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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.

I’d use 3.5 nhl with sharp sand mixed at ratio 1:3. dont make it too wet. Push it into the joints and don’t worry about leaving excess around the joint. Next day (or when it has dried a bit) compact with tool/bit of wood and clear off any excess. Then use a churn brush (or softer) to do a final brush over.

Do you mean that granite should use nhl5? I can’t see why 3.5 wouldn’t be fine and that certainly will knock up next day in this weather

I’ve done a couple of diy exposed aggregate concrete floors to good success. You are correct that you just need to omit the screed and go for a slightly thicker slab. I hired a grinder and spent a week grinding down (I threw in some larger stones after the pour as well), then going through finer grits. Would have been easier if the pour had been more accurate. Didn’t power float mine but if doing again would try to make more effort to get the pour flatter. good luck!

Asking for a friend whose oil boiler has packed up. She has been quoted £10k and that sounds crazy to me. anyone have a reasonable idea? it’s an external one at the moment that works with a hot water tank if that makes a difference but not sure of actual size. Apparently it will involve changing rads to thermostatic valves at the same time.

I’m in the side of it not being worth insulating everything!