SimonD

I'd agree with that. The unfortunate thing is that this is an accepted aspect of "standard" timber frame details, whether SIPS or not. See, for example the Scottish timber frame standard details here. This detail is a thermal bridge, but it is 'okay' (not my words btw). Better would be to add a block with improved thermal performance as a starter - this is actually mentioned in the Scottish standard details. It's absolutely essential. This is where using a service void to the inside of a timber frame is a blessing as it will reduce risk of perforating the vcl. Usually, the vcl in this buildup should extend beyond the bottom of the internal face of the wall and a distance along the floor over the floor insulation, under the screed which should then prevent excess moisture ingress to the sole plate. As long as the sole plate remains dry enough, then the rot risks are significantly diminished, which does mean you need to ensure moisture can get out if it gets in too. Kingspan do have a detail where there is an additional layer of insulation outside the timber frame, but I don't know if that extends to sips, or render board as I've only seen the details for this in brick clad timber frame. It still bemuses me why building practise hasn't moved to standardise wrapping the timber frame with an external layer of insulation. I actually did this with my project. Initially BC were a weary of it, but having given them some research paperwork to back up my design, they've been fine with it. The problem you're experiencing here is so typical. You're probably being squeezed between purists who will detail the hind legs of a design, and try to cover every worldly eventuality, whether it's overkill or not, and the commonly lazy, this will do construction company attitude. But also the answer to your question isn't entirely black and white which means you're going to get variations in opinion. As this is causing you to worry, I would personally look at it slightly differently: A material with better thermal performance under the sole plate would help things out from a thermal bridging perspective and this may help reduce risks of condensation. With that in mind, what is the opportunity/cost ratio if you will? Is it marginal, or significant? Do you have both the time, opportunity and budget to add this detail into the build? If so, would it significantly ease your concerns? If it would, then I'd think it's a sensible thing to do. From a decision making perspective, one of the things I've found with my build is that when I've decided to do something that improves the performance of the fabric of my house, once I've made the decision and done it, I feel good about it, even it if came with cost and inconvenience. When I've decided not to go with a potential enhancement, I've had a lingering question nagging away in the back of my mind of what if (unless that 'what if' was totally out of budget or reality of course! ?).

Oh, that’s where I’ve been going wrong then... On the plus side the timber delivery driver did say he will be praying for me.

Isn't that the one you reach for when you're about to break ground?

As @Rogersp suggests, 'the bible' is a good book and each edition is different as it tends to cover different projects. I'd also ask what information you're after. Are you after something that gives an overview of the self-build process together with advice? And/or do you want more nitty gritty stuff like how a house is actually constructed together with more technical information? For more detailed information you could take a look at The Construction of Houses or Building Construction Handbook For something similar to House builder's bible, you could look at Self Build Simplified by Barry Sutcliffe

I wouldn't lose any sleep over it. As long at the frame retains sufficient vapour control to avoid excessive moisture ingress, it's unlikely you'll suffer condensation problems. Standard stick build timber frames typically have up to 15% repeating cold bridges due to all the studs, top plate and sole plate, which is why the frames nowadays often have an additional layer of insulation either to the inside or outside of the frame. Does your drawing show an internal layer? However, even if it doesn't, there are numerous frames just like it around the world, many in far harsher environments that have performed and survived just fine. As it is, you're probably better focusing as you are on airtightness and vapour control detailing.

Oh my, I feel for you Jilly. What a frustrating situation. So are your plans now to draw a line under this builder chapter and take on the remaining works yourself or are you going to try and find replacement builders? When I was starting my work, I had no less than 4 neighbours come and talk to me and share their experiences with builders. All of them had firms either letting them down, 2 of them disappearing, one leaving incomplete work, delaying completion and claiming they had done to completion. One of the builders actually left one neighbour when they got to the roof structure and when chased just said he wasn't interested in the rest of the work anymore! I know it doesn't help solve your situation but hopefully illustrates that you're not alone in this.

