We use cookies to allow us and selected partners to improve your experience and our advertising. By continuing to browse you consent to our use of cookies. You can understand more and change your cookies preferences here.

Endorsed by Which? Trusted Traders

Core Sash Windows

Profile thumb corelogo

50 Reviews

Opening Hours
Today - 08:30–17:30
  • Monday 08:30–17:30
  • Tuesday 08:30–17:30
  • Wednesday 08:30–17:30
  • Thursday 08:30–17:30
  • Friday 08:30–17:30
  • Saturday - Closed
  • Sunday - Closed


Core Sash Windows is a London-based double-glazing company specialising in the replacement and repair of traditional timber-framed windows and doors. We understand that replacement windows and doors are an important investment, and you obviously want to make the correct choice.

That is why we offer:

• Elegant and traditionally styled products
• Attentive customer care
• Punctuality and reliability
• Considerate workmanship
• Convenient and fully comprehensive service
• No need for Third Party trades

That is why we promise:

Our surveys are always performed by experienced carpenters instead of designated sales-people - there's no unnecessary up-selling and no high-pressure tactics. Our FENSA-registered installation service also includes the hand painting of your new products, traditional sand-and-cement pointing joints, and the repair of any damaged plaster. And our traditionally designed windows and doors come with a 10 Year Insurance-Backed Guarantee.

What we do

  • Glaziers

    • Sash windows
    • Timber windows
    • Window consultants
    • Replacement window services and repairs
    • Double glazing installation
    • Aluminium Windows
    • Double glazed units
    • Double glazing repair
  • Double glazing

    • Double glazing installation
    • Double glazing suppliers
    • Double glazing repairs
  • Carpenters

    • Joinery and carpentry
  • Doors

    • Bi-fold doors
    • French doors
    • Front door
    • Patio doors
    • Timber doors
    • UPVC doors
    • Orangeries
  • Draughtproofing installers

  • Specialised building trade contractors

  • More Services

    • double glazed timber sash casement windows and doors

Customer reviews

Why you can trust these reviews

All reviews are verified as being genuine and a true customer of this trader.

How can we be so sure?

100% of the reviews we publish have been through our stringent moderation process.

