Redbeard

I imagine they will say that the TW55 is the VCL, which is true as long as all joints and perimeters are taped to within an inch of their lives and nobody pokes a screwdriver or a fingernail through the foil.

What inherent 'cooling measures' does it have already? Large roof oversails on the 'hot side(s)', smaller windows ditto, external shading, exposed masonry as 'leveller' There, I avoided saying Thermal Mass - Oops! As I understand it quiet, slow-running MVHR systems rarely shift enough air to have a serious cooling effect, and systems which do may be too loud. Stating the blindingly obvious (sorry!) the main effort should be to stop excessive solar gain, rather than to get rid of it once it's inside. I agree with 'passive' measures where possible, but air-to-air HPs do have the advantage of being a winter heating system as well as a cooling system. I think if it were mine I'd do all the passive measures I could (including IWI) *and* fit a/a HP

Have you been in touch with People Powered Retrofit in Manchester? They may be able to put you in touch with householders with ASHPs. My 2-penn'orth: 12 -17 years ago when the Energy Saving Trust did these field trials https://www.gov.uk/government/publications/analysis-from-the-first-phase-of-the-energy-saving-trust-s-heat-pump-field-trial#:~:text=The Energy Saving Trust's ( EST,83 households for Phase I. the CoPs for ASHPs were in some cases pretty grim. Now they are routinely pretty jolly good if the installation has been done well and insulation spec suits lower flow temps, so I would definitely go for ASHP. Indeed I do not have a field or space for boreholes so ASHP it will be. My HP will be a long way from the nearest neighbour, though, so all cases are not equal.

To add to my post above, you almost certainly need a structural engineer (SE) and a written specification for 'making good', particularly if you still propose to remove the full ground floor outer skin. I would expect a SE's spec to include for temporary propping while you remove the ground-floor support for the outer skin and leave the outer skin intact on the first floor (if I have understood you correctly). I accept the inherent tendency of bonded bricks to, well... bond, but the phrase 'hanging in the air like bricks don't' also comes to mind. Re Building Regulations (both stability and thermal performance), you will at very least need to submit a Building Notice (short-form minimal information application for Bldg Control approval) and BC will almost certainly issue a counter-notice requesting further details, including structural ones.

Ooh err! Only just seen your 2nd pic. A little unnerving! Agree with @ProDave and @Mike re ?? stability. I think your plan to completely re-face the wall is at best ambitious. Even if you drop the plan now you still have a 2nd skin to build which will not be tied-in as it once was. You will have to fit screw-in ties to the old wall so that the new bricks can be tied in, or perhaps you could do it with resin anchors. As you refer to plans to insulate internally can I suggest that you 'check-in here at planning stage for that? Interstitial condensation risk, possibility of thermal by-pass, possibly lack of continuity of vapour control layer (VCL) (or indeed the insulation itself)and plenty of other risks worth running past those who have done it before. Remember that, under the Building Regs, you will be 'Renovating a Thermal Element' by 'adding or replacing a layer'. You cannot just put on what you fancy - you have U value targets to meet too. I am more of a fan of rigid wood-fibre than I am of insulated plasterboard - how do you keep the VCL 'tight'?

But you said: Can you show us a bit more? The 'half-bricks' we can see could be headers (the ends of long bricks) but if that's an opening to the right they may be 'true half-bricks'

Firstly, as you appear to describe it, it is not a cavity wall. Is it all stretcher bond (long bricks only visible?). On a 'solid' (never mind about the 10mm gap - it's effectively solid) wall the ties are in the form of bricks laid at 90 degrees, so for example you may see: header (short brick, i.e. brick laid across the 2 skins); stretcher (long brick), stretcher, header. Other patterns are also available. Can we see a picture? Why are you replacing the bricks if you are going to render?

