I think if you have a 1m wide table and allow a metre each side to pull out chairs you are left with 1.6m of room width which in my opinion is insufficient for a full living area. So I offer an alternative

@rinked Thanks, good idea - i'll see what it looks like later. @Suzanne C thank you for sharing your experience and pictures. We'll be going out for quotations once our planning is granted so i'll make sure i get a cost for wet UFH. I think it would be the preferred route with the warmth underfloor and extra wall space is always good in open plan extensions. @minipie Thank you. The software really is great once you get to grips with it. We've started to obtain budget costs on the roof lights and one company has offered to take us to see a few recently completed projects which should hopefully give us some inspiration and allow us to gain some feedback from previous clients. I'll aim to get at least one opening roof light after all the advice received on this board. Thank you for sharing your experience. I'll look into the small radiator in the bathroom. Good idea. The extract routes are pretty easy as the kitchen hood is on an external wall, as is the utility. The WC fan will follow the existing route above the utility rooms ceiling. Not sure on the subfloor as not taken up any flooring so far but the house was built around 2003 so you'd expect a pretty thick solid concrete slab so it might not be as easy as excavating in an older property.

Hi Teresa, APT Renovation here. We are a design and build company and would love to give you a free consultation and be a part of this exciting project. If would like to view some of our previous builds you can head to https://www.aptrenovation.co.uk/our-projects/ or give us a call on 0207 223 6417 and we can start helping with your project. I trust you will have a great day further and hope to hear from you soon :) Kind Regards, APT Renovation Ltd

Hello and thanks for your prompt reply. The drawings provided show that the support beams are 203mm depth and therefore they will be too big to sit inside the ceiling void. As the weight per linear m is 23Kg as detailed on the drawings it may be worth asking the engineer to reduce the depth and and increase the weight so the beam can be inserted into the ceiling void. I note that there is also a couple of posts in the stud wall and these could be upgraded if necessary. I do not make these suggestions lightly. The main benefit of inserting the beam inside the ceiling is the removal of the shadow cast on the ceiling. The return nibs on either end could be cut back and if needed posts could be fixed direct to the brickwork to provide vertical support. There may need to be a spreader plate welded to the bottom of the post in order to mitigate the point load on the foundation. Obviously this is more of a structural design issue. Is there a good reason for not centring the bifold doors to the external wall? You have so much height on the flat roof why not put a warm deck roof on instead of a cold deck with in cross ventilation? Can I also suggest a warm pitched roof too. You may find Web Dynamics TLX Goldto be a very useful form of insulation as you will only need about 75mm of PIR insulation in between the rafters. I've never been fortunate enough to meet a building control officer willing to accept a heavy duty Catnic lintel over a 4M bifold door. I thought the under stairs might be the position of the meters. I would consider relocating these to an outside wall. Then turn the WC through 90 degrees and design it under the stairs. If I was planning a kitchen diner extension with a beautiful bi-fold door looking out into the rear garden would try and create a direct flow from front of house to the back. I would move the utility room into the middle of the house to provide a direct line of sight from the front door to the rear garden. GD3 would provide access into the utility room. I'd consider moving the door along the living room wall so it could open into the hallway. This would allow a 950mm wide fully glazed door to be placed between the hallway and the kitchen diner. With regard to the position of the new extension wall which is adjacent to your adjoining neighbour I suggest that you look up the party wall act 1996 booklet online here - https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/523010/Party_Wall_etc__Act_1996_-_Explanatory_Booklet.pdf The part that is of interest is "Line of junction - building astride the boundary". If you build across the boundary you should gain at least 150mm of additional internal floor space along the length of the outside wall. Also if in the future your neighbour decides to build an extension they can utilise your wall for if they pay half of the cost of its construction. I'm sure you know that you are responsible for paying all of the costs from all sides relating to the party wall agreement. If the neighbour on the other side is within 3/6m then you will need an agreement with them as well. The architects drawing indicates that the drain is not adopted or shared and therefore you will not require a build over agreement with the water authority. Best wishes Andrew