In my opinion your loft conversion is likely to be in the region of £37,000 (for 2 bedrooms a bathroom and with a dormer at the back. Because of where you have planned the stairs you will need to move the bathroom- £6,000 Your plan includes moving into the garage and likely bricking up the window and making the garage habitable and taking down several walls that might well have originally been the walls of the main house (because garages are rarely built as part of the main house they are often add ons) so this big job is likely £15k. The boiler likely won’t be powerful enough for a larger home so that may well cost £4K to upgrade. Then there is the cost of a new kitchen £15k ? Flooring- £4K. Window treatments £2k. lighting- £1k. DIY decorating- £1k In conclusion I think this is a £85k job. Now of course there are efficiencies that can be made and you may buy some stuff well and building work is cheaper in some parts of the country- but I still think that you should be getting some quotes

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.

I think this might be the quickest/cheapest option. Assuming the space is big enough and is constructed in the same manner as the rest of the house (not single skin like a garage etc). Remove the door and replace with a window then build a wall to separate from the kitchen. Couple of days work plus decorating time.

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?