Redbeard

So the builder has left a 100mm ventilation gap?! Guess you don't need to worry too much about the ventilation, provided he has built adequate 'ins' and 'outs'. Was the instruction to the builder clear? "Build me an extension which meets Bldg Regs ", for example? If so.... I like to have something to at least 'cloak' the thermal bridge of the rafters, so how about pull down the ceiling, add 50mm between and 25mm below the rafters (U val probably less than 0.13W/m2K compared with Bldg Regs target of 0.16. Then you know you have surpassed the Regs req't. Then you ask the builder to pay for re-boarding and plastering. By the way, It definitely isn't. In come circs the BCO might agree to accept it, but that just means you are getting away with more heat-loss than you should have. Not good.

Go for your own TP. Effectively you have already told us why you need to. One fewer thing to bite you in the future.

Thanks ST, I knew you'd know. I stand corrected. I somehow had in mind that XPS was OK. The rest stands, though!

Make the shape in XPS and lay up GRP over it, with whatever 'non-slipperiness' you want to incorporate? It works for boats (and indeed shower trays).

Strongly consider natural materials, such as wood-fibre or a proper insulating plaster like Diathonite - goes on very thick, usually sprayed! Remember that your stone building was probably built with materials - stone, lime mortar and lime plaster, which can absorb and 'breathe out' water vapour without damage. As far as possible you want to make the next layers in the 'sandwich' behave in the same way. Look into air-tightness with regard to 'solid' wall insulation and don't be fobbed off by 'it's OK - it's got a vapour control layer (VCL)'. Acquaint yourself with the Building Regs and in particular how adhering to the U value targets can, in some circs with internal insulation, cause 'interstitial condensation' - condensation on the old surface of the original wall behind the insulation. I'd suggest not getting talked into plastic insulation before you have had a very good look at all the pros and cons. Of *course* it can work, but knowing all the advantages, disadvantages and practicalities in advance gives you the best chance of making the right decision. Think v carefully when/if insulating suspended timber floors. It *can* work, but it can go wrong too. If you cannot get the ventilation (etc.) conditions right you might consider a solid floor, either with 'modern' (plastic) materials or with something self-draining like foamed glass aggregate.

Even if the drainage is functioning OK is there anything about the 'lie of the land' which is directing water towards those walls? (In one case the damp only seems to come in just inside the wall). Can it be 'encouraged away' by 'softening', re-directing, French drain? You might also consider this as bed-time reading (go to bed very early, though!): https://assets.publishing.service.gov.uk/media/5f05d211d3bf7f2be6e0217a/suspended-timber-floors-underfloor-insulation-best-practice.pdf If you can tick all the 'boxes' in that guide you are probably a long way towards being OK.

What you describe is a hybrid Warm Roof - some insulation between the rafters - not really a Warm Roof - and some over - the 'Warm' bit, tucking up the rafters in warm stuff. However, when you do a hybrid you need to ensure that there is not a risk of interstitial condensation at the interface between the 'between rafters' insulation and the 'above rafter' insulation. The 'rule of thumb' sometimes used is to have two-thirds of the R value above the rafters and one-third between, so it is not 'cold' enough to allow condensation at the interface. (A proper condensation risk analysis is better than a rule of thumb). Even if you could 'engineer' your 50mm uplift vis a vis your neighbour's roof that would mean only 25mm between (the one-third to the two-thirds represented by your 50mm). 75mm, even of PIR, may give you a U bvalue of around 0.3W/m2K, about half as good as the Building Regs U value target of 0.16W/m2K.

If it's to a SE's spec, usually on pre-cast concrete 'padstones' too, not just the brick.

Difficult to answer without knowing the SIPs designer's rationale/strategy, but yes, the bottom one could be the combined a/t and vapour-check plane. Although of course a/t layers can be external...

I have not come across @JohnMo's solution before, but there would normally in any case be a non-return valve performing this function. They can fail though or, as you describe (to my surprise), be left out!

