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I'm feeling some what validated in my choice to avoid central heating entirely.

Thank you for the replies. As @Mike says (that link was very useful, btw), moisture buffering is less important if ventilation and heating are decent, so perhaps I can use the clay just for aesthetics with a thinner layer as @Russell griffiths suggested. 3mm clay is only 1kg per m2 heavier than gypsum, so 15kg extra overall. ^ This. So it sounds like I'm overthinking it and the 12.5mm plasterboard, clay finish and tree branch light fitting will be fine for weight and better than the 9.5mm? One other thought - is it worth using wood wool board instead? Presumably it has some moisture buffering too which might help if a thinner layer of clay is used. Thanks again.

Thank you both. That could be an option, @Russell griffiths - I've generally tried to avoid running services on those walls eg putting sockets on internal walls where possible. My concern would be that I still need to pierce through the insulation to the thermalite in order to fix the battens and the plasterboard would be on top of those screws, so it's whether the margin of benefit would be worth the extra space lost. @Mattg4321 I decided to go that route partly for cost (it was much cheaper buying them separately) and partly because I can then foam and tape the PIR so the insulation and its foil facing are both continuous, which I thought would be harder with combined insulated plasterboard. There are some plastic plug and pin fixings here on insulationuk that look similar to the Fischer dipk ones, but it specifically says it's not for insulated plasterboard. I wonder why that is? I phoned them and couldn't get a definitive answer. Maybe because the disc is 3mm. If so, could I recess the disc slightly in the plasterboard then scrim over?

My SAP calc assumes I follow the recognised construction details. On the gable end of the property, I am expected to installation insulation above the fire socks and flowing it into the soffits and fascia. The sketch is below showing this: https://www.recognisedconstructiondetails.co.uk/library/document/mpf-150-e13-02-gable-insulation-at-rafter-level.pdf The question here is, do I really have to install the insulation in this area? Looking at the guidance photos, the SAP assessor does not receive a photo of anything other than inside the wall looking at the insulation between the truss/joist and internal leaf of the gable wall. I was advised by someone else they didn't think it was best practice to fill the soffit/fascia with rock wool? Any thoughts please?

No, this is a scewed perspective based upon microcosms that highlight poor installations. Last year there were probably around 60,000 heat pumps installed, for arguments sake. Do you have statistics that show that the majority of these installations were not good jobs? That you're more likely than not to get a bad job? Have you run your own figures? Lets take a pretty run of the mill materials list for a retrofit using some publicly available prices at Midsummer Wholesale for the heat pump and other online suppliers for other stuff: Vaillant Aerotherm + 7kW - £4724.24 Vaillant controls - VR70, SensoComfort plus internet gateway - £633.41 Telford UCV 250l- £1225.70 50 liter volumiser - est. £350 (not Misummer who want £455 for a 25l volumiser) Installation kit - anti vibration feet, insulated flexi pipes, isolation valves, mag filter/strainer - £270 External pipe trunking (lets say 5m length) with bends and connectors etc. - £250 External Pipe insulation - £14/m x 10 external + sealant/glue & tape - £190 Internal pipe insulation for uvc and heating primaries etc. - £65 Anti-freeze valves - £200 Type b rcd - £180 Other electrical - cable (power and control), mcb, small enclosures, junction boxes, 2 x kwh meters,32A 4-pole isolator, trunking - £360 3 bog standard radiators - £300 2 nice column radiators for the living room and kitchen - £700 5 x good quality radiator valves - £150 Copper pipe mix of 28/22/15mm - £250 Press fit pipe fittings - £ 250 Pipe clips - £50 3-port diverter valve - £110 Expansion vessel kits x 2 heating and potable - £150 This comes to a grand total of £10408.35 and there are other bits and bobs I can't be bothered to list - like system cleaner/biocide/inhibitor and all those sorts of consumables. No UFH pipe or manifolds here either. No long primaries to house or through it. And this doesn't include materials for constructing a base. This represents a fairly small job for a reasonably efficient heating system. Yes, I can probably get some discount on the uvc and heat pump, but I'm sure this gives you a good illustration of what it actually costs to buy materials for an installation.

How do I know if CIL is applicable? My new build is in Cumbria under Allerdale County Council (or now Cumberland council). Is there a way to check if this council is using the scheme? Thanks, Jamie

They're 13.6mm so no battens would be needed. I found that the profiles are aluminium which apparently is a A1 rated material. The following product page states it's A1 rated: https://www.ledspace.co.uk/products/pack-of-10-2m-drywall-plaster-in-profiles-for-led-strip-24mm-wide Although I've asked for written confirmation or a certificate stating this. Does that all stack up and look like I have a solution? Many thanks, Jamie

At what stage are you planning to market the build? I'm wondering if there's any scenario where you might sell off plan and let the buyer choose the heating and internals? You'd also get some validation of the likely sale value. Or any other scenario that would let you build both side by side as there must be economies to be made. Ideally you'd keep both builds as similar as possible but only your own will qualify for a grant which does complicate things. What do estate agents say about ashp versus gas boiler?

