Sash Windows Replacement 

Many homeowners who are looking for replacement sash windows are usually having the same issues: draughty windows, cold double glazing… the list goes on. Although timber sash windows are a great look for your home, when they become unusable there is not much reason to keep them. This is when you will need to start looking into possible sash window replacements.

sash windows replacement

From timber sash windows to sliding sash windows, which sash window works best for you?

Timber sash windows add charm and authenticity to your home but some older traditional timber sash windows may need replacing. Timber windows have been a outstanding feature for many homes across the UK, with regular maintenance this type of sash window can last for years but without this these windows can rot and need replacing. As timber is the traditional material used to make windows, new wooden sash windows are a perfect fit for any period properties or traditional homes. Wood is also a exceptional insulator, therefore, timber sash windows will make your home noticeably more energy efficient.

timber sash window replacement

Another option to consider is whether you want sliding sash windows or casement windows. The biggest difference between these windows is the way they open and close. Sliding sash windows slide either vertically or horizontally within the frame. Casement windows open outwards by means of hinges on either the side, top or bottom of the sash.

How do I know when to get new sash windows?

Even the best quality sash windows will need replacing and double glazed windows will last on average about 20 years. There are several factors which may affect the windows and mean that they will need replacing sooner rather than later, for example, how they are maintained, the weather they need to withstand and the frame material used.

Signs of rot or warping on your windows or that the double glazing is failing are big indicators that you need to replace your sash windows.

Another indicator may be that your energy bills have gone up, many sash windows improve energy efficiency and draught proofing so if your energy bills have gone up recently it may mean that your sash windows need replacing. Therefore, installing new sash windows can be cost effective.

sash window replacement bills

A third reason may be that your original sash windows are becoming difficult to open and close. In many instances home owners have painted their windows shut. Other causes of a stuck window are a warped frame such as uPVC sash windows which can expand and warp in hot weather.

Other indicators could be that the windows are no longer sound proof, draught proof or the windows are leaking. Or maybe your original windows do not have double glazing so getting replacement sash windows will solve that issue for you.

Should I go for double glazing when replacing my sash windows?

To add even more value and durability to your sash windows you can make your windows double glazed sash windows. Double glazing can save you money in the long term as it will insulate your home better and therefore save on energy costs. There is also less condensation on your windows, which may sound like a unimportant factor but if condensation gets into the wooden sash windows after a long period of time, they will begin to rot and therefore you may need replacement sash windows again.

Double glazing

What are my replacement sash windows options?

Commonly, when considering sash window replacement, there are two high performance options available to you: Sash Only replacement and Full Box replacement. To help you make an informed decision, we here at Core Sash Windows would like to give you an overview of the pros and cons of both procedures, so that you can feel more confident in making the choice that is best for you.

sash window replacement process

Sash Only Replacement

With a Sash Only replacement, we will retain the existing box frame, and install new double glazed sashes within the current box.

In order to do this, we must remove the staff bead from around the edges of the box, and the parting bead from in-between the lower and upper sash. At this point, the old sashes can be easily removed.

We will then fully refurbish, restore and redecorate the existing box to its original glory, with 2 primer layers, and 2 top coat layers of Teknos microporous paint. We have a wide range of RAL colour options available to match your current décor, so just let us know if you need a specific colour.

Next, we swap out the pulley system and sash cords and install brand new replacements. This new equipment is designed to take the weight of your new double glazing, whereas the old system was not. Finally, we insert your brand new double glazed sashes into your (as good as) new box.

There you have it; our Sash Only replacement is complete.

sash window replacement in bay


  • Slightly cheaper than a Full Box replacement, as there is less joinery being provided.
  • Reduced disruption to fitted shutters / panelling, as the box remains relatively undisturbed.


  • No FENSA Certificate.
  • 10 Year Guarantee only applies to the new joinery, not the box refurbishment which will have a 2 year guarantee.
  • Can be more fiddly and time consuming, as our carpenters may need to alter the sashes to correctly fit the box.
  • Possibility of unforeseen
  • complications; blockages or obstructions in the box. This is not
  • included as standard in the service, and could incur a further cost to
  • rectify.
  • If the box is not level, or the house
  • has experienced subsidence, the sashes may not fit perfectly parallel in
  • the box, which could lead to entanglement of the lead weights. This
  • could make the window slightly more difficult to open.


Full Box

With a Full Box replacement, we will remove the architrave from the wall, allowing us to then remove the entire box and fitting brand new sash windows.

At this point, you will be left with a clean hole in your brickwork, with no remaining joinery. We will then insert the new full box into the opening, and begin to seal the new joinery in place. We will fit new architrave around the box on the inside wall to hide the join, and use a traditional sand and cement pointing joint to seal the box from the outside.

Sash window replacement full boxes

We will then repair and make good any damage to the surrounding plaster from where we removed the box and if you provide the correct colour paint, we will even repaint the fresh plaster so that your wall looks as if we were never there – except for the gorgeous new windows, of course.

As the entire box is brand new, all the relevant equipment (sash cord, pulleys, opening hardware and security hardware) is also brand-spanking new, and your new sash window will glide open and shut with the greatest of ease. And there you have it! Another Full Box replacement installed.


  • FENSA Certificate provided
  • Quicker to fit, as the new sashes and box have been correctly paired during manufacture
  • 10 Year Guarantee on the entire product
  • No risk of entanglement: we will ensure that the box is fitted level
  • Ease of opening
  • Paintwork will last longer due to the brand new factory finished woodwork.


  • Can be more expensive
  • Can require re-plastering and re-painting after fitting, depending on interior wall condition.
  • A plumber may be required to remove and re-hang any radiators which are too close to the window.

What’s best for me?

Each customer’s situation is different, and there are many factors that should be taken into account when making your decision. If you would like to receive free professional advice, unique to your personal situation, then why not book a completely free, no obligation on-site survey?

All you have to do is give us a call on: 0203 302 2060

In the meantime, to help you in your decision, here are a few common issues that we encounter and our answers to them:

The work needs to be done quickly!

Full Box replacement is typically faster than Sash Only replacement.

Money is an immediate issue – every penny matters!

Sash Only replacement can be a slightly cheaper option.

I don’t know how old the windows are!

Full Box replacement gives you certainty for the future on the whole window.

My home has experienced subsidence!

Full Box replacement allows us to fully account for this, preventing entanglement of weights, or unnecessarily wasted time trying to fit the sashes level.

I will probably have to replace the box later, anyway!

A Box Only replacement is not a service that is offered. Therefore, you should be sure that the box will survive far into the future before considering a Sash Only replacement.

Now you have your new sash windows, what are the best ways to maintain them?

Now you have your replacement windows you can look into ways to maintain them. Sash windows can last up to 50 years with the right care. First of all, you need to keep your windows clean at all times, the best way to do this is with a cloth and window cleaner. If you do not keep your windows clean they may attract more dirt and mold which can lead to more serious problems.

One of the most common problems people encounter with sliding sash windows is that of sticking, the main reason for sticking will be a messy paint job. If you discover this, all you need to do is run a knife or sharp object along the edge to free the upper or lower sash.

For traditionalists, timber sash windows are likely to be the most popular choice as upvc sash windows will rarely achieve the right look. Wood is an excellent natural insulator, extremely durable and, if taken care of properly, a timber frame can last for a remarkably long time. With these windows it is important to keep the windows clean and dry as it will reduce timber decay.

Get in touch for a quote today

You can reach our team by email [email protected], call us on 020 3302 2060 or click on the instant quote links to get a price for sash window repair today.

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Enjoy being warm and comfortable!

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

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