Iceverge

Yeah it's pretty normal. You could apply to do something else but I'd say it's unlikely to be approved.

Google satellite pic of the roof please.

I installed a non borehole non anode stainless steel one and am taking the savings as my own guarantee. 4.5 years so far so good. Copper Industries do some nice guaranteed products. Maybe worth a call if you haven't purchased yet .

This will work perfectly. Controlling vapour is largely nonsense. The aim is to control the flow of air and in doing so not create any vapour traps.

Woah woah woah........ This sounds like the wall has an impermeable layer outboard of the timer frame. Any sketches or pictures of the build up please to help us understand? I very much doubt your membrane is a fancy low permeability one. In any case I very much suspect that the wall was drying to the inside rather than the outside. Putting PIR between the studs would trap the sheathing between two layer of low permeability which really is a no no. Pics please...

Airtight layer placement isn't as important as making sure it's continuous. It's drafts that carry vapor laden air, not diffusion etc. I would just do what's easier to install at this stage. Probably something like FM330 foam to fill any big gaps in every "box" at the end of the joists and then some airtight paint over the top. Airtight tape is also an option. The important thing is that is joins the layer above and below the ceiling. I'm slow to rely on the foam long term for airtightnss as it shrinks.

Stick build on site and fill the frame with blown cellulose.

In other news a tilt and turn will be easy to get. Is it idiot proof enough though. They're more ingeniously destructive than you could possibly imagine.

A door. You want a glazed door.

Also why WBP and not OSB?

What's the proposed wall cladding going to be? I would encourage ensuring the steels are completely insulated. If they are outside the insulation and get they will be a magnet for condensation and the timber will rot where it was attached.

DIY for sure. Draw a line with pencil on the frame to mark the edge and it'll be 100%. It's much easier to do pre install if you have the time alone with the windows. You don't need to go to germany for tape, it's the install that matters. https://airtightnesstapes.co.uk/products/3100-black-airtight-tape?variant=48903193100567 This looks similar to the stuff i used.

Wise. No amount of shading or decrements delay will counteract 30+ prolonged external temps.

Why not just tape the OSB?

Yes that would be fine. The internal layout matters somewhat on the location of your airtight layer however If you have a lot of funky junctions or timbers or internal walls that can't be erected post roof build I'd be in favour of moving the Airtightness layer to above the rafters. It should just friction fit I think. It's nice stuff but much dearer than the equivalent mineral wool. I'm a big fan of including insulation above the rafters. Keeps the timber thermally stable and you'll have less chance of rot etc. Ok cool. Is the design of the cut roof set in stone? Can I get a cross section of the proposed structure? Works both ways actually, structures can dry in as well as out. It's bad airtightness that is the culprit for interstitial condensation. A single hole the size of a 50p will let more moisture into a roof than the entirety of diffusion over a 100m².

Not me. Maybe @IanR

What units are your using for this new parameter?

Multifoil=Snakeoil. Decrement delay is somewhat important but if you achieve any sort of reasonable U value it very quickly pales into insignificance beside things like unwanted sunlight through the windows. PIR between rafters cannot be done correctly at a competitive price. Gapotape and Robin Clevett "insulation joinery" maybe but it's be cheaper to build your house from gold bars. Foams shrink differentially to timbers too. It's a recipe for loose insulation. The single thing that will make the biggest difference here is Airtightness and you haven't mentioned how you're going to deal with this. What stage is construction at the moment? Any plans and pics would help for further suggestions.

Normal House emulsion should do if it sticks. Might need to prime it first but I've found it's pretty good, sticks to glass and uPVC pretty ok anyway.

I would consider omitting the top layer of OSB entirely. It's doing nothing really. I would just diligently tape the joints in the ply too and forget about the vapour membrane. You could spec the trusses with a wider top chord from the Factory to avoid the need for the additional batten. In any case I would use 2x layers of 100mm PIR, joints staggered foamed and taped. Don't fret about thermally broken fasteners. They'll be almost zero performance difference to a metal one as the cross sectional area is so small over 200mm. The counter battens and batten is good for tiles but for metal cladding you could save some work and just put a 45deg (allowing for drainage) 70*20mm batten instead. The recess in the corrugation making up the rest of the ventilation. ( I personally think the corrugations alone are enough.....) Have you a need for overhangs and eaves? Do you have a detail for these?

The whole thing is worded very much like " you really should pay us to do it properly" while stopping short of mandating it. I can't see anything to stop you making a reasoned assessment of the criteria and self installing. I also don't think a good quality single skin plastic tank is much more risky than a double skinned one provided steps are taken to prevent it from external damage. Even an appropriate paint should keep the UV away.

I think single skin is ok if you're more than 10m from a watercourses or 50m from a bore hole. Paving slabs or concrete seem to be suggested though. https://www.oftec.org/consumers/off-gas-grid-guides/home-guide-to-domestic-liquid-fuel-storage-up-to-3500-litres

How stuck are these windows? Stuck on both houses? How about your ultimate neighbours to the very south, can you make more of the south facing glazing here? Maybe a deidentified aerial pic would help. I under stand the desire to keep everything standard but as you will actually be living in one house I would consider making that one as nice as I could by maximising the use of the sun. I would certainly include a walk in shower on the ground floor and a room that could be a bedroom too. The walls appear a little skinny. I would get them to at least 360mm to stand a chance at getting good insulation with a timber frame. 400mm if masonry. work on 130mm internal walls as a minimum rather than 100mm. For me 4 x W/C is an overkill for the size of house. I would do 1 x ensuite, 1 x family bath and 1 x ground floor showerroom. An option might be to move these to the north side of the house and use frosted glass and/ro roof lights to avoid the overlooking issue. Perhaps a pic of the street scape too if you have one might help.

Is this for selling onwards or for occupation? Where's north please?

Yes so long as you make sure to very diligently cover all the ducting with mineral wool and tape all penetrations of the airtightness layer