There is no mention of insulation. Is that simply because you have not 'got there yet', or because you do not intend to include any? If you are planning to insulate the walls then your strategy for the 'damp' (have you established that it is definitely rising or penetrating damp, or could it be condensation?) needs to take that into account. If, for example, you used your 'liquid applied dpm' to 'dry' the wall, and then insulated internally, you would effectively have a vapour control layer (VCL) in the wrong place in the 'sandwich'. If you were not planning to insulate the walls please let us persuade you to do so!

Is the OSB your air-tightness layer, or is that dealt with by a separate membrane? If the former, yes, tape. If the latter, maybe not. (Unless you are a serious pessimist and decide to do both!)

I regret not, but there are compressed air staplers starting at under £50 in places like 'ToolFixstation'. Of course you'd need to buy or hire a compressor but they exist to buy at £100+, and presumably might be useful to you in the next stages of the job.

There are 2 schools of thought: 1. A hole with a fixing in it (a staple in this case) is not a hole at all and 2. (The more pessimistic one: A hole with a staple in might leave a residual hole). Both are valid! If you are at all concerned get a roll of suitable external-grade air-tightness tape (I know this is not an a/t issue, but some tapes are waterproof too) and stick a small piece over each staple. Tedious, but you can tick that off and proceed to the next issue. The butyl tape would work too - double-sided for pref. A mall piece wherever a nail is going through and Robert is your parent's sibling.

A whole other universe if that WC is to be taken seriously... Wow!

To clarify I am talking about the render as used with EWI, not about the EWI itself - no space for that. I think if it were me I'd do 2 thin toothed-trowel coats with glass-fibre/acrylic mesh between, to reduce the risk of cracking. Although, come to think of it, are you suggesting blocks with no insulation?

If you use one of the EWI base-coats I suspect you'd get away with 5mm. Of course you'd want to paint it, or it'll look grey - like concrete blocks.

A piece of plastic pipe glued to a small ball and a clearance hole in the lid. You can even paint 'Full, half-full and empty' marks on it. Of course the clearance around the pipe means that ingress of 'foreign bodies' is not prevented.

Ah, that's it! Thank you!

Ah, now that's interesting! It was Baunativ that I used, and in Mar 2020 I received the following e-mail: "unfortunately, since Brexit, it is no longer possible to send goods to the UK. Our shipments are canceled by the parcel service. You can also have the goods collected from us if you can find a parcel service that offers collection in Germany and delivery to the UK. Mit freundlichen Grüßen Baunativ GmbH" I wonder what the 'mechanics' of it are now. I have seen mention of another merchant on here, but I did not note the name.

If you are really, really tight for space (and your budget does not run to aerogel), you can get 12mm PIR (online - the carriage will probably cost you almost twice the £14+ price, but a bird in the hand...). 9mm plasterboard over that, joint-filled with no skimming will lose you under 25mm and halve the U value ( rough calc says about 0.88W/m2K, copared with around 1.7 for the 'base-case' wall). Insulating sloping ceilings by 'poking things down' is usually a lost cause, as there's usually a joist in the way, nailed to one of each pair of rafters, and keeping an even vent gap *and* getting air-tightness is really hard.

I use Pro Clima. I gather Siga are good too, though I have not used them. Before we left the EU I used to buy direct from Germany. The merchant I used decided they did not want all the import/export faff, but I believe some on here have found merchants in Germany who will supply and sort out the customs stuff.

Ours was 112mm brick, with stone details, but dry. We did lime parge coat then 40mm rigid wood-fibre, plastered and primed/air-tightness-taped, then rough-coat plastered, then replaced panelling, amended as necessary.

Don't plasterboard it! Lime plaster. +1 for external wall insulation, though you will have to build a 'gable ladder' to extend the roof line.

Remove it, insulate behind and re-fit with amended joinery details as required. It's what we did. (Mainly 40mm wood-fibre, and 100mm wood-fibre on the flanks each side of the bay)