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Endorsed by Which? Trusted Traders

Core Sash Windows

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52 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

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52 reviews
Customer Service
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Poor workmanship, followed by poor customer service.
Customer Service
Despite confidently assuring us that they would make good and leave no trace, their installers didn't clear up after themselves, leaving rubble and dust on the floor for several days at a time, even when they were applying the top coat of paint (which any good painter will tell you is a cardinal sin!) - and leaving their empty drinks cans lying around. They managed to leave scrapes, scratches and dents on walls and woodwork throughout the house, and made such a bad job of touching up / fixing these issues that they had to come back several times and ended up having to repaint several walls in their entirety. On one occasion I turned up to meet their Director at the house and he was hanging out of the window with a hoover, apparently cleaning the gutter. When I came in, I noticed that he had splattered dirty gutter water across half of the walls... cue another few rounds of touch ups... The windows themselves seem pretty good (they are made by a supplier in Estonia I believe) but the final coat of paint was very messy and left drips running down walls, on the skirting boards, radiators etc., so again this was something they had to come back and fix over several visits. Worst of all is that through all of these issues, their customer service was appalling and made the whole process extremely stressful. From not showing up to meetings, to simply being rude and trying to make excuses for things they were clearly at fault for, and now simply ignoring emails.
Customer in Greater London Posted on 11/11/2019 , work completed 27/09/2019
The trader replied (on 09/12/2019)
We are sorry that your experience could have been better. You notified us that there were some marks upstairs on the newly painted walls of your home. We agreed that we had been responsible for leaving some of the marks during the installation of your Accoya double glazed windows. There was substantial ongoing works taking place throughout the house at this time with multiple trades on site. We suggested we would fully paint all of the walls upstairs so we could leave you with the best possible finish. This was carried out to your satisfaction and we also gave you £200 in John Lewis vouchers for the inconvenience of having our painters for additional days on site. After this you emailed to say that you wanted £1500 compensation before you wrote reviews about us on various sites. We have rectified the issues you brought to our attention. However, we are unable to provide you with any further payments. We regret that we were unable to completely resolve your complaints but we do appreciate your business. We will of course, honour all guarantees and we will return if you have any issues with our windows in the future. Yours sincerely, Sean Mac Anbhaird Managing Director Core Sash Windows
Very professional
Customer Service
We had french doors fitted in our Victorian/Edwardian house. Attention to detail was amazing. The doors look like they’ve always been there except much less draughty and rattling! The service we had from Core was very professional. The doors took a while to make but they are so well made it was worth the wait. We were kept informed of progress at every stage and installation was fast and efficient. The guys on site were very professional - incredibly polite and extremely conscientious. All in all it was a very positive experience. Highly recommend them.
Customer in Greater London Posted on 25/10/2019 , work completed 31/07/2019
Awful experience!
Customer Service
We recently had four sash windows replaced by Core Sash Windows. They requested 8-10 weeks to make the windows. As we approached ten weeks, they made no effort to contact us to let us know the windows were delayed. After rescheduling to the 13th week, we received a call at 3pm the Friday before they were due to start on Monday to say they didn't have one window and had no idea when they would have it. Once they started the work, they got three days in and then didn't show up for two days. They refused to answer the phone and never provided a credible plan for completing the job. Once complete (finally), they chased us for payment within 24 hours and continued to chase every day with multiple calls and email over the next few days. They are awful to deal with and I wouldn't recommend them to anyone.
Customer in Greater London Posted on 06/10/2019 , work completed 03/06/2019
The trader replied (on 11/11/2019)
We are sorry to hear about your experience. It took us a while to figure out who posted this review. Confusion arose because you were not our direct client. The property management company of your building contracted their builder who in turn contracted us to carry out the window upgrade works in your flat. Our client took some time to decide on several details of the job - whether the sides of the windows should open or not with the Venitian window and whether they wanted a hand painted or spray painted finish. The 8 – 10 week lead-time will only have begun after they clarified these details with us in writing. We provided our client with a ‘Schedule of works’, that outlined the entire work process & they were in contact with our surveyor throughout. However, we understand that this has been frustrating for you and that some information was lost along the way. As a result of your feedback we have made improvements to our systems of communication; particularly when there is a third party involved so that all parties are onboard from the outset.Please get in touch if you would like to discuss this further. We’d appreciate the opportunity to make things right and work towards earning back your business.
Brilliant quality windows fitted by professionals
Customer Service
