Building trade usually sheet whole ceiling first, then install non-load bearing partitions and wall plasterboard.
There’s usually 10-15mm gap at bottom for ease of fitting. The joiner will use a timber wedge (with hammer of similar under) and lift up board tight to ceiling board with their foo

I’m sure you easily get <1.0 🤞

I also tell the battery software / app to charge between 11.30pm-5.30am, so that that the battery doesn’t discharge into the car during the off-peak rate.

I have GivEnergy battery and 4kW roof solar, but went with the Ohme ePod. The Ohme connects to the cars API to get current state of charge and you tell the app how much charge you want in the morning.
Intelligent Octopus pays 15p for export to grid, so no advantage in using solar to fill your car.

Could it be reflections on a foil membrane ?

Is it going to be an air-tight box ?

If you want maximum Acoustic deafening, specify passive standard windows with at least 2 or 3 seals, triple glazed with at least one pane being laminated.

I can recommend Ecology Building Society for low energy projects every time.

I agree. There is element of boosting their profit with high postal charges.
I used an Irish website 2 or 3 times to buy some tapes, but Brexit scupper that plan.

Impressive results. Well done.

Yes, inside the thermal envelope.

Yes, very happy.

There are systems that do that. Nilan Compact P is one.

Another option would be. Sunamp hot water storage battery. @sunamp.bsky.social
Works using phase change technology and static storage losses are very low. You can charge it up overnight on an Octopus 7p tariff.

Takes over 5 hours to heat full cylinder from stone cold, but we’ve run it for 2 years now without any shortage of hot water. You never need to use the whole tank in one go, even at Christmas….. when we had relatives staying.

We have a integral hot water cylinder with heat pump on top and ducted to outside air. Only need to connect ducts to outside and connect hot and cold water feeds. Simple and very cost effective.

Our Passive House only needs 6No x 300watt infrared ceiling panel heaters on the ground floor. No heat emitters on 1st floor. Peak load is 1.5kw.
Another option in low energy passive standard housing is to install a central air-2-air heat pump.