Sadly not. Its got to come across a field, then a driveway/yard. And i need to go big on cable size, because its, a) a long way so voltage drop becomes a real issue, b) if i want to increase the size of the array, which i almost certainly will as secondhand panels are so cheap now, i dont want to re-vsit the cable.

Clay plaster does have better moisture buffering qualities and can moderate daily variations but, if you have adequate heating and ventilation, that won't make a big difference. If you don't have adequate heating and ventilation, consider those first. Unpainted clay plaster can look good though! For more, see my comment in this thread. ^ This.

I'm not a renderer but this sounds likely to me, having seen a scraped coat done on a neighbour's extension - they put on a thick layer then next day when it's set but not fully hard they scrape a couple of mm off to leave that flat but grained finish. I don't think it's been patched this afternoon, it wouldn't have hardened enough to finish.

Good evening everyone, I wonder if I can get some help/thoughts on how to finish the below: I recently got a room renovated in my 1930s house, at the end of the room an extension was done sometimes in the 50s/60s, the extended part has a patio door which was recently replaced with a new bifold sitting on the outer leaf. The workman put down new joists (suspended timber floor) and the joists was run resting on the inner leaf of the masonry as in picture. Also, telescopic vents were installed under the bifold which crosses between outer and inner wall to help with subfloor ventilation. I now have the cavity to finish, so I can run the floor (chipboards/plywood bords) going all the way up to the bifold door, the workmen suggested no need for cavity closer when they did the work. I am unsure how to finish off the cavity up to the bifold to avoid cold bridging and any damp. I am concerned the plywood/chipboard in that area will build up mould. What is the best approach in this situation, all thoughts are much appreciated.

No space in a 1,750 square foot house? I'm not the only one that's fitted one in an apartment a fraction of that size; they really aren't that big. Could go on the wall or ceiling of the laundry room, or study next the hot water tank, or the kitchen, or the largish entrance hall, or the WC...

Why didnt you use plasterboard that comes already attached to the PIR out of interest? I'm not sure there's any approved method of using mechanical fixings into masonry to fix plasterboard.

If you want a healthy & happy home you should have MVHR. It doesn’t take a lot of room, you can self install and will save on your heating bills.

Did they not sheet it up? When we did ours in an October, much later (as ever) than originally planned, we were watching the weather like hawks, and sheeting up with hessian after every pass.

Fire doors have a reassuring heft and sound deadening benefit as well... Not always a bad thing to have that in a high quality home!!

Heat pump cylinders are generally big because they store water at 45 to 50. A typical direct cylinder could just as easily be at 70 degs, so effectively a much smaller cylinder holds just as much energy.

How are you running services, you could run a service batten on top of the insulation then fix plasterboard to that.

Just need to vent a little frustration and see if I’m the only one… I imagine like many professionals, this comes down to personalities and probably workload, but getting hold of my building control inspector (private) to actually speak to is a real challenge if I can’t take a valuable day off work to be on site for the day he visits. He visits, leaves, writes report and often asks for documentation I’ve already submitted, or refers to details that are inaccurate and need correcting. Latest visit he has stated that the first floor height to ground is over 4.5m and so we need a full fire-protected stairwell. This will result in a lot of fire doors. I previously discussed this with him in person (on an earlier visit when I’d taken a day’s leave to make sure I could speak to him); the ground slopes and the finished house will have decking on 3 sides at floor level, and so all those windows are very comfortably less than 4.5m (this was his words - so in this case it’s a pragmatic first floor to the surface outside the window, rather than ‘ground’, which is below the decking). This leaves two windows at the end where ground is highest and the first floor height to ground I’ve measured to be 4.0m. Now, I’ve read the Part B many times, and it just refers to the ‘first floor’ height which, being as it doesn’t say first floor window, I have taken at it’s word as first floor height to ground. Has anyone experienced or seen it defined as the window to ground rather than floor? (Our FFL to ground is 4m and the window ledge is, from recollection, 550mm above FFL). I’m looking (hoping) for support / examples that it’s FFL to ground. I am prepared to be disappointed however 😕. We’re aiming for a high standard of build, but I’d rather have the choice over which doors to fit rather than have fire doors imposed upon us.

Can you not surface run it?

Have you looked at clay plaster that is applied at thinner thickness a mate of mine did a couple of walls in a hotel recently and I think he said it was thin like skim coat, he troweld it up for hours and it changed colour the more he worked it.

Its the 150m cable run thats the killer! That needs trenching in.

Couple of Q's You say their are "plenty" of good installers. What does "plenty" mean? There might be plenty, but if the majority are not good, then, realistically, unless you are in the know, its more likely, than not, you will get a "not good" job. Which is what seems to be happening in the real world. This house with £11k of materials, was it some kind of mansion? I struggle to see how this would cost £11k in materials on an "average" house. For mine doing a "johnmo" as it were and as suggested on this thread, you have a ASHP, a UVC, some sort of wiring/control center, some UFH pipe and some rads. I couldnt get that close to £11k in materials even if i tried.

By smaller cylinder, you mean a smaller UVC than you might otherwise install?