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What are my options?

Commonly, when considering sash window replacement, there are two 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 Only Replacement

With a Sash Only replacement, we will retain the existing box frame, and fit 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 sashes. 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 with 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.


  • 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.

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.

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 completed.


  • FENSA Certificate provided
  • Quicker to fit, as the 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, not just the sashes.

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.




Enjoy being warm and comfortable!

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

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