Mr Punter

It will take too long to respond as lots of heat will go into the slab. A small amount of insulation on the slab would work.

With our schemes we normally have a full set of planning drawings at 1:100 that have been produced in CAD format. You would need to decide on the build method, then get both architect and SE to coordinate with the design. Architect should have a decent idea of what to expect as many components for a house are standard and known to them.

If the additive is not approved for this, why is he using it? I thought that normally you would get readymix for ICF, not site batched.

If I were your neighbour I would not be happy with a 2 storey flank wall 3.3 metres away from my South / East facing corner feature window. It sounds like they will allow you to have a 2 storey extension, but no closer to the neighbour. You could probably also have some single storey element. Are you unable to get satisfactory accommodation within this restraint?

165m seems a long way. I assume that none of you neighbours are connected to mains sewer?

Well those costs seem to square with @IanR and are quite reasonable if they do a good job. Sadly this is not always the case and I have had experience of the job being rushed, wrong materials (cheap substitute for Compriband etc.) glass and powder coating scratched as the units are manoeuvred etc. As ever, if you are lucky enough to get a firm that are professional, skilled and at reasonable cost then you would do well to use them.

Could you not just get it done in lead?

It looked OK before it was done. Sold 2016 at £630k. https://www.rightmove.co.uk/house-prices/detailMatching.html?prop=47349349&sale=67432260&country=england

So is this stricter than England where I thought it was either / or for the staircase / escape windows?

Yes, fit them yourself. Lots of the approved installers charge a fortune and do a crappy job.

You may do better to work out what cooling will be required now. Could qualify for VAT refund, but others could advise. The electrics and condense drainage also need to be installed. You need lots of insulation over the copper pipes.

You can router the door to take intumescent strips fairly easily.

The Egger adhesive is D4 and will bubble up between the boards. If you cannot see any they have not applied it correctly. If they used PVA you may not see it as it dries fairly clear and does not bubble up.

You would need to make sure that the notices you served contain the correct information and there are suggested proformas on line. Your neighbour would need to give their consent in writing for you to then go ahead. If they do not, it is best for you to agree to appoint a surveyor. If you cannot both agree on the same surveyor you neighbour can appoint their own. You will pay all fees. If you just go ahead the neighbour could apply for an injunction and get works stopped, together with costs.

The most recent floor fitting instructions specify D4 adhesive on top of the joists and in the T & G. The stuff bubbles up and generally drips down to the floor below. The old instructions just used PVA adhesive on the joints.

You often get this in flats. I guess they use a decoupling mat on top of the chipboard.

The Party Wall Award is like an agreement and covers things like working hours and method of construction. It includes a schedule of condition and photos, together with your plans and engineers drawings. The £8,000 fees was because 1 neighbour was a professional PITA who did not want the development to go ahead, appointed their own surveyor who they contacted at every stage, racking up fees for muggins here.

If you get a Party Wall Surveyor to issue the notice they often make it easy for the neighbour to appoint them as the Agreed Surveyor which speeds things up. As an indication I have just got one through and the cost was £1,590. In contrast, one we had a couple of years ago with 2 neighbours costs £8,000 in fees plus £5,600 in award monies.

Are there any battens or are the slates fixed through the felt into the OSB?

If there is a door between this and the rest of the house and you have no fixed heating you can do as you like. If you could have ventilation above the insulation, with a decent clear path it would be better. Cover the lot in polythene before you add the plasterboard.

No this should not be required if they are just being topped up. Clear it first with BCO.

I think you need to get it tested.

It is worth checking to find lead times on the stuff you want, especially if it is not mainstream. Contractors do not want to be waiting around for gear to turn up or trying to work around without it. If you can get some stages planned where you can have a few weeks of slack between, it will help ease the stress, but lengthen the programme.

It may be that you need an adapter after the non-return valve.

Because you have a curve in the corner instead of a right angle?