Redbeard

Well that sounds a bit positive. Is that the floor dpc I see in one pic? If so, take the opportunity to tape the dpc to the plasterboard (ideally it would be to the VCL -foil - behind the plasterboard but you cannot win them all. Gaps can be air-leaks and since (esp. if you are having MVHR) your ideal is to have the house lined with an air-tight 'bag', those junctions are important. When you deal with one plane think of the joints with all the others, and of continuity - insulation and air-tightness. For example is the kitchen single-storey? If not, my future plans would include taking up floorboards as req'd in the room above, sealing (I would use air-tightness primer and air-tightness tape) around the joist ends (potential source of air-leakage) and then insulate from the kitchen below up to the ceiling (or to the underside of the floor if you intend to 'come back to it later'. I suspect you may have missed a trick in that I assume the insulated plasterboard was fixed up to, and touching, the exg ceiling. If I do a GF room my ideal is to cut back the ceiling and run the insulation all the way up to the floor above, with air-tight works as described. (Yes, on the wall with the jsts parallel you might find a tight space (or no space at all) but cross that bridge when you come to it. It's all tedious, but think of the feeling when you know you've cracked it! Good luck.

"Perhaps we're simply better off double glazing (prioritising on the poor windows) and just living with the weak roof insulation? " Noooooooooo! Please don't think that. You are in the relatively rare position (in that most of us inherit part-insulated buildings) of potentially going from 'nothing at all' to 'something' in terms of insulation, and that is the steepest part of the curve. It's all diminishing returns after that. If you think you can add 100 mm (50 between, 50 under, resulting in a net loss of 50mm 'head-space') then, with PIR, you should get a U value of around 0.25 - 0.3W/m2K (includes a very crude adjustment for the 'timber fraction' - the amount of the insuation depth which is not actually insulation, but timber instead). The target is 0.16W/m2K, but the un-insulated 'base case' which you have is 2.00! Do it, do it, do it, please! Windows can be subjected to 'quick fixes', particularly with regard to air leakage. If you do not have to open them why not tape them up for the winter? And don't discount the 'cling film' 'secondary glazing' - remarkably good. Both short-term measures (and make sure you retain enough 'intentional ventilation') but can yield good results while you concentrate your major interventions on the roof.

Forgot to say, where do you think the air is leaking from? Is there a ventilated suspended floor? If you are 100% satisfied that there is no air-space between board and wall then maybe you don't have to worry re that leakage cooling the whole wall. If you are that satisfied then maybe just seal the bottom of the board with FM330 (though I prefer belt, braces and other measures!)

So was there plaster on the wall to which the insulation boards were attached, or bare block? If the former, maybe OK (although personally I don't like trapping gypsum plaster in a 'sandwich' on the cold side). If the latter, there may be leakage. My preference is always for a parge coat (lime for me) as an air-tightness layer before insulating.

How were the boards fixed? I think I'd be asking a lot more Qs. Perhaps worst case is that they are on adhesive dabs without a full perimeter bead (meaning a risk of - cold - air movement between wall and insulation). If so the best you can hope to achieve (without taking it off again) is perhaps to drill a series of 10mm holes at say 40 - 50mm centres and gun in Illbruck FM330. all round the perimeters. Make good with jpint filler and scrim (or ask the plasterer to do it).

Agree with @ProDave that it won't, as you describe it, have been done under Bldg Regs. Agree that the 'joists' may be spindly, but until you have looked further I would not automatically say don't spend £15k insulating it. A significant percentage of the 19th Century terraces where I live (many of which were built with attic rooms - and some which weren't) have approx 75 x 55 joists. Yes, things get a bit 'springy' if you push the stud walls further into the void, and I am not saying that a SE would be deliriously happy, but delve a bit first. In the terraced house example above there is a spine wall mid-way through the (?9m) depth of the house and stud walls which (albeit with too few nails) to some extent 'hang' the floor from the purlins reducing the front-to-back floor measurement to around 4m. If you can do the insulation work without significantly increasing the loads (and if there are no signs thus far of 'distress')then do consider it, after the aforementioned 'diligent investigation'. What are the joist and rafter sections? It's worth noting that although since 2010 common practice has been to put 50mm PIR between 75mm rafters leaving a 25mm vent path, the 'new' (and poorly-publicised) Gov't guidance (search room-in-roof best practice) suggests min 50mm vent gap, leaving you only 25mm of PIR. Of course we don't have dimensions but it looks like there's little room to spare. In your exploration I would include checking that cross-ventilation is not blocked at the ridge. Even with PIR it is highly unlikely you will achieve something 'Regs compliant' - that would need abt 150mm. Wood-fibre (undoubtedly 'nicer' in my view) would need nearly double that. Not much room left after that. Interesting Q - although the 'conversion' may have been unauthorised it is now part of the house, and the Regs (Part L) say that if you 'add or replace a layer' (add to or take down the exg ceiling) of a thermal element you must either meet the target U value or agree with BCO a lesser std if accepted by them. I would say that you are within the remit of part L in what you do. Other views may be held. Plenty more thoughts to come if required. Some sort of structral opinion once stripped out would be desirable. (IANASE*) * I am not a structural engineer

I note this cheaper one is 145g/sq. m rather than 160-165 for my previous purchases, but seems fine to me.

