Iceverge

I think that was @DannyT restricted to 350mm. Maybe OP is too. I would just do a 200mm cavity with stainless ties and 036 batts. Should be able to pick them up for £15/m2 for 2 x 100mm. Or 175mm and EPS bonded beads.

I'm glad you've found a good company. That's probably more important than anything. I know I'm banging a PVC drum here but I see they do Veka profiles. I would price Alphaline 90 and Softline 82 and go to see a house with them and alucald both installed after 10 years and compare. You could see a £30k swing the other direction and a lower maintenance better performing window.

Apologies for my hiberno slang. Just glancing at the section of the window I wouldn't be sure it was a top performer in terms of air sealing and thermal conductivity. I would like to see more seals and insulation. Something like this with 4 seals and thermally broken too. The Uw figure looks fine as a whole but just be cautious of it as large areas of glazing with a low Ug can hide poorer Uf figures.

Those frames don't look hectic. What's the Uf value?

Wider cavity. It's not rocket science. We have 250mm.

Where's North?

I have a basic cheap flymo from about 10 years ago. It works fine on a flat lawn. I never bothered switching it off. Let it run all winter in the old house. I never got around to installing it in new build. It will get stuck in any hole bigger than a cup. One thing to be careful of is the mowing height. Too low and the grass will get weak and the leather jackets will have a field day.

Preach.

Nope, it's about 60% dearer than the readymix lorry. The cheapest way to get concrete is from the mixer truck..

Having used pumped insulation in the house attic and mineral wool batts in the garage I would happily say it's one of the best things I have done with the house. No itchy and scratchy show. I think @Gone West priced supafil when doing your house. Any idea of the cost installed? If you could find a machine to blow this behind a clear membrane you would have a cheap solution.

What's the UK price now? It's 4-5 years since I priced it here at €150/m3. Fitting mineral wool isn't particularly nice as jobs but it's very doable. Has anyone done blown mineral wool?

Tilt and turn baby. Tilt and turn!

Are you planning on stick building the frame? Have you considered blown insulation AKA cellulose. There's lots going for it.

Good layout, Nice to see a sensible square foot print. Personally I would pay the digger man another hour to level the site and forget about the step. It will make half the house unusable for anyone with a wheelchair or a pushchair.

Sliding sash looks pretty but is the draftiest window you can buy. I was in a new build of some neighbors, 0.15 walls floor and roof, compact foot print, wet plaster and plenty of airtight tape and MVHR. And sliding sash windows........ You could feel the cold breeze on the back of your neck sitting in the kitchen.