Frame Materials:
Aluminium

Double glazing, aluminium as a frame material

Quite a subject, this, because since the start of aluminium as a double-glazing frame material there have been so many advances.

To begin with:
Aluminium, as a double-glazed window or doorframe material, was extruded in some fairly simple single-chambered profiles. This was pretty basic, anodised to 8 microns, and 'battleship grey', with a 6mm air gap between the glass panes. When the silver-grey aluminium windows first started appearing along with their expensive-looking hardwood frames, in one or two houses here and there, the homeowners were often the envy of the neighbourhood, and were regarded as making little short of a fashion statement in those days!

I remember it well - and what a marketing coup for the outfit that told us that you change your windows only once, so 'fit the best'. What did the backroom marketing boys dream up? They contacted all their old customers with the message: ‘we will take back in part exchange the secondary glazing we did for you for our new replacement windows’. An absolute masterstroke! Since then, of course, the myth that you only ever fit new windows once has been well and truly dispelled and all those old battleship-grey aluminium windows are now being replaced again. They were only ever in the secondary glazing market at one time, before complete new replacement windows came in.

Next:
The anodising depth for silver-grey was increased to 25 microns, as I believe it still is today. A finish in ‘gold’ and brown was also done for the domestic market. The 'gold' finish always had a problem with shade consistency, which would vary depending on how long it was in the anodising process. The other main finish is polyester powder coating 'painted'. As I understand it, this process is called 'electrophoretic' where the metal has an electrical current running through it and the powder is 'attracted' to the metal in a uniform layer some 75 microns thick, when it is heated and liquefied and then baked on.

Metal is inherently cold to the touch and as an insulator nothing like wood (or plastic), and something had to be done about the aluminium frames 'sweating'. Along come ‘thermal clad’ and ‘thermal break’. The latter won the day and is the most favoured today, although thermal clad is still made, as far as I know. Thermal clad really fell by the wayside after a major scandal erupted when a national window replacement company’s products were alleged to have fungus growing between the interior plastic cladding and the main aluminium frames. Thermal break describes a frame where the outside and the inside of the frame are broken thermally. This means that the inside can be as warm as toast and the outside freezing, but the two are disconnected thermally. The name of the process that achieves this is called 'cut and fill', where a chamber in the middle is filled with an insulator, and it works very well too.

And now:
Double glazing that looks just like PVC-U but is in fact the latest generation of high-security aluminium windows, direct fix without a wooden sub-frame. Excellent, but expect to pay a lot more than for PVC-U, say 25% extra. Also, the new Building Regs, which came in on 1st April 2002, impose extra demands on aluminium frames. This is good news, as it means they have to have better thermal insulation qualities than before.

Double-glazing aluminium still has a justifiable place in today's market, most notably with recent 'composite' innovations, where the aluminium is on the outside and you have the traditional wood inside, for aesthetics. Also, there are 'direct fix' aluminium window and door systems now, which remove the need for the traditional hardwood sub-frame. Expect to put your hand fairly deeply into your pocket for either of these, though. Some people agree the extra is worth it and I might just side with them under certain circumstances, especially if I were in the ‘’If you have to ask the price you can't afford it’ bracket. 

Tip on cleaning silver aluminium: use Solvol Autosol aluminium polish, from motor accessory shops. 

Tip on repairing damaged white aluminium: use Humbrol white as a touch-up paint, it's just right.