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Published on September 1, 2017 1:30 PM

Compared with casement windows there are only a handful of manufacturers extruding UPVC sash window profiles. This is because sash windows are generally only found in the UK (apart from the Americas and other old Colonial countries) and the machinery and tooling required to make the profiles costs many millions of pounds.


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Quite a few window manufacturers use the same profiles, supplied in long lengths, to fabricate the windows themselves.

One of the best, but not so well known, is the Spectus profile. It’s a well tried and tested, award winning profile.

One of the major UK suppliers of the Spectus profile is Colin’s Sash Windows. They can supply this window with many non-standard features such as:

1. Deep bottom rail
2. Security upgrade to PAS 24 and Secured by Design certification
3. Seamless welding. This is very beneficial with woodgrain windows as there is no protruding filler in the 45-degree corner joins. Unless you are very close you can’t usually see the join
4. Mechanical joints. This makes a uPVC sash window look exactly like timber sash windows.
5. Slim 37mm midrail (transom)

PAS 24 is a relatively recent requirement for windows and doors in new build projects. It’s in the Building Regulations, Part Q which relates to unauthorised access to dwellings. In everyday language it means making it harder for people to break into your house. Briefly it applies to all windows and doors on the ground floor, basement and other easily accessible doors and windows in the house.

Rehau were the first to develop mechanically jointed sash windows for the UK market. The 90-degree butt joins mimick timber but because of the very high cost of these their sales have always been a quite small percentage of the overall market. Spectus have revolutionised this product with pricing maybe 50% less than a Rehau equivalent.

The Spectus uPVC sash window profile offered by Colin’s Sash Windows also features the very high quality Mighton Angel Ventlock safety restrictors. We don’t know of any other manufacturer offering this safety restrictor, let alone as standard. They alone, cost in the region of £18 per pair.

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The Spectus sash window can be specified with spring balances or constant force springs. Sometimes size and specification dictates which type has to be used. They both look a bit different; constant force are inside the frames and can be damaged by screwing into the frame, balance springs are visible when the sashes are tilted in. Some people prefer the constant force springs because they are slightly smoother and easier to slide, others prefer the more rigidity of the balance springs. They’re both covered by the same warranty.

Another quality feature of the Spectus profile is that sashes and frames are strengthened with galvanised steel. Although the outer frames of sliding sash windows are big if you need large frames this is an important consideration and not offered with some other profiles.

Which uPVC Sash Windows Provider to Trust?

Although Colin’s Sash Windows was the first to offer fixed price sliding sash windows a few other suppliers are now offering one price for most sizes up to 2400mm high and 1300mm wide. This is a different profile. Only Colin’s Sash Windows is offering the Spectus profile with galvanised steel strengthening with fixed prices up to 1250mm wide and 2300mm high.

Would you like to learn more, or order a product from us? Visit our uPVC sash windows page and take a look around. If you have any questions – don’t hesitate to contact us! We will be happy to provide the information you need.

Colin Greenslade
Written by Colin Greenslade
I'm the founder of Colin's Sash Windows. I disrupted the sash windows market in the UK in 2014 by introducing fixed prices for uPVC sash windows in the UK. Before this they were generally only available at very high prices through window installers. Today our business is one of the market leaders in supply only windows, doors and roofs in the UK.

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