Redbeard

So there are no soakers below the flashing on that chimney? I am not a roofer but surely you always have soakers on abutments? I do. I don't fully 'buy' the condensation reduction argument. Increasing insulation will not reduce condensation - it could increase it (because you are making the void even colder) unless something is done at the same time to effectively incorporate a VCL in the entire 1st floor ceiling(s).

I am not an expert in the crushing strength of clay, but I think if you ram the disconnected part of the pipe full of concrete then it will do a very good impression of being part of a concrete foundation...

@iant63, are you most concerned about potentially blocking (and restricting future access to) the drain, or weakening the footing? If you want 100% peace of mind can you dig down, re-route the drain on that corner with swept bends to sit outside the line of the footing, and ram the old drain full of concrete? Of course I know nothing else of the job but that would seem to perhaps to sort things, even if leaving you with a slightly 'bendy' drain run.

Hessian wrap. Others may correct me but I am not aware of asbestos ever being 'implicated' in connection with this. It's not just anti-squeak - it is thermal insulation, and I sometimes use it as a wrap when I cannot get plastic sleeve on the pipe(s).

Ah! You added the otters and 'now that the roof is covered' after I'd read your first post, I think. Obviously if the tiles/slates are on you won't be taking up my suggestion. Am I right in thinking those are 150 (perhaps 200 at a stretch) rafters? What's the proposed lay-up in terms of ventilation gap on the cold side, and depth of insulation? I assume you will have insulation both between and under the rafters or (it would appear) you will have difficulty meeting the Part L U value target. (I think... probably) If the OP takes @Alan Ambrose's suggestion perhaps with collars and insulation above the collars, he could maybe solve both issues.

Does your architect have any site supervision responsibility? If so arguably he/she could instruct the builder to remedy and build as per the dwgs. Those rafters appear to bear on a timber plate on top of the steel, and are presumably tightly butted to the ridge board, so the archo could arguably instruct the contractor to cut out between each rafter pair. They will probably meet as tightly on the bits of ridge board as they would have done on each other. Can't see how they are fixed so far anyway. Plainly the suggestions made so far would be simpler. Just depends whether OP wants it built to the plans.

Not a problem if the alu foil is intended to work as a VCL. DPM was just an example of something stronger than 'ordinary' VCL

The insulation status of the rest may not help you, but 'practicalities' probably will. Different BCOs have different views, but the 'ideal'being entirely impracticable (or in some cases 'looking stupid' - although that's subjective) should get you some sort of acceptance and a waiver. Alternatively you may not even be asked how much insulation you are installing. I always insist on telling them - and usually showing, too, via a 'step-back' in the work, even if the rest is near-complete - even if they don't want me to! There are a few 'get-out clauses' with part L for refurb. One is that your proposals (for internal insulation of solid walls, for example) might cause moisture issues in a building originally built to allow the beneficial 2-way passage of water vapour, another involves pay-back time (but try to make that stick - it is hard to make it work), another relates to unacceptable loss of floor area. 'Practicability' and 'not looking stupid' are, unsurprisingly, not actually written that way in the Regs, but (if you actually get to see and talk to a BCO) you should be able to reach an agreement. You also asked: Q2: is the VCL necessary and can anyone recommend what type to go for? It is advisable. In reality your average apex void probably has a bog standard ceiling below it with no VCL, so water vapour can enter the void. Hopefully, though, there is a Howling Gale in the void, which blows away the moisture-laden air before it can condense out. I think in your case, you have the opportunity, so take it, and 'fit a VCL'. This could simply be the foil on the PIR, taped at all joints and perimeters. Or you could use a plastic sheet. When I do, I tend not to use the thin (often green) VCL, but heavy-grade DPM, as it's more difficult to make accidental holes in. Q3: should I use double sided butyl tape on the face of the 25mm PIR in line with the rafters to avoid any holes in the VCL? Well.... The optimist's view is that a hole (in a VCL) with a screw in it is not a hole at all. The pessimist's view is that it might still be a bit of one! Your idea is not unreasonable. I used to use 25 x 50 battens over (under!) the over-the-rafters layer. If I was feeling obsessive I would pre-drill the holes, gun in silicone mastic, then drive the screw through the silicone, so each screw gets its own air-tight and vapour-tight (??) grommet. Not fully proven, but pragmatic! Clean up the silicone carefully or your joint-filler will fall off!

Don't know which part of the UK you are in (assuming you are in UK), but the 75mm you propose would not comply with Building Regs. 125 or 150 is commonly required, depending on the 'timber fraction' (how much of the 'insulation' is actually rafter or joist). The Regs (Part L) refer to Thermal Elements and, when doing work from the inside, refer to the room you are in, not to the whole house, so when they say that if you 'treat' more than 50% of a thermal element you either have to comply with Part L or show why you cannot (and pay for a Building Notice, it is no good to say 'well, it's only one of 3 rooms, so it's not even 35%'. If you are insulating more than 50% of the roof in that room, you have 'triggered' Part L. My comments refer to England. I think Wales is probably the same or similar, and I understand Scotland is significantly different.

