Not sure exactly what your question is here.

Seeing as Kingspan advertise K5 as being suitable for EWI, and don't advertise K103 as being suitable for EWI, I would be more comfortable with a system that uses K5.

Maybe the company proposing the K103 would be able to persuade me it's fine - I would simply ask them - why are they proposing a material that isn't advertised for that application by the manufacturer.

Ideally, I'd be looking for someone proposing a "system" (that is, the combination of external render, the various layers behind it including the insulation, and the fixings) that is recommended by one of the larger scale manufacturers, whether that's an insulation company or a render company. In the ideal ideal world there'd be a BBA certificate that described the whole system, what its limitations and appropriate applications are, and described what's important about the way it's installed.

Sometimes a "system" like this won't actually specify a particular insulation product, it might just say what type it needs to be, and then you can check whether whatever's being proposed satisfies that.

It kind of depends how deeply you want to get involved in choosing and specifying things. I would say that depending on exactly how the insulation installers are presenting themselves to you, they are effectively the designers of the installation so in theory if it all goes wrong it's their problem, but of course generally one wants to minimise the risk of that happening. That's why I'd be more confortable with them installing materials that I can see are clearly intended for the job.

Out of curiosity - why kingspan, which is not breathable rather than EPS which is (slightly) breathable and whilst thicker for an equivalent U value usually works out cheaper.

I used 2x50mm alternating K5 but left a gap and put on cedar cladding. I did not want a render over it even though the extension in block is rendered but that has a cavity as well as insulation. We live in an exposed area and did not want any risk of damp penetration through render. The stone work that is covered by K5 has shown no damp ingress but there would be a chance if it had been rendered. Cavity separation from the weather has provided dry houses for about 100 years now and see no reason why not to continue with it. ( A bit longer actually my previous house built1898 had cavity walls). The internal of the stone is either left uncovered or lime plastered. For EWI I would always opt for a rain screen cladding any time. The Kingspan manual does show various options of rain screen. The K% plus rain screen should not be any thicker than an equivalent u value of EPS.

Posted By: Peter_in_HungaryOut of curiosity - why kingspan, which is not breathable rather than EPS which is (slightly) breathable and whilst thicker for an equivalent U value usually works out cheaper.

Good question! I looked at EPS and it comes out about the same price (since one will need a larger thickness to get the same U-value). The main driving factor are the space constraints as there is a passage between houses involved.

Is your worry that vapour will not be able to escape from the solid walls through the K5?

Or is it the condensation? (the dew point should be well within the K5 for UK temperatures)

Posted By: revorFor EWI I would always opt for a rain screen cladding any time.

I think the choice depends entirely on location, including exposure. Our house has lime render exposed to the elements, rendered directly on to the notoriously damp prone straw. We haven't seen any signs of a problem so far. We do have the traditional good hat and pair of boots. i.e wide overhangs on the roof and 6" height above ground before the straw starts plus 2' of gravel border around the house. But we're in the East of England and I know of cases in more exposed locations where an external timber rain screen has had to be added because of driving rain. So horses for courses.

Water can't penetrate a closed cell rigid insulation board though, can it? It's stuff like rockwool that can be made ineffective by getting damp.

Also, the type of render that goes onto EWI is not the same as cement render.

It's not surprising that cement render would have cracks and that somewhat porous stone underneath would soak up water. But I'd not extrapolate from that, that damp is going to get through the render and the insulation of an EWI system. If stonework were getting damp behind EWI it would most likely be because of something like a leak at an eaves detail. And if water is getting behind the insulation a rainscreen cladding isn't going to help. The water will remain trapped behind the insulation.