Wil

Thank you for the advice, much appreciated. I’ll discuss with the contractor tomorrow if they can give assurance on the quality control.

So that would be 100ish hardcore, sand, concrete(how much?), 150mm insulation, plastic membrane, 60mm screed with UFH pipes?

Realistically, every little helps. That’s a useful breakdown, thank you- I’ll discuss with the contractor who’s bidding. A couple of questions if I may? In my spec above it looks like there’s a vapour layer over the insulation with a damp membrane/ radon barrier under. Is this second barrier necessary? I was imagining pinning the UFH pipe to the insulation direct with the concrete and reinforcement poured directly on top (or even follow the spec and tie to the rebar). Does 100mm concrete differ from 100mm screed poured?

I lied- here’s the spec- it’s 125mm concrete and much more hardcore/ blinding:

Hmm spec for my retro fit floor is hardcore and sand 160mm. 200mm PIR. 150 concrete. Pipes in the concrete. Tiles likely on top. Sounds like there are options to cut 50mm off the concrete at least. So useful post. The 200mm was me insisting on exceeding BR, architect and contractor not keen. I have a QS cost for rates of digging I can try and find if useful.

@JohnMo My goal was to limit/ avoid peak electricity use hence the batteries as the buffer to allow for the sun going behind a cloud etc. If I let my ASHP (18kW 3phase) take the solar, I can’t guarantee it won’t pull way more than the solar can give. Once it starts the HW cycle I don’t want to be faffing in and out- hence just let the immersion go (it can also go much higher). I went for the 3kW immersion at 3kW as it avoids complication and the batteries are more than capable of buffering that. My issue is the ASHP is huge so can eat the batteries pretty quickly at full chat. This hopefully wouldn’t be an issue on a more modest system

Agreed! my 5kWp system facing south only managed 5434kWh in '23. 4622kWh so far this year!

Yep, I’ve got one of these controlling the Cool Energy Reverso unit I’ve got. Works well enough and integrates with Home Assistant ok. You can have it in auto or always set to one speed so leaving it on minimum means noise isn’t an issue.

Just for completeness, I email Megawave about their FCUs and got the following data sheets if anyone is still considering them: I haven’t gone as far as an order. FCU Data.pdf MWES Concealed FCU data sheet.pdf MW Free Standing- FCU（DC motor）manaul 23.6 wifi 1.pdf

This is a brilliant thread, thanks to @Rob99, I rang National Grid and they created an export MPAN for me today (my solar and batteries were registered with them previously). Now the key question is- will Octopus take just an export MPAN or do I have to produce all the MCS malarky still? Watch this space when I try tomorrow….

My version for the OP is: I use HomeAssistant in the middle of batteries and solar and ASHP. I have 3phase heat pumps, single phase immersion in a 300ltr UVC. 5kWp solar and 26kWh batteries. ASHP is set to 24/7 keep the tank above 48degrees. Batteries charge overnight on cheap electric car tariff, bit of morning usage knocks them down to approx 90%. 2x grown ups shower in the morning pre-solar, 2x kids in the evening, post-solar. If sun comes out during the day, solar boosts batteries back up. If batteries change above 95% and solar >500W (just a check to make sure the immersion doesn’t come on when charging batteries at night with cheap rate- if the batteries go up during the day it can only come from solar) then- I turn the immersion on (limit stat set to max). It heats the tank for 1hour or until the batteries drop under 85%. If the immersion is on and batteries hit 98% (solar still > immersion) I turn the car charger on. Then boost the ASHP buffer tank. Until it all drops back to 85% battery and I let the batteries take the solar until it hits 95% and kick off again. If the sun doesn’t shine enough, the batteries hold my house load and if the tank drops below 48, the ASHP kicks in to top it off. TL;DR Basically use the batteries as a diverter for solar to immersion. Forget complicated 3 phase or trying to use the ASHP. Let the solar pump the immersion and take the tank to max (about 85dC in my case- make sure you have anti-scald fitted!).

oops, wrote this and then logged off for a week! Craig- we've changed the infill panel above the door to solid to put a beam across horizontally. This will form a small overhang/ porch over the door and split the glazing into 2 sections- this should be plenty to avoid deflection? Updated elevation here: Although not sure why the architect has chosen to split the glazing above now! Need to get that line taken out. Should make two fairly even 2.4M panels. @SBMS We will clad the spandrel and cap it in Aluminium or similar for the rain. Will match the top beam detail.

I thought the idea was to keep the bottom of the joists exposed to the external air so that the cross flow could/would remove any chance of moisture and rot? If you encase the joists in PIR but the ends are still in the cold wall isn't this exactly the worst case to be avoided? I have slightly deeper floor voids. probably 500mm under the joists but can't see why I can't just 'bung' the vents and then fill the void with micafill or similar non-wicking insulation up to full depth of the joists? I've seen it posted on other sites but it seems to be held as a no-no and I can't understand why compared to putting insulation under and on top of the joists when you still can't do anything about the cold ends in the walls?

We're having exactly this debate with our double storey infill (3). We've introduced a central beam across above the door (where 3 is marked) which will give a covering over the front door and split the glazing in half top and bottom. old plan below. The two stone gables are existing and we're retrofitting the entrance lobby and the single story extension and replacing all the glazing for simpler more modern.

HA runs on an old laptop so a few hours of battery life. House and all automation runs off central batteries, so only the tripped circuit is lost. It's definitely worth knowing if the smokes have gone off. Someone on here connected their Aico alarm relay to a shelly which is great. With a shelly pro (ethernet connection) it's even more reliable. Of course if the fire isn't extinguished and you aren't there- knowing about it is a bit of a moot point.