Nickfromwales

Fit it and say feck all. I doubt anyone other than the next door neighbour, if you've pissed them off, would ever pull you up over it. If they do, just go for a retrospective amendment to get it approved. This country is an ass!!!!

If you don't ply, you'll be re-tiling 6 months later. Tile adhesive does NOT take to the P5 chipboard at all. Main source of my income for about a decade, doing insurance work repairing such shoddy (and subsequently failed or failing) work. Stop guessing!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Even with normal concrete it can be a nightmare. Most are simply too keen to get the wagon emptied out, so the next one can back up and empty that too. No time for the slump to be properly checked unless you're ferocious in insisting this gets done for each wagon. And then, if it's not right, you need a plan B in place ready to effect.

315mm of 'slab' to heat...... I think you should reconsider this, as cooling via your slab wold be quite a nice thing for the summer months. Is it a Heb home? Or independant?

It's not hate. It's a pragmatic discussion involving some strangers on the internet I just doubt it's necessary, and my advice not to DIY is caused by the shiver that goes down my spine when someone, as a complete novice, thinks that this product will in any way make this easy or 'lay itself'. Regular concrete and a dapple bar, a home-made one at that, will be all that's needed. (IMHO).

I'm against the 'magic' stuff btw, and I've seen enough concrete pours go tits up to know it's not a job for the feint-hearted or uninitiated.

Yes, very. Clients architect spec’d it to go around the subterranean parts of a walk out basement, and I remember them raising an eyebrow or three when the builder quoted for the quantity needed. I still think two layers of EPS would have done the job perfectly well, but their architect and SE were setting fire to money at an extraordinary rate of knots, and what they came up with was usually a pile of shite. Foamglass wouldn’t take kindly to being compacted either.

Thanks for this Will be very helpful to anyone who is stuck with the same issue. Any chance of an RS part number please?

Of all the places to have a go, this isn’t one imho. If this goes wrong, it’ll be spectacular. Having any pour is manageable, but if you take charge then you accept full responsibility and liability, and can’t look to someone else to redo it at their cost if they feck it up. I doubt the cost saving vs risk makes any sense here whatsoever.

👆. Airtightness is of paramount importance, eg more than just draught-proofing it. I’ll not fret about the planning etc, thats another subject but i assume it’s in hand. A demountable building escapes these constraints as per @Crofter’s cabin / hut build. @Waterworks, have you read that thread yet? This will need a portable genny and some solar PV, and probably a leisure battery as anyone staying there all year will need even basic cooking facilities and hot water / fridge etc?? Fridge and hot water can be done via propane, a-la a camper van, and ao could the heating. Gas is defo a major help here if it’s off grid and you need to be as least reliant on electricity as possible. Going to need some power from somewhere unless you’re going full on Neanderthal.

No mains electricity

Anything’s possible / doable with the right people and mindsets. You may have to pay them for dead time, and latex in 2 sittings. Latex the whole area up to about 300mm away from the fridge, and then lay 60% of the LVT. Cover an area with 4mm hardboard, then sit the fridge on it. Then latex the remaining area, block the joint and smooth it out, and then lay the rest of the LVT.

Every stroke of the 'pen' has been considered for my current client, a plot on the highest elevation in their locality, which includes mitigation of the noise of water dripping from the window heads on to the metal that forms the window sills below; nothing worse than the 'Chinese torture' of a single drop of water hitting a window ledge like an annoying metronome. I've recommended installing sound-deadening 'killmat' to the underside of each of the sills before installation, to prevent such annoyance. Folk just don't know what their next (albeit preventable) enemy is going to be. That's where I come in lol. One look at the section for the above roof, and I would have said "feck, no!". Simpler to solve when it's on paper or a screen, where the drill and hammer are the left and right clicks of a mouse.

You roof leaks. My thoughts are, that your well regarded builders have made you a house with an indoor irrigation system. That's a pile of shite. Get them to come back and remove this optional extra, end of. I was referring to them being further out, not further up. They are defo way too far 'in' as shown in your first pics. Sorry, but it looks (and preforms) like shite. No dice.

If we were giving out trophy’s for opening one’s mouth to change feet, @Benpointer would need a bigger mantelpiece

You can’t wet plaster these reveals in, over a modern cavity / cavity closer, so your example of a 60’s returned masonry reveal isn’t apples for apples re the OP question. For your job the advice would be different again.

If you need to cover 100mm then you’d be looking at minimum 2 runs of 60mm tape to do that, I’d go 3 for robustness and to give a decent overlap. You can buy thicker tapes, but you just end up trying to buy the right thickness tape for xyz locations and as a contractor it just isn’t economical. Wider tape costs more than narrow tape so 🤷‍♂️. Yes, self builders are mostly all loonies, so I am making plenty of adjustments lol. Sand and cement doesn’t really parge well, unless you mix a bit of SBR in and get the consistency perfect each mix, then it still goes quite granular as you spears it out and the masonry almost immediately sucks the moisture straight out of it. Then it’s like making thin sandcastles on vertical surfaces, give it a go if you wish, which is where you will thank me. I accept all major brands of beer / IPA. Remind me are you using AeroBarrier or just tape / foam / parge / liquid AVCL? Are you saying you’re going to spray the whole house interior with liquid AVCL??

Yup. Let’s be honest, if you’re ‘accessing’ the plywood you’ve smashed all the tiles up and binning them so are ‘all in’. If you want the tiles to stay down, you go ‘all in’ on the installation and enjoy the longevity. You could always fit 27, randomly positioned access panels on the ceiling downstairs.

I just don't like the brittle nature, and I've done UFH with P5 + plywood so many times with great results, I just don't want to change. If it works, then happy days, plus the plywood conforms to the floor shape / undulations, whereas cement board will just snap or fracture, no Bueno afaic, sorry!

Who are the intended occupants, and what are they going to do in it?

Go for spreader plates, but allow some rockwool under them, atop the PIR, so the plates are sprung upwards slightly. Then, when you screw the 22mm P5 deck down there will always be great surface contact between the aluminium plates and the underside of the P5. Without this, the heat transfer suffers somewhat. I've never used backer board and only ever 6mm or more of plywood (glued and screwed down) and then tile straight onto the ply. For 6mm ply and 22mm deck you use 25mm 4.0 x 25mm screws to lay the ply so you don't hit a pipe.

Great progress again. Fingers crossed for the move in.

...or "home slaves". MVHR just ticks over and you go about life. Just why would you go for anything that needed any such diligence aka compromise on lifestyle.

Insulation means zero if there’s a draught. As said, I use a pair of £15 2kw fan heaters, in increments of 1x 1kw, 1x 2kw, and then fire up the second to the max of 4kw of space heating. 6m x 3.6m totally uninsulated ‘shed / workshop’ and the last 1m x 3.6m (partitioned off) is my desk / pc / printer and man sanctity zone. All the cost and faff of insulating it wasn’t high in my list as I only use it sporadically, or for planned days of Teams meetings with clients etc, and within 5-10 mins the space is plenty survivable. If I’d have made the metal profile roof roof less draughty then I expect it would require even less heat, but hey-ho! Does what I need it to.

Yup, including the surface of the plasterboard, meaning the whole thing needs doing again. Rod. Back. 👎