Mr Punter

Yes, the vapour control layer should go on the warm side of the insulation. It is not crucial in your case as the final layer of insulation is thin and is not bridged by timber etc. It will be much easier to staple onto the studs than the Kingspan. That was why I suggested just alu tape, but it really does not make much odds either way. It would be a much bigger deal if you have mineral wool type insulation fit the vapour control layer outside of it.

I would fix the insulation boards with screws and penny washers, then foam and gaps, secure the polythene with staples, then plasterboard.

125 Micron (mu) / 500 Gauge. Transparent is better so you can mark the joists on the insulation with a sharpie and see where they are.

Fit joist hangers to a timber ledger and nail the ledger on with Hilti?

After you have fixed the top sheets you can either use foil tape over the joins or polythene over the lot. I would use foil tape as it is not easy to staple the polythene onto the 25mm Kingspan.

@James94 are you also @James1994?

Hi @James1994. We have not even started construction so I am afraid I can't be much help. We did a bit of demolition to find out what was what, then had to do some redesign. Not got pre-start conditions or building regs approval yet. Also, I was going to do the gutter with some flat roof on another part in the same material but building control wanted BROOF(t4), which is a fire resistance standard and I am not sure is GRP will comply. We will be doing similar to your abutment gutter detail. I am not sure how we will do the outlets at the ends. Probably leadwork into a hopper. We will get a roofing contractor to do the job. Your flat roof looks nice and neat. Hopefully you have some OK weather for the GRP. Can you post up some pictures of progress?

Well worth 5cm to avoid a kick in the bollocks!

@Faz & @Conor I understand this but there are times when you need to connect below ground. I am surprised that the fittings are so poor. It is a pain if they go wrong and the are 700mm below your nicely paved drive or patio! There are a lot of below ground MDPE fittings out there and there must be millions underground. I think everyone would agree not to join but sometimes they get damaged by excavators, tee off, reduced etc. This seems a very high failure rate. Is Plasson, JG, Floplast etc all the same poor quality / high attrition?

Insulated plasterboard is quite pricey. Are there many sockets, switches and rads? Thicker one makes stuff a bit easier to run but not much in it.

If this is the full width of your property can you not set it out as @ProDave has suggested, so the edge of the wall comes out at 90 degrees from the house? I assume there is an internal party wall that you can use as a reference to get the external line. Even a sniff that you are building where you are not entitled to and you will be asking for trouble. Hopefully you have taken account for gutters, fascias etc. The party wall surveyors are not interested in boundary disputes or who owns the fence.

He meant the house build cost was £200k which equated to £815 per square metre. Trouble was he was driving with one hand and rendering a wall with the other, while supervising some tackers and quoting on another job, so the texting was not the perfection we have come to expect from young @nod.

How so? I have not read them.

@tanneja do you have pictures of the floor from underneath? Interested to see the ends of the joists and the mid spans.

I really think the job looks excellent. Well done!

Agreed. To all other readers, don't use 18mm chipboard onto joists. 22mm only please. It is cheap enough anyway.

But the OP, who is not an experienced builder, is asking if they can build a 315m2 house for £250k. My answer is no they can't as it is less than £800 per metre.

Interesting. I did not know this was an issue. Is there evidence for this? Any particular make / type?

I think you will need to part ways. It is not unusual for decent builders to get pricing wring and try to recoup it by charging extra. Do you think he underpriced? How far through the build are you?

It would still be good if you could put some floor insulation down, but no so crucial as you are not heating it up. Any is better than none but I get that digging up the floor is a no-no. For floor finishes, have you tried LVT / Karndean / Amtico? Properly fitted it looks great. Still nice to have carpet in the bedroom though!

Quite a few on. here have used https://www.ecology.co.uk/mortgages/residential-mortgages/self-build They are a building society not a broker

Thing is, we all know that mug punters may pay more for UFH because they don't know it has been fitted with insufficient insulation. If you are happy to live with that, so be it, but don't expect a round of applause on here.

The reviews were Google at 2.7 and Trustpilot at 2.8. May not be at all representative. The only time I have specced UFH has been John Guest and Nu-Heat but for new build. The system you propose will chew through lots of fuel. Just about acceptable in a bathroom but not a whole flat. If you have decent ceiling heights you will not notice a threshold at the entrance door. Most houses have this. If you can get min 30mm Celotex type insulation under I will give you my blessing for underfloor heating.

Having a flush threshold all round can cause damp issues. They are not so bad with doors / windows as they should not be affected but adjacent to walls will be no good. The sole plates should be 150mm min, pref 225mm above DPC / ground level.

The setup you have at the moment relies on trickle vents to provide fresh air. You may be best making sure the trickle vents are left open and changing the extract fans for ones that are quieter and more efficient. For the kitchen, if it would not be too focal you could look at an externally mounted unit or change for a better / quieter one and make sure the exhaust hole is 150mm diameter.