Core Sash Windows London

What We Do

Core Sash Windows offer a professional, yet relaxed and friendly service. All our surveyors and sales representatives have years of experience in the double glazing industry and many of them have worked as fitters of double glazed sash windows and doors in the past so have real, hands-on experience with the product. They’ve designed our sash windows from scratch and gone on to successfully market those same sash windows throughout all the boroughs of London. We have over a 10 year history in the window industry and in this time have installed casements, doors and sash windows and providing a first class fitting service, including in conservation areas and listed buildings. We choose not to work with UPVC sash windows and focus fully on our timber sash windows range in order to ensure that our workforce and our surveyors are totally in tune with our product, our service and our ethos.

Our Product

Like our traditional casement windows and doors, our sash windows are a unique product, designed specifically to look like traditional sash windows without forcing you to compromise on the warmth of your home by ensuring that the benefits of double glazing are retained.

Why we don’t use UPVC sash windows

We believe that our traditional timber windows and doors retain the traditional style and quality that many UPVC sash windows and doors in the double glazing industry just can’t match. We’re so confident in the long lasting strength of our product that we’re willing to supply a 10 year guarantee to ensure that it lasts and that you have peace of mind. Individual parts of UPVC sliding sash windows are tricky to replace. Over time, upvc sash windows can become discoloured and can be ruptured by too much heat. If you’re getting windows installed, it’s worth investing in different kinds of sash windows.

Our On-Site Teams

With all of our on-site teams being contracted on a permanent basis by Core Sash Windows as opposed to contacted on a per job basis, you know that your new sash windows are in good hands. No one in our workforce is brought on just to do one particular job and we make sure that we train our new fitters with our regulars for an extended period before we send them out on their own.

What are sash windows?

A sash window is made of two movable panels, or “sashes”, that form a frame to hold panes of glass. For an easy user experience, we fit cotton cords with a nylon core  that run over the pulley wheels to connect the lead weights to the sash windows. By far the most common these days are double glazed timber sash windows. Popular in many areas of London, traditional wooden sash windows are often a mandated replacement. Before you make any decisions on your sash window replacements, contact your local council and make sure you’re doing everything above board. If you need to supply technical drawings, just let us know and we will be able to provide them.

What are sliding sash windows?

A traditional sliding sash window is usually made up of two panels that slide up and down one in front and one behind, in vertical grooves, counterbalanced by lead weights on cords. Sliding sash can be opened at the top or bottom, or both. Traditionally, they have no outward swing but modern designs tilt in and out for easy cleaning.

Our Design Philosophy

Core Sash Windows is a sash window company with an eye for window design. Details that were common in single glazed period sash windows are very important to us; that’s why we’ve made sure that the design features carried over into our double glazed timber sash windows. We pay careful attention to the narrow profiles, the elegant glazing bars, ovolo detailing, and the sash horns. Our dedication to the conservation of new sash windows in London’s original aesthetics means that your double glazed replacement sash windows will be like-for-like. In other words, you will enjoy the modern benefits of double glazing, without ruining the appearance of your home or your sash windows. We make our sash windows with one double glazed unit to increase performance benefits like energy efficiency and reduce cost and heat loss at the same time. We can also produce integral double glazing (all the different units will be separate). In addition to sash windows we also produce timber casement windows and doors.

When should I bite the bullet and buy new sash windows?

Over time, most wooden sash windows, casement windows or doors have suffered from periods of neglect which can lead to poor energy efficiency. If any wood becomes exposed to the elements for example, timber sash windows can become a chore to use and maintain rather than being a great addition to your home. Repairs or draught proofing can help, with your average timber sash window being far more repairable than a UPVC sash window, but it’s also possible to fit brand new replacement single glazed sash windows or double glazed sash windows in the best tradition of the originals so draught proofing or repairs aren’t your only options. When your sash windows become difficult to use, they should be changed. If you notice that the sash windows are heavy, or shudder in the frame then it might be time to call us or get in touch with a quick email. Take a look at our sash window replacement page or our draught proofing for more information.

What's Included In Our Service?

For full sash windows replacements (when we replace the entire box), we offer basic and comprehensive fit. For Sash replacements we can provide a comprehensive fit only.

Comprehensive Sash Replacement

Replacement timber double glazed sashes installed in renovated box frames (includes painting & draught sealing). For a full rundown please check the sash replacement service page.

  • New sash windows
  • All sash window woodwork painted with Teknos micro-porous paints
  • Existing sash window box frames fully restored & repainted
  • Full draught sealing of the sash window
  • New lead weights
  • New sash window hardware & security fittings
  • Additional hand painting
  • Insurance backed guarantee

Comprehensive Full Box Replacement (New Double Glazed Sashes In New Engineered Timber Box Frames)

Replacement timber double glazed sashes & replacement box frames (includes painting & draught sealing). For a full rundown please check the full box replacement page.

  • New box sash windows & double glazed sash windows
  • All sash window woodwork painted with Teknos micro-porous paints
  • Full draught sealing of the sash window
  • New lead weights
  • New sash window hardware & security fittings
  • Plasterwork surrounding the sash window made good
  • New Architrave supplied & fitted
  • Exterior sand & cement pointing
  • Additional hand painting
  • Insurance backed guarantee & FENSA certificate

Basic Full Box Replacement (New Double Glazed Sashes In New Engineered Timber Box Frames)

The old boxes are removed and replaced but that’s about it. This is a great option if it’s part of larger refurbishment job in your property.