50 reviews
Customer Service
Sort by
Quick installation & great looking results
Customer Service
Great job on installing windows and door - very efficient all round & making the new kitchen/bathroom look really light, the existing repaired ones feel a lot better insulated too.
rn1980 Posted on 24/04/2018 , work completed 24/04/2018
The trader replied (on 05/08/2018)
Efficient and stylish double glazed sash windows
Customer Service
Good standard of workmanship and truly effective and attractive product. My windows were big & draughty, now they are light & stylish and I'm cosy and warm!
Bartholomew Posted on 04/04/2018 , work completed 04/04/2018
Great work
Customer Service
The workmanship on a not so simple couple of sash windows is remarkable. the quality of the finished and installed product is excellent.
Christina Z Posted on 26/03/2018 , work completed 26/03/2018
Excellent job!
Customer Service
Our windows and door are fantastic, exactly what we wanted. Everybody that we dealt with was excellent -professional, kind and helpful. Core sash windows did a great service and I would definitely recommend them. The quality of the windows and door is really second to none.
Bea Rob Posted on 24/02/2018 , work completed 24/02/2018
Very happy
Customer Service
The windows look amazing. I didn't realise how bad they were until they were replaced. Seems like excellent quality and the installation was carried out quickly and efficiently
Whichone1 Posted on 23/12/2017 , work completed 23/12/2017
Sash window refurbishment and two windows replaced
Customer Service
The windows are great, the installation team delivered as agreed, they covered the rooms well to protect from dust and cleaned up after themselves well. The decoration after the windows were installed was of high quality too and it was great to see that there was a team visiting daily during the installation process to check on the work and answer any concerns we had. In particular, Mario was great from when he first came to take final measurements to the end when he made sure our roman blinds were back up properly. We used another company before finding Core Sash Windows and had 1 window and 1 door replaced. Their installation was poor leaving cracks on the outside and they did not restore the inside to the original state. They were also quite a bit more expensive. I'm sorry I didn't find Core Sash Windows earlier, it was such a more pleasant experience. Thank you!
Makeda Posted on 12/12/2017 , work completed 12/12/2017
Good quality and good workmanship
Customer Service
Excellent workmanship, nice windows, courteous workers, cleaned up thoroughly. This was done very recently so I can't comment on longevity but the windows look and feel great. I could have used a more detailed description of the windows: I wasn't told about certain details - e.g would I want 'security' knobs, why I wasn't I getting decorative 'horns' on inside? But on the whole really good service ~Many thanks though for a lovely job.
Phyllis Creme Posted on 07/12/2017 , work completed 07/12/2017
Draught proofing front door
Customer Service
Very proactive - surveyor turned up on time as did fitter. Extremely tidy job and very effective"
Bridget1056 Posted on 07/12/2017 , work completed 07/12/2017
Unfortunately not able to recommend Core Sash Windows – 2 windows they installed 17 months ago have not lasted and now need to be replaced.
Customer Service
Core replaced 2 small single glazed sash windows in summer 2016, problems arose straight away. Despite 6 attempts to rectify, 10 different people from Core attending, they were unable to resolve to acceptable level. They spent total of 8 days, over a 10 month period working on 2 windows. Some of the issues (too many to list)-initial fitting–left a gap 5 cm wide, 2 mm high, could see straight through to outside. Wood severely splintered in the corner joints, paint on glass, holes in timber, paintwork lumpy, dents in putty. When the second fitter saw the newly fitted windows, they asked me twice if they were the old windows. On another occasion, strips of sealant were left hanging off wood, sashes made screeching noises when opened/closed. Manager did attend once, used his credit card to try & smooth out uneven putty, he admitted putty & paintwork was not good. Within 2 weeks of installation, the putty developed multiple deep cracks, within 2 months it was loose and moved. Core replaced the putty-their attempt was wonky, uneven & lumpy. A few months later, Core returned to paint the putty. Paint started creasing within hours, within days started cracking & flaking off. Their reasoning was that it ‘must have rained and been sunny on the putty’. Paint continues to flake & fall off. Core had the substandard windows made by another company. Core’s manager refused to take responsibility for windows. Ungenerous discount given doesn’t cover distress, upset & major inconvenience caused to me + I will have to pay for new windows.
Anonymous-15 Posted on 16/11/2017 , work completed 16/11/2017
The trader replied (on 11/12/2017)
Dear Anonymous-15 We agree that elements of the finishing by the fitter after Day 1 were in need of improvement, which is why we immediately returned to rectify the issues as soon as you brought them to our attention. As we explained when you decided to go ahead with single glazing replacement, putty will crack as it dries out, but the painted finish will fill these hairline cracks resulting in an unblemished finish. Also as explained, we could not paint the putty until it had fully dried, as putty can dry unpredictably which will affect the painted finish if applied prematurely. Nonetheless, at your request we replaced the putty resulting in further drying time before the windows could be fully finished. As you were dissatisfied with our explanation and resolution, at this stage we were mediating through the Dispute Resolution Ombudsman and Which?, and the discount you received was intended as a gesture of goodwill to repair our business relationship. We subsequently made several attempts to return to your property to paint the putty, as this was the only outstanding issue on the otherwise perfectly functional and finished windows, but unfortunately you did not allow us to do so, resulting in an impasse that we were unable to overcome. We're sorry that you are not entirely happy with the windows you have received, but we feel that we have genuinely done everything within our power during our business relationship. Yours faithfully. Core Sash Windows
Good quality windows and quick installation turn around
Customer Service
We recently had timber sash windows installed into our property. We ended up going for the basic fit as we were having a number of other work done to the property. This made installation much cheaper and affordable. In comparison the windows were much cheaper that competitors on the market and this was not reflected in the quality as we still got great windows installed. Highly recommended and great service by Dalan Rustemoglu!!!
Halil Posted on 07/08/2017 , work completed 07/08/2017