Thank you siriuskey. Yes that's what I was referring to, but I think I wasn't giving credit to the island sink, which would also serve for food prep. I was thinking about efficiency from my perspective. Euro bins next to sink in island, would be beneficial for ease of handling waste. Another consideration is: when using cooktop and extraction fan, will noise from fan interfere with person in study? Also, will steam from say, boiling water steam bother anyone using the study desk? I am not trying to throw cold water on the plan by my questions, I'm merely trying to imagine diff scenarios so as much as can be taken into consideration is. I have a glass splashback behind induction cooktop and a very effective extraction fan; however, when a large pot of water is at full boil, the glass steams up something chronic and I have to constantly wipe it and the underside of exhaust fan or else water drips down onto the cooktop (and any food I'm cooking).

i have a problem with the awkward location of stairs that wastes the sunroom, makes the rumpus room difficult to furnish and the front door has a view of the toilet ...beginning with central stairs and potentially modifying doorways to allow for the stairs without having to walk across the rumpus or upstairs living room attempts to avoid the big wide hallways affect without useful locations for furniture ..the rumpus room now has space for comfortable furnishing and private access to a full bathroom and good sized laundry...using the old sunroom for a compartmented bathroom retains the original walls and windows and includes space for a bathtub and shower with big views.. we should always include real scale sized furniture to establish the best walking paths across rooms and my suggestions also retain the size of the original kitchen to keep more of the original walls and ceilings and retains the proportion of the bay window and allows space for an alternate access to bed 3 (preferable the linen cupboard would remain in this location) and consider avoiding the enclosed pantry (would the door ever be closed?) in favour of a more open space for better light and ventilation and maybe a herb garden window box in the bay window with external blinds to exclude western sun.. there's a fridge closer to the outdoors, stacked wo and MW to define the pantry and only a small sink in the island for more useful set down space for shopping and serving meals

I had a similar idea to your one oklouise , of building above the new garage , but I had a couple of alternative tweaks -- I wondered about coming 'forward' with the garage and upstairs , thereby having the upstairs front rooms closer to the street . The one slight problem I can see with your plan is that the dining area could be a dark area -- by coming 'forward' you keep an extra window on the downstairs side profile . The problem with that suggestion though , is that the roof may look funny , with a lower centred peak and then an upper one , so I then wondered about still going above the garage , but having the upstairs wider in profile , effectively 'stepping' 3 metres or so over the 'old' house , effectively removing that 'corner' of the existing roof and having a floor above instead of roof trusses , and have the existing roof butt up to the new upstairs side wall -- it would look more balanced IMO , you won't need to remove all the existing roof and strengthen it -- by utilising the existing brick walls it may not need any additional strengthening ? By tying the existing roof trusses to the new side wall it won't need too much strengthening either . It should also look a lot less like an add-on if the styles and materials are matched correctly IMO .

moving the stair doesnt help the existing upstairs if your plan is to not change much. the living area would reduce from 3.5 to 2.5m width and would limit options unless you want to use this space as office/playroom. the existing door would have to be relocated to bed 1 and the green line is an existing beam which looks to be tight on the 12th stair down which is usually the minimum head height clearance.