Cox Format Developments Limited is a professional building company working within parts of north London and Hertfordshire specialising in Loft Conversions and Extensions with the majority of our work coming through personal recommendations.
We pride ourselves on quoting a good price and sticking to it. Because we are professionals we can see what work is necessary to achieve your objectives and we price accordingly.
We can offer you a full planning service project management and where required structural advise and local authority permissions.
Cox Format have been helping clients maximise the use of there Loft and garden space for over 46 years.

Trades offered

Builder general
Garage conversions
Loft conversions
General extension
Bathroom fitter
Roofing general
House Builder
New build
Disabled/elderly home adaptation
Accessible Bathrooms
Accessible Kitchens

Case studies

Double Hip to Gable Loft Conversion and Rear Extension - Whetsone North London N20

  • 02 Aug 2017

Loft Conversion - High Barnet EN5

  • 02 Aug 2017

See more case studies

Customer testimonials

11 Feb 2019

We engaged Cox Format to design and build our dormer loft conversion. They made well thought out plans with our input and took care of the planning permission and the subsequent appeal. They communicated the start date and from then on were at work solidly until they finished. Arriving everyday without fail at 07.30 and getting straight to work. Starting at this time allowed us to discuss and take any decisions the team needed before leaving for work ourselves. The team were well presented, professional, polite and hard working, paid good attention to detail and always tidied up before leaving for the day. The back office staff produced a detailed quote and payment plan with an itemised list of any additional payments. I would absolutely recommend Cox Format for your loft conversion. - Samantha

Shenley in Hertfordshire

29 Nov 2018

Dear Peter We just wanted to thank you for all the hard work your guys have put into our project. The work was done to a very high standard and we are thrilled with the outcome. James, Graham & Mark’s inputs were invaluable to this project. Mark has given consistent support from beginning to the end - his professionalism was one of the main reasons for choosing Cox Format as our contractor. His promptness in dealing with issues was second to none. Both Graham & James exceeded our expectation as foremen. Their managerial & organisational skills on top of their craftsmanship were the catalyst for the success of our project. Also Graham’s carpentry skills are superb, which must be a real asset to your company. Thank you again for all your support for the past 5 months. All the best, James & Yoko - Yoko

Highgate, North London.

26 Jul 2018

The whole project ran like a military operation and if things fell behind due to unforeseen circumstances Cox Format caught up with things by sending in reinforcements. There were regular site visits by the Managers and constant feed back. We received helpful advice throughout. We were very pleased with the work which was finished to a high standard and on time and all of the workmen were very obliging. Danny - Danny