Temp

What about drilled piles? Thought they weren't too bad for vibration. https://www.self-build.co.uk/piled-foundations-explained/

There are plenty of conventional programmers available from the likes of Honeywell they might find more familiar?

Im not very familiar with the Hive controller but isn't it App based? Are they young enough to cope with that? Won't find it too confusing? Youtube has guides on how to install hive but it's not necessarily straight forward.

What problem are they having? Is the existing controller faulty or are they just having difficulty working it? That thermostat is pretty crude. A small turn of the dial can change the temperature several degrees. Is it possible they are just over controlling it?.. too cold.. turn it up.. too hot.. turn it down repeat?

I should have quoted the next paragraph as well...

Has weight per square meter.. https://regaltiling.nz/tile-selection/tile-weights/

Yes. No you should get it ALL back as its been empty more that 10 years. https://www.no-use-empty.org.uk/advice-and-guidance/property-tax-and-vat/reduced-vat-schemes/ However its important to pay any trades the correct VAT rate. If they charge you too much VAT (eg 20%) you cannot reclaim that as you should not have paid it in the first place.

As its been empty >10 years you can do it all yourself, none of it yourself, or any combination in between.

Class Q does include the land (but there is a but).. but most of the sections/classes that allow people to add extensions or construct outbuildings etc have these words.. So in short getting Class Q removes a lot of what would normally be Permitted Development on a regular new build or conversion done under Full planning permission. You cant even add a patio, porch or oil storage tank without planning permission. Planning permission isn't normally needed to convert an outbuilding to a gym or similar that is incidental to the main dwelling but I'm not sure which Class it comes under in the GPDO. Probably Class A but that also has the same words as Class E above. Its also worth noting there is completion time limit on Class Q.

VAT708 section 5 covers the rules for zero rating the sale of a bulding, but it also has this on what evidence might be required which I expect is similar for self builders..

My understanding is: 2 Years - Contractors should charge you 5% VAT under section 8 of VAT708. I believe that's the only provision. I don't think a self builder can reclaim the 20% VAT he pays on any materials. The 5% paid to a contractor cannot be reclaimed. 10 years - VAT paid by a self builder can be reclaimed using Form431C. I'm not 100% sure what rate contractors should charge you. I think its treated the same as a conversion of a non-residential building, in which case they should charge you 5% and that can be reclaimed.

+1 The form.. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1110167/VAT431C-form-and-notes_22.pdf Whats the planning status?

Just remember the £30k limit on section 75. If the total order value is over £30k you aren't covered. Not even the first £30k.

Perhaps make up a small batch from bagged materials and see how much area it covers, then you know how much to order for the rest.

Some LED floor standing lamps similar to this one have the transformer in the plug. Sould be easy to insert that flat cable between the plug/transformer and the inline dimmer. Just check the output current from the transformer is less than about 6A. Should be written on it. https://www.lampandlight.co.uk/design-floor-lamp-black-incl-led-5-lights-sixties-trento?gclid=CjwKCAjwitShBhA6EiwAq3RqAxrQv_uHGA7xh7eJau_drOi1TLmbuqe7-_emfq462tk7ppOMRcMqixoCTj4QAvD_BwE

+1 Perhaps the super thin cable in the OP could be used. Eg Cut off the plugs and use it between transformer and lamp. The spec says it's ok for 1500W which at 240V is about 6A. So should be fine for 6A @12V or about 70W. Plenty for an LED. Perhaps fit a suitable fuse on the output of the transformer.

No Earth in the cable? Insulation must be extreemly thin if it's only 0.9mm thick overall.

+1 If you have to keep topping up the system pressure that suggests water is escaping somewhere. Either out of the PRV or a leak. I know you said the PRV has been replaced but PRV can be a bit temperamental. If they let water out once for any reason they can often start dripping or letting water out at less than the rated pressure. Perhaps put a plastic bag over the outlet pipe for 24 hours and see if it collects any water. If its not the PRV I think you may need to start isolating and pressure testing parts of the system to narrow down where the leak might be.

Most conventional shower mixers can be serviced through the front plate with no need to damage tiles.

Presumably he's not going to fully fill the foundations. Most likely he will pour a slab over the whole bottom of the pit or dig deeper trenches around the edges. Then build up in blockwork and install a suspended floor. You might prefer a Beam & Block suspended floor with insulation and screed on top rather than a timber floor, especially if tiling any of it. Ask him what his plans are.

Whats what I did. To stop them falling over before the concrete set you can fix them into some wood beforehand and just push them in until the wood is on the surface of the concrete. Put scrap waste pipe over them once set to avoid impaling yourself if you trip over. My bolts were long enough to go up through two courses of brickwork and the wall plates. I made them from threaded rod and nuts. Don't leave it too late to install them as I found the concrete set up faster than expected.

There must be some calculators online.

I think the membrane approach is best. If it had to be PIR I wondered if you could shoot long nails right through joists and into the side of a PIR block to holding up. Then foam any gaps. Might need a slightly different solution for the edges of the room. I can think of a few ways to fix battens under existing joists without needing to fix up from below.

I wondered if it was possible to make your own insulated "blocks" from thick sheet insulation.

I can't quite remember the spacing but it was a match for the width of the UFH panels. Eg we fitted one batten then one ufh panel then the next batten so they were no real gaps or over tight panels. Yes feels pretty solid.