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Yes I recall now you mention it. To be fair the heat pump is, for the most part working well. The house is over warm now, so I have turned it off until I can get some more info from the manufacturer about controlling the curve. As it stands although I thought I had control of the two endpoints on the 'custom' curve I don't so I am awaiting an update on how to get control of it. I did think today, in the midst of my frustration with this, that now I have my MCS certificate I should just pop a Willis heater in to run it when the output required is less than the heat pump minima - how cheeky would that be?

I've been asleep at the wheel on this one and should have realised I need to put in another VoC. Due to a pain in the xxxx neighbour, I put the steels in for our retaining wall set forward 400mm to avoid ripping out all of their hedging to the boundary. This has meant that to maintain a reasonable width path (900mm) on the far corner of the property, I need to pull one corner forward 400mm. At the same time, I'd like to raise the ridge height 200mm so that FFL is a bit higher than the surrounding ground level. The houses on the land are all orientated differently and set back from the road by different distances. So I don't suspect it will be refused, but I suppose I don't have any options but to wait the 8 weeks for it to be processed, before making a start?

Congratulations Zoot the Hoot. Hopefully you will both sleep well, and get some low bills coming in.

Thanks @SimonD - appreciated. I have spent part of the afternoon reading the standard and yeah - it seems to me that you need to be able to heat all the rooms to the figures in Table 1 (18C for bedrooms and hallways). It does not require a heat emitter in every room.

Not just a building trade trick 😉

Hi chaps, UPDATE! been a while since I posted. Hope y'all doing well. Good news & an update on this heatpump! I finally won the battle with Vaillant, & they've come up trumps, by replacing my problematic Split system with a Monobloc. Installed 10 days ago. No mechanical noise in the house anymore! hydraulic unit gone- good riddance! My goodness, what a long battle tho. I got the final agreement & date set, after approaching a different female at Group Service dept, picked up my sword for one last effort, & with careful navigation (tricky & complex & 5 years of stress tbh) she empathized.. & got the ball rolling for me. Which had been stalled for over a year & my energy spent, & I was defeated & demoralised tbh. And with it I had a fantastic installer too. Extremely competent & friendly. Fab work done, you can just see the difference. Vaillant's west UK choice, so had tiptop credentials. Thanks to all who offered help & advice on this. Zoot

Mat well for main doors every time. Rubber backed coir. Comes in various depths. Cut to size. If you want something a bit more you can go with something like Forbo Coral. It’s industrial but they do some more „premium” colourways and patterns…

They are quite assertive that they cannot give tips/tricks or recommend anything really, just confirm or deny design suggestions due to liability reasons. I really think that with a bit of dpc and those sloped brackets that they will be happy so we are goign with that for now.

The best thing about slurry you could pretty much add the wash out contents of the mixer to the slurry. Just use shovel if no mixed. Bit of elbow grease its a sloppy mix anyway. Don't add all your water at the start get it mixed first then keep adding water to get consistency you want.

Why hangers instead of building into the wall?

I was happy to minimise pipe in floor and designed in loopcad. The insulation values at the time didn't get down to my levels, and even then at -9 had a design flow temp of 35 deg. Actually the highest flow temp I need doing WC is about 32. Just installed a new smaller heat pump, as previous one didn't modulate well at all (it's being reused for hot tub). The last few days the CoP has been (in order they appeared) Average 4.5 day temp CoP 5.11 Average 6.8 day temp CoP 5.68, Average 5.6 day temp CoP 5.8. Still fine tuning WC curve, so performance is improving. Even with 4 poor running days, my weekly SCoP is 4.56. in a weeks time, I expect that to closer to 5+ even with more snow on the way for NE Scotland. Heat striping - pipes are 100mm down and by the time the heat gets to the surface you cannot feel any difference in temperature. It also works acceptably well in cooling.

It's ironic isn't it? They ask for reference to the standards, but don't seem to know them. But the big warning bell that's ringing for me is that they're using an umbrella company. I assume you have a separate contract directly with the umbrella company too? So the actual MCS Design Standard (both current and redeveloped schemes) say this: As you can see, this does not stipulate that you have to have an emitter in each room. It is just assumed by the designer and installer, probably because they have no experience dealing with low or ultra-low energy buildings and therefore don't understand how a passivhaus would perform thermally. I'd recommend you have a good think about using these people as this is not a good start. But also, have a think about your design - at some point you may want additional heat and be able to have cooling, in which case you can use fan coils or UFH to provide this. I saw some very neat fan coils by Panasonic today. Very unobtrusive. I think definitely try to find a good designer and installer who can discuss the options with you. Plenty of help on here should you want help to diy instead.

Tempting, but if I've learned anything in my self build adventure so far, it's not to be too ambitious about what I take on myself vs what I ask a responsible adult to help with.

200mm seems to be the 'go to' spacing for ufh - can you explain: why you went for 300mm? does that result in any 'heat striping' across the floor? what impact does it have on the SCOP of your heat pump (I understand higher target temperatures that 300mm would require would heavily impact the SCOP)?

