Nickfromwales

It's down to available space tbh, but I'd say it would be useful to know the possible tariffs p/kWh before deciding on capacity. You're burning natural gas which is reasonably efficient and cheap enough (you could be on LPG for eg) so this is just down to the amount of DHW that you go through. Typically I'd say a 210-250L tank would be suffice, but if the maths can be swung by a good cheap rate of electricity, then you could be up at 300-400L with dual immersions without being silly. Not much uplift for the larger cylinder and the installation costs should be pretty much like-for-like. Viessmann tech support will confirm, I do little to nothing with gas these days sorry and even less around those particular boilers. I was a Baxi and Vaillant man I'm afraid.

Won't matter, as air is usually humid for a decent % of the year anyways The MVHR duct is a sound tunnel, so acoustically it may not be sensible, but also if there is even the slightest vacuum applied to it (the ASHP fan can be going at some serious pace for DHW) then you'll pull the MVHR out of balance, as stated above. The energy in the stagnated air in the under croft would be gone in 10 mins or so, then you'd be solely reliant on sucking fresh cold / humid air in and through to get to the ASHP, so also pointless, sorry. No harm in thinking about these things, and defo worth asking

https://www.kore-system.com/insulation-series-using-eps-for-cavity-wall-insulation-applications/

I've said my bit. Based 100% on facts, and with me kneeling in water, clients effing and jeffing about dehumidifiers not even scratching the surface, etc etc.

There were 3 stories of ICF on that project (4-storey house if you count the basement), hence the choice.

Will be easier to employ one company (imo) to just do the lot in one visit?

Cheer for the clarity. Rodding points not so much of a worry, and usually just a tick-box for BCO's. AAV's defo need access or locating strategically Good that you have that in hand already.

Then you were very lucky indeed. What I wrote was entirely 'my' (clients) experience, and no exaggeration whatsoever. On both the Velox project, and the Isotex project, the uplift to get rainproof and airtight was "significant". 5 figures for each project. The Isotex was marketed as being ready to take plaster directly.......wtf?! Whilst installing the UFH I was literally kneeling down and getting soaked by a series of mini-rivers running over the sub-floor, and that was with a meticulous builder installing the Velox! Woodcrete is absolutely definitely porous, so don't expect the same results with that as you'd get with EPS (which is pretty-much rain-proof and AT by default) as you won't. I would be surprised if anyone could demonstrate otherwise, maybe not the rivers but there is no way on this earth that rain doesn't get through / soak into the woodcrete systems. I've done enough to know.

You could also use the immersion to heat the cylinder off cheap-rate electricity (overnight Octopus etc) if available? Cheaper than gas is great, but even better is going same price but zero wear and tear on the combi too!

£80 here?

Woodcrete has a boat load of them!! EPS is a no-brainer. You can with Velox, but that only solves the issues of the shape. Then you are still left with the list of cons / caveats.

That was because it would give you a lower structure that was nearly 100% non-hygroscopic. If a flash flood actually took water levels up to the house, the EPS ICF would be unaffected. A TF would have to be cut open to evacuate lost insulation / clear crud out of cavities etc, whereas with EPS ICF you'd only be replacing the bottom of the plaster boards.

If it was my house, I'd cap everything and go to the nth degree to get the actual ACH of the fabric. What is the point in doing all of the work up to that point, if a slightly faulty / leaky valve then gives you a shite ACH score!?!?!

These need to remain accessible?

They minimise airflow (convection) so would be my choice. The cavity can be fully blown, and very few gaps/cavities are left when done by a good company.

1000% the right thing to do! 👍. Tightening metal onto soft plastic is just bonkers. The insert just stops the pipe from caving in, but doesn't stop the nut and olive chewing into the plastic. If you even slightly over-tighten (or tighten as you would with metal / metal) then the olive will start cutting into the plastic of the pipe. 👎

Time is expensive, and has a specific value to the right self builder. Quick build = less rental costs.

Was the overheat recognised in the PHPP analysis? If so, what % did they give this, and was it a general analysis or room by room? I’m managing a 5% “risk” with air handling units on the MVHR for a current (certified) PH clients build. The idea being that prevention neutralises the need for the cure. This one doesn’t have a huge amount of glazing though to be fair. Yours therefore may be north of 7%which would likely mandate A/C, but as PH gives with one hand, it takes with the other. As always, there’s nothing for nothing and a compromise often needs to be struck. Was your MVHR ductwork insulated for the fresh air supplies to rooms? If you do go A/C, I doubt 10kW is massively oversized tbh, and it may be beneficial to have that headroom for cooling, with the added benefit that these will give a smudge of heating too. Most rooms / spaces which need cooling “could do with a little bit of auxiliary heat” in the depths of winter. PH is a bit of a merry dance, with the perfect balance often just out of reach.

Random internet grab = https://springvale.com/ecobead/ Ask on here for possible recommendations for installation companies.

🤦‍♂️ If elevated above the known (historic information) flood levels, then anything can be built as it will never see flood waster. Neither has to be "expensive". EPS - based ICF would seem to fit the bill, but vermin protection would be an issue, so would fire-proofing the EPS. Block undercarriage would defo be the best option here, as the flood defence/ platform, then build whatever you like on top

150mm of blown, bonded beads?

Yup. You won’t notice it in the length, only IF you walked side to side. Lay off the pop and you’ll be alright.

These would need to be hinged "flappers"

Yup. And the "slope" is sub 20mm over 900mm which only a spirit level will notice. If you fit an 1100mm tray you'd better tank the room underneath too! That is a VERY small room to not have a shower screen, even a flapper panel (or 2). Is this the kids room or yours? Doing this in the kids room would be suicide.