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Endorsed by Which? Trusted Traders

Core Sash Windows

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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

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

50 reviews
Customer Service
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Sash window box refurbishment and double glazed sashes installed to the front.
Customer Service
Three years ago Core replaced some sashes and refurbished others on the back of our Victorian terrace. We also had replicated French doors and a back door replaced. I had no hesitation in asking Core to return for the front window. The information given was clear and no pressure or exaggerated promises were made. Core is able to offer a variety of options e.g. repair and refurbishment and replacement which is helpful if you value original features. I like the open accounting system and the option of insurance for the initial deposit. Financial arrangements were therefore straightforward and reliable. The team as before were professional, punctual, polite and honest and tidied up each day. The finish is excellent and being able to open and air the house more easily is wonderful. Both Daniel and Sean made sure to check that there were no issues. I am very happy and have recommended the company to a neighbour.
Ritten Posted on 27/07/2017 , work completed 27/07/2017
A less than satisfying experience - delays, incorrect charges and recurring issues
Customer Service
It started well, though there were delays and prices seemed on the high side. The team were competent and largely efficient regarding the windows though left the paper on one set of sash cords. The two doors and managements response were a tale of misleading pricing, leading to initial overcharging and lengthy delays because there was, it appears, a lack of internal communication within Core. The new basement door fitted well, but it took months to get the right colour hinges. The front door was much bigger negative issue. There were months of delays as a complaint to the original contact at Core was seemingly never passed on. The workmanship left paint bubbling, this was repaired but then bubbled up again. I was also, more seriously, but not clearly indicated on the estimate, charged for a full door refurbishment. I challenged this repeatedly and was only acknowledged as correct after repeated emails despite a full invoice requested - the discount for the one sided treatment, especially given the faulty workmanship was not generous and the door still required attention. Most of these issues could have been mitigated by more efficient customer service and better internal communications at Core and a better attempt at recognising poor customer management and service
Anonymous Posted on 19/04/2017 , work completed 19/04/2017
The trader replied (on 26/04/2017)
Hi Anonymous, Thanks for your feedback, and we apologise that you aren't entirely satisfied by your experience with Core. You've highlighted that many of these issues were either caused, or exacerbated, by poor internal communication, which we do acknowledge. Unfortunately, our internal resources have been stretched thin due to our company's rapid growth, but we understand that this is no concern of yours, and we will be improving in-house conditions to ensure that these issues do not arise again in the future. With regards to works carried out on your front door, you were originally over-charged as we had initially been contracted for a more comprehensive service than you were after, which we appreciate you have said was due to unclear indication on the estimate. This issue was then further compounded by our painter not informing us that he had performed the door repairs in line with your specific requests, as opposed to your accepted quotation, meaning that our office staff were unaware that you had received a downgraded service and therefore did not lower your price accordingly. Whilst there is no excuse for the poor internal communication, we would like to make it clear that the price you had originally was never intended to reflect the works you ultimately had performed on your door, and that these issues arose from miscommunication as opposed to malice. Kindest regards, Core Sash Windows
High Spec and Stylish Workmanship
Customer Service
I had researched the well known window and door manufacturers, but Core easily came out tops as they offered the most comprehensive service. The price is also reasonable given the outstanding care and workmanship. Ryan and Marco were full of tips and not pushy as this company has no need to be. Core produced a new front door for my Victorian terrace with a style in keeping with the era, though I chose a colour with a modern edge which compliments the front of my house brightening the exterior and interior. There are a large range of colours to choose from so you can create a bespoke look. The additional warmth created by the insulated door was immediately noticeable. And now I've commissioned core to replace all the sash windows in my home which will be natural wood inside (for a cottage like effect) and white on the exterior. I don't think other companies can offer that level of individual service.
Alison Posted on 13/02/2017 , work completed 13/02/2017
Superb professionalism and outstanding quality
Customer Service
We have been extremely impressed by the level of service and workmanship provided by Core. From the professionalism of the survey to the skill of the workmen involved with the installation and painting of the windows, it was been a flawless process. It may be a bit more expensive than other companies, but it is money well spent with quality that is second to none.
Jon S Posted on 03/02/2017 , work completed 03/02/2017
Very happy with our new windows!
Customer Service
Professional, friendly service and excellent workmanship. Reasonably priced, not the cheapest but reliable, clean and trustworthy. Head carpenter Ryan is responsive, helpful and a very nice chap. I wouldn't hesitate to recommend them.
Mrs B, Islington Posted on 21/11/2016 , work completed 21/11/2016
Very very happy with Core
Customer Service
I was so nervous about appointing someone to do our windows given some of the horror stories you here. However, I couldn't have been happier with Core. They are excellent quality windows, the builders always arrived on time and cleaned up after themselves. The communication and service with their office was always spot on. Payments were easy to keep track of and make through their customer site. And it makes the house so much warmer too - such a noticeable difference. Very happy to recommend to all.
Vicky V Posted on 09/11/2016 , work completed 09/11/2016
Fantastic work
Customer Service
excellent workmanship, amazing cleanliness and finishing off that goes beyond expectation - and great windows!
Which? Trusted Traders Consumer Posted on 04/08/2016 , work completed 04/08/2016
Fantastic Company
Customer Service
Excellent service and workmanship. Everyone we have dealt with have been fantastic, especially the fitters whom we're friendly, passionate and extremely diligent. I heavily researched the market and found that Core were the only company to offer a comprehensive service. In that they were willing to undertake the minor building work (repointing and plastering), as well as redecorating that results from the replacement of the windows.
stewlauder Posted on 04/08/2016 , work completed 04/08/2016
High Standards of Workmanship and Materials
Customer Service
Ours is a typical London Victorian terraced house. After much research and a recommendation from neighbours, we chose Core to replace the windows in our lounge and three bedrooms, and draft proof and re-glaze the front door. From the outset (the initial contact and site survey) it was clear that this was a company that prided itself on a first class product (their website is also very comprehensive) and the quality of its workmanship. The quote was competitive and a start date was agreed. It was to take ten days. At the end of the first week I emailed Core's management and included the following.... Just to say how impressed we are by your team - skilled, diligent, respectful, hardworking, conscientious, cheerful... The superlatives were fully justified and, as the work progressed, it was obvious that the box of each window was being completely refurbished and, with the new windows installed, they would have been fully restored. Neighbours began to notice and ask after the process. On completion, we were assured that 'if any problems arise...' they would be remedied and we were provided with a written guarantee. Put simply, the investment was very worthwhile, the quality of finish was of the highest standard and I can recommend Core to you without hesitation.
Which? Trusted Traders Consumer Posted on 03/08/2016 , work completed 03/08/2016
Which? Local Review
Customer Service
We were absolutely delighted with the quality of the work carried out by Core - both double glazing and draught proofing. We immediately felt confident with Sean when he came to give us an estimate. He gave a very clear explanation of the options and the relative benefits, all without any sales pressure. The work was then carried out with huge professionalism and dedication and with great attention to detail.The quality of the joinery and of the painting on our new double glazed windows was staggeringly good. And they cleared up so you would't know they had been ! We got a number of quotes including from the major 'known' companies. We felt Core was the best option in every sense having checked exactly what was included in each quote. We were right and would highly recommend Core for the quality of the work and the value for money.
Adrian Paterson Posted on 08/06/2013 , work completed 08/06/2013