Iceverge

My day job isn't climbing scaffold or screeding concrete so barring any disastrous health problems I expect I could do it until at least then.

At brief glance I reckon they're inline with most other European economies? Exemptions being the Nordics with good hydro and nuclear and Hungary and Turkey with government price controls? On the other hand I think private enterprise short termism is a bad fit for vital public services like transport, energy, water etc . The likes of EDF and Thames Water should be trading only in decades long bonds to force them to take a long view rather than normal shares and dividends.

It's an issue. In the UK 60 years ago there was 4 workers for every pensioner. It's closer to 3 now. In the 1960s pensioners were 6% of the voters, now they're closer to 18%. Policy is following the votes. Underspending on new housing, infrastructure, energy and education in favour of protecting homeowner tax breaks, pension protection and old age healthcare. These policies aren't economical productive so the county is suffering. Retirement should be raised to 75 years old to match the 1960's ratios or this problem will deepen.

Grants typically just shove up prices. A progressive carbon tax would have been better money than any grants in my opinion. And government to get out of the way. For example a blanket planning (and listed building ) exemption to any house changes reducing its energy use. Triple Glazing, EWI, ASHP, solar etc etc.

72.5mm insulated plasterboard chamfered top and bottom and screwed through the existing plasterboard into the rafters. Foam either a good low expansion foam, tape and skim the joints to wall and ceiling. Don't bother taking down the existing plasterboard. No space gain in the room and will create an enormous mess.

The roof will be able to dry inwards. I would just tape the OSB for airtightness and leave it at that. You could sandwich a VCL between the OSB and PIR but it's unnecessary in my view.

For not an awful lot more cash you could have an insulated metal panel shed. Or if you want plug and play... Should be saleable in years to come or it'd be easy enough to tart up if you didn't want to be continuously reminded of choc ices!

Strange. Do you have a trunk and branch system or a radial?

Just tape the OSB for airtightness and forget the YBS. Insulate the service cavity with mineral wool. Ideally run the battens at 90deg to the rafters.

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.