According to the text it's a '10-story building'. Can't wait to hear the other 9.

I understand 'through-flow' tubes are pretty rare now. We had a 'through-flow' array at S. Yorks Energy Centre and the vandals discovered that you can drain the system down via the 'alternative method' of smashing a tube!! I have not looked at Navitron for years but they used to be among the cheapest. I share your fondness for SWH - it's so crazily simple! - , but more and more find myself recommending PV/diverter. That would have been somewhere between counter-intuitive and madness in 2009, before the 'Feed-in' Tariff.

Appreciate you may have meant other Regs, but B. regs and PD (or not, in some v limited circs) will, I think, still apply. Bldg Regs predominantly re structurals and HW storage (but you have that already), I assume. Ages and ages since I had anything to do with a ST install.

I think it's Planning (potential breach of PD conditions) that the OP is concerned about, not BC.

Agree with @JohnMo and @ProDave. Do it now and you have 'right on your side'. Obviously if everything is tight to the ground you will have to be careful not to make anything soggy, but hopefully (if it's not a solid floor) you left some 'breathing space' anyway.

Are you assuming then that the 'cill' of the door is wholly 'hung' off the jambs? I had taken it as bearing on the CF, as per the larger dwg. I am assuming the pics shows a side-hung door in a frame but the annotation is a bit fuzzy (or my eyes are failing and I don't realise yet!)

Is that not exactly what is shown in GBS's dwg, or have I misread it?

Hmm, perhaps depends on which way the joists run and when the floor goes in. Could you saw the facing bricks to half depth, sit CF across the cavity then fix thro to inner leaf as previously suggested? Trying to think in 3D and failing, so have I missed a bridge there? Don't *think* so...

Not sure I know what you need. I think it *is* supporting (or partly so) the door-set, but it gets its 'supportingness' from being bolted to the slab. I assume your circumstances are different. Can you confirm what you would need it to do as opposed to what it's doing here?

Soudal do an air-tight foam. The one you link to does not claim to be. Decorators caulk I suppose could be, but a lot depends on adhesion, substrate etc. I think this may be somewhere where you use Passive Purple as 'belt and braces, but see if others agree.

Yes, lots more info and pics, please. How deep a reveal are they on? Is the leak all round? Is it concentrated at the top/sides/... where? Have you established that the leak is at the window-frame - timber frame joint? Could it be the opening lights somehow not sealing? Lots more please!

Forgive the Q if the answer is too obvious, but you say ''the gap between the screed and the external walls has been filled with expanding foam''. Was this air-tight foam? AIUI All air-tight foam is claimed to be air-tight (of course!) but not *all* exp foam is air-tight. I would not bother is *air-tight paint* over *air-tight tape* unless you feel some of the adhesion is less than 100%

Use lime if you can. If you want to use a fair bit of time just chop out the 'baggy' bits, fill with NHL 3.5 (or lime putty) 1: 3 with grit sand, and then re-skim the whole with 2 or 3:1 sand and lime putty (or NHL 3.5). A little more tricky on the L & P ceilings, where chopping bits out may dislodge the lot - but it may not. If you want to experiment a bit, as it does not have to be too strong, you could buy hydrated lime (available at most builders' merchants as it is sold as more of an admixture to sand/cement than as a 'use it alone' thing), soak it in a metal bucket or bin and make your own lime putty. As long as water stays on top of it it will remain usable - for years.

Youtube has gun-fettling videos. I have probably 5-10 guns waiting, and I have done a couple in the past. From memory it is a PITA, but it works.

Good! Glad that's cleared up then!

When you say 'pitched warm roof' I think you are referring to PIR board fixed *inside*, under the rafters. Strictly a 'Warm Roof' is where the insulation is *on top of* the roof structure, just below the membrane and slates, thus all of the roof timbers are within the thermal envelope. Can you confirm that you mean the former (or that I am wrong in my supposition!)? Either way, pre-June 2022 (target 0.18W/m2K) you'd have just scraped through with 125mm, provided the 'timber fraction' (the part of the 'insulation layer' which is actually wood, not insulation) is not unusually big. As far access goes for the remedial work how deep are the rafters? Common practice since 2010 regs in retrofitting roof insulation to sloping ceilings has been to fill rafter depth minus 25mm, leaving a 25mm vent gap between the membrane and the insulation. BEIS Best Practice guidance now states 50mm as the ideal, so you might, if your rafters are less than 175 deep, find that you have to fit insulation under the rafters too (which is in any case good as a cloaking of the thermal bridge - if you don't do that then add up the width of your rafters to see how much 'full-depth wood' is in your insulation layer. Anyway, yes, ceilings down - no way you could do it properly without. If you try, and can slide the insulation in easily then it is too loose. Sounds like you have a really irritating issue, and I wish you luck with the remediation.