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As you're DIYing for DHW I would recommend using Hep2O push fit. I thought it was excellent. A radial layout from the tank. 10mm pipe for everything except the showers, bath and kitchen/utility taps. Keep the UFC as close as possible to the kitchen tap. I preheated the hot manifold by convection by positioning it directly above the UFC. I'd have liked to have included a floor drain in every room with a pipe joint or a tap just in case of a leak. Next house.......

Sounds like a top spec build. Good luck with it. I think someone here built an MBC twinwall over a basement. The name escapes me. It may be an option for you.

That number I used was from Siga's website. I don't think BS defines it unless you have more insight than me? To @Rick734s question. Something like this would be fine. https://insulation4less.co.uk/products/vc2-air-leakage-vapour-control-layer-1-5m-x-50m-75m2-roll To connect the membrane to the brick I would use an airtightsealant. Orcan F is the one that popped up first. https://www.earthwiseconstruction.co.uk/product/airtightness/adhesives-primers/orcon-f-airtight-sealant-adhesive/?attribute_pa_orcon-f-size=310ml-cartridge&gad_source=1&gad_campaignid=21761028231&gbraid=0AAAAADqL4zA7HZs48ZWRJyFGMUuzu-U3k&gclid=CjwKCAiAu67KBhAkEiwAY0jAlZBJ-cvv1xqU3kk-2xm2BrsDsiiC-IiArhamJDFKawbitr-HRg56cRoCRbgQAvD_BwE I would always be in favor of a service cavity to avoid puncturing the airtight layer. If you have enough space 50*50mm battens work nicely for 50mm mineral wool to insulate and boost the U value a bit. Maybe Santa will bring some, I think I can hear him rattling around up on the roof.🎅

Thank you Conor, I shall speak to the SIP’s company after the holidays, maybe have to install a double panel or something to accommodate, the meter box shall back onto a storage cupboard, NIE said I could build a block built box that was attached to house but dimensions were nearly 1.8mtrs tall x 1.2mtrs wide

Of course. The index circuit is the part of the heating circuit that has the greatest pressure loss. So each meter of pipework, each fitting, like elbows, and for each valve the water in the heating system flows through there is a loss of pressure due to resistance. If you start at the outlet of the primary circulating pump of the system, often now inside the heat pump itself, you will have an available head pressure (usually specified by the manufacturer where they often provide graphs for how this changes according to flow rates) and this is what is gradually lost as the water travels through the system. The index circuit is just the total length of pipework that has the greatest resistance. Once this is known, you know whether the pump for the main circuit produces enough pressure to supply the heating circuit at the required maximum flow rate. This is what should primarily tell you if you need hydraulic separation and secondary pumps. The total resistance of the circuit is done by calculating the total heat load that is carried though each section of pipe from the heat pump to the end of the circuit along with using pipe diameter and resultance resistance of the pipe together with fittings. This should be done with every heat pump design. Yes, these are useful. There are already some discrepancies here. Earlier you said the design temperature of the system was a flow of 35C but the data re the ufh loops says the design temperature is 45/40. The tables each state the output of each manifold, being 4kW and 4.3K which is obviously more than the 5kW unit. I don't know the Samsung units so don't have the technical specs but you need to know what the heat pump is capable of outputting at your outdoor design temperature, which should be given in your design from the heat pump supplier. The tables suggest, I assume, that each manifold has less than 25kPa pressure drop across the manifold flow and returns whcih equates to about 2.5 meters head, but nothing more specific. However this can be calculated more specifically as the relevant data is there in the tables. What is the estimated heat loss calculated for your house?

Have you considered ICF, if you have a basement?

How much insulation is under the slab?

For design I got a lot out of loopcad in a Virtual Machine so I could do repeated trails.

What is the ‘sd’ value of a vapour control layer? Also where are these numbers defined?

absolutely. I find that a bit strange, but if that was your experience then I can’t argue that. In our previous place we had a screen above the fireplace and a projector behind us, no one ever had issues (old, young and in between) watching films, sport etc. day to day viewing was an normal TV at normal level (which actually was probably looking down a bit). In our new place we have a large TV at an above fireplace level because it’s a picture/photo when it’s ’off’ and that’s the only TV we have (no fireplace this time). No complaints from old, young or in between.

Reflections from the windows ruin many a good TV room. TV needs to be on the same wall as the windows, not opposite. I reckon the top of the TV should be no higher than your head when sitting. TVs above the fireplace are for massicists. The Fireplace will get a bag of logs at Christmas probably and the rest of the time you'll heat the house ussing common sence so I wouldn't compromise the audio visual experience for the sake of moving the sofa once a year. Sofa at 1. TV at 2. Two nice light arm chairs at 3 and 4 that can be turned to watch the TV or spin them around to sit facing the fire

I can see the logic of choosing it along with a contractor experienced in it. But otherwise I'd use whatever is normal locally The basement is not building but Civil Engineering so both SE and contractor need to be expert. By piling I assume you mean sheet piling to retain the earth while digging and building. What structure are you allowing for the basement?

