Hi zack, I like your roof idea. (Vaulted and flat) best talk to a design person to see how achievable it is. We are having a roof lantern in the middle of the flat roof extension and went to see one with it. It looked amazing, making the ceiling look a lot higher. If your original house has high ceilings like ours, you might need to reduce it a bit in the extension as PD allows 3m for eaves. For a flat warm roof, you might need to go down in ceiling height. I found out that you would learn so much during planning! As for your utility, if you don’t mind the utility closet idea as opposed to a room, it is a lot easier to fit in without side extension. We toyed with side extension too for a utility but didn’t want to loose side access to the garden. So we are putting a utility cupboard in where your ‘dining room’ is. But it will also function like a hall way to the extension. I would go for an island to define zone too if there is room. Although in our case, it is more because I succumbed to island envy.

Excuse the crude drawing over your existing one! One idea could be make your studio in garage as you were thinking. In your extended end, house your utility and then downstairs bedroom and ensuite with doors onto garden. Combine your original kitchen and dining room to make a gorgeous kitchen living/dining area with sliding doors. Close off your front room for peace and quiet 😁. Only one idea, I'm sure there are others. Need any more help... I offer interior design and 3d visualisation (which help you figure out your space) all online at https://www.no60interiors.co.uk/

Thank you @Jonathan @Devy brilliant plan. On a second thought I did not factor in the fact if we communicated the garage and the house we wouldn’t have access from outside to the back. So perhaps not the best move. And maybe to connect them the garage has to come down. 🥹. However like Jonathan has suggested may add value overall to the house. One thing I forgot to add is a bigger kitchen is needed as well and possibly a playroom/study. Also perhaps the garage can go as not fit for purpose. Any suggestions for plans to increase downstairs living space and hopefully get an en-suite upstairs?

If you made outer wall then its okay to build window on the side, your neighbor privacy will be maintained and you can get the sunlight needed, I would advise to move the garage to the front so it can be accessible for a car from the main road, you can still have direct path to the garden from the front if you move the enterance to the right and just put a fence, if it were me here's the layout i will do, it'll give more space for closet, bigger bath, utility room, and additional storage unit, so basically move the wall to the left and focus buildng that side, the previous garage will become the new master bedroom with en-suite