JohnMo

No it's definitely not a a DPM of vapour control. It keeps the screed from going under the insulation and stops hydrogen being produced by the contact of aluminium and cement, leading to lots of small holes in the surface of the screed. To save going so deep just dump the 100mm EPs and use 50mm of PIR instead. So you have 2x layers of 100mm PIR. Save you 3m3?

https://www.epicair.co.uk/products/ae48c-dbox-adaptor Instead of a Y piece use one of these, duct in and the other vent use the second termination point. https://www.epicair.co.uk/products/ubbink-ae48c-valve-adaptor-90-degree-125mm?pr_prod_strat=jac&pr_rec_id=e37282fe1&pr_rec_pid=4581960974424&pr_ref_pid=4581960417368&pr_seq=uniform

Buy by the lorry load is the cheapest and direct from the quarry, not the builders merchants. Bags have a bagging fee in the cost, builders merchants just get from the local quarry and add profit and a bagging fee.

I would look to use something like RockWool Flexi. It's nice and dense, easy enough to cut and squishes into uneven gaps. Plus it's not massively bad to work with. Another is Knauf Frametherm 32. Similar to above not quite as dense.

The window at the opposite side of the shower. So you have a 1200mm long shower base? From what I can see in the video your shower configuration doesn't match the instructions of the linked shower screen as that is supposed to have 3 walls around the shower? Maybe it.is and just don't see it from the recording. Is that what you have?

Looks like you have a top rail not installed - looks to be a bracket there, but attached or not being used. Is the window opening the issue?

Never realised there were regional areas, not sure I would bother using them anyway, just use the technical areas instead.

Well done retrofit with decent amounts of insulation 😃 make sure the insulation is gap filled with expanding foam and all joints are taped. Not really sure what the heating grid brings to the party though, I would delete it, replace with polythene sheet (separation between the aluminium foil and cement in the screed) then use staples to hold the UFH pipes in place.

Do you have a plot? Either way you need a design that is fitting for the location. There are several ways to go about a project and it's a balance of time, cost and value. Also of consideration is house price ceiling where you propose to build. Centre of London you can spend what you want and still make a good profit. Where we are there is a price ceiling, so we had to be careful with our design and build cost.

You take it through the house as shown by the photo by @nod. And your middle drawing (lintel). You then take it into an inspection, use the chamfer to get the drop you need. We have several chambers and drop about 2 to 3m.

Just cut a noggin to add height to the sole plate. Insert between the vertical studs. Like below

I did

Think you are over thinking things. Why do you need to tell BC anything about the hot tub? Only inform them on what they need to know - no more, no less. Your post was too long, you are over thinking a lot. Your combi needs to be in an unvented circuit, so it gets a permission to start. Get yourself a plate heat exchanger - cheap enough on eBay. Plumb your primary circuit to the primary side of the PHE and the hot tub to secondary side with a circulation pump. Use a thermostat and timer on the hot tub to heat as and when you want. Set the heating side flow temp to about 40 to 45 so you don't boil yourself. But a return water pipe stat on as well set to protect you should things get a little hot without you knowing.

That's not really the issue G3 protects against, it's the phase change to steam and the expansion of circa 1500 times and the resulting side of the house turning to rubble.

Never experienced just a single circuit tripping, normally throws the whole board off

The drawing shows the long L shaped room need supplemental heat, could see any others that do. There is a calculation sheet you can print out in LoopCad, it shows all the room by room details including what is required heat wise and being supplied and temperature and flow rate etc.

F-Gas certified is for refrigerant, gas safe is for natural gas. Not all MCS certified techs (they are not Engineers) do not need to hold F-Gas certification, so probably don't. Monobloc ASHP always come pre filled with refrigerant.

Didn't everyone just loose the will to live on this thread, to resurrect it again. @Pocster is just having fun with you.

Think you need to careful it doesn't look like an office. Curtain walling and double glass front doors leads you that direction. I would look to simplify.

Don't forget the CO detector. In Scotland you are now not allowed to install smoke detectors in a kitchen you have install heat detectors - less false activations

Wouldn't the following occur with a decent fire (likely to initiate from an electrical issue unless you smoke). Main MCB - Power trips - so the battery in fire alarm is now powering it. Home assistant off, as there is no power MVHR off, as there is no power So why bother with the automation - not sure going to do anything.

@Ozpos Hasn't visited since Nov 23. So don't hold your breath for a reply.

Is it bouncing on and off a room thermostat? Tell us how your heat pump is configured - buffer, zones etc.

I would read the manual and make sure it does what you want, think it's a pretty simple heat pump

Do you have UFH with a pump or a buffer and secondary circuit pump?