Honestly, I would go with @ProDave's suggestion, or a variation thereof. A bought-in 'caravan' or 'chalet' is highly unlikely to give you the level of insulation you would wish. Yes, you would/may have to go for another PP but that seems a relatively minor issue. 55 years old - does it have retrofit cavity insulation. I have in mind (in complete ignorance of your floor-plan) 2 possibilities something like: Poss'y A: Re-roof, re-wire, extension and external works to suit future mobility needs. When I say 'may have to go for another PP' you might not if the size of the extension is within the 'ordinary PP' or 'Neighbour Consultation Scheme'. Poss'y B: Chop the house at first floor level, form wall-plate and bungalow roof, integrating a new extension at the same time (Full PP). In both cases I would suggest cavity fill and external insulation, including 'proper' detailing across the wall-plate so that external wall insulation can connect tightly with roof insulation. Obviously we do not know about your ground floors. Insulation is desirable, where it is likely that you do not have it at present. If you can give us more detail we may be able to 'build' an idea for you.

OK, I have only used their all-wood offerings but I really rate Green Building Store (21 Degrees) windows. Their in-house fitters were really good too, though come 2021/22 they could only offer fitting in certain areas. I gather they have more sub-contract fitters now. Yes, according to the dictionary definition they are not specialists, but they have a specialist window section. I do not regard them as any less 'specialist' than those who concentrate on windows only.

I'll put on a pretty good bet that it isn't cellulose. AFAIK cellulose is not normally (ever?) used in masonry cavities in UK. If it's white and fluffy it is almost certainly (CWI-grade) Rockwool. Is it only the v small patch we can see? How about chopping out and inspecting (and repairing if necessary) the DPC? Approx age of house? Was it originally done with CWI or was this a retrofit? (I think I have answered my own Q as the 2nd course below the cill course seems to show 2 (CWI) drill-marks at the centres one would expect.)

If a negative can prove a positive this may help... My Water Authority confirmed that my combined (RW and soil) drainage is Private because there is no connection *on my property* with anyone else's drainage. If your 'central pipe' runs from house to house that seems to me to suggest a Public Sewer. Though I could be wrong...

In 2022 I paid £3.90 for a radon report from BGS. Among other things it said: Is this property in a radon Affected Area? - No A radon Affected Area is defined as where the radon level in at least one property in every hundred is estimated to exceed the Action Level. The estimated probability of the property being above the Action Level for radon is: 0-1% Guidance for new buildings and extensions to existing properties What is the requirement under Building Regulations for radon protection in new buildings and extensions at the property location? - None BCO accepted this. I did not have to take any measures at all.

Use lime mortar if you are mortaring, and if you are not, have you built a drystone wall before. I have not, but I have worked with enough people who teach it to know that I would not do so without tuition. I am not a retaining wall expert but I should have thought a gravel footing to a retaining wall was asking for it to rotate and fall flat on its face, but then if you mean for example consolidated crushed limestone then it is probably much less of an issue than I foresaw with round washed river gravel.

+1, plus I think we need to know more about the building and the wall build-up (is it already an insulated cavity wall, for exampler? Is it old and retro-filled? Is it new. to Bldg Regs? You may need a vapour control layer in the 'sandwich'.

What is 'it' in this context?

Have you had a look at this? https://www.gov.uk/government/publications/preventing-and-resolving-disputes-in-relation-to-party-walls/the-party-wall-etc-act-1996-explanatory-booklet If not, see what it says about your situation. I think I would have to see a sketch plan and section to understand that, and without understanding it I cannot tell you whether I would accept it or not, I am afraid. I would have a read of the guide and decide whether you feel the works require a PWA. If you do I would suggest you ask your neighbours what they have done about that. If your reading of the guide suggests a PWA is req'd and they say no it doesn't I suggest you send them a link to the guide, or print out the relevant section, and ask them to explain how their interpretation can differ from yours.

After. I had to complete the relevant pro formas. I was client, PD and PC. To the end of that sentence I would add 'without a WUFI calc'. In this particular case I did not have one, but have had them for the same house and same orientation so I was confident to go on past experience in this particular case. My starting-point with IWI is always trying for 100mm unless WUFI says 'no'.

