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Is that because someone measured incorrectly? The joists twist may or may not be a problem. Ideally the forces need to go directly though the web, the greater the twist, the less load the joist can take, which causes buckling. Buckling tends to be a catastrophic failure, not just a bit of extra 'bounce'. This is because as the sin of the angle increases, the sideward forces increase (or is it the cosine, makes no difference, it is the angle that is important). I would not be happy (structurally) with walls in the wrong place, twisted joists and brackets not fitted right. You seem to be doing the right things in involving the manufacturer, builder and possibly a SE.

ChatGPT and other generative AIs (don’t get me started on the terrible misuse of the term) are simply stochastic language parrots, and unable to perform any actual maths calculations. So wouldn’t trust them to actually deduce anything!

>>> the chat bot is talking sh*te Yes, for a random lvt: https://s3.amazonaws.com/a.storyblok.com/f/231903/x/e64b397b14/amtico-signature-technical-specification-sig-ts-20240731-12-en.pdf it says: 0.014 m2K/W (underfloor heating suitable) - for a thickness of 2.5mm i.e. conductivity of 0.18 W/m·K, u-value of 71. A random web site ( https://www.vcalc.com/wiki/thermal-conductivity-of-porcelain ) gives porcelain as 1.5 W/m·K and porcelain flooring tiles are 12mm from memory, so u-value of 125. i.e. not a lot of difference in the scheme of things and they're both v good thermal conductors in building material terms. The big deal with chatgpt et al is that there is no deductive logic there - in fact no logic at all. I'm tempted to suggest that is similar to the quality of your salesman. If it finds the word 'Alan' close to the number '125' often enough it will be happy to conclude that most 'Alans' will be 125 years old. Ask him to do the above calculation to verify his thoughts?

Meant to reduce noise by 40 dB or so, but that is very subjective (why there are different decibel scales). You can get acoustic plasterboard. Or headphones and slippers, all conversation by text. But as you get older, you go deaf anyway, and forgetful.

Most of our floors are 14mm laminate with wood fibre underlay. Pretty much worst case (other than thick carpet) scenario for UFH. Works fine. Low bills. It is noticeably "cooler" to the touch than the floors with LVT or tiles. But no different from carpeted floors. No difference in room temp or comfort once flow rates adjusted.

This is how ours were done Short sections of I beam came with the kit to go in between the main ibeams where they rested on a supporting wall. They did not fill in the web, but that might be because our beams came made up as 11 metre long beams to span the entire length of the house resting on supporting walls on the way, so no joint between separate ibeams as you have in your case.

Thanks Steamy. This is just what the technical manager explained yesterday - about the risk of failure by the joists not bearing the forces in the correct plane, and because of the supporting walls not sitting directly atop each other. The joists simply won’t function as they should and this could cause catastrophic joist failure. I’ve drafted and polished the email to the builder. Will see what he has to say in response….

That is a good question. Like all good questions, there is not a simple answer as there are several interactions taking place at one time. The simplest answer is that it is down to the power delivery (the W/m2). That can be increased or decreased in two ways, pump more energy in (closer pipes) or raise the temperature (for the same size pipes). In reality though, which is where it gets complicated, are the physical characteristics of the systems. You cannot easily have pipes sitting next to each other as that would need a huge manifold for dozens of pipes to connect to. You cannot have too high a temperature as you would not be able to stand on the floor, and the efficiency of the heat source may suffer. You cannot change the weather, which is very dynamic, so you have to accept some compromise (an emergency fan heater). The temperature difference between the flow and return (in and out of the time) needs to be within a sensible limit (you cannot extract all the energy supplied), this limits pipe diameter and pump size. The more complicated answer is that as temperature rise and fall is not linear, even of it looks like it at small temperature changes. As temperatures rise, so do loses, as it falls, the opposite happens until you get to parity (Laws of Thermodynamics explains it all).

20%?? I’d be tempted to put it in the cavity if this was true.

Amtico publish thermal resistance (R values) in these technical documents: https://www.amtico.com/commercial/technical/ 1/R = U, so U=59ish for the Amtico Access. I wouldn't lose any sleep.

Mostly bollox. For UFH, it’s useful if you have good insulation below and good thermal conductivity above - think tiles, lvt etc. You can use e.g. solid wood flooring, but it’s more of an insulator, so slower to warm up. Amtico and most ‘R11’ is pvc, so fairly thermally conductive. The ‘cost to hear a house’ is a function of the overall wall/roof/floor u-values, you would need the whole build up to tell. Actually, I revise my opinion - total outrageous salesperson BS. Ask him ‘what u-values would we be looking at’ and see him flounder.

