G and J

My understanding is that there isn’t a huge airflow typically below BnB floors, the vents are more to prevent gas build up than humidity control. On the build of our current house we switched last minute to BnB as a land drain was discovered where the house was going, although we diverted it to where it was supposed to be on medium elasticity clay it still meant BnB was cheaper than continuing with a solid floor. On the new pad we’re going for them as the slope is such that at the back of the house we’d have to dig down circa 700mm and then put lorry loads of stone is to build up, on a sight where we can’t bring in a tipper. With BnB we cart a lot less away. There’s also no need for a BnB floor to be any higher than a solid one as long as you are happy to dig down a bit to get the void under (opinions appear to vary between 150mm min and 225mm min. In our case we might have to push some soil towards the back of the house, but that’s it. However I’d go for solid if I didn’t need BnB, but I think it’s potentially a ‘save having to think’ option for an architect.

On the brightside, if you did have a problem at least you would know about it as your socks got wet through when you walk into the utility room.

Oooh you got a blank look from Iceverge lol What was you largest span?

Thanks folks. It seems to me the risk vs benefits don’t look good for our build. I’m not as brave as JohnMo. So it’s back to either a temporary floor or simply sticking with a standard bnb floor.

I’m assuming that the network is the balancing item/buffer in the system. Sizing for max need may incur a lot greater cost than is economically sensible.

Accepted that the primary role of the VCL is to keep moisture out of the structure, in our case a standard 140mm stud based OSB skinned timber frame. But I am working on the notion that from floor to ceiling VCL, with wall VCLs joined by Tony trays, is effectively a balloon with as few penetrations as possible. At all points those VCLs are sandwiched between either OSB, plasterboard or insulation, so there should be no possibility of ballooning.

Ouch. Hadn’t thought of that. I’m going to have a long pipe run from ASHP to UVC so that might require some thought. As it will only happen when I need cooling - therefore on warm days - maybe it’s not an issue but a simple delay on the 3 port valve might sort it.

That’s the bit we are worried about. Others on here having described using pipe temperature sensors to control the fan on the Fancoil in what sounds like a relatively simple and elegant set up. I think our FC will be used for cooling only, in which case the fane will only come on if the room controller says ‘cool me’ and the pipe sensor says ‘I’m just soooo cool’. Hopefully that will mean that the ‘burp’ of unwelcome hot or cold from the FC will be minimised.

I’m having an insulated beam and block ground floor. I’ll happily set out my reasoning if peeps are interested, but…. What downsides are there to putting in the insulation/dpm/UFH/concrete screed from a lorry before I build me walls? The fibre reinforced sand and cement screed can be poured from a lorry and once cured it will give us a good base to build off of. It’s not my original idea, I stole it from a buildhub stalwart, but I think it’s a good one. But practically, what issues might it cause?

It’s a bit like alcohol and sound logic. Both exist but not at the same time. In our case we might use spare solar power directly to heat the water when the sun shines and we need cooling. But we might not, we might just use schedules to have a blast of hot water (should be reasonably efficient on a warm day therefore not take too long and still have a decent COP), and then run on gentle cooling the rest of the day. At the mo I think I’ll be wiring to allow the installation of a solar diverter but start without one. Less (kit) is more (money left in the piggy bank). Or maybe less (kit) is less (balance on the mortgage).

Not finally, as we won’t be buying them till next summer at the earliest and availability changes and new stuff is launched. I’ve been working on the premise in various design areas that by finding one solution that is economically and technically viable, and allowing for the requirements that that option requires, we have a base case which we may be able to improve upon when the time comes to order. I’ve been looking at Reverso units, which seem a sensible design and cost.

Maybe they spent so much on the build they can’t afford heating lol Being serious our design started timber frame and no masonry skin. We did a good few hours research and concluded that at least a partial masonry outer skin increased the number of normal mortgage lenders (and we think house insurers) which would accept our house, and more importantly for us a significantly greater number of lifetime mortgage companies which would accept our house. We changed our design to just over 50% rendered block as a result. We will never know whether it would have caused us issues….

We’ll be running drain pipes to our Fancoil locations in case. The cost of a bit of pipe for first fix is tiny. The hassle of doing it later is huge. However, to get lots of supercool from our fancoils I’ll need to zone them and that won’t be day one, we’re going to try using them above the dew point. (Crumbs, I almost sound like I know what I’m talking about!)

My word that’s what got Gregg W in trouble lol I keep reading steel is inexpensive but I’m damned if I can find sensible ways of guesstimating broad costs.

What spans are these across?

In another thread @Indy expressed doubts about them having a woodburner. As you have added a woodburner @Andehh do tell, do you use it and do you leave sweat puddles or simply watch the main heating system ease off (or both of course?)

Noting the wildly differing views on insulation levels may I suggest playing with Jeremy’s spreadsheet might help, it did for me.

You could be describing our architect, and our experience with planning has been, perhaps partly as a direct result, a pleasant one. We did the actual house design ourselves, with a very carefully thought out aesthetic balancing our desires with what would look right in the street. Then that was drawn up and packaged by our architect, and I’m convinced that our application was received in a better light for coming from them than it would have been from us as individuals. So the usefulness of the hoary old whatsit role you describe I agree with, and I’d suggest that there are multiple sources of said experience.

We have a twinkle in an MCS plumber’s eye right now, we are planning ahead. Our plans will be vetted by BCO and SAP assessor in the next couple of weeks, so still lots of decisions to be taken.

A variation of conditions. In Suffolk it’s about £450 and takes 8 weeks. But a woodburner is a beating heart….

We built ours in ‘91. Better than the then building regs insulation but compared to our planned new pad it is a wind tunnel. We are used to cool bedrooms and significant temperature variations during the day on cooler days. Hence me asking so many stoopid questions…. How much will you be doing yourselves?

Then you have an advantage over me as I haven’t and I’m struggling to imagine how it will feel.

Indeed, I've been having a play.... OK, so I've some numbers, and gut feel says a 4C change in floor temp will feel f chilly - but what should I be aiming at? The complicating factor for me is that on a -2.something day we will have the woodburner going, and maybe even on a 5C day. But I'd like the system to work well on a normal cold day without a fire.... So what floor temp drop should I aim at?

@Indy Question: Have you ever lived in an airtight well insulated house?

So, the concept enshrined in 2) holds, the question is how much the screed would cool during the off period. I have difficulty finding stuff on here, do you happen to know how to find that?