Not sure if that is entirely true. You can still submit a Building Notice (which just says 'in no less than 2 days time from now I propose to start this work. You can come and look, and here's your fee). It works for work you are confident about, but you cannot guarantee that your BC will talk to you about it before you start. In my LA I am fairly confident they will agree with my rationale, even if the U value achieved is slightly worse than the B.Regs target. I don't think the Bldg Notice procedure has changed from what I describe. It hadn't in Oct last year, anyway, when I used 100mm wood-fibre to achieve a U value of around 0.35, against a target of 0.30. Under a Bldg Notice I *have* been asked (where relevant) to provide structural calcs. I *have not* ever been asked for 'proper' dwgs, SAP calcs or WUFI (though I have sometimes offered the latter.

It's not the structural soundness I was worried about - It's the holes in the insulation. Small, yes, but if it has concrete in it it is not insulation.

...and something I forgot to add about the box gutter. It is not just a condensation risk but also a whacking great thermal bridge, even if you mitigate it. Re area-weighted U values: Very roughly: 300 on the flat in eaves and 300 on walls, @lambda 0.044W/mK (U = 0.15W/m2K approx (no allowance made for 'base case' U value, but equally no negative allowance made for bridging thro joists/studs, so assume they cancel out. From https://www.pbctoday.co.uk/news/building-control-news/glazed-home-extensions/93045/ Calculate the overall area-weighted U-Value This calculation can help to show that the area-weighted U-Value of all the elements (walls, floors, roof windows etc) in the extension is not more than that of a similar extension having the same size and shape, but which complies with the minimum U-Value standards for all the walls, floors, roof, and the opening areas as set out in the Approved Document. The area-weighted U-value is given by the following expression: {(U1 x A1) + (U2 x A2) + (U3 x A3) + …)} {(A1 + A2 + A3 + …)} Where: U = the U-Value of the element e.g.: wall U1, roof U2, floor U3 etc. A = the total area of the element (m2) e.g.: wall A1, roof A2, floor A3 etc.

Are the top 2 layers (under the rake) stacked or laid? If the latter, why the through-joints? Of course joints should, in practice , be so tight as to be non-existent, but in any case joints are generally staggered. I would be ripping out those 'trimmings'. Yes, I am all for economy, but those are just joints which will not be filled properly (maybe, perhaps...)

It is a long while (happily!) since I had to read the PW (Etc.) Act guidance, but if the wall is built up to the boundary surely the footings go under your land, thus triggering an obligation under PWA. Others will have more recent experience and better memories than I do! As above, I am not sure he can... Anyone got more recent knowledge than me?

In all the jobs I have done or seen with a service void there is usually a VCL immediately behind the battens. Some use 2 battens at 90 degrees so cables can pass up and down as well as side-to-side. Remember that in screwing through (??) the insulation to form a service void you pierce the VCL. Optimists say a hole with a screw in it is not a hole at all. Pessimists gun silicone into the hole and then screw through, giving your screw and airtight (hopefully!) silicone grommet.

That's *really* not a messy cellar! It looks like you can find some space to put your feet. We really need a SE along, but (as a NOT SE) the only comment I would make is that, as drawn, maybe the remaining pier on the RHS is a bit thin?? In reality I suspect that the treads are to some extent cantilevered off the neighbour's wall. We took our stone steps out to aid comprehensive waterproofing. You might also get more useful space if you did that (though it is not for the faint-hearted, and the wall in question was , for me, not a Party Wall. (PWA may be triggered?? - not sure about that.).

"RWA45 insulation slabs achieve Lambda 0.035 W/mK and are available in seven standard thicknesses from 25-100mm, with a density of 45 kg/m3." 'Raw' insulation value (not taking into account anything 'offered' by the structure or 'depleted' by it (joist thermal bridging, for example)) would suggest a U value of around 0.2W/m2K for full fill. I'd also look at making everything (e.g. round the joists and any other penetrations of the 'envelope') as tight as a tight thing in terms not only of 'thermals' but also airborne noise.