JohnMo

Similar tensile, A4 has a lower yield than 8.8. Stainless is also very susceptible to galling. But 8.8 is the minimum standard for anything structural, depending on exact application.

Very minimum would be 100mm of PIR, then screed. But ideally 150mm+

UFH either do lots of insulation or none, thin is the worst of all worlds. But - If you do none, you really need the heating on 24/7 otherwise the floor heat just moves into the ground and dispersed, each time you start stop you waste huge amounts of energy. Simple, do low temp radiators. Get a decent boiler that will do priory domestic hot water (PDHW), this will allow boiler to run high temperature for DHW and low temperature for heating to get optimum efficiency. If you are getting a new cylinder, get one with heat pump heating coil, this will reduce heating time of cylinder and again also get efficiency from boiler. Or get a heat pump connected to max 35 deg flow temp system.

Stainless steel screws in aluminium is another corrosion issue waiting to happen. The stainless steel is using the aluminium as a sacrificial anode.

I do have a legacy UFH manifold controller with room sensors. It's connected to heat pump, a simple standalone timer to immersion, and standalone PIR sensors to various outside lights. The other automation I have is related to battery, but that is via the GivEnergy portal to control charge times. Home assistant is used but as simple monitoring tool, it has 2 automations, one to collect solar forecast, the other to tell me if PV generated is behind forecast, so I can check to make sure nothing has tripped off or panels aren't dirty. Nothing that actually matters if they don't work.

Are you using stainless steel fasteners or structural elements? Are you in a high chlorine area (directly next to or on the sea)? Are these elements exposed to a salt spray or chlorinated air atmosphere? Do you have these fasteners or structural elements exposed to above ambient temperature conditions? If you answer no to all the above - no issues. If you answer yes to all of the above, you have issues to address. Stainless steel has zero place for structural elements or fasteners in almost all situations.

Have been in his man shed?

Home automation = hours/days arsing about, to save seconds or maybe even nothing in reality.

These are 402mm long https://www.shop24glasgow.co.uk/en/windows-accessories/836-manual-trickle-vent-vt600.html

First hit in Google https://www.bpdstore.co.uk/glidevale-energy-saver-humidity-sensitive-trickle-ventilator/p/182

There's your second issue, not just ventilation, no heating.

But when air is heated the dew point moves. We have a heated summer house it has dMEV fan, humidity inside hasn't been above 40% for that last month. We have bearly had a dry sunny day in the last month humidity outside closer to 100% most the time. Are you heating the house?

Making chlorine - rigs make chlorine and add to the cooling water - this is generally seawater. The chlorine is to kill stuff and act as biocide. Otherwise you get mussels etc growing within the heat exchangers. The chlorine makers take seawater, the by products are highly corrosive, the off gas from the process is hydrogen. Generally chlorine making is a very simple, but at the same time a very unreliable process.

It is routinely for offshore rig and ships, it uses plastic and titanium components.

But not in a warm chlorine environment, still not good enough.

Yep

PIR detection, they will pick up heat from the car. Works well with my driveway lights. Doing it that way may be too easy, if your going to add another layer of complexity via Loxone

Don't move to Scotland then - mandatory for better than 3 to achieve building sign off! The mechanism is building regs.

You can go down the easy route - if you don't have proven airtightness don't go MVHR, you are just chunking money away. Smart dMEV. Change the trickle vents to humidity activated one, but only in dry rooms (bedroom, living room etc). Seal up any in wet rooms. Install Greenwood CV2 or CV3 fans in all wet room including kitchen, set fans to smart humidity control. This system will run fans at a low rate 24/7 and automatically boost when needed. The trickle vents will respond to room humidity levels. All internal doors need 5 to 10mm clearance at the bottom of the door.

I moved in prior to completion, no 3rd party trades expected after that date, got normal house insurance and declared all the work to be done.

This is what it looks like lagged

All depends how you buy and install. In Scotland, we have no option, if you are better than 3m³/m² airtightness, balance supply and extract is mandatory, so cost and and or pay back isn't a discussion. I would (did) buy from eBay, for pennies in the pound. Then (didn't do) do the supply just like PIV, inject air or most of it in a central area, maybe in an odd supply terminal for odd areas where through ventilation doesn't work in your layout. Then extract like MEV. Minimal ducting, minimal terminals, good air quality, billy bonus heat recovery. CO2 not CO, CO carbon monoxide kills you.

When it was finished - so when you have a completion certificate. Without that it's not home, it a build in progress. Where is the confusion?

When we did similar - some years ago, we had weekly site meeting where progress and financial affairs were openly discussed. Either myself or my wife were always in attendance, these meetings were all minutes by architect,with us approving minutes. No work was progressed until fully priced. Variations always come and bite you. Push back if not in agreement, get them line by line itemised, don't pay until happy.

Are you trying to use a hybrid inverter in wrong situation - it's designed for grid connection - you don't have one. Isn't the correct inverter an off-grid inverter?