Exactly this. https://passivehouseplus.ie/magazine/insight/the-small-passive-house-problem-a-solution

PassivHaus is all about energy/m², rather than total energy. Which I think is wrong and drives up house sizes. We don't measure cars in mpg per ton of vehicle. Also, it's very difficult to meet PH standard in a small build because the volume: surface area ratio favours larger buildings. Another thing counting against a PH Shepherd's Hut is the exposed floor. You've got a very large surface area and a small volume inside it. I came up against all of this on my own build, which is a 5*10m house on legs.

Don't underestimate the potential costs of using one of these. The wear charges on diamond discs is eye-watering. When we did our spalled garage floor (about 45 m2) with something like this a few years ago, I think the wear charge would have been hundreds of quid on top of the hire (we got it through my wife's family's plant hire company, so thankfully we didn't have to cover it). Admittedly the slab had been there for several years, so under the spalling the concrete was very hard, and I had to take quite a lot off to get it even roughly flat, but just be aware of the potential costs. An alternative would be to scrabble with something like your first machine to remove anything loose, then a primer to stabilise, followed by a thin layer of epoxy floor covering to smooth over any residual roughness.

Thanks for all the great ideas - I think this could work. Will now be checking other aspects of it including the lower floor as well.

Bin the aircrete and the PIR. Dense blocks and mineral wool batts in the cavity will out perform it in reality.

Of course. But any time you open the door most heat will shoot out so I can't see the point. And the surface area compared to volume also provides a poor figure. Spending a fortune on sustainability for a building that is far from sustainable through the material/carbon content doesn't make sense. A shepherd would not do that.

Mike, it looks very much as I'd expect, that is no surprises. I did warn you about the consequences of the 185s before you poured concrete but that conv obviously went into the information overload bin, but this falls into the 'it is what it is' category rather than something that needs fixing. The main consequence is that the flow speed is double what it would have been, with the increased circulation noise, and hit on your pump life. Your return temp is still 5°C more than room temp, so the avg slab surface temp is prob 7+°C warmer than the room env, and so you are dumping ~100W/m2 from the slab into the house, which seems to be heating the house by maybe 5°C per day. That's a hell of a lot for a passive class house, and you'll need nothing like that once the internal fabric is at target temp. You might want to experiment setting the house set-point to say 18°C and let the system reach equilibrium, leave a day or two; then step up the set-point another °C; rinse and repeat. That way you aren't going to be stressing anything too much.

i have a timber subfloor - 18mm floorboards on joists. I'm having electric UFH in some of the area. I'd like some insulating properties to make the UFH heating more efficient. 1 tiler said he would only use 6mm hardiebacker cement board. another tiler said he would use 10mm Delta board (which is cement coated but foam centre). he didnt just say this for insulating, he said he prefers it as it 'absorbs' some movement. 1st tiler said only full cement board is rigid enough. he also said if i want insulating, will still need a cement board first - but this is not an option for the floor height. 2 views on the same puzzle.... its confused the hell out of me.

Either find an installer that will play ball or just cut out the middle man and DIY the install. R290 Haier heat pump 4kW or 6kW from Wolesely are £2100 and £2300 including vat. Do a direct cylinder for DHW heat via immersion on cheap rate and a simple time switch. About £500. Connect ASHP directly to UFH and run WC. Two pipes, strainer on return (supplied with ASHP), couple flex hoses and isolation valves, job done. £200.

Holy thread bump...... Coming to this thread as we’re in a similar situation. 2 storey (plus loft) house being built in masonry (Celotex 7.3kN high strength blocks) which will be rendered on the outside and wet plaster on the inside. Floor will be Posi-joists which I always assumed would be done using joist hangers. Spoke to one of the brickies/foremen on site who mentioned that they would be using resin anchors rather than joist hangers as it’s easier to level up using a laser level – compared to joist hangers. Not sure I fully understood it when he mentioned and spent the weekend reading up about it on ChatGPT and Gemini. The unanimous verdict was not to use the resin anchors into the Aircrete blocks as the fixings were going to come loose in the long term and masonry supported joist hangers are the way to go. Spoke to the builder / boss man who confirmed he was going to use joist hangers. Feels like a win but I’m not sure reading some of these comments. We are aiming for an airtight house with parge coat/wet plaster inside and silicone render outside. Is there a preferred way to go? I don’t want squeaks/mechanical fixings failing on me in the next 10-15 years.

@SimonD That's a really helpful response - thank you. Unfortunately my installers have responded with this: "As with regard to the heating on the first floor have your acquaintances any further details of the library of standards as I have spoken to Ofgem and MCS as well as our umbrella scheme and they are all saying each habitable room needs to have a heat emitter. Happy to get our umbrella scheme manager to give you a call to discuss further and she is also happy to speak to your acquaintance if necessary. This is what I have been given:" ..see attached.