ProDave

Your stove flue should at least continue up into the ceramic flue above the slab and be sealed with a closure plate.

Build internal walls of timber and plasterboard. Then only supporting walls will need proper foundations.

Ditto to above. You want simple and reliable, then old fashioned hard wired light switches like we always had.

On mine the axle is just a tube between the 2 wheels and I lifted on that and put the first two supports under that. It was well balanced on the axle. It is not an officially marked jacking point but it is certainly strong enough. It won't tip up or move because you will have it hooked to your cars towball at that point won't you?

Here is what I did: some basic points. It will weigh something like 3 tons. So you need a good stable jack, I used a 2 ton trolley jack, much more stable than a bottle jack. They don't have brakes on the wheels, so nothing to stop them moving. To prevent mine having any notions of going anywhere while I was under it jacking, I kept the tow hitch attached to my Landrover. For support I used ordinary 100mm concrete blocks on their sides. You will also need plenty of small pieces of assorted thickness bits of wood for the final packing to get the heights right. Start by levelling the axle. Jack up one side and pack it with blocks then the other side. You need to get the axle level side to side as your starting point. I just used an ordinary spirit level on the floor of the 'van. These first supports only need to be high enough to just get both wheels off the ground. Once the axle is level and the wheels are off the ground it won't go anywhere so uncouple from your car that was acting as an anchor. Now use the jockey wheel to get the 'van level front to back. Then it is a case of blocking and levelling each jacking point. Starting with the ones at the extreme ends and then all the ones in between. I think I ended up with 12 piles of blocks and timber supporting mine.

All your plans show blocking direct access from the hall to the new kitchen. I would not want to have to go round through the living room all the time to get to the kitchen. If the "Sewage hole" (you probably mean inspection chamber) is in the conservatory then you probably have some drainage relocation and re routing to do before you can build a proper extension.

When buying my velux windows I was on a tight budget at the time and did a similar sum, and the energy saving on such small windows would never repay the extra cost in my lifetime so I chose doubles.

Turn ALL GF thermostats down. That should shut off all downstairs loops. And will also test my question, does the upstairs manifold continue to work and does the ASHP continue to work.

Then it should all work. Are you SURE it has been wired properly so when all downstairs rooms are up to temperature and the downstairs UFH controller is off, does the upstairs UFH continue to run and most important does the ASHP continue to run? Agreed some balancing needs doing, but apart from different rates of heating at the moment it should work.

You mention it "clicks off" at 23 degrees. Is this a room thermostat if so where, and is there a separate one upstairs and downstairs?

True, but that is probably a morning problem. Someone flushing a loo and the cistern re filling on a wall joined to yours can happen any time of the night, perhaps more than once in the night. so i would avoid at all costs a WC and it's cistern on an adjoining wall. If you can avoid a shower on an adjoining wall then do so, in this case the pipework and shower head (water flowing noise) could be on the external wall not the adjoining bedroom wall if you swap bath and shower positions.

Bedroom 4 and bathroom is not so much of an issue. The WC is shown on the wall adjoining the void and it is the WC flushing and re filling that is the biggest issue. So with that in mind, re think bed 4's en-suite layout so the WC is NOT hung on the wall adjoining Bed 3 The fact we are discussing such details shows the basic design is pretty good.

For some bedtime reading look at this thread Where he bought a large derelict stone house and has gradually rebuilt the stone outer structure and built a timber frame house inside it.

It should have been drained if not used over a winter. It it wasn't, your first job will be find and fix the leaks. (guess how I know that) Assuming it has been drained, as above connect the water, flush it through and good to go.

But that is 9 metres away and if the blockage is downstream you will need 30M of rods. I am sure BC wants rodding points closer than that?

I suspect you would want a new IC right next to the existing 450IC so you have rodding access.

No we didn't make new holes in the steel, we worked with what we had. Fortunately I knew the plumber well so we could decide what had to go through the steel, i.e. how tap pipes as runs needed to be short and some high load cables for the same reason. I routed a lot of the smaller and less demanding cables via a longer route to avoid the steel. The point of my post was if only someone noticed while the crane was there installing the beam and got it put in the right way, it would have been a lot easier. Or just drill a row of holes all along it at manufacture so it would not have mattered. I do know about where and how big to drill holes in joists but this I learned from self building. As is evident looking at any older house most trades are not routinely told this.

Holes in steels is an important one. One house I wired the designer had specified several holes in the steels, but then installed one steel was installed backwards, so most of the holes were at the wrong end, leaving just 2 useful holes in the beam separating 2 ends of the house for me and the plumber to fight for to route our cables and pipes. If only someone had read the drawings and checked when being installed, that beam could have been put in the right way round.

Just what are you using? We spend £1200 pa on electricity including all heating and hot water (ASHP) I assume your house had the panels fitted under the old FIT scheme, so you should be getting a quarterly payment for that, if not ask your solicitor about it and why not? Best way to self use it is a diverter to put surplus power to the immersion heater (assuming you have a hot water tank not just a combi) and to use all the big appliances like washing machine etc in the middle of the day.

Flex outlet plate, would typically be used for a heater or similar in a bathroom and the power switched from a switch on the wall outside the room.

I think it can even vary between one BC and another. if @Robert K would come back and tell us where he is and what system he has we might be able to advise him further. Until then we are guessing.

I don't think you would be in Scotland if discharging to land. We only needed one to discharge to a watercourse.

No that would be a SEPA licence and BC in Scotland would not have issued a building warrant to start until that was in place. EA covers England and Wales.

With the caveat you do just that, maintain and repair it, one bit at a time. Don't dismantle the whole thing expecting to then replace it without at least getting a certificate of lawful development first.

On the point about filling, you should fill the tank with water as you backfill the hole, keeping the water level in the tank level with the backfill. Our previous house we had bad advice from the installer and that tank is just backfilled with gravel. It is okay if you ONLY have it pumped out in the summer preferably after a long dry spell when the water table is low. It could end very badly if pumped out in the middle of winter. we made sure the buyers of the house were aware of that.