TLDR: 1. DRYING MUST EXCEED WETTING 2. Forget about the microscopic holes (diffusion)!!.Worry about the big ones (airtightness) !! 3. Some moisture will always get in, just ensure it can get out again. Low Sd materials are king here. Merry Christmas!

Try playing with the numbers, there's always truth there. I'm sure @SteamyTea will concur. All the formulas are online or there's also chatgpt. Take your 11mm OSB. It has an Sd value of 2.5m which is quite vapour open. A house with an internal RH of 60% at 20deg will exert a vapour pressure towards the outside on a winter's day. Assume it's 5deg and 90% outside. Over an hour about 0.18g will diffuse through 1m² into your wall. Now put a 1cm x 1cm hole in the OSB and exert a 50Pa pressure difference on the wall representing a strong breeze blowing on the wall of the house. Over an hour an extra 7g of moisture will end up in the wall. In short a 1cm² hole will loose as much moisture into the structure as 40m² of very vapour open wall on a typical February day.

Got it in one. In layman's terms all that matters is that "drying exceeds wetting". Vapour barriers will in theory have less diffused moisture making its way into a structure than Vapour control layers. However they have such terrible drying qualities that in practice the trade off is they result in wetter walls than VCLs. In any case moisture diffusion is the hill that too many people die on unnecessarily. Holes in imperfect airtight layers are massively more significant. Often carrying hundreds if not thousands of times more moisture into a structure.

Overall, not too bad really, 25 minutes from a cold 15.6C to 60C Target/flowtemp in 25 minutes isn't outrageously slow IMO.

Welcome Is there a reason that you have chosen Structural Insulated Panels and not other methods of construction?

Presumably the stripping is in the quote? And scaffold? Our solar is only on one side and in one block, but it took longer than the other side to do, and the roofer came before the solar was installed to help the solar guy set out to make sure he could do best job of setting out the slates. In the end for the same m2 the roof with the solar in was 50% more cost in labour than the roof without.. does your quote take into account working around the solar? If so I can see that adding significantly to the work. We also do not have any roof windows, or valleys. All that said your quote does seem high......however others may chime in.

Sd value above 100m is a barrier. Barrier will be worse. It won't allow construction moisture to dry back to the inside. In practice there will be holes and imperfect sealing of any membrane. Any moisture ingress will dry over time through a lower Sd material and won't through a Vapour Barrier.

The other interesting thing is the DT at the boiler On initial start it doesn't apply full power to hit target temp because the DT would be greater than 20 Once the DT is at 20 Deg it applies full power Once the DT starts shrinking it modulates down (it's not doing that by knowing the return temp it doing it based on the flow temp rising above target and then it modulates down At the end of the day you are intermittently heating - your circuit temp at the start is less than 15 Deg C (now the rads will normally be at the same temp as the room when the system has been off for a while so clearly your tolerance for cooler temps is greater than mine or rather Mrs Alien) I do wonder if you would be better of heating low and slow rather than blasts of heat, cool down, blast of heat etc If your flow temp was say 45 deg C and initial circuit temp was 15 the boiler wouldn't have to throttle back and wait for a DT of 20 before hitting the circuit with full power. The return temp would rise and the boiler would modulate down sooner and probably much more........ However with a flow temp of 45 you'd need to have rads that were big enough to emit the heat the rooms needed.

I would think it's managing the modulation based on flow temp target Anyway kWh usage below for the for the two sessions 100% being the first one shows the boiler is really chucking everything it can at the circuit 49% being the second one shows it's modulation percentage is not far out

Difficult to explain but here’s what I’m thinking. The difference from what seems to be the norm is not taking the perimeter strip all the way to the concrete slab. It feels better to make sure the insulation is tight/snug to the edges of the room. Unless the perimeter strip (green) is supposed to also provide some compression/expansion around the pir.

Yes. Just the ground floor so far with a manifold and nothing else. Can you explain what that means? I am finding that I have to double check everything the "qualified" professionals tell me because it seems no one cares nowadays. I'm happy to do this myself if I have the means, I really want to get this right before it goes in. These images may be of interest, maybe not.

Looks great! Yes, it would get stripped, not sure how many tiles we will save, below is the best image I’ve currently got. I mocked up a solar layout, the gaps are for roof lights plus with the hip we might be spending a bit of slates and a half by the sounds of it.

The pictures are better on radio. One problem solved. Fires in homes are coming under more scrutiny and legislation, so why bother. Another problem solved.