  • New box sash windows & double glazed sash windows
  • All woodwork factory finished with Teknos micro-porous paints
  • Full draught sealing
  • New lead weights
  • New hardware & security fittings
  • Wedge the window in place and fill the gaps with expanding foam
  • Cut back the wedges & foam
  • Touch up installation marks only
  • Insurance backed guarantee & FENSA certificate

Unless specifically agreed, the following services will not be provided on a basic fit:

  • Sand and cement pointing or temporary silicone seal
  • Rubbish removal. Rubbish will be left at an agreed location on site.
  • Additional hand painting.
  • Architraves, Bullnose / Window boards.

Additional Options

All our products are bespoke, so additional choices for sash windows include, but are not limited to:

Paint Options and Colour Options:

  • Any option from the RAL classic range of colours or a woodgrain finish. Door or window colours are not necessarily limited to a RAL colour.
  • Two-tone paint – separately match both your internal and external colour schemes.
  • Any paint colour or brand (Farrow & Ball included) you choose, or colour matching to those colours. Certain brands are more difficult to paint with and so may increase the price.

Design Options:

  • Your choice of hardware colour.
  • Your choice of glazing bars. Glazing bars are the strips of timber on the surface of the glass.
  • Curved tops or square tops.
  • Your choice of unique timber moulding.

Other Options:

  • Your choice of obscured, safety or acoustic glass.
  • Click here to view or download a catalogue of obscured glass options.

The History Of Sash Windows

As a staple of North, West, East and South London architecture throughout the Georgian Period (1714-1837), the Victorian Period (1837-1901) and the Edwardian Period (1901-1910), the traditional sash window can still be found on almost every street in the city.The varying designs available are indicative of the glass manufacturing techniques used during these periods, and the architectural fashions of the day. Sash window designs steadily evolved as the glass manufacturing techniques became less and less restrictive, and as a result, you can rather accurately date your home based upon the style of the original timber sash windows!

Georgian Period: 1714 – 1837

The window manufacturing process during this period first relied on Crown Glass, a manufacturing technique that was only capable of reliably producing small individual panes. As a result, this period is famous for a high number of panes within a window, and popular designs were ‘6 over 6’ or ‘8 over 8’ styles. Most Georgian Period wooden sash windows were incredibly symmetrical – both in terms of division of the individual sash, and the uniformity between top and bottom sash.

Victorian Period: 1837 – 1901

Sheet Glass manufacturing for sash windows and doors became more efficient in the 1830s, which overcame many of the limitations that had previously been caused by Crown Glass. This newly refined manufacturing process led to the production of far larger individual panes than was previously possible, or practicable, which led to a significant reduction in the number of panes needed within a window. As larger individual panes became more readily available, the popularity of ‘maximum glass’ designs skyrocketed, and this period saw the popularity of ‘1 over 1’ and ‘2 over 2’ designs.

Edwardian Period: 1901 – 1910

Glass manufacturing techniques for sash windows and doors did not dramatically change between Victorian Period and the Edwardian Period, however, the designs did not remain static, and window manufacturers began to experiment with far more ornate styles. There was often a staggering disproportion between the simplicity of the bottom sash and the complexity of the top sash. Bottom panels tended to remain as plain ‘1 over 1’ or ‘2 over 2’ styles, whilst the top panels began to implement beautiful curves and decorative ‘lights’.

Take the first step to getting new sash windows today by contacting us.


Enjoy being warm and comfortable!

call us: 020 3302 2060 or email: [email protected]

Instant quote
Casement window with green wall paint

What did we do?

We’ve replaced 3 sash windows and 1 casement window for this customer. We carried out the ‘sash-only’ service under which the box frames are refurbished, which can reduce cost for the customer.

What did the customer think?

I can’t recommend the Core Sash Windows guys enough. From start to finish the service was excellent, the level of craft and finish exemplary and the installation team were polite, professional and worked in an extremely clean and tidy way. I wish I’d known about them when I was having the sash windows at the front of my house replaced a couple of years ago.


sash-and-casement-replacement-in-westminster Casement window with green wall paint Hackey sash window in green room Hackney new bathroom sash window

window replacement in nw5 camden

What did we do?

We’ve completed the comprehensive fitting of 2 double glazed sash windows for this customer.

What did the customer think?

“Excellent job, very happy with the new windows. Communication very straightforward with the office and the team turned up on time, kept us informed as the job progressed and cleaned up thoroughly at the end of each day.”

window replacement in nw5 camden

What did we do?

We’ve completed the comprehensive fitting of a 8 double glazed sash boxes for this customer.

What did the customer think?

“Good standard of workmanship throughout and I love the new windows”

window replacement in E3 Bow

What did we do?

We’ve been contracted twice by this customer, and in total we have completed a comprehensive fit of 4 double glazed casement windows for this customer.

What did the customer think?

“Excellent work with a tricky installation and a great finish. The fitters were clean, tidy and very professional.”