Cambs

I think that the PassivHaus standard is the best that we have available to us at the moment - it is specific and measurable. "As built" performance can be compared with/evidenced against "designed" performance to make sure that the building has been built to the required standard. Compare that with the big developers throwing up houses, rigging it so that they meet building regs (e.g. siliconing all the gaps, air tightness testing, getting a pass, and then removing the silicon before decorating) and then only being required to prove that a sample of their houses meets regs. Right now, my view is that the PH industry seems to be populated, in the main, by people who care about what they are doing - architects who want to design to the PH standard, certifiers that do a thorough job of certification, builders who care about air tightness etc..... It's not (yet) been invaded by the get rich quick merchants that we have seen around the RHI technologies. As Craig says: It really is up to the individual whether they want certification or not. I don't think it adds to the value of the house, at the moment. An alternative, perhaps contentious view, is that paying for certification helps to maintain and build an industry which is generally going in the right direction.

Slightly worrying that the fingers of his left hand are covered in what looks like blood....

Green Building Store do something called CompacFoam which may be suitable. Prices shown on this page (not cheap!) and also some installation diagrams showing how they've used it in thresholds. https://www.greenbuildingstore.co.uk/products/compacfoam-200/

We paid £625+VAT for ours about a year ago. Local firm, plot only about 20 mins from their office in Cambridgeshire. The plot is in a conservation area.

I remember seeing this some time ago ..... American, but might be of help. https://www.youtube.com/watch?v=mmUJQHN7ALw