What is 'A Rated' Glass?

Whether you are a domestic customer or trade customer you may have heard the term 'A Rated Glass' being used. There is however no such thing.

This term is becoming frequently used in the uPVC industry to describe a glass specification that will allow a window to achieve an 'A' rating. The actual glass specification they are referring to is:-

4mm Clear Float - 20mm Argon Gas Filled Spacer (90%) with Swiss V (or similar) Thermal Spacer Bar - 4mm Low-e (softcoat). This glass make-up achieves a centre pane U-value of 1.2 W/m2K.

In the majority of uPVC window systems this glass allows the window to achieve an Window Energy Rating of A, hence why it is being increasingly referred to as 'A Rated Glass'. Unfortunately, it does not always result in an overall A rating when Glazed into window systems and it is becoming more and more confusing for the end customer and trade alike.

The Window Energy Rating (WER) system applies only to windows, it also only applies to the window as a whole. Individual components cannot themselves have a window energy rating, i.e. the glass or frames.

This so called 'A Rated' glass specification we use as standard for the majority of our products. Using this so called ‘A’ Rated glass in one of our aluminium Smarts 47 windows (for example), achieves an overall 'C' Rating. Although this is still fully compliant with current building regulations, it may not be what the customer is expecting.

Find out more about WER’s here: http://www.duration.co.uk/Window-Energy-Ratings.asp

Internally or Externally Glazed

The glazing bead is the aluminium profile that secures the sealed units (or glass) into the aluminium window frame or opening vent. When inserting glass into a window system (often referred to as Glazing the window) the glazing bead and wedge gaskets are the last pieces of the window that you fix into place. Some windows are externally glazed (also known as “externally beaded”), while some are internally glazed (also known as “internally beaded”). Some window systems will use a mix of internally glazed and internally glazed sections within a single window.

There have been many arguments over the years as to whether internally glazed or externally glazed windows are better for security. With people using arguments such as: “If you glazed a window from the outside then you can de-glaze it from the outside. Therefore externally beaded windows cannot possibly be secure.” Along with counter arguments such as “Internally beaded PVC windows can simply have their glass units forced in”.

The majority of people in the industry once considered externally glazed windows to be less secure. This is simply due to the fact that internally glazed windows were developed, introduced and advertised as the more secure option. This is no longer the case due to the fact that the majority of externally glazed windows use modern technology, which means that the external glazing beads simply cannot be removed without removing the internal wedge gasket first.

The simple fact is that both internally beaded and externally beaded aluminium windows are secure and the industry standard tests are there to prove it. Therefore if a window system can pass these tests they are deemed to be secure. If a window can pass the British Standard 7950 and also the Police Preferred Secured by Design Standard, it is considered to be highly secure. So in the absence of any other even more stringent tests and standards, which should you choose, Internal or external glazed?

Key Points About Internally Beaded Windows:

• Can make installation far easier by allowing the installer to fit the frame from inside the building, without the need for scaffolding.
• Once considered to be more secure than externally beaded windows, however due to modern technology and the strength of aluminium, externally beaded aluminium windows are just as secure.

Key Points About Externally Beaded Windows:

• Externally beaded can provide a slimmer sight-line than internally beaded.
• From inside, the window may look neater as there are no bead lines.

Both external and internal beads on a single window:
Often you will find that a window system will mix internal and external beads on a single window. This is generally due to the fixed lites being externally glazed. Windows that do not open (otherwise known as fixed lites) are generally glazed from the outside directly into the window frame. Therefore, a window which is made up of an opening sash next to a fixed pane - would be internally beaded on the opening vents and externally beaded on the fixed pane. This gives the best looks and slimmest sight-lines. If you wish to have internally glazed through-out your windows you would normally have to opt for dummy sashes or a double beaded window frame. Dummy sashes provide equal sight-lines, as all the fixed lites are created by fixing opening vents into the outerframe, and are internally glazed.

Visit www.duration.co.uk for more information on glass and glazing.