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That also increases U value, I looked at additional PIR on our build but the difference between an unventilated air space and actual PIR is too small to worry about.

When I mentioned thickness I was thinking of 0.7mm as the standard but you can get thicker. 0.9/1mm IIRC

That's what I'm saying, those values aren't reflective of what is there. Even based on the standard Nudura figures of 0.24 for their blocks (keep in mind these were ordered before the new regs came in). I don't understand the technicalities, but ICF houses seem to perform differently to their relatively poor quoted u-values. At least half of the building is going to be rendered and will receive a 30mm layer of EWI in the detailing. The Architect designed a 50mm battened service void on the inside, which I may do away with on the perimeter walls or replace with PIR, yet to be decided. That "design" is very preliminary, perhaps should be taken at this stage with a pinch of salt. The software I played with was Heatpunk, maybe I could try Loopcad.

For some reason the nudura icf blocks have a poor u value, when in reality we know they are very good when coupled with good airtightness. all these spreadsheets don’t deal with common sense 180m ground floor, nudura walls, eps in the floor rockwool roof, excellent air test. 5kw Panasonic heat pump.

At 0.26 your wall insulation must be very poor. I would look to add 50mm or more externally, if the figures are correct. Floor is likely to be around 0.08 U value. 32W/m² is huge. Similar build to ours is closer to 15W/m² at -9. Heat loss at 7.3kW sounds excessive.

It's probably not very relevant to you, but I've just self installed a 5kw Samsung Gen 7 with a 300l Oso using the "umbrella" scheme for an overall "profit" of about £1000. Free heat pump! If you do the course you can get a 7 year warranty for it. Our build sounds rather different to yours, but as we're in North Somerset you're welcome to visit for a look.

Timings as @ProDave says is pretty real. If your using a ToU tariff, I do and have the following 4kW heat pump - Hiaer monobloc. Then a use a direct UVC, so is charged via immersion (have plenty of solar also). Heat pump is then not trying to do heating and DHW in a cheap period, they are independent of each other. Going that route Heat pump under £2k when you claim the vat back. Cylinder £600 incl vat. Drive via simple time switch. £20. Plumbing very simple. You have loads of water volume.

Before they start check they have the drawing. Ask them if there are any issues arising. That is their moment to explain that they disagree or agree to build it as designed. Then you have an agreement and they work to it, or you don't and you have to manage the situation. You'll often find that they haven't got the drawing, or that your workers are not the one you agreed the job with.

Your plumber may be limited in choices if they use a single merchant, as many do. Best discuss with plumber ASAP. Try talking to Trade Underfloor Supplies or similar. They supply the whole kit and I'm sure many plumbers get it done this way. But check you get the grant benefit.

This was 10 years ago. Just something called garage floor paint and a diy product as well as from paint merchants. Just had a look. Leyland seem to do one. You may be stuck with grey. It was just paint so it dried and couldn't possibly be tacky afterwards.

I've had a preliminary ASHP quotation which included a heat loss analysis. Keep in mind that no commitment has been made to any of this. This is the output of that in terms of heat loss. Seems high for a triple glazed Nudura house... Then I noticed that they appear to have used "placeholders" in the construction materials section... The standard Nudura blocks are 0.24. The figures for the floor and roof seem off. I'm having 230mm PIR in the floor (I'm sure that'll be substantially better than 0.18). There are 3 large rooflights, but these are Vario by Velux triple glazed units (1.1 u-value I think) I'll be very disappointed if I don't achieve sub 1.0 ACH, I'm looking for 0.5 really. I don't want to go too far with this design as I'm not vested in them and don't want to end up too deep in obligation to them. The house will also have MVHR of course.

@Great_scot_selfbuild, curious about what the 110mm pipe coming through the wall is for?

I recon from experience 2 days of electricians time and 2 days of plumbers time to install one on a new build. And I am in the camp that does the sums on that plus materials cost and wonder just how most of the companies that quote get figures as high as they do. If you are going for self install, then look at the other option, some companies will supply the kit for £0 using the grant for you to install. MCS sign off for a heat pump is not mandatory, in fact I struggle to see what that expensive bit of paper will actually do for you.

