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But installing a GSHP and ground loops for unrequired cooling isn't Joking aside, I have a 12kW HP and my PHPP calcs estimated a worst case 6.4kW heat loss. My HP has an easy time, the house performs slightly better than PHPP calculated, although not PHPP's mistake, I make better use of solar gain than PHPP had allowed for. Even with an oversized HP, the house can still be slow to react. This is all my own fault, as I don't allow the HP to heat the house in the morning if the forecast is either sunny or only partially cloudy, knowing that by 11:00 an average house temp that was say 19.5 @ 07:00 will be sailing passed 21.5, without the heating on. On the days the forecast is wrong or mis-timed it has a bit of catch up to do, and when it does it takes a little while to do so. I should be clear, if I wasn't playing games trying to predict the solar gain, and allowed the heating system to maintain a constant temperature, this wouldn't typically be an issue. Similarly, cooling is effected in the same way, but more acutely. Solar gain is far more powerful that heat loss, so is able to rapidly change the internal temperature. If it is "allowed" to get to 30, it will take a long time for the ASHP to bring it back down, and will generally have to wait till the evening ambient temp drops to allow our stack ventilation to dump heat out the roof vents. This has taken quite a lot of tinkering with to get UFH circulation, external blinds, and roof vents working to minimise the solar gain so that the HP can do the rest, but it is not always successful.

Is that your calculated energy loss? So you need 2kW to maintain say 21 internal at -10 external? If so, I wasn't comfortable sizing my HP on this value, I felt a bit of head room was needed, so that in the same conditions the heating was sufficient to raise the internal temp from a lower value (in the case there'd been a heating failure), as well as heating a tank of water up in a reasonable amount of time. Or does the 2kW already factor that in, in which case it is a very low value, could you not just go with electric duct heater in your MVHR,

I also looked at both, the small additional efficiency of the GSHP didn't outweigh the extra capital cost and extra maintenance cost. Add into you comparison the maintenance cost (there's a lot of antifreeze in a GSHP that needs replacing). In the GSHP flavor is the option for "passive" cooling.

Take everything that is the same, out of the equation. ie. from the price of the ASHP & controls + the extra cost of a 25% larger HWC + say a 90l buffer (just in case you need it) + twin pipe insulated duct of required length, take away the price of the Gas boiler & controls. The install may be a small amount more due to the MCS requirement for RHI, and a bit more copper pipe and brass fittings for the buffer.

Yes, you have to fund the Install and you then get the money back over 7 years, index linked. So, you could add it on to your borrowing, if you're not already on the max the banks will lend. A correctly sized ASHP will not lead to any temperature issues with either the house or the water. The better the insulation and airtightness, the smaller HP you'd require. UFH is perfect for the lower temps of an ASHP, ideally under 35 degrees flow temperature for maximum efficiency of the HP. If you are using rads upstairs then they would need to be sized larger than they would for a fossil fuel heated house. You would also need to have a HW Cylinder, and it would need to be larger than fossil fuel heated one again as the temp will be around 50 degrees rather than 60 to 65. From 2022, building regs will require new builds to be designed for low temp (under 55 degrees) systems anyway, in order for them to be future proof and require no retro-fitting for when the 2025 Future Homes Standard comes in and heating systems in New Builds will have to be low-carbon. Even if you don't fit an ASHP now, it would be wise to ensure one could be fitted in the future without replacing all the heat emitters and trying to squeeze in a cylinder where one wasn't planned for. BTW, redo the RHI calc with a higher SCOP. It's really worth getting your flow temp down and having a higher COP ASHP, something over 4 if possible.

Advanced Foundation Technology have some innovative solutions for poor ground conditions. ie. a Suspended slab on piles. Luckily Olof is a better Structural Engineer than web designer, you may struggle to find the details on his website, but here it is: https://www.advancedfoundationtechnologylimited.co.uk/wp-content/uploads/2019/01/aft-groundshield-designs-2018.pdf While your timber frame company is supposed to be doing the raft getting AFT involved may be a lot better than a 1500mm excavation. I have a standard Insulated raft from AFT. They're happy to do design, supply and install or just design and install, or somewhere in between, and can include the UFH as well.

If you don't want to have a full sized tractor on there, find a landscaping company with a Stoneburier and a compact tractor. Blecavator make a range of sizes and are the well known brand. They create a fine tilth and push the stones down, and give a nice flat finish. It would only be a couple of hours work. Edited to add: Looks like they can be hired too https://www.fthhiregroup.co.uk/hire-products/landscaping-and-groundscare/groundcare-equipment/blecavator-stoneburier-attachment as an example.

Is that your interpretation of the new regs? The change is supposedly to lower CO² by 33% from current standards It's not going to work if you just have to design the system to be low temp, but can still run it as high temp.

Any low temp systems needs to run a "legionella" cycle every 14 days to lift the temp to 60°

I believe there will be an update to Part L building regs at the end of this year requiring a maximum flow temperature of 55 degrees, so that all new build hot water and heating systems are "designed" for renewables.

RHI would pay for the ASHP. It's worth considering, yours is an ideal build. If you are already going with UFH, then it's a decision you can make later in the build, although putting an insulated twin pipe duct in from where you would site the ASHP to the area of the Hot Water Cylinder would be beneficial, while your ground works are being done.