If you build up as the OP, using plywood or osb sheathing on the inside of the frame, you don't need an additional vcl as the sheathing does this job and then you just need a breather membrane on the outside, this is particularly the case if you're using a vapour open insulation. AFAIA there is not requirement in building regs that you have to have a plastic vapour control layer, it depends on your buildup. You simply need to ensure that the internal side of the wall is sufficiently less vapour permeable than the outside. No, you don't need an extra layer of plastic between the ply and the stud as you're using a different wall buildup than is being suggested by @Marvin who is suggesting a traditionale wall buildup. You are using what is called a reverse wall. If you decide to put your plywood on the outside of the timber frame instead, then you would need a plastic sheet. With your buildup, taping the joints is fine. If you want independent reference, have a look at this article that explains the differences in wall buildup and why. https://www.architectsjournal.co.uk/archive/the-breathing-wall-is-a-simple-concept-but-often-confused-by-linking-it-only-to-particular-wall-constructions-all-timber-walls-breathe

It's a pretty standard detail, not a lot you can do about it other than design the timber frame to have an external layer of insulation, which is what wood fibre is often used for. You could also bring up the eps to above the sole plate. What is your timber frame buildup as from the drawing it looks like there is something outside the timber frame before the battens and cladding?

Yes ?

The irony here is that this is exactly how the international tax system works and why we've got massive multi-national companies avoiding local taxes. It's called transfer pricing where companies allocate earnings and profits to low tax regimes, utilising various tax treaties between individual countries. Rather makes a mockery of these dearly held EU mechanisms even if the EU is trying to clamp down on this practise. I'd hazard a guess that the Brexiteers thought they could implement a similar system with Brexit and trade agreements, but who knows...

It is a weird thing and as @SteamyTea says, when it's about investor speculation, it's just one facet of rentier capitalism - if you've got the money you buy up finite or in demand natural resources and then restrict supply for your own income. However, there is a contract where they do technically buy the commodity, it's just agreed at a specific date in the future. The contract is then settled either with the actual product or cash, but the contact can be bought and sold anytime until the contract is due as the value of the contract varies, so it's a popular way for traders to make money. During the pandemic oil futures went into negative territory because those who had futures couldn't sell the contract, or the oil, so would be hit by huge storage costs and were offering to pay to get rid of the contract.

Ply doubles up as vcl in this buildup. Agree with other comments re 9mm as the board for epdm. I'd suggest considering using the 9mm play on the inside of the roof (unless that's already planned) and then either doubling up as @TonyT suggests or getting in either osb or ply in 18mm.

I think all our timber supplies were decimated during WW2 and never replanted enough so we've had to rely on imports for timber. I read an article fairly recently that UK timber plantation owners were preferring to limit local supply because the capital value of the plantations was comfortably increasing year on year, making a good investment. I wonder whether, with the current lumbar prices, we might see a wave of local British timber hitting the market....

For me it's interesting that those 2 are also traded as commodities where their futures values have rocketed recently as have all raw materials. Unfortunately this can decouple their value from mere supply/demand because the high values attract investors looking to make a quick buck, which of course inflates their value even more, producing an unpleasant inflationary cycle. As you say, it's interesting that construction isn't back to full steam yet. According to this article https://www.building.co.uk/data/market-forecast-high-hopes/5111690.article construction output is still below pre-pandemic levels. Another point the article mentions is that infrastructure projects are maintaining demand. Something else I came across was that supply capacity hasn't been keeping pace with demand for a good 10 years or so, thus we already had a foundation of a constant upward trend in materials prices. I suspect that as recovery continues, we're actually going to see further problems with supply and thus price inflation, and some opinion suggests it's going to continue for at least a year or so.

