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What size are the floor joists going to be? If you know that you can use span tables to work out the max allowed unsupported span. This ignores the issue of them sinking into the ground though. If you decide to use fewer blocks than option 1 then don't do option 2! Put the rows of blocks the other way so that every joist has three blocks under it. As currently drawn some joists have 4 blocks and some have none at all.

I would try the engineer that did the previous one. He can probably just reissue/reassign the previous one to you for a modest fee rather than the full cost. Try asking Building Control if they have a record of it?

If we assume 2.4m ceiling height that's a volume of about 468 m^3. 60L/S is about 216 m^3 per hour. So the ACH works out at around 216/468 = 0.5 ACH. https://www.epa.gov/indoor-air-quality-iaq/how-much-ventilation-do-i-need-my-home-improve-indoor-air-quality To achieve 0.35 ACH you could reduce the flow rate to 60*0.35/0.5 = 40L/S 15 cubic feet per min is about 7 L/S. So 40L/S would be ok for 5-6 people. It would seem that's OK.

Photos in here and your comments suggest its the wrong way around.. https://www.beneathheat.co.uk/uploads/1518187003_Beneathheat Installation Guide 2017 Proof.pdf I doubt it will affect the efficiency of the system but it might affect the life of the loop actuators and noise if any.

I put Fernox F1 in our oil fired UFH system. I think sludge from corrosion products is less with UFH than rads but still don't want it.

I reckon it will be OK.

Think you might be confusing units... I think the recommended level of air tightness on a pressure test is ideally below 3 m3/(m2*h) measured at some pressure which I forget. The ACH figure is what your MVHR is designed and set to deliver. I think its normally less than 1ACH. Passive houses 0.7 ACH I think? So I think you have it set too high in the spreadsheet. Someone else can correct me if I have those numbers wrong.

If you don't have expansion gaps in screed at doorways I would use some sort of isolation mat before tiling. It's not enough just to have a gap in the tiles because any crack in the screed most likely won't be straight, it can curve into one room or the other.

Are building control are involved? If so best not tell them that the new render has insulating properties as they may want the upgrade to meet better standards than can be achieved without EWI or IWI.

I think Quinetic claim to be the first with battery less switces?

+1 I was really replying to the original question about choosing a gas boiler.

I don't think there are any building regs issues other than the height of the floor.

I don't think it makes sense to put hydrogen into gas until the electricity grid is using as much renewable energy as possible.

Nearly all gas boilers can run on a mix of hydrogen and gas as well. My guess is that _if_ hydrogen is used at all it will be just a few percent perhaps increasing over many decades like we have done with E10 biofuel.

The installation instructions appear to be online.

Normal recommendation is to allow about 1 day per mm thickness. Think you are at about 45 days? How thick is it in the bathroom and can you remember if the screed was very wet when it went down?

If planning to replace with a larger building make sure you have applied for and received the CIL exemption for self builders. Starting work before you have that can mean loosing the exemption.

The electrician should check to avoid drilling into joists when planning exactly where the spots will go. If he has any sense he will have taken photos or marked a plan previously. When he drills the plasterboard it doesn't usually damage the wire because the wire moves offering no resistance. That and a bit if care is usually sufficient. Then he reaches through the hole to find the wire.

Welcome to the forum. I'm not an expert on insulating render but there are limits on how effective any thin insulation can be due to the basic properties of materials. Aerogel is expensive and not easily incorporated. PIR is probably second only to Aerogel and typically 50-60mm is needed used to achieve only reasonable u-values. If building again I'd be looking at 100mm+. So don't expect miracles from any render alone. Is it a cavity wall or solid wall?

We have a 12mm step from the landing down into the bathroom. Hasn't caused any issues at all. We have a narrow strip of wood with a 45 degree chamfer on it at the transition.

I doubt it will be an issue on walls. We have a relatively low ceiling in our bathroom and have had mould on ceilings radiating out from the shower even with MVHR (but no extractor fan). Zinsser paint sorted the problem.

Be careful if looking at plots without any planning permission. You have to wonder why it doesn't have it. There are scammers about.

If possible try connecting the TV direct to the router. I don't think it will make a difference but rules out any issue in the switch.

+1 If the neighbour is happy with your plans you don't need a formal PWA agreement. I think there is a template letter they can sign to agree drawings. I wouldn't go offering any other deal as might complicate any insurance claim. Insurance companies dont like it when clients make offers before they get involved.

No but I think most (?) smart meters installed rely on 2G and cant use 4 or 5G at the moment. Anyway it looks like the smart meter program is going to have to pay to keep 2G going.. From that first link which @joth posted.. . So it looks like the smart meter program can insist 2G is continued until 2033 but they may have to pay for it to be maintained.