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The intricacies of the sash window

November 5, 2018 by harp_admin

Are you a homeowner looking for replacement sash windows? Do you want your new windows to have a tasteful traditional aesthetic with modern performance levels? Do you want the best uPVC sash windows for your home? If so, our Ultimate Rose uPVC sash windows could be just the windows for you.


Ultimate Rose uPVC sash windows incorporate many authentic style features

Ultimate Rose uPVC sash windows incorporate many authentic style features

If you’ve been doing some research into sash windows you may come across a variety of unusual terminology. To help you to make a fully informed decision about your sash window replacement, here’s some essential information about the intricacies of sash windows.


When it comes to industry specific terms, you don’t get much more unusual than astragal bars. More often referred to as Georgian bars, they are the thin pieces of wood or uPVC used to separate a larger pane of glass into smaller sections. Originally used in the 17th and 18th centuries when flat glass could only be made in small sizes, they are now used for purely aesthetic purposes to give properties a traditional, heritage “Georgian” look.

There are two main types of Georgian bar used on a double glazed sealed unit (two panes of glass). The conventional double-glazed style bar that sits in between the gap of the sealed unit – this is usually 18mm wide and whilst it does create the grid effect, it doesn’t look very convincing. A newer technique known as astragal uses a more authentic looking bar that sits on top of the outer pane of glass on the sealed unit. Within the sealed unit itself, a grid is created using spacer bar, so aesthetically you have a much more convincing looking Georgian style window. Some better quality astragal bars even have what is called an ovolo putty line, which replicates the lines of a timber Georgian bar.

Close-up on our Ultimate Rose sash window, showing the run-thru sash horn and the astragal ovolo putty Georgian bars.

Close-up on our Ultimate Rose sash window, showing the run-thru sash horn and the astragal ovolo putty Georgian bars.


Sash horns are an essential part of traditional sash windows, used to strengthen the window frame’s joints and limit its opening capacity. They are now used for decoration and to achieve a realistic period appearance. The Rose Collection uPVC sash windows can feature run-through sash horns which are an integral part of the window’s design.

When it comes to “stick on” sash horns (known as bolt-ons) vs. run through sash horns, run-through horns win every time. From more than a few feet away stick on sash horns will look fairly convincing. However, the closer you get the more obvious it becomes that they are just extra pieces of plastic added to the window.

Run through sash horns are incorporated into the structure of the window itself. All of our run through sash horns replicate the traditional joinery techniques used in the creation of traditional timber sashes. This gives the overall window a much more authentic appearance than sashes with bolt on sash horns.

An older style uPVC sash window with bolt-on sash horns. (Look closely and you will see the join).

An older style uPVC sash window with bolt-on sash horns. (Look closely and you will see the join).


Window profile refers to the sections of window material that are joined together to create the frame and sashes (not the window when viewed from the side!). uPVC window frames are created using multi-chambered profiles. The chambers help to boost the window’s thermal performance and strengthen the overall structure.

Transoms and mullions are also part of the window’s frame. Transoms are horizontal sections of profile which separate the window into sections while mullions are their vertical equivalent. The window’s meeting stile runs horizontally across the centre of the window, and describes where the bottom of the upper sash and the top of the lower sash meet, where the locks sit. The bottom rail is the horizontal section at the bottom of the lower sash which is usually much deeper than the other profile sections (Deeper bottom rails such as ours are much more authentic looking).

When you want to make the right decision for your window replacement project, it’s important to know as much as possible about the products you’re buying. If you’d like more information about our Ultimate Rose uPVC sash windows, check out our online PDF brochure and our information video, and visit our Watford showroom where we will be happy to demonstrate all the features discussed here on our showroom displays.


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10 Verified Review

Fantastic service from beginning to end. Local showroom in Watford with a super variety of windows and doors The fitment of the sash for my son's bedroom, best decision. Quality window and beautiful finish Paul and Miles are polite and friendly. Paul is a master at his job and Miles is super when finishing and completion. Thanks guys and thank you Harp Windows

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All appointments on time. Advice useful when choosing design. Fitted in less time than expected.

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I have to say I have been impressed with HARP from start to finish. I was guaranteed the best price from John at the beginning, There was no hard sell or tricks, Just simple and honest. I ordered 1 window to replace my old bay which I was advised would take 6 weeks from ordering. My window arrived slightly earlier than anticipated and was fitted without delay. The fitting team worked in a clean and tidy manner, were punctual and had a great attention to detail.

Location: WD24July 2023

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Excellent service, most helpful and friendly. Highly recommend.

Location: BH10May 2023

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Very pleased with product and workmanship. All done with no fuss and no mess. Brilliant job. Billy even hoovered up afterwards !

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Excellent service from both the showroom staff and the fitting team . Quality of the windows and doors is very good , and would highly recommend this company

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  • Harp Windows (Watford) Ltd
  • 91-93 St Albans Road
  • Watford
  • Hertfordshire
  • WD17 1UL



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