Hi I also stand with the advice you were given and would suggest staying well away from UPVC bifold doors! Origin bifold doors are a great products and our most popular doors out of the bifold doors we provide. When you consider the 20 year guarantee, security and safety features on the door I believe they are quite reasonably priced and around £1000 + VAT per panel can be used as a very rough costing. If you are looking to reduce the cost you can reduce your opening to 4.8m and this will allow you to have 4 door sashes within your bifold door. You are able to contact Origin directly and they will give you a list of 5 local suppliers to you, it might help if you shop around for the best deal, different companies are able to offer the doors as different prices. We may be a little out of the area but if you'd like more information on Origin, Schuco, Solarlux, AIR or Centor doors take a look, it might help with your decision. https://hbdsystems.co.uk/  I hope you find what you are looking for! Hannah

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try bladerunner everroll by jaymart. it is what is used in many gym locations. Best Rowland

Permitted development is not permitted in Conservation areas. However changes to Windows normally only need permission at the front.... so you should phone the council for their local opinion but likely you will only have to comply with building regs.