I recently had 7 one-over-one, top and bottom opening, engineered box sash windows fitted by Core Windows. The original site measuring and ordering process was very smooth with detailed breakdown of each window (materials, window furniture, glass, openings mechanism, cills painting and undercoat systems) which was provided a couple of days after the first visit. I opted for a basic fit as I had builders onsite renovating, and this was carried out to a very highly standard. The windows look amazing and are very solid, with decent weight, smooth opening and cut out a lot of external noise. I’ve already had two neighbours enquire where they are from and whether I’d recommend - in answer to that, I would highly recommend Sean, Tim and the team at Core and would not hesitate to use them again should I need to.
Customer in Greater London Posted on 27/09/2019 , work completed 18/08/2019
Exactly what we wanted and extremely professional
Customer Service
Core made and installed 3 sets of French doors for our Edwardian house. We took ages to decide on a supplier as so many door manufacturers only provide off the shelf products which look cheap and insubstantial. We chose Core because they were prepared to make bespoke doors to our specification at a competitive price. We are delighted with the doors now they're installed. They are beautifully made and finished and the design is completely sympathetic to the age of the house. We had dreaded the fitting process, expecting lots of mess and damage to existing decoration (old doors had to be taken out and new frames installed along with new architrave and skirting). We couldn't have been more wrong - the carpenter and painter were incredibly clean and tidy, clearing up any mess before they left each evening. They were professional, friendly and polite and a real credit to the team. The finish is exceptional - they really went the extra mile to make sure everything was perfect and we were happy. There is no need for any further decorating work - they made good all damage to plaster and trim - you really would not be able to tell that the doors are new. We were so happy with the whole experience. In fact it was so incredibly easy and painless we're thinking of replacing the windows now... Thoroughly recommend them.
Customer in Greater London Posted on 28/07/2019 , work completed 20/07/2019
New french doors
Customer Service
We were really happy with the service provided throughout. The survey and install team were friendly and polite and everything has been finished to a very good standard. We wouldn’t hesitate to recommend Core Sash to our friends.
Customer in Greater London Posted on 24/07/2019 , work completed 10/06/2019
Professional outfit delivering a quality product
Customer Service
I had a new front door made and fitted by Core Sash Windows in June and am very happy with the end product. I'd originally asked them to quote for sash windows over a year ago, so had dealt with some of the staff at that time. Learning from that experience it was important to me to contract a local company this time. I found them professional and helpful to deal with, from the back office all the way through to the workmen installing the end product. The door itself is a quality product which, in my opinion, is good value when I compare it against some other quotes I received. The only area I could pick out for improvement is communication. I found myself calling up or emailing, asking for updates on a few occasions as the lead time was around 12 weeks and installation would likely have been during working time, requiring some planning on my part. Nevertheless customer service gets 4/5, the only area that wasn't 5/5. Happy to recommend Core Sash Windows given my experience.
Customer in Greater London Posted on 14/07/2019 , work completed 25/06/2019
Installation of new glazed patio doors
Customer Service
Core Sash Windows installed our new patio doors recently. First class service from start to finish, I can't fault anything. The doors arrived a week earlier than expected, and were installed in 2 days. All work was done carefully and in professional manner, and the end result is great. The doors appear very sturdy and good quality. The installers were friendly and professional and left everything immaculate. They even touched up the paintwork and also recycled the old doors. I would be happy to use Core Sash Windows in future and can recommend their services.
Alexia, Essex Posted on 24/06/2019 , work completed 24/06/2019
Beautifully finished windows, draft free windows and a pleasure to deal with
Customer Service
We had the large sash windows on our 2nd floor flat replaced in a conservation area. The windows are absolutely stunning and have transformed the rooms and the level of finish both outside and inside was excellent. I had not realised how much work and what a detailed task the finishing would be to make it good as new. One of the window sills had to be adapted on site around a unit that we had purchased that was bigger than expected, this was done free of charge and very neatly. The rooms are draft free and the windows just slide open so smoothly, I wish I had them replaced before. Every member of the team was helpful and pleasant and responded to questions immediately and Core managed to flex delivery to coincide with other building work. The installers were excellent and carried the huge front window up 2 flights of quite a narrow staircase with no problems - I absolutely would recommend - worth every penny!
Customer in Greater London Posted on 28/04/2019 , work completed 22/02/2019
Still warm feelings after three years.
Customer Service
We were having major house renovation works and started off with the windows. All the windows except the sitting room were renewed. The sitting room has the old, interior, wooden shutters and couldn't be replaced with the double glazed units if those were still to work, so these windows were successfully renovated. It was a very happy relationship with Core from start to finish and three years later we are still completely satisfied and happy. The house is warmer and, above all, much quieter. The new sash windows work beautifully. We strongly recommend them.
Willis Posted on 27/09/2018 , work completed 27/09/2018