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Published on December 17, 2023 11:19 AM
Spectus are one of the top performing and best-selling sash windows in the UK. Here at Colin’s Sash Windows, we have been supplying this profile for the last 4 years. It’s got lots of features that I’ll go through below. Please refer to our uPVC sash windows page for more information as you read.


Lots of options here:

• Smooth white is the most popular. It’s the usual white that you see all over the country.

• Woodgrain We’ve got the most popular woodgrain colours. You can see them here. Some of our woodgrain colours can be the same colour inside and outside and some are smooth white inside. This is often the best option because if you decide to change your colour scheme in the room white fits with everything.

Colours colours available
Mechanical joints - white sliding sash window with run through horns and middle astragal bar
One thing to keep in mind is that although our Spectus sash windows tilt in for cleaning if you have a woodgrain colour outside and smooth white inside the top sash won’t tilt in.
• RAL colour You can have your windows sprayed any colour in the RAL chart. They can be sprayed just outside or both sides. This is a special paint and is guaranteed for 10 years like the smooth white and woodgrain.

Transom drop

A sash window is split in 2 – the top sash and bottom sash. Where they meet each other is called a transom (it’s also sometimes called the meeting rail). 99% of our windows have the same size top sash and bottom sash. You can change this to any percentage you want. For example 1/3 top sash and 2/3 bottom sash. You might want to do this if you have a really nice view outside and the transom is directly in your sight line.

Glazing bars

These are bars that divide up the glass into sections. In the early days of double glazing they used to be inside the 2 pieces of glass. This is still possible but it doesn’t look authentic. Most of our customers choose astragal bars. These are stuck on the inside and outside of the sealed unit with a warm edge spacer bar inside the sealed unit. You can choose any design you want. For example Victorian sash windows often just had 1 vertical in the top and bottom splitting the window into 4 panes. Georgian sash windows typically had 6 squares in the top and bottom. Edwardian sash windows often had squares in the top and no bars in the bottom.


The cill is the bottom of the frame on a sash window. If you are placing your window on a stone or concrete cill you just need our standard size which is 152mm. This protrudes about 10mm from the front of the frame. If you are placing your windows on top of bricks you will need a 210mm cill which protrudes about 70mm so when it rains the water drips off the cill and doesn’t get the bricks under the window wet.

Sash Horns

These are the 2 decorative finials on the outside of the window. We offer what’s called a runthrough horn (sometimes called continuous horns). You don’t have to order them. In fact, original Georgian sash windows didn’t have them.

Corner Joints

3 types available here:
• Standard welded – these are diagonal with a groove like you see on nearly all windows.
• Seamless joints – these are available on woodgrain finishes where windows are more than 475mm wide. They are still diagonal but virtually invisible.
• Mechanical joints – Our most authentic, these are where the uPVC is what’s called butt joined like timber sash windows are made. Only available on woodgrain windows.

Trickle Vents

As of new regulations these are required in 99% of windows we sell. This is because houses are more airtight than ever and ventilation is required to help avoid condensation leading to mould and health problems.

Travel Restrictors

These are an optional extra. Sometimes called safety restrictors, we use Angel Ventlock restrictors. Once turned on they only allow the window to open by about 100mm to stop children opening it further and risk falling out.

70-30 split white sash windows
They’re only available in white, gold, chrome and satin chrome. If you choose other colour furniture for the locks etc we suggest you have white safety restrictors if the inside of your window is white.

Deep Bottom Rail

Our uPVC sash windows offer a unique blend of modern efficiency and classic aesthetics. We offer a bottom rail as a customization feature, even though it’s not necessary for functionality. If you want a historical look, you can choose this option. It looks like classic sash windows.

Frame Extenders (add ons)

We offer add ons at 15mm, 30mm and 50mm in the same colour as your windows. They are supplied loose and are for filling gaps. For example if you have slightly arched brickwork outside you can hide part of it with the top frame but you might need a bit more cover.

Window Furniture

Our sash locks come with keys. In some situations they need to be non locking for example if you have a fire escape window. There are many different colour options and an antique heritage style. Please refer to our uPVC sash window page for details.

Fire Escape Sash Windows

If you need windows suitable for fire escape they need to have a minimum opening size so you can get out. When ordering we can check to make sure they’re big enough.

Fixing Brackets

These are an optional extra and not often required. They are metal straps that attach to the sides and top of the windows with screw holes for fixing. They are normally required for new buildings to conform to building regulations.


As standard we include toughened glass in the bottom sash of all our sash windows to comply with building regulations if your windows are less than 800mm from floor level. Toughened glass (also called safety glass) is required to avoid serious injury if, for example a child falls against a low window.

Our sealed units are A rated 1.4 u value. We have many different obscure glass options. You can have obscure glass only in the bottom sash or in top and bottom.

We also offer acoustic laminate glass. This is required in new buildings in ground floor windows (and some 1st floor windows) to avoid break ins. It’s also useful if you have windows facing busy roads as it absorbs noise.

Spacer Bars

These are inside the sealed units to keep them apart. In the old days they were aluminium. They’re now called warm edge spacer bars with new technology to avoid condensation and cold spots. They’re available in black, grey and white.

Security Upgrades

Our standard sash windows are extremely hard to break in to. New government regulations state that new buildings need to be even harder to break into. This is called PAS24 or Part Q Because our windows are so secure, unlike some others available they don’t need laminate glass. We offer security upgrades with slightly different hardware to comply. Visually you can’t tell the difference.


This is covered in a separate page. Click here for details.

I hope you have found this guide helpful. While you’re here please have a look at two more of our best-selling products:

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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