Redbeard

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!

I agree there are epc assessors out there with a huge amount of general and 'eco' nous. I also know there is at least one who cannot recognise EWI. Yes, his certifying body was as nonplussed as me. I wouldn't have asked him to give any opinion on air-tightness and I am not sure that the (basic) training equips them. Some of the air-tightness testers I know only do it with a 'blower-door and thermography package', but I would guess a 'pressurise (or de-pressurise) and go' person might do it for £400 or less. Any members with recent experience?

Fingers are crossed on your behalf.

Thanks for this. No PP a/c at present. Will look at getting one. It accepted my details 'in English', but then when I moved to (card) payment it reverted to German.

I'd still encourage pressure on the developer, though I note that you said at the start of the thread that he was not particularly 'forthcoming'.

Do you like the Albert Hall? Small 'mushrooms'? More seriously I think previous posters are right that 'softening' is the most important bit.

I wonder if someone who has used this firm could advise. Unfortunately I speak no German. There is a 'translate' tab, but it seems to disappear (with no obvious way of getting it to reappear) when I get near paying, so I don't know what to click on to pay... Thanks in anticipation of your help.

Was there anything in your purchase 'stuff' which states an air-tightness test result. If not, ask the developer what is was. It may cost around £400 to get a basic A/T test which will give you a 'number' (in m3/m2/hr or air-changes per hour), or a fair bit more to get A/T and thermography at the same time. De-pressurise the house with the fan on a day when you can get a +10 degree C diff between inside and outside temp, and you get an IR 'pic' of the leaks. If the discrepancy between the developer's stated no. and yours is significant, ask awkward Qs.