The one thing I would not do is lower the height of the doors - you will reduce the view towards the sky and it will make the whole place feel smaller and darker (and less luxurious), and the proposed height might just look wrong with the dimensions of the room.

I would consider only having one big set of sliding doors that open up as you probably will rarely open up both? The other one could be used for a nice window seat - you could still have the windows above seat as sliding doors though, so you could open the space up but not just walk straight out - then it could be seating for indoors and outdoors which would be nice.

That's assuming sliding doors are your preference though - perhaps more traditional French hinged doors would suit the property or your style more?

Regarding heatloss/gain, am not sure if this will make much difference, but I quite like glazed doors that are solid at the bottom section - even just up to around knee-height, if not waist-height - gives the look of more traditional doors, but can be done as sliders/bifold/hinged doors as necessary.

Another option which is very nice is to have the sliders slide into a pocket in the wall - which does mean you need enough wall space to the side of the opening for each panel to fit.

I'd also speak to kitchen designers to figure out your kitchen layout before finalising the glazing - I'd want more units along that left wall, so the bit of wall would need to be a bit thicker there to accommodate deep units. Might also want a bigger island, which might then impact on seating and dining spaces and therefore how you want the windows/doors laid out.

Having a view all the way through to garden from front door makes sense, so keep that in whatever you do.

Re rooflights - I agree the positioning and sizes are not right. I'd have them closer to the old part of the house, to make sure light got into the Hobby room in particular, but also the kitchen as they have no/little natural light. Having a rooflight above dining table just makes it annoying for placing pendant above table - and lighting up a dining table with daylight doesn't matter so much when a lot of formal dining happens when it's dark outside. Rooflights let in so much more light than a regular window, it would be worth looking at Velux website to show the effect on rooms.

I agree don’t change the height of the glazing but it would be good to apportion it differently with wider glazing on the left to match the width of upstairs windows.

And for me the kitchen and wc felt too small and so I offer an alternative

Thanks so much for taking the time to reply. All very good points. We are going with solar control glass which I hope will help with mitigating the bleaching. Planning to have blinds and sheer curtains too for verstaile shading options. Good point about the planting...we have lots of trees in the garden including a 60ft fir tree and a few other evergreens. The back of the house is a sun trap though so will consider more. Thanks again

@Jonathan Thanks for taking the time to mock up an alternative. We did consider more open plan options for the layout but ultimately we wanted a flexible space with options for closing off areas in future if desired. We aso considered the loo on the side you've put it but we are limited by the drainage on our property. The first floor extension is the same width as the wider glazing, but ChatGPT couldn't handle the dimensions and mocked it up wrong, so they are apportioned appropriately as in your suggestion. We're also keen that when you walk into the room at the back that your line of sight is into the garden.

@CWD Thanks for all your suggestions and insights also. We have reflected some more and I agree that the full height doors will make a big difference, especially to the light flow to the back of the room, so we will definitely keep that. At this stage we are thinking to just have a single lantern above the extension on the hobby room side to maximise the light into that space. I take your point on the windows, but I feel it's more important that the windows look cohesive fromt he inside of the house, e.g. when walking thorugh the landing seeing all the matching original stained glass (I also love the original windows). I think it will be rare to be sitting in the garden and looking back up at the house as a whole. I like the sound of the pocket sliding doors but sadly i don't think we've the space for them. thanks

Good luck with your project but I wonder if its too late in the process for you to re-evaluate the massing, form and construction spec to better cope with the site context and climate resilience challenges? The design form of the extension doesn't appear to address the key site factors of orientation, form, summer overheating protection, winter solar gain or any critical climate resilience factor. glass coatings and curtains are not design solutions, in my view.

I have helped a number of clients at your project stage to reassess these critical issues and adjust the design parameters for significantly improved that support optimum occupant well-being, energy efficiency and comfort outcomes. Appropriate material choices (avoid PIR or any 'lightweight' insulation) and design forms responding to context, when considered early in the design process improve every aspect of comfort, health, energy-efficiency and value. A basic box on the back of a house built to basic building regs compliance standards, very rarely achieves good quality internal living conditions, no matter how many thin coatings and coverings you add.

Future buyers and lenders will become increasingly interested in these performance factors as policy and lending criteria are clearly moving towards demanding sufficient performance criteria, not just the minimum regs.

Good luck

@RVI Architectural Design Thanks for commenting. The builders are coming on site in 3 weeks, so I'm not sure if it is too late to review? What do you mean by " The design form of the extension doesn't appear to address the key site factors of orientation, form, summer overheating protection, winter solar gain or any critical climate resilience factor"? What aspects? Do you see some red flags? We worked with an architect on the design over a long time and arrived at this current design. Unfortunately they have now effectively gone out of business and so can no longer consult and we are on our own and having to navigate these decisions ourselves.

You mention that it is SW facing. This presents a significant challenge to preventing summer overheating. I don't see that the design responds to this at all - BUT - I've only seen a snapshot of the proposed. Perhaps the material and detailed specification they produced is robust - not seen it so can't assess. I'm sure it meets minimum building regs but I have helped clients over the years to retrofit extensions that are only a few years old because they are too hot, too cold, too uncomfortable, too inefficient etc... the regs are mediocre at best. (There's a video online of a talk I gave about retrofit design that references a case study on this).

Given that 5/10 of the hottest average summers in the last 140 years have occurred in the last 23 years, overheating protection appears to be an ever-more critical design consideration. 2022 saw the highest ever recorded temperature in the UK at over 40degC.

What I mean is that the design is simply a rectangular form that provides additional space and doesn't necessarily consider the quality of that space for year-round comfort, health and resilience in summer or winter. Good design must consider these and the apparent increasing need for improved climate resilience as we see evidence of it changing.

Here's a SW facing extension design that I have just submitted for planning in a conservation area. It responds to these factors and has been modelled to minimise summer overheating and maximise winter solar gain - free heating in the winter! The original proposal by the previous architect was a £250k 'box' on the back of the house. This design is expected to come in at c. £150k and perform far better whilst clever internal remodelling provides sufficient space for the occupants. The form responds to the site context, constraints, orientation, human needs and climate imperatives. (This is how I choose to approach design, anyway)