Redbeard

"Countryside"

Forebears: The 3 bears' 'plus 1'. Sorry, I'm drifting!

Oh yes! Whomsoever will do for me! Favourite Uxbridge English Dictionary is possibly unrepeatable in polite company!

Don't worry - we are not suggesting foam cavity insulation. @SilverShadow and I would recommend expended polystyrene (EPS) beads. They are mainstream and fine if you can get someone to do the job. We have seen what has been done. I am now worried re what else has not been done, or has not been done right. I rather think an RICS surveyor would be a wise move. You want someone who is prepared to 'dig deeply' to spot any and all potential issues.

@Farah Jones, So sorry to hear this. The issue you may have is persuading a cavity insulation co. to 'get out of bed' for a small job. They are generally so busy with full-house jobs that smaller (in your case 'one-room' ones may be considered less popular (or if you're lucky, the fact that your job is small may mean it's just the one to fill in that unexpected gap that's just popped up). Assuming you know who the BC provider is (is it the local authority or a private co.?) it will do no harm to contact them and raise your concerns. Sending photographic evidence of your inspection of the cavity should mean that they will not sign off, and until they can sign off, assuming the contract is clear, the builder has not finished and does not get the final payment. Is the roof a pitched roof and is there a hatch (your post suggests not). Can the builder reasonably answer that the roof insulation was to be put in at the end, and they haven't reached the end yet? Harder to argue for the CWI. If it were me I think I would be on to Trading Standards as well.

*Would you expect to find a ventilation slot on the eaves for a house of this age?* Probably yes. Not in the (modern) form of a plastic extrusion but in the rather more time-honoured form of one bit not touching the other very well. 25mm gap across the eaves on 2 opposing sides is good. *Will the gap in-between the slate and the super quilt be enough for ventilation at the roof level?* It's an interesting point, and will in part depend on the R value of the multifoil you use. If you were doing a loft conversion you would have a U value at ceiling level of 0.16W/m2K at worst, and you would expect that all of the 'cold side' ventilation would be 'North' of the insulation at ceiling level. You would also have supply ventilation to the finished room. If you are just making a storage space it wants its own ventilation, as well as the ventilation on the cold side of the multifoil. Particularly if the multifoil is not giving a 'regs-compliant' U value there could potentially be condensation at the coldest points.

Is there a gap between the insulation and the 'deck' on top of the stilts? There should be, preferably 50mm, and that vent path should be 'fed' from a ventilation slot at the eaves, allowing free airflow from one side to the other. Impossible to tell the nature of the loose-fill insulation from the pic. If in any doubt whatever send off a sample. Search 'asbestos testing' and you'll find everything from specialists in doing the whole lot to 'mail order' services where they send you a paper suit, an FFP3 mask and a sealable bag. The cost of this includes analysis of the sample which you take.

Sand/cement pointing to front wall in a form ('strap pointing') which was common in the 1980's but is almost certainly not how the original pointing was finished (it was (a) lime and (b) probably 'rubbed' quite flush. The good news is that, as far as I can tell from a picture, your stone does not look soft. If it were, there could be a risk that, years down the line, you could have stone which erodes because the pointing is stronger than the stone. The opposite should be the case; lime is 'sacrificial', and will succumb to frost damage before the stone will. How are you measuring the percentage moisture content? 'Pointy-pokey' damp meters are generally most accurate in wood, and much less so in masonry. 18% in wooden joists is considered healthy, so I am not sure if the reading you are getting (if it is accurate, which it may well not be) is a major issue. (I know a lot less about moisture content in stone than in timber). Most of all I note that, as far as I can see, you have no insulation on the walls. It therefore would not be surprising if you get condensation in cold corners, particularly if there is no airflow the 'chase moisture away'. This is not to say that it could not be penetrating or rising damp, but these issues (while sometimes blindingly obviously the case) are sometimes overstated. The most reliable damp test in masonry is a carbide test (sometimes known as a 'speedy' test). It does not rely on a meter which performs best in wood. Tony on GBF is known for drilling out dust samples and working out % moisture content by weighing them before and after a spell in the oven. There is, I feel, a big difference between 'specialists in using proprietary damp 'solutions'' and real (old building and) 'damp specialists' I would suggest an accurate test and diagnosis followed ideally by insulation of external walls with a breathable material. My preference is wood-fibre or cork. As far as ventilation goes, while there may be reasons for the 'damp' other than condensation, use this 'opportunity' to review your ventilation provision. Older houses have often had all the original ventilation (which included the leaks round sash windows) 'improved out'.

Welcome. I like your 'kitchen units'. Look like they'd also bee good for storing power tools in.

Feeling the need to mention fruit...

