Iceverge

There's no magic with dMev Vs PIV. Both are just a method of moving a continuous stream of air through the house. I used to leave the hob extractor on when I went out in an old damp rental cottage we had to dry the place out. It's just a fan moving air after all. In both cases you'll still get condensation if you have trapped pockets of air like behind curtains etc. @TakeshiKovacs as an experiment try leaving a bedroom door open to the hallway, curtains open and the bathroom/kitchen extractor fan on constantly for a night. If you can manage the light and noise. It'll solve the condensation I bet. You could also crack the window open a few mm and leave an air gap to allow some air flow through the bedroom to the extractor. Keep us posted.

Masking tape along the perimeter would avoid the need to scrape it from the floor too.

What is under the timber floor? Has this change only come about since you applied the parge coat?

You could do a hybrid roof too, Or maybe SIPS depending on your span. Both work and reduce the thickness of the roof substantially.

Using the chimney to vent the underfloor isn't a good idea thermally. As Nick says it'll cool the house 24/7. Forget rigid boards, impossible to put in there properly. Instead make some Larsen truss type joist extenders with flanges on bottom to tack to the side of the existing joists. If you could rip a 300mm I-joist in half it would be perfect. The OSB webs will be plenty thermal break. Imaging something like these hanging from below your existing joists. Drop in hardboard to sit on top of the new flanges. Use acoustic sealant/tape/foam to make it windtight. Drop in mineral wool insulation. Glue all joists in the flooring deck as your airtight layer. The process is much like this apart from your Larsen trusses. Cover the ground with polythene if you're worried about moisture.

Insulated metal panel roof. https://www.kingspan.com/ie/en/products/insulated-panels/roof-panels/quadcore-roofliner/

What @Temp said.

I really wouldn't get concerned about inlet and exhaust spacing either. Even if they're exactly beside eachother the mixing will be minimal assuming it's an open wall they're going. Think about how to keep snow off the ASHP. Lots of damp snow getting sucked into it doesn't do much for performance right when you need it most.

I would be much much more concerned with the heat loss due to the external length of water pipes to and from the ASHP.

The numbers will tell you like @SteamyTea has done. ASHPs move vast amounts of external air and drop it by such a small amount that there MVHR and ASHP won't notice eachother. I suspect the microclimate effect people are feeling is very much due to the wind chill from the movement of the air when standing nearby rather than an explicit drop in the air temperature .

Until you take it apart. Knock and rebuild.

Slating from the bottom up is tricky. Other than. Than I don't think it's much of an issue just to slate and batten and felt down over the edpm..

Sketch or photo what's built already and we'll give you a sensible proposal. Vapour driven moisture damage is a tremendous red herring. The volume of transmitted water is absolutely miniscule. The real issue is airborne vapour carried by bad airtightness. This is where you need to focus your energy.

Ubakus isn't perfect. It just takes a snapshot and isn't representative of reality. It uses -5 Deg and 80% relative humidity externally which would not be representative of long periods of time in the UK. Depending on where you are I would happily adjust this up to what might be a more lightly medium term winter average.

I would add a couple of extra vertical posts at the house side against the wall. If the pergola is ever roofed in future it could hold quite a lot of snow weight and screws into he masonry could give way under the load.

When the ground dries up level it with a mini digger. Rotovate with a tractor and scatter seeds by hand and roll. Make sure you do this preceding some moist mild weather. For drought resilience plant some deep rooting grasses like @Mr Punter says. Beware continuously cutting the grass too low as you'll impede root development and make it vulnerable to pests like leatherjackets and also drought. Keep it 6-10cm high if you can. Another option is to do what @saveasteading says and let it seed naturally and grow longer. You'll get a tremendous variation of native wildflowers (AKA weeds to the less enlightened) and they whole thing is quite pleasant really.

How about something like this. You could keep the steel inside the external layer of insulation which would stop any condensation and rot issues at the metal timer connection in future.

I would recommend a better fan than a £15 off the shelf intermittent one from b+q. They're far too noisy and will just get turned off. A dMEV one would be a good start like the one I linked. ( No connection just a happy customer)

It's hard to eat electricity though.

Did a back of the fag packet calc a few years ago and reckoned biofuel for planes would use about 25% of the worlds useable agricultural land.

Firstly I'm not seeing any ventilation in the bathroom? I would make sure this is completed as part of the remodel. Get a Greenwood CV2GIP ( keep an eye on eBay for a cheap one). Get an appropriate hole in the wall/ceiling venting to the outside. In any case I would maybe remove one bay of insulation to inspect the plywood sheathing behind it. If it's in good condition I would replace the glasswool. I would buy another pack of it and fill any voids in the current insulation. Don't use PIR or something impermeable. You'll only make trouble. Then buy a variable SD airtightness membrane. Something like Gerband Vario, intello pro clima or Siga Marjrex. Diligently cover the walls with it, taping all joints and penetrations. Do the same on the ceiling and tape it to the floor also. The aim is to 100% ensure that any drafts cannot blow through the wall Via gaps and cracks in the structure. Tape the membrane to the doors and windows with airtighess tape. Next run 50x50mm battens horizontally over the studs at 400mm centres to create an insulated service cavity. Add extra blocking for any heavy fixings needed in the bathroom. Insulate with 50mm mineral wool. Add some marmox board of jackoboard to the window reveals and head. Plasterboard and tile/skim as needed. Wall u value will be about 0.25 but it's the Airtightness and lack of drafts will make it quite comfortable. ( Ensure the floor+ceiling is well airtight sealed and insulated underneath too).

Good to know about the 50mm. I'm toying in my mind with methods to avoid the human suffering if concrete pours.

An option you could explore to save a few £ is to pour every floor to say 25mm short of final level with concrete and tamp it to get it fairly flat. Then get a pumped screed to make the final bit perfect.

When it comes to concrete work and newbies they will be of limited use, (myself included when I first did it). I've seen the pattern too many times. They'll appear full of enthusiasm, gloved and booted up. The first 5 minutes will be all action but they'll quickly tire, start leaning on rakes and wondering "is there a better way to do this" because they can't fathom how much suffering it is. They'll start job switching and going off on side projects "I'll just start over here in this room" forgetting they're making a mess for later. They won't have the "touch" required with concrete. When raking in front of a screed they'll be constantly banging it, or taking huge lumps and making holes or dragging the surface so it's like a rice Krispy cake. They won't be used to the time pressure and heavy work and will respond to the robust direction of the gaffer by sulking. When given a lighter support task like washing up (very important) they'll see it as punishment for being sent away from the main action. What you require is someone who has spent some time in the military, is a strength endurance athlete and is also a plasterer.

I would recommend you get some experience help with this as it'll be a mess if it goes wrong. What kind of team have you currently lined up? You could build an expansion joint into the doors to allow it to crack there. I wouldn't fret too much about DPC's in the walls but would ensure that the localises water table is well below it. You might need to add a french drain to the house if it isn't. The rest of the plan sounds fine.