £50 a year and have a 20 year lifespan.

Which is the best value for money?

Matching the right replacement window products to your specific needs is essential.

Compare the performance requirements for an exposed third floor window with that of a sheltered ground floor window where security might be a concern. The appropriate replacement window product for the third floor would be one specifically designed to have a high exposure rating capable of keeping out high winds and driving rain where as the sheltered ground floor window requires a replacement window product designed to keep out intruders. Fitting the wrong replacement windows for the job would be pointless and a waste of money.

Matching the right replacement window products to your specific needs is essential. Your Window Advice Centre Consultant will first help you source the replacement window products that match your needs and then source the most cost effective double glazing contractor able to to carry out your installation to ensure that you do get the best value for money.

How Big Are The Differences?

Thermal Performance

The average heat loss through replacement windows can range from 50 watts per square meter to as little as 13 watts per square meter. For a three bed house, this can amount to a huge difference in annual energy use. To maintain a constant comfortable room temperature of 21 centigrade across the year, the difference could be 11,400 KW hours compared to 3,150 KW hours per annum. In financial terms, this could be a difference of over £500 a year.


In contrast to correctly fabricated replacement windows or doors which use quality materials and could last more than 30 years, some replacement windows and doors can present major problems within 5 years. The quality of the material from which replacement window and doors and their component parts are fabricated and the way they are assembled, will directly affect the windows or doors lifespan. Some PVCu windows are more prone to ultraviolet degradation than others, making the replacement window frames discolour and become brittle in the process. Some combinations of metal components result in sacrificial corrosion and rapid rusting. Some seals are more prone to compression sickness that can result in draughts. Some replacement windows with inadequate internal reinforcement will sag and deflect over time resulting in draughts and leaks. The way in which the double glazing units are installed is also critical. Incorrectly installed, a double glazed unit that could have had a 20 year lifespan could fail in less than 5 years.

Weather Resistance

Windows are tested to measure their ability to resist air infiltration, water penetration and deformation under wind loading. Some replacement windows will only be able to resist low levels of wind pressure before they leak. Others are able to resist the equivalent of a gale. The three broad categories for weather resistance for replacement windows are Sheltered, Moderate and Severe exposure rated. Some replacement windows that are severe exposure rated can resist four times the wind loading of some sheltered rated windows.


Replacement Windows and Doors can be subjected to vigorous testing to assess how resistant they are to forced entry. At best, they will be a total barrier, resistant to the greatest force any attacker could bring to bear. At worst, they will offer virtually no resistance at all. Some replacement windows and doors can be deglazed from the outside without difficulty. Some multi-point locking systems can easily be manipulated from the outside. Some door lock barrels can be snapped. Some door panels can easily be driven out of the door frames.


Architects and other professionals with responsibility for selecting windows and doors, on a regular basis, make their selection based upon information from independent testing laboratories where the windows energy rating (WER), weather resistance classification, durability and security are tested using standardised methods of assessment and testing. This information allows the Architect to ensure that the windows and doors will be suitable for purpose.

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Glasgow 0141 332 7878
Edinburgh 0131 225 7999
Dundee 01382 200345
Perth 0141 332 7878