I don't have this particular experience but I have worked subject to the PWA on a number of occasions and am pretty convinced in my own mind that this is a Party Structure. https://www.redbridge.gov.uk/planning-and-building/building-control/chimney-breasts-removal/#:~:text=The Building Regulations require that,1.2. suggests that Bldg Regs approval is required, and if it is a party structure I think it must be covered by the consultation etc. rules in the PWA. Also my take on it is that it is quite clear cut; you cannot remove next door's part of the stack without their consent. So I think if they do not wish to lose the whole stack not only must you work on your side only, you must also work according to the requirements of the PWA, which will include making good, insofar as turning a 'party wall' (the wall between your flues and theirs) into an external wall and all necessary slate/tile and lead-work. If there is any suggestion that the flues on the neighbour's side may be used in future (and the retention of the stack would seem to suggest that this is a possibility) you will probably also have to prove that no rubble from the removal of your part of the stack has blocked or in any way affected their flues. This is covered a bit in the link above. As I said I have not had this specific issue before so I am happy to be proven wrong!

The only GRP frames I have 'met' in UK were imported from USA (or possibly Canada - long time ago). User was very happy with them.

I have only used a few m2 of cork, but I have used a lot of rigid (and latterly some flexible) Wood fibre. I *know* it is a great deal more expensive than plastic but I do not want to use plastic (and I hate even handling rock-candy-floss) so I 'invest in my preferences'. I don't try to stop anyone using what they want to use, but I like what I like. I have not bought PIR since 2020 so I am out of touch as to the differential, but I usually sit down a long time after I get the quote.

Is this a new-build or a refurb? Either way it may be permissible under Permitted Development. Have your PD rights been extinguished?

It was Knauf, IIRC, and in fact the principle has, I believe, been 're-born' in SWIPS, which I have not seen, but I understand is an IWI system using 'insulated studs'. It is apparently used quite a lot in ECO4 -funded schemes.

Hello. I think we need to know more about 'where these studs are' before we can comment much. What is on the other side? The outside world? Another heated room? An unheated room? You mention 'bridging' but not 'thermal bridging'. Is sound-proofing more the issue than 'thermals'? More details, please!

Sadly not, if you really need it to do exactly what ply would do. Even if you could find a rigid board claiming insulation qualities at that thickness it would be likely to have all the insulation value of a thin thing. I am aware that anything is better than nothing but I feel that no 10mm board is going to give you an exciting effect in the lay-up you describe.

OK. Got it! So your proposal is 100mm total PIR, as per your original description: *not* as per the drawing. Confusion over. Thanks!

@thetdog666, noted the OSB and membrane missing, but apart from that is that *the* dwg of what you plan to build, with a total of 145mm PIR, as against your description, in your original post, of 100mm? Edit: Cross-posted with @sgt_woulds

@sgt_woulds, I think it's down to the difference (see my post above) between the dwg and the description. The OP's description (above) has OSB over the studs.

I am very confused! Thanks, OP, for your response to my last post. The annotations (notably the dimensions) on your drawing do not seem to match up with the words in your description. The dwg suggests a total of 145 PIR (25 and 120). Your description below suggests a total of 100 (80 and 20). Can you clarify? @Russell griffiths above referred to terminology. Am I right in assuming that the reference to 'battens' below actually refers to the (vertical) structural Studs?

Not sure what you mean by 'on the face of the battens'. Do you mean between them? Have you found 20mm PIR? On the initial assumption that you were not having PIR between the battens I was going to suggest the VCL goes on the face of the 80mm, with the battens over, but if you have PIR between the battens that changes.

Unless something has passed me by *all* PIR boards are made of foam. I have done a number of floating floors on PIR,on XPS and on rigid wood-fibre, and in none of those cases has the floor felt anything other than solid. No discernible bounce whatever. I have never done one with rigid rockwool, though, so unfortunately I cannot comment, except to say that if I were trying it as an experiment I would start with the external wall insulation grade of rockwool. BTW the web says this about thermal conductivity of the RW boards you mention: "Thermal performance. ROCKWOOL Thermal RockFloor has a thermal conductivity of 0.038 W/mK. ROCKWOOL Acoustic RockFloor has a thermal conductivity of 0.040 W/mK". So just over half as good as PIR for a given thickness, but it has the acoustic properties which PIR neither has nor claims.

Have you thought of EWI? You could consider building the extension solid and EWI-ing it, carrying the EWI round, at the same or lesser thickness, to the main house. Given the choice between EWI and IWI I would usually choose EWI.

What's the finish on the house? If it is rendered watch out for staining from run-off from the lead. We had similar with EWI to gr floor only which we capped with lead. Happily the staining is confined to a relatively small area but it is noticeable on the light-coloured render.