Redbeard

"Does it mean I should put some extra insulation?" No. Not if the insulation is, as I assume, on the ceiling of the room(s) below, and the vents are on the slope at the top of a cold void. There should be a howling gale up there anyway for water vapour control. As long as it does not infiltrate to the 'warm side' of the insulation, no problem. If you want to put more insulation in top up to 400 - 500mm, but make sure not to block eaves ventilation. You could staple some membrane at the 'point of the triangle' in the eaves to deflect ventilation air above the insulation.

I am no stone wall expert but I would be trying to find out whether the wall was *originally* rendered externally (granted that it probably would have been in lime then). I have seen a few houses where people have removed the 'horrible render' only to find that the house was originally built with render, mainly because the stone was not of high quality. Take it off, point up the stone, and they had a damp issue because the stone was poor. The system you describe above sounds OK but I would prefer it if it were ventilated, which basically means at least 4 air-bricks per wall in diagonally-opposite corners. If it is not vented then that thickness of insulation is potentially cooling the wall a lo, without anywhere for water vapour to go. Ventilate it and you effectively have the same situation as in a cold roof.

It is also relevant to note that Thermafleece used to (I don't know if they still do, but I guess so) require that a breathable membrane was used to separate the sheep's wool from the wall itself, for exactly the reason which @SimonD is suggesting - that the outer (currently cement-based) render *may* fail at some point in the future, in which case the sheep's wool does not want to become a sponge. I second the ventilated (and I mean properly cross-ventilated) void. See for example Stirley Barn, done by the Green Building Company (Green Building Store's building arm).

@MarkAldo11said: "New regs propose vents everywhere, trickles in the windows, so there’s plenty of areas for air to escape rather than breathing through the walls." Important point is that 'breathability' (water vapour permeability) is not ventilation, and even less to do with air-tightness strategies (someone will find connections I don't have in mind while typing quickly, but this is broadly true). For example you can have a very airtight breathable house, you can have a very airtight non-breathable house, and you can have a non-breathable (or breathable) house which is not very airtight.

A few lengths of CLS, unless you actually need a cupboard. If you just need a plinth to mount a sink on make an open table out of CLS screwed together.

Chequer-plate alu? But as others have said, can't overlay the ply if it is at all soft. It doesn't look very happy.

Along same lines as @Russell griffiths, I got some fibre cement boards as verge undercloaks. I just put the leftover one in a 'safe place' yesterday, and cannot find it to measure, but I think they were 3-4mm. Thinnest tile-backer I have seen is 6mm.

Is there access to the void above? If so, access it and search. If not, get the Stanley knife out. Explore.

Hi and welcome. You wrote: "Any hell much appreciated" We promise not to give you any!! And now seriously... Generally: Please Please Please Please Please Please insulate, as much as you can, now. You will have loads and loads of time to regret not doing so, or doing it insufficiently, later. Having said that... Floor. Yes: Insulate. Any is better than nothing at all. At risk of having to do a bit of door-chopping (can we have pics, as I might not be so blithe on that if it's a uPVC door) how about 25 or 50mm PIR (Kingspan/Celotex-type), damp-proof membrane as vapour control layer, taped at all joints and perimeters, T&G OSB18mm with glued T&G, then your tiles. Walls: Gov't best practice guidance (search BEIS, best practice, solid wall retrofit) suggests that if you are using anything that is not 'vapour-open' ('breathable') you should have a *ventilated* cavity behind the insulation. Some have been doing it otherwise for many years without issues but I understand they (the gov't) have v knowledgeable advisors and good reasons (interstitial condensation risk) for their suggestion. Anyway, more from me or others later. Got an extension to finish!

Not just an air gap, but a *ventilated void* (which I would take to be served by 4 air-bricks in diag opp corners on a rectangular wall) according to BEIS https://www.gov.uk/government/publications/retrofit-internal-wall-insulation-best-practice Obviously then air-tightness becomes even more important than it is anyway, or else you just feed cold air into the room via leaks at perimeters.

@newhome said: " I’m not sure about the floor difference as yet but thought that I could place the frame 100mm higher than the floor level to create that if needed? If it’s just to stop potential flow from liquids then surely that would creat that effect?" I think it's about heavier-than-air gases, and specifically petrol and perhaps LPG w.r.t. garages. I don't quite understand the 'frame higher than the floor level' bit. Surely there's either a 100mm difference or there isn't, and if there isn't, one has to go down or the other has to come up. We are after all, talking about a potential 100-deep 'pool' of petrol vapour. (Note, in my head it was 150, but 100 has been mentioned, hence I am repeating 100. Haven't searched for the info.)

Why not face-fix the frame to the wall inside the garage, so that the frame is wider than the opening? If we assume the stop-beads to be 0.75 inch each (a guess) then that gives you a door width of 34.5 inches.

