ProDave

And what is "wrong" with 200mm pipe spacing? Care to post the design?

And my other, trying and failing to sell our old house in a depressed market, resulting in a "plan B" a 6 1/2 year very much more hands on "self build as you earn"

More of a concern to me as someone with only weak 2g phone signal at home, is will the 2g switch off mean they finally get their finger out and give is 4g coverage? Or will we be left with none?

Hi and welcome to the forum. Plenty with health issues self build though obviously not full hands on. You plan is good, your idea of budget sadly is not. £100K might get someone to build and erect a timber frame but that is a long way from being a habitable house. With the recent rise in materials cost allow £2000 per square metre for a finished house. The economics are not always in favour of a self build, it is more about getting the house that you want built how you want it. Going forward that should also mean very very well insulated and air tight etc so you get low running costs. Edinburgh is probably the most expensive part of Scotland, others will have to advise where you might find a sensibly priced plot within an hour. Start by looking at https://espc.com/

Re UFH in the original house. You have limited headroom and you NEED at least 100mm of insulation under the UFH so your only option is dig up the present uninsulated concrete slab, dig down further and re lay with proper insulation under it.

What you are seeing there is a woefully poor lack of design and lack of detail. the rafters are probably supported on the wall plate on the inner leaf of the wall, something is supporting them, they are not just levitating there. That is the least of your problems. The way the insulation is fitted, it might as well not be there. you need to ventilate the gap between the rigid insulation and the roof deck board, but you DON'T want to ventilate the space under the rigid insulation and what looks like a poor bit of glass wool insulation below. To make the best of a bad job you want to seal up underneath the rigid insulation so that the necessary air vents in the soffit board only ventilate the space above the rigid insulation. so the space between the rigid insulation and the wall plate needs to be completely sealed, and when the soffit board goes back it needs vents at the top to vent the space above the insulation.

^^ the above 2 posts give me no confidence you know what you are looking at or trying to achieve. Be VERY careful. Yes there can be a lot of wires the same colour in a light switch or a light fitting. It is important you identify them some way before removing a switch so they can go back as they were. I have lost count of how many times I have seen on a forum "I removed the old light fitting. I now have 4 red wires and 4 black wires, which one goes where please?" It sounds like you have neither loop at switch or loop at light but all cables connected from a BIG junction box, and at the rime that used to be common, it was common practice to just twist all the earth wires together outside the box, sometimes over the top to make it impossible to even get the lid off.

I would definitely use twin wall flue right from the stove, otherwise a single wall flue is likely to end up too close to the flamable walls so would require heat protection all the way up the walls. My finding with the cheap little stove in the caravan is the flue gets very much hotter than the quality stove we have in the house. Probably a measure at how poor the cheap stove is at putting the heat from combustion into the room and instead a lot more heat goes up the flue compared to the more efficient quality stove we have in the house.

Small air source heat pump driving wet under floor heating, will be about 1/3 the running cost compared to resistance heating. NO problem with wet UFH under engineered timber floor. It depends what you want, cheap install or cheap running cost. I would say the way energy prices are going cheap running cost is most important.

MVHR is the way to go. It is constant ventilation you want (with a boost speed when showering) Just get the smallest unit you can find, fresh air into living room and bedroom, exhaust air from bathrooms and kitchen.

My ASHP is an outdoor monoblock unit but I still have the noise described. It is the circulating pump and the water circulating in the pipework and the noise can be heard anywhere where there are pipes above or below the room. It is not very loud but I am very sensitive to noise especially at night in a bedroom. simple solution. set the timer so the heating is off at night. In a well insulated house you will not notice much temperature drop over night. And changing the circulating pump for a quieter one (Grundfoss or Wilo) will also help.

And just how do you propose to tape the membrane to the inside face of plasterboard? And if you manage that every switch and socket is a hole in your air tightness. The results will be poor. Do it properly, membrane the entire wall, battens to form a service void then plasterboard all nicely inside the air tight envelope. That keeps all your wiring sealed inside the air tight envelope.

Right at the front of the side wall would be my choice, i.e. facing about south west. I think sun does make a difference, certainly here, when we get a cold spell the north side of the house becomes a permafrost in winter but the south side is definitely very much warmer, so probably less defrosting issues. And although it may seem controversial to put it almost in the front garden (actually the side garden I am proposing) people tend not to spend time in their front gardens so it keeps any noise away from yours and your neighbours back gardens.

Who sized the GSHP at 12kW? If that is correct then an ASHP would also be 12kW. There are reported shortages of ASHP's as well so best of luck. some suggest the last gasp of the RHI is producing a demand peak to get systems in before that runs out.

The membrane is your air tight layer, why are you wanting to seal it to the inner face of the plasterboard? Normally the plasterboard is just something that happens to be inside the sealed envelope of the house.

200mm for me as that worked out nicely with 400mm joist centres. Works very well.

That link does not work for me. That might be because I am not (and don't want to be) a member of facebook.

Ovens don't actually use that much power, typically 2kW for a single oven. It is hobs that draw much more power. If you feel more comfortable and future proof use 4mm or 6mm for an oven feed, nothing wrong with being too big.

I would suggest something like paving slabs on top of your frame as the hearth. Cheap and some are quite good looking. Line the 2 walls into the corner with some cement type tile board stood off slightly on spacers and tile them with ordinary wall tiles. Get an IR thermometer and on first burn see how hot the adjacent wall surfaces get and add more protection if anything looks to be getting a little too warm. I forget the exact measurements but the hearth is supposed to extend about 400mm in front of the stove.

This is the one I fitted in our static caravan It does NOT comply with building regs, it was just something I did the best I could. The hearth does not extend far enough in front of the stove for a start. We used to keep a cheap tough mat in front of it to protect the carpet. The stone sides and back are to protect the timber cupboard and plywood wall covering, and there is an air gap behind both bits of stone, not easy to see in the photos. These were some offcuts of stone worktop I got from freecycle years ago in the principle they might come in handy some day. This was a very cheap stove from the internet, not one I would use in a proper house, but it served us well and we managed not to set fire to the caravan.

11 hours towing the snail only stopping for fuel and comfort breaks.

That is only a ridge board at the top, so you WILL need to retain the "ceiling" height beams that span wall to wall. They stop the roof sagging and pushing the walls outwards. A structural engineer might be able to come up with a scheme where some are removed and some remain, but you would not want to try anything like that without professional input.

Lightweights. Try doing Oxford to Inverness in one journey towing a caravan.

If that is a major factor in your choice of unit, take a minute to think why. When I was doing my system I had much the same debate, and a learned forum member concluded that if you have treated mains water and if you have an unvented hot water tank, then there really is no risk of legionnaires as the water treatment plant will have eliminated any that might have been present and there is no way win an unvented tank for anything to enter. Hence I heat mu UVC to 48 degrees with the ASHP and the only time it gets any hotter is when there is surplus PV generation diverted to the immersion heater.

I think the theory is the stilts it sits on are not part of the building. He discussed it with his BC and agreed if you got a big enough crane and a big enough low loader, you could pick the whole thing up in one piece and put it on the low loader. The low loader would never get up the slope and out of the gate but that didn't seem to bother anyone.