Redbeard

Given the site restrictions it's the overflow which worries me. IIRC soakaways (if your ground is suitable to Soak Away anyway) need to be 5m from buildings and 2.5m from boundaries. That suggests a max dia of soakaway of 1115 if I have read the dwg properly. If you can get them now, how about one of the 1400 ltr(?) cylindrical recycled containers (which used to hold fruit juice concentrate) peppered with holes? I have not seen them on sale in a long time. You can see them in use (above and below ground) at CAT.

Maybe, unless the plaster has been contaminated by hygroscopic salts pulled from the brickwork, in which case based on my understanding (limited, t.b.h) and experience (many many 19th C houses) is that the more that plaster pulls salts through the more likely it is to do so in future. I guess if you managed to make the wall as dry as a bone then there's nothing to pull, but I might be (nay, *would* be) tempted to hack out and replace that plaster (and a bit around it,) at the same time examining the brickwork for any 'symptoms' (whatever they might be).

@peekay, I have a somewhat newer cork-tiled floor, though still probably nearly 20 years old. I am not sure I have ever re-varnished it. I will post a picture later.

As ever I shall deal with the easy ones first: Move the loft hatch: Sorted. You also said: ...which is good. However you have a chimney breast in the way. Why not run the ducts above the ceiling in the void (*very well-insulated*, of course) and, with some 45 degree bends you can dodge round the ch. breast: Sorted (??) Very sensible plan. I don't have a better idea than that.

Is the top metal rail perchance by that nail-plate? In which case could the moisture be where the rail bkt has (*if it has*) perforated the membrane? Of course whatever flashing detail was used should prevent this but it looks like you have a point of entry and then it's running down (or not; I may be wrong!).

Our bathroom floor is looking a bit tired approx 35 years after laying, and having been re-varnished twice at most (perhaps only once!). It is still perfectly serviceable; just looks a bit ratty. These are bog-standard Wickes cork tiles c 5mm thick and approx 300 square. I intend to take them up and replace with... cork tiles.

Glad you said this, @Russell griffiths. It's the first thing I thought of, which avoids loads of complication AFAICS, but I wondered what I was missing. Am I right, however, in remembering that Durgo valves have to be inside?

Do they have to be sliding sashes or would inward-opening mock sashes do? Do they need to be 'scrape-through-the-Regs' double-glazed or 'Fully Monty' triple?

Re air-tightness, ultimately everything wants to connect to everything else! So if the internal plaster is the A/T layer, floor membranes want to connect and be taped. Ditto windows. Have you got your ground-1st floor detail sorted.? Search for 'Tony trays' if not.

Re the roof, yes, go for more. 120 is very borderline. I would put more in a refurb roof. Are you building the roof or others? The thicker the insulation the harder it is to find the timbers with your HUGE screws! I have seen a warm roof where most of the fixings were to the under-layer of 18mm OSB, not to the timbers.

Assume this is a neighbour? Was PP granted or was it PD? It's a while since I looked at PD. https://assets.publishing.service.gov.uk/media/5d77afc8e5274a27cdb2c9e9/190910_Tech_Guide_for_publishing.pdf Some enlightenment on p.12.

Easiest 'application route' is via a Building Notice. Look up your LA BC dept and search Building Notice. It's basically a fee and a pro forma which says 'I'm about to do this. (Strictly!) I will be starting in no less than 2 days, and you can come and look'. That's it. I don't know the fee for elecs but in my LA at least they 'buy in' a suitably-qualified person from 'outside', so you'll probably pay commercial testing rates plus a mark-up, I guess.

Care to share the maker?

+1. Can you post pictures so we can see the roof oversail (or not) etc? If you decide EWI is a no-go: I do wonder if trying to get a solution for the *whole house* using your existing plasterboard and frames might be blocking you from doing a high-quality wood-fibre or cork and lime plaster IWI solution to, say, 2 key rooms as part of an x-year 'rolling programme'.

Usually double-up the rafters either side and trim across as required, but don't take my word for it! Ask your BCO. I have seen 'standard requirements' vary from place to place.

Re sourcing the board, short answer is I don't know either, but a search yields https://www.builderdepot.co.uk/12mm-fibreboard-sheet-2200mm-x-1220mm I used to use a lot of thicker wood-fibre boards, and the pallets often came with 'spacers' of 8-10mm board, but the merchants in UK did not sell it! That's a pity, as it was really useful for the occasional really tight reveal.

EWI? - Supasoft? Superfoil? Can they be used for EWI? Why would you? I cannot see the logic in using a floppy insulant for EWI, necessitating studs and render-board. Wood-fibre is good. Cork board is good, but IME a bit more expensive. Diathonite I have not used, but EBS say it can be used for EWI as well as IWI. See 'luneretrofit' for details of it sprayed on. Lune Retrofit https://luneretrofit.com Don't know Cork Sol. Hope that helps a bit.

Can you draw that? Are thinking to install them 'in check', where the win frame is tucked partly behind the outer skin of brickwork, so the timber lining in line with the inner skin? Is it solid walled?

New Welsh would be the 'go to', but at a premium. If I had the choice of fibre-cement or second-hand I'd go for second-hand Welsh, but I'd want to choose them. That's a bit rare nowadays!

Cross-posted with @markc. Yes, they can be very dirty, but I have been quite happy with 2nd hand slates; it's just all the sorting - not only into good and cr*p but also into thicknesses. I don't think I would have won my 'junior roofer of the year' award, but 'not too bad' would be a fair accolade!

I have seen suggestions that you should allow at least 30% wastage. I was kindly given the slates from a friend's house (OK some which had suffered 'Turnerising' or hessian and bitumen) but even of those that hadn't I reckon I had about 50% wastage.

Do you have pics? Is this on the reveal? If so my suggestion of scraping back 150mm might not work as there may not be 150mm of reveal! But if you have the space, chop back (say around 150) till you find the mesh (and then you'll also see where it isn't), thin toothed coat of base-coat, mesh in, thin coat over, and try to recess about 1-2mm (depending on top-coat grain size (if indeed you have top-coated with 'from-a-bucket' stuff). This is what I have done. You *will* see the join at least a bit unless you are very lucky, but after a while you will have other things to look at.

Lead, done right, will last 100 years. GRP can last well (and ST will have a better idea than I about GRP longevity, but still a lot of old GRP boats around) but I would have thought a lot less than 100 years. Lead gets my vote.

Pic does not open for me, save as a microscopic 'box'. Clicked on the box and got 'Gone! Error 410' (or 4 hundred and something anyway).

Similar issue to when you are installing PIR below rafters with timber cross-battens over the PIR. One schoolof thought says that a hoile with a screw in it is not really a hole, and another says 'yes it is' and guns silicone into a pre-drilled hole to give each screw a 'silicone VCL grommet'. I have never used phenolic in a floor before but I have used PIR with T & G OSB overlaid with a VCL (well, thick DPM, in fact, but acting as a VCL) between, as a floating floor. No weakness detected in several years' use. Reason for the thick DPM is so that your big work-boots don't kick holes in rather wimpy thin VCL.