Takes a matter of seconds, yes, but it is very local, so as you move around the house, you need to take it with you and plug it in. That's not how I personally wish to live, and not suitable for a family. Even if I took the hot water requirement out of the equation I would want a heating system. I personally want the convenience, plus the house I built needs to be saleable, and I don't believe the general public are ready for a house without a heating system. You can't however take the hot water requirement out of the equation. So with a heat source needed, it's there for space heating too. A carbon neutral large property has no more impact on climate change than a carbon neutral small house. Any democratically elected government is going to find it very difficult to legislate on house size.

The MVHR has too low a flow rate to transmit 6.5kW to the house, and to provide the required heating via electric radiators would need them to be placed in more or less every room so the capital cost is not insignificant - probably similar to the cost of the UFH system (not the ASHP). In reality, I didn't consider electric radiators, or in fact radiators of any description, because I didn't want them on my walls.

My house was PHPP calculated to be at the 15 kWh/m2/year energy loss threshold. In reality it's slightly better than that due to making the most of solar gain. But I still need a 6.5kW heat source at times to maintain 21 degrees. ie. when it's been overcast for several days and the average temperature hasn't got above 0 degrees. I didn't at the design phase, nor do I now feel that the peak heating demand could realistically be provided by an electric heat exchanger in the MVHR and some electric radiators. And combine that with the need for Hot Water, an ASHP absolutely makes sense. That is based on a Big 6 Standard rate for electricity of 19.43p a unit and a 2011 "best" COP 2.7, and the result is 2.7 times more than gas. At an actual 11.725p per unit of electricity and an average COP of 4, the ASHP cost comes down to 2.93p per unit - slightly cheaper than gas.

I guess yours was a badly matched install then. Works fine for me with a family of 5 and 450m^2 house You've not considered how much hydrogen may cost, should they ever work out how to produce it in the volume that would be required to heat homes. The future will be better insulated and more airtight homes with a mix of hydrogen and heat pumps. Heat pump prices will come down, hydrogen will be more expensive than gas.

Paid for by RHI, so not the case Not a limitation I recognise - have you had an ASHP and experienced these issues? It's no "niche" now, and certainly won't be when Natural Gas is switched off.

Is that price the average for the year, or for the last couple of months ie. March and April? I also have a 12kw ASHP, which is a little oversized to the 8kw calculated, and I have 500l UVC + a 200l Buffer for the UFH. I'm around 450m^2 I think. While I did put my heating back on for a couple of weeks in April, it's mostly been off since the start of March, so my current usage doesn't include heating and is around 1350 kWk for each of March and April. That's around £160 /mnth on my tariff. I do have a couple of servers that run 24/7, that aren't the most efficient, so that pushes my usage up a bit. I wonder if your Air tightness is effecting your energy losses, how much has your heating been on? Why is it more expensive than Gas? I pay 12p kWh with a COP of around 4, so that's costing 3p/unit?

Pricing does look very good, would you mind sharing the supplier either here or via PM? It's around £350 - £400 cheaper than I've managed to get quoted for similar.

I keep coming back to this same question myself, for a similar length of drive. We're using a shared entrance at the moment, but wish to put in our own access, however the numbers are off putting, even though I have 200t of hardcore "tucked away" ready. My thinking at the moment is to go with a structural grass drive way for the majority, using grids like these: https://www.ibran.co.uk/products/grass-parking-grids (I've just picked this from a random search, and know nothing of this particular product) The build up suggestion is 50mm - 80mm Type 1, but that doesn't feel enough. I'd be looking at going with 150mm of crushed hardcore (as that is what I have). I've found other similar products that are 60mm deep rather that 40mm, that say they are good for occasional HGVs. If you can get away without an edging, it could be relatively cost effective.

Have you seen such a finish? From your description I'm picturing the edge of the board flush with the main wall plane, but then a recess around the board making it appear to be sitting proud. You may need to sketch what you are hoping to achieve.

The wall joint to the cill board is already in a shadow (under the overhang of the cill board), so there is no need to create an artificial recess to disguise the joint.

Yes, if you've concealed a breach, you'd be denied a CLEUD. Council Tax would be separate, and it wouldn't surprise me if they were chased for it.

Once it's been inhabited continuously for 4 years, the owner can apply for a Certificate of Lawful Existing Use or Development The Owner has to prove the breach is ongoing and has been continuous for 4 years. If they can the LPA has no choice but to issue the CLEUD. But, that's not the same as having planning, it just allows the existing breach to continue. If the breach is discontinued, ie it's empty for a while (at least 3 months seems to be the threshold) then the CLEUD is no longer in place and the 4 year clock starts ticking again. I don't believe Banks will lend Mortgages against such a property as it doesn't have planning permission. If the LPA become aware of it before a CLEUD is applied for they would likely give the Owner the opportunity to normalise the breach by applying for retrospective planning. If they do so and it's rejected, or they fail to apply then the LPA will issue and enforcement notice. Enforcement notices do seem to go very very slowly. It would be years before it got to the point of the Council demolishing the build and charging the owner for it.

50mm gap between sheathing of warm roof and 18mm OSB deck for metal rain screen.

Have you seen any? Are you happy with how they look? I don't personally feel a single ply membrane roof could be confused for a metal root, while I agree that sticking a "seam" detail on them is intended to make them look similar. Do you wish to fix anything to your roof? ie. PV, satellite. The seams on single ply aren't structural, so you need to find another way of fixing. I'm assuming fixing through the membrane is a water leak risk.