Redbeard

Hi @flanagaj, I tried to send a private message, but I gather you cannot receive them. Have you intentionally disabled the PM function, or has it just disappeared and is this an issue for Forum mgt?

... and I was just about to write that too. PIR externally amounts, in my view, to a VCL on the wrong side of the 'sandwich' - and I wince every time I see a TV show depicting it. How about rigid wood-fibre with a scratch-coat of lime render before the battens and (?hit-and-miss?) larch?

I know someone who tried to use NHL for the same 'economy' reasons. I think the main problem was using it as the 'adhesive coat' behind the boards. As I recall it simply did not stick at all - not even the 'light tack' afforded by RK70. I don't think he ever tried it on the boards, since he had to buy RK70 for the 'adhesive' coat anyway. Particularly if you are doing it yourself and have not done a lot of plastering I'd recommend RK70. It is so 'forgiving'. Slow, in colder weather, but relatively easy for non-plasterers to pick up.

I think we need a pic of the other end (the end nearest the camera position, where the stairs open up and there is no wall on the L). Likely no problem spanning from wall to wall in the 'distance' of this photo (where the coats are), but then nearer the camera you only have one wall... Is there a 'stub' of wall behind the camera on the LHS so you can bridge across the stair opening?

I used to hate doing footings and blockwork in trenches, because I did not do it that often. However these were generally small - medium extensions where the footing job was too small to be of interest to a busy brickie. So I was really picky of my own work... So my out-of-plumbs' or 'out-of-squares' were tiny, as I was always pulling myself up - and checking again... and again... To lift a term (thanks @BotusBuild) you need someone who gives a sh1t - sounds like @BotusBuild knows the person. Good luck in the 2nd go.

Hmm. What does that out-of-plumb bubble represent? How far is it leaning in how tall? From LABC Warranty: "How far out of plumb can a wall be in the UK? Wall panels should be erected to the following tolerances: • +/-10mm from plumb per storey height. +/-10mm from plumb over the full height of the building. +/-3mm from line of sole plate, with maximum +/-5mm deviation from drawing". In pic 3 (with a slack line on top of the blocks) where was the line when the blocks were laid? Is this the brickie you were planning to use above ground?

Glad you've found a window of opportunity.

When you say 'partially' do you mean 'the roof, not the walls' or 'only some of the roof'? The former I'd say is OK, but if 'un-airtight' means 'breezy as owt' it probably won't gain you a great deal. If you do propose to insulate the roof can you get to the gables to drill ventilation holes in the gable at each end (you'll need a good few between each pair of timbers)? For minimal structural diminution you ought to drill on the centre line (75mm if they are 150 timbers, for example) but that limits the insulation you can get in. It could still allow 50mm though which (crudely) could drop the U value from say 2.0 to say 0.5W/m2K, roughly adjusted for the 'thermal intrusion' of the timbers. If you are pumping in heat it will reduce the heat loss. If you are expecting it to keep you discernibly warmer on a cold day with the only heat input being the c100W of you I doubt you'd feel a huge difference.

No-one (except me!) has yet picked me up on the fact that using PIR on the top would in effect act as a 2nd VCL where you do not want a VCL. If you substitute 30mm rigid (breathable)wood-fibre you'd get 0.1609W/m2K. I don't think BCO would quibble. I have no idea of the size of the job but it may be that if you took it outside the roofing job it may drop in price. How many m2 are we talking about? Possibly the trickiest bit of all will be removing the floorboards without excessive damage, but it can be done by punching the nails through the boards before you lift them. I did that on a 32m2 floor. We allowed for 20% replacement boards and got away with <5%.

Clarifications: 1. I should have said 'replace the floorboards' after adding the layer of PIR. 2. The VCL goes in 'hammock-wise' first, and the insulation goes over that - the mineral wool within the hammocks and the PIR on top.

And another thought: Are the 'rooms' in the 'attic' habitable rooms, or are they used as such? One assumes not as there is only ladder access. If, then, although there is a floor, they are storage spaces only, then the thermal line above the habitable spaces is arguably the floor - like any conventional 'loft'. Lift the floorboards, put 220 between joists (with lambda value 0.044W/mK that would give you an R value of 5m2K/W) and sit a layer of 25mm PIR (Kingspan/Celotex-type board) above. That will give you a U value of 0.1629 without the 'base case R value' (which is 1/an assumed U value of 2, so 0.5). Add the 'base case R and you get 0.15. While laying all this 'engineer' the ventilation so it all comes in the eaves and over the insulation and the job is a good one. For extra peace of mind lay a vapour control layer (Pro Clima Intello Plus is pricey but good) between and up and over all the joists in 'hammocks', and tape all joints and perimeters to keep water vapour out of the void space (and get a really well-sealing hatch too).

The only time I saw a contractor try to invoke the '15 year rule' it was for an external wall insulation job where they had installed 40mm phenolic board, not 50 as per their quote which would have met the wall target of 0.35 at the time (pre-2010). BC insisted that the '15-year assertion' was backed up by a SAP calc. The SAP assessor totally misunderstood the builder's 'brief' (if there was one) and (with a torturing of mathematics which even I - a relative mathematical ignoramus - could not have managed), managed to 'prove' that 50mm of phenolic *would* pay back in 15 years (remember he was supposed to prove it *wouldn't*! So BC insisted he install 50mm (which in reality meant a layer of 20mm over the existing rendered 40mm. Not the world's most impressive moment.

Before you can 'dial it in' you need to know what flow temp the system was designed for. I always used to ask for a re-calc if I saw a quote assuming a flow temp of 55 degrees. That can be a way of getting out of changing many (or even any) rads, but I'd rather consider changing them and get an answer as to what the CoP would be at a lower flow temp.

Bldg Regs require 0.18W/m2K for an extension. Yes, yes, yes!! Do wet plaster. If you must adhere plasterboard do it either on full-coverage adhesive (rare as rocking-horse poo) or with full perimeter bead and close cross-hatchings. Better still, don't use it!