-rick-

Aren't MicroLourves fairly widely available? ie: https://www.solar-shield.co.uk/microlouvre-screens

All good. I worry a bit that I'm coming across a bit negative. I do like your design. This is all a matter of choosing where you want to spend your money (or otherwise control the cost) and as long as you consider that things you like might cost more that's fine (so long as you have the money). Sure. I was saying that more just in case you were concerned about losing space. I think if you have extra space it should go more to the bedroom areas. Equally, you could go overall shorter if the building is a bit wider. Good points. Wider does potentially have undesirable consequences vs longer. Extra length is easier/cheaper but maybe doesn't help with layout as much. True. You can get some very 'stair like' loft stairs that should be easier to climb. But if you are planning for everything to be fully accessible then it's not the way to go. Again if the building is 1m wider you could move some plant to cupboards along the corridor. If longer, could be cupboards against the kitchen wall around the door way.

I'm more familiar with it being a version of a portal frame too. But it both came to mind and your images came up in response to searching 'space frame buildhub'. I could easily be wrong about what @Gus Potter is thinking of here. In any case, I can see your type of build being a good way to build something like this (with the exception of the big windows on the long wall being a difficulty)

Used to be true, rules were changed recently. (Last year or so)

I had a bit of looking around and I think @Gone West went with this type of construction and I'm sure there is more detail in past posts but I can't find them off hand.

Sure, not dissimilar to me. I'm just saying you don't have to go all the way to hemp/sheeps wool type insulation. You can get mineral/glass wools with pretty good eco properties without the premium you pay for the eco marketed stuff. Look at Knauf. If you've already found a low priced source of eco stuff then go for it but it sounds like your budget is going to be really tight so every saving should be looked at. Missed no, just didn't stand out before. Which means its lower on the list of things I wanted to talk about. Any time you introduce angles you add complexity. I like the overhang and think it could be quite easy to construct if doing space frame (though I think it's much easier with traditional foundations vs insulated raft). Just think the angle itself isn't adding much. With a straight wall you can still have the overhang as protection, you'd actually have more outdoor space but you have a simpler foundation and junctions. Offset is you likely use some more roof/wall materials. If this build is literally DIY max and you intend to do all these bits yourself then the extra labour in making the angle happen might not matter. But there is also the point that every detail that you need to deal with once is a learning experience and you will make mistakes. Keeping things simple means trying to minimise the number of one-offs. The more repetition you have the easier it is to get good at something. So you can start where the mistakes will get hidden and work your way towards the areas where mistakes will be visible so by the time you get to them you have figured out how to do things nicely. I think my inclination would be to try and build the building 1m or so wider. No annex, take 1.5-2m from the expanded living room area to build that lobby area in the to main space (overall 0.5 to 1m loss of space in that area, offset by more room for kitchen/dining). If straightening up the external wall on that face you likely gain space overall. Total footprint of the building would be broadly similar but would be easier to construct and specify (no need to negotiate SAP for the lobby space or deal with wierd airtightness details on the inside/outside bit). I would scrap the plant room and put it in a loft above the bathroom/study.

Really good idea this. It's not novel but not something you see in the UK and would solve the overheating problems in many properties.

Tend to agree. Didn't really stand out to me first go round but noticed on the most recent version. Keeping the wall straight but with the roof/walls overlapping the outside (as shown in many of @ETC's previous designs would seem nicer and less complex/expensive to build. Might get your covered area automatically if doing a space frame construction. It's just another unit or two in length. @Square Feet by space frame do you mean the i-joist/beam type that one or two others here have done? Could see that being a good way to go if doing a lot yourself and likely doesn't need that kitchen wall/divider to extend so far as no roof supports needed.

You might consider whether the lean to part adds more cost than it's worth vs a slight larger main building. Yes you plan lower insulation etc, not part of the main space but I'm not sure that is a saving (more likely a cost due to extra complexity/junctions). Could still have covered porch area but remove the need for proper foundations. Are the eco insulation products part of a concept to get planning? If not, they are generally a more expensive way to build for relatively limited environmental benefit. Choosing the low impact but more standard options might save money without a big environmental impact (especially if that then allows you to use the money elsewhere for other low impact things). Keeping to dimensions that allow standard off-the-shelf construction materials likely is a benefit, though I'd guess Gus has already talked about that. But that leans towards longer but narrower vs wider but shorter in trade offs.

One question: What restrictions are you working under with the overall size of the design. Obviously cost, but in terms of planning/site? I'm thinking whether it would be possible to add length or width (or trade one against the other) if it made the overall layout easier? I could see a wider but shorter layout possibly solving some of the trade offs we have talked about for example.

https://www.studybed.co.uk/ Not a recommendation. I'm pretty sure I've seen better implementations but the concept probably works. One thing about the lean to is what view you get out the side. I got the impression that view was better than the one where it currently is. Another possible benefit is if you or someone you live with ever move to a work from home/invite clients to your home office type situation then the separation of this space from the main house could be good. Swings and roundabouts though all down to how you will use the space. Well if you moved the study then moving those stores into the pantry would create a bigger space for the study. Potentially making it a convertable double rather than a single. If the lean-to is not built to the same spec as the main house then obviously it's less desirable but I'm assuming it's all considered one heated/insulated space.

I had assumed the toilet in the lobby was going to be the main bathroom for 'day' use. Otherwise I'm not sure I see the point of it (other than an relatively small space to change out of muddy clothes) I'd guess you can address sound insulation if that's a concern. Wouldn't let that guide the placement of the room. Other nice thing about swapping them is if the bathroom door is opposite bed 2, you create a nice short path for that occupant for their primary bathroom. If you no longer need the plant room due to using the loft space, you could consider moving the study/bed 3 to the lobby area. Use the expanded space for a bigger kitchen and maybe pantry/laundry space. You'd have to make the cloak space smaller but maybe thats worth it.

If you don't mind a flat ceiling in the corridor/study/bathroom area then you could easily create an insulated loft space there and potentially use it as a proper plant room (take back the space allocated at the end of the building). You can get horizontal HW tanks for difficult spaces but I would avoid those if possible as they don't stratify the water as well. Downside is getting things in and out of there but if you plan for that then it's a solvable problem (nice big access hatch with a strong point above to mount a hoist is belt and braces) Using that loft space as plant room would also centralise the MHVR pipework which will make things easier and cheaper.

It's going to depend a lot on individual circumstances. I suspect you use relatively less water than others and you also have a long, inefficient, pipe run to the heat pump that adds loss when switching between space heat and DHW.

I'm feeling too lazy to try and draw this. But if you made the master 3m wide then you would have room to rotate the wardrobes 90 degrees so the doors face the bed. That would give you room to expand the bathroom. I think overall that gives much better proportions to the master suite. I'd also be tempted to switch the second bathroom/bedroom. That would mean the bulk of plumbing could be centralised. Ideally, I'd want the hot water tank to be co-located there to minimise pipe runs for hot water. The current location for the plant room is ideal for the ashp but not much else. A more central location would make various runs easier but I'd guess that central space is more valuable as is. I think @Square Feet mentioned some reasons not to do this earlier. I'm not sure either way, there might be a 3rd option. However, will point out that by doing as you propose there is the potential for the 'corridor' from the front door to act as space around the dining table (double duty) that might allow room for the bathroom/study given the expansion of the master.