If you could reduce your joist depth to 202mm - 2 layers of super quilt plus 40mm PIR making 242mm yields 0.15 u value. All warm roof. We’ve got a 202mm posi joist with green roof loading… alternatively if it’s the Mbc detail then it’ll be a 300mm joist (0.14 u value with cellulose) which you could do with a 202mm with 1 layer super quilt and 80mm PIR.

This is where we got all our UFH from, if your local they install as well.

With difficulty. It's possible but once I started looking into it, I realised that the detailing had to be exact and a warm roof was much easier. The detail you've posted looks like MBC's flat roof with cellulose. Are you sure the joists are 254mm and not 300? 254mm cellulose filled wouldn't be a great U Value.. probably 0.16 or something?

Ventilated upstands at each junction.

I think that’s exactly what we are facing. We’ve a 3m x 5m flat roof with a fair bit of that taken up with a skylight. I think the difference between internal ceiling height and the top of the parapet that surrounds the flat roof is between 450mm and 500mm. Posi joists will be 254mm, plus we need to be able to walk on the flat roof for maintenance/window cleaning. Reading this thread it sounds like we’ve no choice but to have a cold roof, but how on earth do you ventilate it?

make sure its ventilated. Warm roof much easier to detail but you need the build height which is what most people struggle with.

>>> why would i want an expensive architect plus a structural engineer and someone else drawing all the required drawings IMO you want an architect for ‘magic’, SE to make the judgements and calcs on construction methods and techniques and a detail person to worry the insulation, damp, ventilation, rain screen, BC regs etc. Anyone can do the drawings if they understand what they need to draw. That could be one person or four, or more. Maybe a planning consultant too.

Just came across this thread and found it interesting. For the record, I retrained as an Architectural Technologist from 2009 to 2012 at UWE having spent a long time in IT. I had always had an interest in Architecture (having wanted to be an Architect from a young age only to be dissuaded by the careers teacher in the 70's) and we had always worked to varying degrees on our own houses. I stopped working in IT in 2005 and spent the next 4 years renovating a couple of houses (until the recession hit). When I say renovating I did nearly all the work, only the dark art of plastering and large scale brickwork was left to someone else. It was at that point I decided to scratch the itch that had been with me since I was about 8 and went back to Uni to study AT. I really enjoyed the course, and being in my 50's meant that I didn't have the callowness of youth and was happy to take full part in my course. I then spent 10 years or so working as an AT, working on relatively small scale extensions in our locality in Wiltshire. I had been self employed in most of my IT years and so the thought of going to work for someone else didn't appeal. So to the question in hand! I am of the view that you just cannot generalise in this arena. Titles play a part, education is not the same for AT as for Architectural courses, and as in any profession there are good and bad. What I would say is that my experience at UWE taught me that once the basics were taught in the first year (where the AT and Architectural degree students were taught together) that the courses diverged somewhat. There was a degree of pragmatism and practicality that was taught to us as AT students that gradually began to fall away in the Architecture courses, to the point that when looking at the Part II and III degree shows at the end of the course I was actually angry at what I saw. I suppose that there is no right or wrong in this discussion, its buyer beware in reality. Take your time in assessing the professional that you are going to use, look for and ask for examples of their work. The actual relationship with the designer is very important and like someone further up the thread said, one of the first things I said to anyone that took me on is that we wont necessarily agree on designs, it is an iterative process and as much as anything else I was there to guide people through the minefield of design to reach something that was as close to their desires as possible but was also possible both from a financial and technical standpoint. Some would come with plenty of ideas and others had no idea and simply left it up to me. One other thing to add is regarding titles! I spent so much time trying to disabuse clients that I was an architect, I was always very upfront about what I was qualified to do. On a scale of importance titles rank low, and as long as someone is not trying to pull the wool over their eyes with regard their qualifications then I think is low down the priority list of things to look for.

Feeling stressed, walked round the site this evening. Plastering has started, probably will move in end of November. I don't know what made me think we could do this, till it's signed off I guess we haven't. It's been way harder and more expensive than I thought. What about you, if it wasn't plain sailing, at what point did you feel it was worth it?

Speaking of @Nickfromwales looks like he has not been on here since July - must be having a good long holiday somewhere let's hope.

But this is based on thickness of material - as thermal conductivity is per metre thickness of material. So actually looks like the chat bot is talking sh*te - like they mostly seem too.

Will it be worth more with a shiny coat on it.

As soon as planning passed and my plot of land previously was worth 5k instantly was worth 500k . I was jamming like a mofo that day

I would have guessed Plockton from the choice of user name.