Yikes, that's expensive! But yes, OSB supply is a problem. Is the pine plywood you've been offered definitely a structural grade? Probably Elliottis pine if it is, I'd guess. The pine plywood should be fine for sheathing, it's been used for donkeys for sheathing. The only times you need to worry about mould is if the moisture content in the wood becomes too high, but then you're likely to get problems with the osb too. If your shed is built right, it'll be dry enough and ventilated enough so no need to worry. Don't whatever you do put that vapour barrier you linked to above on the outside. You need a breather membrane. Your builders merchant should have something on the shelf that'll do the job. I'd recommend you go for 100mm insulation at least. HTH.

A few weeks ago it was £240 + VAT for grab up to 18t for us - Bristol/North East Somerset area.

My sister used Wiltshire building control for a project and it was fine, no problems there.

I've recently received an expensive front door which is 2.1m high by 1.2m wide. I'd seriously thought about making it myself but my wife talked me out of it. I'm glad she did. Ours is made with Accoya and is well insulated. I has a steel reinforcement frame, necessary due to its size, plus multi-point locking etc. The door weighs 107kg. It's also manufactured as a door set with inset heavy duty hinges, three at the top, one at the bottom. Overall, I wouldn't have managed anything even remotely close to this and I do think it takes a lot of skill (and tooling) to produce something like this diy that will last.

I kind of meant it in jest but there was a more practical undertone. Since self-building, my head has been so full of questions and information on how to get it right, there's no room for how not to do it. But in any case, if you want to learn how to do something well, it's surely better to spend your time listening to and watching someone who's good at it, not someone who's crap at it, no? Understanding how not to do something doesn't get you anywhere, other than maybe some entertainment value from other peoples' disasters. ?? I haven't watched one of these programmes in probably 10 years now but one thing I did always wonder was how on earth so many people seemed to find an extra 300 - 500 grand or so behind the sofa to complete the project....

Stop watching Grand Designs (or any other self-build programme) ?, spend some time learning how to make decisions and save up your money. Think about how much of the work you want to do and then try to develop any necessary skills and some experience ahead of time - or not if you want to pay someone else to do it all; then you can sit back, drink beer and consume design inspiration ? Otherwise I'd just be repeating what others have said..

Those seem like good prices at the moment and they have availability. My local timber merchant said they can't get osb until maybe June sometime. Having just looked it up, it's interesting that price difference is now only a few quid between chipboard, osb and ply (I know, I'm slow on the uptake ? ). I've not used Radiata pine plywood yet but by all accounts its quality is up there with the usual European stuff - however, I'm off to a specialist plywood supplier later this week to look at samples of some other Chilean plywood for furniture making. If you like, I can report back on that visit if there's anything helpful in what I find.

Yes, context is important, I agree. That said, it won't always end up with additional cost and wastage. E.g. at 400 c/c the equation changes. I don't know what board pricing is right now but last I received comparative quotes for Egger v osb, the osb was significantly cheaper. My approach would be to use the materials most suitable to the situation and design. A developer or contractor will no doubt approach it all differently to a one man self-builder. I lay out the board arrangement in CAD first to know how the boards will work. The last time I calculated and boarded a floor @ about 100sqm I ended up with less than 3 boards in total wastage as off cuts and zero noggings. The last time I left it to builder & supplier, I ended up with 4 boards extra from an approx 12sqm room including noggings..

I disagree. It's just as suitable for modern floor systems. You'll typically still frame posi and JJI joists at either 400 c/c or 600 c/c (or 16" and 24" c/c), so there's no problem there, other than with a little measurement and lining up the board properly at the start of a run. No big deal. If you really need noggins with posi and JJI, I think in many cases it's easier as you're clipping and nailing these to the top flange, just as you would to support a partition wall with these systems. Alternatively you can use full depth LVL or timber with packers and full depth blocking. James Jones have a great technical library illustrating all these details https://www.jamesjones.co.uk/assets/uploads/assets/downloads/brochures/site-guide-floors-3rd-sept-20.pdf

Wow, plywood used to be about 2.5 times the price which is why I went with osb. I'd go for plywood without any worry.

Yes, of course, but isn't that the case with any floor board? And surely you'd frame your floor to avoid that problem.