JohnMo

By far the easiest is to put the insulation on top of the rafters, is that possible?

Looking at the drawing, not sure how you will be able to assemble without loads of joints. The material between the rafters will be fine, just a pain cutting. The under drawn sheets you will never get them in big sheets in place there isn't the space. Needs a bit of a constructability review

Depth for depth, done perfectly PIR on paper out performs mineral or natural wools and cellulose. But getting PIR to fit perfectly isn't the easiest job. So realistically natural or mineral wool may out perform PIR by a country mile. Plus there is decrement delay - how quickly the insulation allows heat to penetrate in to the room. The denser the better PIR is pretty rubbish.

Good luck cutting that straight and square. I would fill with cellulose or mineral wool. A drawings may assist visualisation. Why not make it vaulted?

Think you have missed my point. In Scotland you are not allowed to install smoke alarms in kitchens - you have to install heat alarms. They are not the same thing.

That's why you don't install smokes in kitchens, you do heat detectors so they detect real fires, not a cooking smoke. Been using heat detectors in kitchens (various houses) and smokes elsewhere - never had a nuisance trip.

Dust collection just use a Henry vacuum. Use a HEPA filter version, and get plenty of bags as they clog before they fill. The guy that did our jointing for the dry lining used a cheap hepa vacuum from Screwfix, he binned them every couple of years, but way cheaper overall than some of the stupid priced ones. A tip I found many years ago, when joint filling is allow filler/joint compound to dry. Use a good decoration sponge or a cloth, wet in lightly wring out and use as a sander lightly. It will take all the lumps and bumped off between coats, with zero mess or dust.

Really wouldn't do stand alone get them linked. Buy ones with a 10 year lithium battery units, that self radio link together. No smoke alarm in kitchen, use a heat detecting alarm, which interlinks to smoke alarms elsewhere in property. Alarms need binning after 10 years, so no advantage having mains powered really. Wouldn't touch a smart smoke alarm, get tried and tested brands. Aico, etc. If you want a robust system, follow the Scottish rules, way more robust than the English rules. https://www.mygov.scot/home-fire-safety

You would normally pre plan and have a pull cord in the conduit prior to install. You may find it easier starting one end or other end depending where the bend is. You can get electrician Flexi rods for doing cables

That's a good price, make sure he has the G3 certificate. Once the pipes are at the cylinder, which is job from the sounds of it there really isn't that much to do piping wise. Is this new build or retrofit? What are you doing with cold water going the taps, is that coming from the cylinder multibloc control valve? If not you need to plan a pressure regulator valve where the water comes in to the property after the stop cock, so hot and cold pressure stays in balance. If going that route you also need a check valve at the hot water outlet from the cylinder. Isn't a 210L cylinder pretty big for a direct cylinder where you can easily heat to 70+ degs?

We had a similar reaction a decade or so ago in our last house. Plumber wanted to install loads of radiators., way more than needed. Start from the basics, work out room heat loss, then size radiators appropriately. Go with manufacturers data, not a finger in the air from a plumber. Ensure you size to radiator to temperature differential between mean radiator temperature and room temperature. All the data is the manufacturer datasheets.

Don't bank on any size staying around long. Just bought some 500W panels and they were actually smaller than the datasheet, things move pretty quickly. If you have space to store, buy some extra panels just in case?

Have you seen recent threads? Several failures, wouldn't touch them with a barge pole. Pretty rubbish for a heat pump as it requires heat pump running at high temperature for the whole heating cycle. Just get an unvented cylinder - tried, tested, cheap, installer friendly. Does the wheel need to be reinvented? No

Wouldn't have any locked storage on site, just an open invitation for a toe rag, to look at nicking whatever is in there. Tell trades to take tools and equipment away at end of the day. If it nicked from your site you have to replace it. Think site offices are fine on a major build site, but a self build, why? If the contractor needs one let them supply, otherwise don't. Welfare cabins end up filthy, that's why the trades sit in the vans. I didn't bother with any of it. I got a portaloo and it was serviced by the hire company.

To quote someone, so they get notified, you type '@' then start typing the name, a dropdown list appears and you choose the person. Whole front, one end and a full height gable on the rear. The rest is stone slips.

It's pretty easy to do yourself.

I do cooling (UFH) all summer until about October (weather dependent) then flick the switch to heat. As I am on the cusp of heat or cool, when I swop over the ASHP may run a few hours until it gets the slab where it wants then Weather compensation takes over, then it will just blib heat in as needed. The floor although slow, is as quick as the house when you and running at temperature response. If running WC you really don't need a responsive floor, start heating and leave it well alone, no thermostats are needed, just run nice low flow temperatures. My WC curve is something like 25 flow at 20 degs 32 flow at -9. Heating doesn't actually start to kick in until outside is about 10 degs average.

Scottish larch.

As you have approved drawings, wouldn't you have to build to those or go for an amendment? Why would it? If it does we are stuffed, but do I care - no. House wouldn't look the same or as nice with a different finish.

Isn't that way with all parties, only there for the next vote. Landlord - been there got the T shirt, but wouldn't bother again. If people don't like with rules sell up, do something else with the money. Perhaps build a house, that's what I did.

As a side note to others: On its own the decrement delay is tiny, plus if you do not respect the minimum air gaps either side of the product - you may as well not bother buying or installing it. It needs the same amount of depth as any other insulation once the required air gaps are accounted for.

In theory better u value, in practice a pain to seal against rafters to get perfect seal. If you don't get a very good fit, you get bridging. So a softer material like mineral wool fits tight and no bridging. Real U value is better generally for way less work.

And if you hadn't been watching them, the next trade would have covered it up, without even questioning. Work force skills and appreciation of airtight building is appalling.

Very different beasts from a structural perspective. A cut roof needs a ridge beam, trusses don't. Wouldn't you fill with mineral wool - perfect fit every time. Use something like Rockwool Flexi. Better decrement delay than PIR - keeps heat out better. Then under-draw with PIR?

Clearing site has nothing to do with planning (assume you aren't taking down an existing building). It's just site or land maintenance. Again digging holes for whatever reason is just digging holes. Make sure no-one can fall in them, if staying open. We did loads of similar stuff prior to getting our building warrant. The only things you are not allowed to do are foundations work as they are part of the legal process called planning and have to follow your legally approved drawings. Our work start was a photo of a digger taking soil away for development of an access road, well before the building warrant was even applied for (building warrant is similar to building control drawings). Chat with who ever does your approval - Scotland is easy it's the council - not sure what England does?