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Can’t you just cut out the stud wall section? Just use 60mm or 80mm wood fibre board fixed directly to the walls with plastic pins, render/plaster on top. I just used sand/lime for the render with mesh. as to paint why not lime wash - you can buy large tubs of white and some powders for colour. Maybe a little restrictive in colour options but it’s pretty straight forward to apply so long as you wet the walls down before and as a bit after it has been applied.

Fair enough. whats the best way to waterproof the duct? A bit of expanding foam as a backing and then a bunch of bathroom sealant ? Any advice on the best type?

So I have a brick built manhole (engineering bricks on a concrete pad base) where the water supply is split into three and when it rains heavily it fills with water (very high water table). I presume water is getting in through the joints in the brickwork. Water is then getting into the duct and reappearing where it comes up in a barn (which is lower than the manhole level) causing a minor spillage. two questions: 1. Best way to waterproof the manhole itself ? 2. Best way to waterproof where the duct starts (as in the blue pipe and the blue duct in the picture)? any suggestions? I do see some blocks where the ducts exit so don’t suppose those are waterproof but I presume some water is getting in through the joints.

Are you sure about that? I was under the impression that if you are including cooling with the ashp you can’t get the grant

Correct. Though it was a little more tricky because the bricks had a slight arch to them

You might want to do a test dig to see what your walls sit on. 650mm is a lot to dig out.

Can you not cut a slot in the back of the stone lintel to fully cover the catnic? pretty sure that was what we did for our French doors (though we had an external steel beam not a catnic and were using bricks to finish)

Why? The plasterboard isn’t the airtight layer is it?

I would say that what your joiner has suggested is reasonable. It’s basically what I did on mine. I didn’t use dpc but can’t see any harm in it. mine sat on existing cills that fell off immediately from where they were sat. Lime mortar to finish. i spent some time getting the inside details right for my setup as I was installing wood fibre board insulation internally. So got full layer of insulation on reveals and under the internal cill (wood on the inside) before rendering. expanding foam can probably do the fixing job on its own (make sure you get low expansion stuff designed for windows) but straps for belt and braces.

Rockwool r45 (I think it is called) will friction fit if cut right

Looks a little sketchy to me. For example, what is in place for the water supply? A sub meter on your bit? What’s to stop the main house from cutting the supply to yours without some legal details in place?

I’m surprised they suggested an ashp based on what you said initially. first thing I had to do was send over room details/insulation levels. think I sent room volumes and insulation levels. You could always under size the rooms a bit or over sell the insulation if you are confident your house is being well detailed/built.

I had an alto design/install which I am very happy with. my design had three different flow temperatures depending on the size of rads I used upstairs (Ufh down). The 50 degree figure seems very high for Ufh throughout. I know for a fact that they do over spec on the (generally correct?) assumption that insulation/air tightness design levels can underperform in real world. And they clearly want to avoid the problem of under specification that has caused many problems in the ashp market in the past. Self builds are I would think much more likely to perform as specified so you can make a case to them that their calcs can be adjusted for that. How many m2 is the property and what air tightness level is it ? who was your main contact at Alto?

I had a similar sized sips cabin built for me by a couple of Canadian builders. It had sips as the floor as well built on concrete pillars. Very happy with it. Can’t tell you the exact build details of the floor construction. But I think it was something like metal straps concreted in to the pillars fixed to the studs between the panels.

Yes as you describe. I did the pours as well. The actual polished area was only a max of about 40m2 though. had to do the whole as house at the same time so certainly could have laid a more level floor! Definitely not the most straight forward to get things super level. and much harder over a larger area. would be interesting to know what margin for error the contractor offers (maximum mm discrepancy over the whole area). also you have to factor in some expansion joints. I have some minor cracks in mine as I didn’t have any but no big deal for my place.