Which make? We used one as a temporary measure and parts of it are still tacky after 3 years

I have had 3 quotes for my ASHP install on my new build. The cheapest was 10K for a 5k system but they have just come back with a re quote and it is now 12.7k, which is pretty much what the others came to. So I have got a bit fed up and decided to look at a DIY install. My plumber suggested he would do it last year and said I could get MCS sign off and claim the BUS grant and at the time I thought it was a lot of hassle for little gain. Since then I have established that the ASHP installation market is full of contradictions so I thought I should look at this again now I have more knowledge. I am building an efficient 3 bed house with MVHR, UFH on both floors with very high insulation. Total heat loss circa 3.3kw. The latest heat loss survey showed the heat output of the floors to be between 150 - 200% of requirement at a flow temp of 35 degrees. So I have always planned to run the system completely open loop. Total UFH volume on both floors is 105 litres so I have been advised I don't need a volumiser, which is a good thing as space is tight in the plant room. Now the thing is I have been quoted for a Samsung Gen 7 5kw unit and a Grant 4kw unit. I am planning on a 250l UVC. The thing is there are so many choices and brands so I thought I would ask you good people for some pointers as I don't know whether there is a huge difference between brands. Whether I should look at a kit etc. I am not actually going to do this myself, my plumber will but I am probably going to spec much of it myself. I am based in Somerset. Thoughts?

When I was forced to teach the younger students I found that giving them loads of small, achievable tasks kept them busy and improved classroom behaviour. With the older students, once they were broken in, more self learning could be introduced, this gave more opportunity to deal with the ones that were struggling. Project management is the same. Set simple tasks achievable tasks that you have the skills to check, find out who does as needed, and give them a bigger job next. The ones that struggle with the simple stuff need guidance, maybe from one of the better workers, before they can move on to bigger jobs. Project management generally has (expletive deleted) all to do with technical abilities, more to do with people interacting. I also use a simple metric when assessing trades (generally was for maintenance work). If their van has non standard wheels fitted i.e. larger alloys with lower profile tyres, I find they tend to rush a job. They usually drive like (expletive deleted), and park inconsiderately, as well.

Unless it will be used for other purposes with nasty spills and lots of movement, I would just paint it. One coat of single part garage floor paint. A commercial garage has dozens of movements. Yours presumably won't. Even commercially I once suggested to a client that they ignore the spec of hi-tech flooring and just paint it. This was a commercial vehicle service bay so getting lots of movement. They saved many tens of £k. Once a year they overpaint the slightly worn area of the repeated wheel routes.

The only self build I would recommend as financially advantageous to amateurs is renovation. Something tired but functional. Then don't remodel it but just bring it up to date with lots of diy. Conversion may be more advantageous with the VAT benefit, but not if there are major works to structure.

Your question is fundamental. It goes to the heart of the horror that self-building can become. And is the main cause of self-build-sleep-deprivation-syndrome Humility, respect, time, trust, effort, plain speaking. And knowledge of their (the trade's) networks Self builders are - to the trades we deal with - mostly one off customers. And because we self builders have to invest so much more time , emotion and 'fizz' into our builds than those who 'simply' sign a cheque, many self builders ( not all) think we're special. To trades people, we aren't. We're one of many jobs they have on the go at any one time. Either invest in someone who can manage the situation for you or take the time to understand the trades networks so you can break through their communication blocks and accept that substandard work does occur and that some work will have to be remedied but most of all - be lucky DIY know when an error is something you just have to accept - and when not. After more than 10 years at it, I'm only just getting to know like and trust a core of people who communicate well, do what they say they will do, when they say they will do it to an acceptable standard. 10 years to many people is just too long.

Here you go, one of many places that do hire them without an operator.

That’s really lovely, you must be so pleased!!! I’ve always loved border oak and been a bit jealous how they can get their timber posts to work in between windows like that. I’ve always ran into issues with security and cold bridging.

The stupider they are, the less they realise you have knowledge or deserve respect. So if they are not paying attention or respecting sensible questions... beware. I don't wear a badge saying " I know this stuff" and it helps me test them out. Of course I don't know everything eg electrics. Advice to a first time self builder? You do have to ask these questions but not all day. You do have to get tough. You do have to handle the master programme. Be there doing secondary work, even tidying, and it goes better. Praise when due.

Interested in contact details of anyone offering this.

So forget the problem.

@Mulberry View if you need a UFH pipe stapler (depending on what the pipe is going down onto) then I currently have the BH one - In the Tool Loan section of the hub there’s also a decoiler available (essential item!)