Please critique my extension plans

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Currently in a 3 bed semi detached house, well 2 doubles and a small box room (will fit a single bed and bedside table just). Me, DH and 2 primary aged boys (who are likely to grow to be 6ft plus). We have a drive all the way down the side of our house with a garage at the end. I love where we live, good neighbours that are here for the long term, large south facing back garden and a stones throw from forest/hills/walks.
Looking to extend to give us 3 proper bedrooms, study/box room plus another bathroom (only 1 right now). In the future we could also take down the conservatory and extend out the back (7m x 4m) which would be a kitchen/living space with current dining area staying and current kitchen becoming a WC and utility. That’s for the future though.
Issue with extending out the side is that it blocks the kitchen window until we extend out the back opening up the space. Has anyone found a way to fix this with some kind of light tunnel?
Black is current layout and red is the proposed extension. The green garage would be demolished if we extended.
What would you do/does what I want work?
There is the possibility of buying a 4 bedroom, kitchen/diner, living room and snug house in a few years. However this house has a north facing garden but it it tiered so gets the sun at the top in the summer.

All looks very sensible. However, as you're planning on perhaps extending out across the back, I'd consider double doors or even another garage door from garage to garden unless you've room to get down the side past the garage with equipment.

The upstairs layout is very similar to my SIL's.

The bedroom above the garage is quite narrow. Would the garage have to be rebuilt/strengthened to support building above it?

Would a loft conversion work as well/better for you? If no rebuilding of garage needed, I imagine it would be more expensive, but may be a more usable space?

@Ariela Thank you, I had thought about that as the extension would be up to the boundary. At the back of the garage would be a door and window or another garage door with appropriate lintel regardless. The house is higher at the front than the back so garage would have good head height to get mini diggers etc through. We really need a garage as if we didn’t the bottom level would be another living space, utility etc. Boys and their bloody vehicles/crap etc and we wouldn’t have to extend out the back.

@Schoolchoicesucks Down the side of the house is driveway right now so would be a 2 storey extension with garage in the lower half. The room would be 2.5 metres wide which would allow a king size with space to walk around the bottom. DH wants to incorporate the box room into the extension but that wouldn’t allow any other size of bed plus would be £££££ as it would mean supporting a long section of exterior wall.
Unfortunately there is not enough head height in the loft for a loft conversion. Not a single house in the whole estate has been able to do this with dormers. Some have velux windows but they are really just a floored loft which we plan to do for storage anyway.

2.5 metres is far too narrow for a garage nowadays. The average car width is 1.8 metres and you need room to open the doors.A Ford Focus is 2 metres wide! The absolute minimum garage width is three metres wide. I would use the ground floor space for the utility,pantry and WC. These would all be useful now with a growing family. Depending on how close the existing garage is to the house,you may be able to keep it,particularly as utility,pantry and wc don't need a lot of natural light.

@ItsDinah Garage would not be for a car but for motorbikes, bicycles, garden stuff. The garage would be the same size as an integrated garage in a new build right now. We would need the ‘garage’ for planning as it counts as a parking space and I think a 3 bed needs 3 spaces (1 in garage plus 2 in front of the house).
All the things you mentioned about wc and utility etc would be great right now but would mean totally redoing the kitchen to accommodate them which we can’t do right now without extending out the back as the space in the kitchen is just too tight
Old garage is to scale in the picture so would be demolished to give a bigger back garden plus space to extend at a later date.

Can you make the rear part of the proposed garage become part of the kitchen? I think while upstairs works really well, the lack of downstairs loo and utility makes it unbalanced. Or knock down the conservatory and extend the kitchen out back as well?

@titchy The plan is to extend out further at the back at a later date. The current extension plans would allow for that to happen in the future but we can’t do it right now. What is currently the kitchen would become a wc and utility and a wall would be put up between it and the dining area. WC and utility would be internal which would be fine.
The rear extension would be 4m x 7m and include an open plan kitchen with living area and would open out to the back garden.
I’d love to be able to do it all right now but just can’t afford it. I’ll do a plan tomorrow and post it then.

The problem with house builders putting in garages too narrow to accommodate modern cars was flagged up a long time ago. Some councils now insist that garages have a minimum 3 metres width. You sound as if you have already hammered it out with the Planning Department. I know councils sometimes insist on having some sort of secure bike shed if you don't have an actual garage. What a pain.

Looking at the upstairs, could you make the new space above the extension into two equal sized bedrooms, then instead of the new bathroom turn the box room at the front into a shower room? Obviously current plumbing is at the back but you could run a new drain under the garage extension from front-to-back to take away the foul water. We've just done an almost identical extension.

Have you researched your local planning rules? I doubt you'd be allowed to do a double storey extension to the boundary. You have to leave at least 1m here.

Also is 2.5m the internal or external width of the extension? an exterior wall is 30cm so if you're looking for 2.5m internally, you'd need to extend 2.8m. Obviously if the external width is 2.5m you'd only have 2.2m internally which means you wouldn't be able to walk around the bed as you've drawn it currently.

Most double / kingsize beds are 2m long so you need internal space if 2.8m to allow easy walking past end of the bed. So 3.1m external width . My advice would be go as wide as you can but not narrower that this.