The Zero Stress Guide to Double Glazing


What You Need To Know Before You Buy Double Glazing Windows

  Request Brochure for Conservatories, Kitchens or Windows  
Home Conservatories Kitchens Windows

Choice of double glazing materials

Top tips

  • PVCu is a good budget option
  • Frame thickness determines structural strength
  • Aluminium is best choice for commercial locations


PVCu, uPVC, PVC-U, and PVCU all essentially refer to the same substance. The most popular choice, this is an excellent material which has the advantage of needing little or no maintenance. The least expensive of all the available materials, it is most popular in white but is also available in mahogany and oak wood-grain styles.

pvcu windows

Rear view of large PVCu installation with both two pane and four pane patio doors fitted.

Problems with discoloration are negligible and most suppliers will provide warranties against this. The design of the windows varies from company to company but points to look for include:

Internal or externally-glazed windows – an option offered by most PVCu systems. Internally-beaded windows, where the glass is held in from the inside, are generally deemed more secure and burglar-resistant. However, there are also perfectly satisfactory externally-beaded PVCu systems on the market. Many feature either internal wedge gaskets or a double-sided tape that firmly fixes the external bead.

Thickness of PVCu wall – most PVCu systems for window and door construction are ‘multi-walled’ with internal reinforcement provided by either aluminium or galvanised steel box section. Wall thickness can vary from system to system, most being around 3mm or 3.5mm. In general the thicker the walling, the stronger the section. Ask your supplier to show you a sample section and establish whether the frames are fully reinforced. Be aware, too, that the greater the number of internal walls, the greater the strength of the building.

Depth or thickness of frame – the depth of frame extrusion can vary from as low as 50mm to more than 70mm, although most are in the 60-65mm range. This, too, has an effect on the structural strength of the window or door.

Note that PVCu is unacceptable to planners for use on listed buildings, nor is it popular with planners in conservation areas.


A more expensive material, hardwood is the choice of those seeking a traditional design with an authentic look and is a particular favourite for use in listed buildings or period properties. It has the twin benefits of being suitable for the recreation of virtually any traditional design or feature, while incorporating the contemporary advantages of double glazing.

timber windows

Hardwood is available in a variety of stains such as mahogany and light oak, as well as various painted finishes and, while it does require periodic maintenance, this is not an onerous task thanks to modern paints and stains.

As with PVCu, the frame thickness will affect the structural strength. It is also important to ascertain which jointing method is used – most suppliers use a traditional mortice and tenon joint but other systems do exist.


This shares many of the features of PVCu, although aluminium is more expensive and does not provide such efficient insulation.

aluminium windows

White Aluminium Door and window installation. Note the patterned glass in bottom of door.

When double-glazed windows first became popular in the late 1960s aluminium was the usual choice of material due to its strength and durability. It is more resistant to warping, twisting or sticking when subjected to the elements. It is also virtually intruder-proof and neither absorbs water nor rots or rusts.

Its popularity declined with the advent of the cheaper PVCu. However, aluminium remains an excellent choice for commercial locations and any circumstances in which strength is an important factor. It is advisable, if choosing aluminium, to specify frames with a thermal break as this improves the insulation properties.

Aluminium windows can be fitted as 'direct fix' – ie directly against the brickwork or, alternatively (and more often) into a hardwood subframe.

Sash windows

Replacement sliding sash windows are also available but are usually more expensive than the more common casement style windows.

sash windows

They are made in both PVCu and timber. The main difference between PVCu and the more traditional timber box sash window is the method of holding the sashes in position. Instead of weights, pulleys and a cord, a pair of sophisticated spring and spiral balancers provides the sash retention and can carry weights of up to 40kg.

The traditional glazing bar arrangement may also be replicated on PVCu by concealing the glazing bars within the double-glazed unit or by surface-mounting the bars onto the external faces of the unit.

One of the biggest advantages of timber sliding sash windows is the ability to replicate any period design feature required although this necessitates the use of a specialist joinery company with associated cost implications.



Home | Conservatories | Kitchens | Windows

Click here for a Conservatory Quote

For more Zero Stress Guides visit:

Zero Stress Guides - Providing you with information, advice and quote requests.

Please note: All calls may be recorded or monitored for quality and training purposes.

The Zero Stress Guides
The No-Excuses Guides to Zero Stress Home Improvements

Quotatis Ltd
Suite 1, Joseph King House, Abbey Farm Commercial Park, Horsham St Faith, Norwich, Norfolk, NR10 3JU
Tel: 08448 044 344 - International: +44 1603 899910 - Fax: 01603 899919
Registered in England 05643725

Copyright © Quotatis Ltd. All rights reserved