Hi. Apols if you've said this before, but what is the existing eaves ventilation like? The staining on the membrane on the RHS looks like mould due to poor ventilation. Are you going to mess with the roof at all? For all I've said about not usually venting the ridge, if there's any Q over the 'quality' of the ventil'n at the eaves you might want the extra 'belt and braces' of the ridge vent. In terms of how much of a 'drop' to have at the apex, answer is enough to get a really good level of insulation at that point - say 300 mineral wool or other quilt - 'on the flat' . Make sure to get a really good 'hug' between the PIR and the quilt.

@ProDave, what I have in mind as a ridge-board in a typical Victorian terrace roof (approx 125 x 25) is (a) definitely not a beam, (b) meant to have collars below. However I have on a number of occasions seen 'rusticated' attics where the collars have been removed and the soffits plasterboarded right up to ridge-board. Droooop! If you are lucky there are 2 purlins each side lower down and the rafters were spiked in (or some of 'em). @Mr Punter I may be wrong but I have always been of the view that, unless the ridge is vented (which most old ones aren't) you *do* need ventilation from one side to the other. You need an 'in' and an 'out'. Air is drawn through, AIUI, by differential pressure at each 'end', and if there is an 'in' but no 'out' the potentially incoming air has no incentive to travel. I am not as convinced as some that ridge vents are essential, but if there is no ridge vent (in my view) there must be eaves-to-eaves through-flow. One of the ventilation acoutrement manuf'rs had some good info on this but b*****ed if I can find which one.

"Floor? Not sure but my googling says this may be up to 1.2. Does this sound right? - If so, I guess the windows don't make sense to go for the extra £4k." Search Floor Perimeter/Area ration for an expl of how floor U values are calculated. This site (https://warmafloor.co.uk/support-centre/u-values/) has a good explanation. Not sure that in actual 'comfort' performance it's going to seem the same for a solid floor as for a (ventilated) suspended timber floor.

@Mr Punter. You said "It is fine to insulate right up to the apex". True if there is no ridge-board but if it is like the roof in the OP's first link the between-rafter insulation will surely close off the cross-ventil'n. I always go for a small dropped ceiling. I am even doing so in my extension which does not have a ridge-board, 'just in case'!!

@Furnace, I am sure you have 'been here' already (https://www.gov.uk/government/organisations/natural-england/about/complaints-procedure) but there is at least an escalation path (however much one might feel that it might be made of fudge and long grass). How do you get on with your MP?!

Is this just for aesthetics? It may be too late but I'd have had the blocks flush-pointed and simply painted. It is, after all, a garage... Also not sure you'd want a gritty top-coat inside, unless you don't like skin on your knuckles! @ProDave: Snap!

"What im after is general building skills to take me through my projects" . Can you elaborate? What skills do/don't you have, and what do you need?

And if you are really good and thorough your clients will get used to the fact that they effectively get a project management service for free. One of my long-standing clients (ex-clients, I am not contracting anymore) said 'we love working with you, as we don't have to worry. You do all the worrying for us!'

As above, if it is on an external wall vent it to outside. That way it does not pick up warm moist air from the house and then condense it near the top of the flue. Win, win!

''Is there a certain way they should be replacing the door to maintain airtightness.'' As you imply - 'properly'!! Yes, no less tape than was there first off, and if the original taping was as cr*p as some I have seen then not so much more, as better applied. And if they go to use plastic 'plank' ask them to do a proper job. Good luck.

Thanks @Mr Punter. Bit scary on price, but then I guess Lindab (steel) would probably be no less. Anyone got experience of Lindab Ogee? Edit: Ah! Don't think Lindab do Ogee!

For cable and ducts you can buy grommets from, for example, Green Bldg Store, or make your own with EPDM and air-tightness tape.

Where is the ventilation going to be? If the PIR is very carefully and tightly installed you can run the ventilation up between the PIR and the membrane, having a dropped 'ceiling' at the ridge so that the ridge board (if any) does not block the cross-ventilation. But 2 comments: 1. BEIS Best Practice guidance now suggests 50, not 25mm gap (https://www.gov.uk/government/publications/room-in-roof-insulation-riri-best-practice). Yes, it's not really a room in the roof, but you are seeking to mimic the insulation strategy of one. And (2) You are going to all that faff of insulating the entire sloping roof simply to house the MVHR unit. Why not just stick-build an insulated 'MVHR shed', with no insulation on the 'floor' (the first floor ceiling within the footprint of the 'shed') and you can wrap it in cheap mineral wool at 300-400, rather than a relatively unexciting 75mm PIR? Note that what your roofer describes is not a Warm Roof at all, though it may give you a slightly warm(er) roof space than if you had not added the PIR. It won't be that warm, though, as you have added 400mm of mineral wool on the first floor ceilings to make it cold.