Redbeard

Where? Not in this dwg, unless I am missing it.

Good call on the INCA guide @MikeGrahamT21 but, @EinTopaz don't necessarily expect the 'blokes on the tools' to be keen on what some see (and some avoid) as 'sub-DPC work', to be avoided in case of future dampness claims... Agree with @SimonD re EPS sometimes being suitable for the plinth layer. Some system providers insist on XPS, while at least one (Possibly Back to Earth? - 'twas a long time ago) used a denser grade of EPS for the plinth. The rationale is that XPS being completely impermeable could, theoretically at least, cause capillary movement of moisture from the plinth (below DPC) to above. The next bit mixes concepts of 'Breathability' and porosity, but bear with me... The thinking, as I understand it, is that using EPS increases the chances of any sub-DPC moisture being wicked away *through* the EPS and ('somewhat breathable') render rather than rising and breaching the DPC. (Normal stuff re 'softening' the layer below the base layer, and French Drains etc. in order to deal with potential moisture before it can even *think* of rising...) As for the insistence of some on using the metal (thermal bridge?...) or plastic base-rail as well as a plinth layer... Last time I did EWI I tried, so that no-one in future could quibble on any claim ('You didn't do it according to 'the system'...') but the plastic base-rail distorted and gaps resulted. In the end I ripped it out, pointed up the adhesive at the bottom of the 'above DPC layer' and simply butt-jointed. (This, BTW, was on a wall where the 'above DPC' was done first on the rail, and the base layer 'retro-fitted'. By far the better way was that used by a colleague in the NW, to lay the 'below DPC' base-layer first, and then build off that. No wibbly 'tray' required). In the OP's case, where there is to be no EWI above the 'Plinth layer', there are 'capping details' (usually seen at eaves and verge level). I would strongly suggest using an 'Upstand Capping Detail' with a flashing over than a 'Downstand Capping Detail'. The 'Downstand' one is mechanically fixed before the insulation goes in (?gaps?) and sealed with Silicone mastic, which in site conditions almost certainly has less of a life than we'd wish.

Sorry it was ****, but 7.2m lengths? Wow! Never managed to find timber so long at general timber merchants.

Have you got the rafters already? Could they not be built in quite simply? Or would that need you to take time off work to do it? If you go for built-in hangers who's responsible for getting them all level? Brickies or you?

Like you, I have no idea about the different grades, but I have bought 90mm Graphite EPS from EWI store (www.ewistore.co.uk) and they are still listing it. This was, as you might guess, for EWI, not for a footing. They will almost certainly know where, if anywhere, you can get the grade you need.

Cross-ventilation may be your issue. One air-brick in that space won't do much. You need 'ins' and 'outs' and ideally diagonally-opposite air-bricks to ensure as much 'scavenging' of warm moist air as possible. Given how shallow that void is a solid floor might be sensible. It may even need digging out further to accommodate sufficient support and insulation.

Please do. Fibre insulation 'sucks' a lot of rain. Visqueen and block/brick offcuts will keep a lot of it off.

When you or your builder start talking about 'soakaways', be sure you are on the same wavelength. IIRC the PavingExpert site used to have a really good 'primer' re soakaways. Apart from anything I often see 'soakaways' (or reference to them) which don't comply with the rules re proximity to buildings, boundaries, neighbours and so on. Equally a shallow pit full of rubble may function as a soakaway for a while and then cease to do so. If you go the soakaway route get some good drawings and follow them. Also, given that conservatories may be exempt from quite a lot of 'the regs' (and may also just not necessarily be built well) beware of excavating around something which may have very minimal footings. Do test-pits first. Given the extent (or lack of it) of the job and the price quoted, if it were mine I'd be looking at whether I could do it myself and do it carefully, prudently and in line with 'the rules'.

Assuming this refers to a past thread could we see a link please?

Any insulation better than none at all, but 60mm for the 'whole sandwich' just seems far too minimal to me. Others may disagree...

So perhaps a simple vent on one wall and a dMEV on the opposite wall? Exactly that, and in response to your Q 'are they noisy?' - I have Greenwood CV2's in 3 wet rooms and barely ever notice them. Yes, I don't sit on the bog as long as I'd sit in an office, but the fans emit, at their loudest, a gentle hum.

Hi @flanagaj, I am sorry you have had no replies, and I am aware that you have already consulted 2 SEs, but I think any reply would have had to refer you back to whichever SE spec'd the windposts. They will, I think, have ad more information than we have. Sorry!

That'll be the one! (Though there may also be others). Thanks for that.

Since it seems they were trying to blind you with (whatever they were trying to blind you with!) I wonder if it would be worth getting a 3rd party involved. I cannot remember who they are, but I think some 'on here' have used a 'VAT Reclaim-Chaser'. Someone will know. I am not in any way doubting your ability to make a claim, but I know (not with VAT, but other stuff) what it is like when one party (which is not me) holds all the cards, and effectively only has to say 'no' and I am powerless. Having someone who has dealt with dozens of claims might get you a 'but hang-on; HMRC said the exact opposite in this claim, and that one....' re-balancing of power. Good luck, whatever.

...but, to be clear, I am not saying you do not need the 'paper' - you need, overall, to ensure compliance, probably via 'sensible conversation' followed by the document.