Redbeard

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....

I don't know which bit of NW you are in but have you tried Manchester-based People-Powered Retrofit for pointers?

Title's changed - too late!! 🙂 Sorry...

Am I allowed to say anything about garages and marsupials?

Is your garage really brick, or block. Just that if you are looking to render it it seems to be an expensive way to build...?? Uselessly, cannot answer the render Q, I am afraid! I think my first port of call would be to ask the manufacturers/suppliers of EcoRend.

But ST, that was probably ever thus to a very small extent, and, though traffic is lower, there is still some good knowledge and good debate on there. I am not a regular reader of other forums except this and GBF, but I guess any forum has to 'gloss over' the grumpy and (sometimes) the misleading.

Still there!

Years ago I had the most basic Black and Decker model. (Maybe think cheapest 'own-brand' from SF or TS now). I made my own windows, routed details on existing windows and generally used it a lot. I killed it in the end but it was fine. Just for an edge on window boards I'd go cheap-but-'known'. I bought a very cheap paddle mixer from a hitherto unknown source (I have stopped contracting and have just a little of my own stuff to do. My long-standing mixer died just at the wrong time) and, though it works, the quality is truly pretty awful. It does mix plaster but I would not normally buy something that grim.

From Eco Therm's website: "Eco-Versal is a 5 in 1 insulation board with a thermal conductivity of 0.022 W/mK. " The relevant values are the thermal conductivity (Lambda) values. In both cases they are 0.022, so the Eco Therm product will give you the same result. Yes, 100mm Celotex will give you a (not very exciting) U value of 0.22 for the insulation only, but so will the Eco Therm. This figure does not take into account the perimeter/area calc, but the 0.13 U value does. So Celotex will give you 0.13 and Eco Therm will too, using the same calc. Therefore the minimal extra cost will be a minimal extra cost for exactly the same result.

How old is the house? Could some of it be lead paint? Check the precautions required

Don't expect much acoustic performance from PIR. Density is your friend there.

60mm wide is generally what you'll get in UK, with 150 for taping holes for Warmcell-blowing. I used to get 100mm from Baunativ (now less keen to supply to UK, or were when I checked) which has a split backing tape. I rip it down to 50mm. For general use that's enough width for what I need it for. Leave a roll 'un-ripped' for any areas you need wider.