I have previously paid between £38 and £50 + carriage + VAT per 50 x 1m roll of render/plaster mesh. I ran a bit short and needed just one roll. I was expecting to be charged at the top end of the price range plus carriage. Almost by accident, yesterday, I found E-Roofing, who have 50 x 1m pink mesh at £28.99 including next-day delivery and VAT. It arrived this morning. Excellent service at a very good price. Can't fault it. (I have no prior experience of this company nor of their performance and prices w.r.t. other products.)

"This sounds like the stuff i have found in other other wall, i imagine it was done a long time back (can't really tell, only been in the house a couple of years) crumbles to nothing when you hold it. I was able to take it out in fairly large chunks. You can see some of it hiding in this small cavity, it's the white stuff protruding, comes out it largish chunks, but will crumble quite easily." Yours looks to have fared a great deal better than my former client's, then. If it is cohesive, as it seems to be, leave it, in my view. Do I need to worry if it is formaldehyde?" As I said, quite possibly not really. Most UF foam was done in '60's and '70's AFAIK and is very likely to have done all the off-gassing it wants to by now. Don't take my word for it; do an internet search.

EWI does not need a void. It is generally a 'straight-on-the-wall' system. Agree with @ProDave re the blockwork - may well be single skin. I worry about the piers as a thermal bridge. The foam in your cavities - was it done a long time ago.? A lot of 1960s (and older houses 'done' in the '60s) have urea-formaldehyde foam CWI. Do not, at this stage, worry too much re formaldehyde, but do bear in mind that it can degrade. I took apart parts of a house to replace spalling brickwork and the UF foam was mainly crumbled to dust in the bottom of the cavity. Not everywhere - oddly - but in places. You will know if it is UF. If you find any 'overblow', say in the loft, it will disintegrate as you pick it up.

Just noticed @SteamyTea's ref to "industrial minting wasteland". Do they have that in Kendal too?

It involves retaining walls, which will probably have more depth and breadth below ground than you might expect. If you have, or can get, a spec for that, and have confidence in your building (and can do the necessary drainage too) then perhaps do that (x3) and the hardcore and tamping in preparation for the final finish (but you'll need to know the depth of the intermediate and final finishes in order to finish at the height you want to finish at).

You appear to have an unmitigated thermal bridge at the sole-plate. You could just take your PIR upstand higher, perhaps.

PIR is very rare in EWI. Plinths are often done in XPS, but thereare 2 schools of thought here - the system providers say it makes everything safe because it is waterproof, and some say that if any water does get in the sandwich the (impermeable) XPS helps to trap it in. For this reason some (including me) use EPS below DPC. If relevant check your BCO is happy with this.

Who specified the OSB? What do they say? Do you have no secondary waterproofing layer (breather membrane)?

Of the 3 I prefer C. As long as you keep the cold ventilation air on the 'right side' you cannot really have 'too much air' (flow). An empty loft void is not regarded as 'too much air', so your vent gap won't be. The flow is to some extent governed by the cross-sectional area of the 'ins' and 'outs'. What vent provision will you have? In terms of the gap after adding battens I don't think you want less than 50mm. Is the roof already built up to the top of the rafters? If not I would take down the ply inside and add 25mm PIR, taped at all joints and perimeters, to cloak the thermal bridge. It's regarded by some as permissible to have the VCL a little into the sandwich, so you do not have to move your existing VCL. You'll just be doing belt and braces by taping the 25 PIR as a VCL too.

If you can anonymise the deed plan and show it to us I think that may provide some enlightenment, as I am not clear exactly what the situation is. If you could also provide a plan showing the original building and the extension that would be very useful. Apologies if you have done this already but if so, perhaps it's on another thread. Thank you!

It obviously depends on quality control, but do not assume that simply because they are marinated in sh** reclaimed railway sleepers will be fine long-term, particularly if used in a retaining situation or as a raised bed. AFAIK railway sleepers in their 'original habitat' were bedded in free-draining ballast, which tends to draw the water away from them, where raised beds or retaining situations may tend to hold the water against the sleeper. I bought several, some of which still seem OK as a retaining wall with loose fill behind (again - drainage, not wet soil) and others which rotted out pretty soon.

Welcome! I am slowly working my way through a single-storey extension of similar size which I have made as complicated as I possibly can! It's post-and-beam (where stud would have been far quicker) because I like post-and-beam, and it is wood-fibre EWI'd (which is good, but I didn't *have* to do it that way). My major issues have been delivery delays and winter. Enjoy the process!

If the site prep and edge retention is good you need not get any sinking, and will only need conc for the retention, not under the blocks. Most 'droopage' is due to perimeters moving out, unless the hard-core was not compacted properly. I take it your proposed gravel area is the top of the pic. Probably a fair chance of it ending up at the bottom of the slope without some form of retention, especially if you put your clog down as you drive up.

I hope so; I did it on my extension roof abutting the main elev. No problems in 6 mths. I think the width of mine was nearer 125 than 165.

Work out your stud spacings, length, section size etc and convert to m3. Multiply by 350-500 (kg/m3). I bet similar figs are around for tiles, pl'bd etc. Try 'engineering toolbox'.

Loosen with manual impact driver then use an electric drill/ electric impact driver? Should have thought that would work as long as you can stop the bit bouncing out.

I did this because I like building timber frames, but it tends to end up looking like any other structure, and not very 'woody'!

TBC, do you want to swap 'sails' to 'Proper' Sail? Was wondering recently what to do with the *heavy* dinghy sail in the shed....