SimonD

18mm OSB only needs support at short ends on joist, no extra framing required.

I missed that. Yes, not great. I've come across uk framers who believe that if you tape the insulation joints you don't need a vcl - I've also seen it approved by building control.

Why are you looking for 22mm? The 18mm osb is at least 'equivalent' to a 22mm P5 and good for 600mm c/c. I think the only times 22mm is used is in commercial projects and I suspect special order only.

Interesting video. At about 5:50 there's a picture of the stud wall with an octo-stud arrangement! It looks like some of the studs are sistered but surely the timber frame company could have found a more efficient solution?

Tapcon screws are good for this. For your timbers you'd need the 82mm length: See https://www.metrofixings.co.uk/main/product/productinfo/606/5 x 82mm 3F82 Countersunk Concrete Screw/1 Installed at 400 centres should work fine. You just drill a hole, clean out the hole and screw them in. For belt and braces you could add some straps. The first method you mention is the traditional way of building modern stick timber frames. Frankly for a workshop, I don't think it matters that much. However, if it's going to be insulated and possibly heated then with the OSB on the inside, this creates your vapour control layer (providing you tape all the junctions and corners between the sheets) that prevents too much moisture entering the frame from the inside of the building. Then, as your builder has said, you just need a breather membrane to the outside. If you go for the osb around the outside, you'll need a vapour control layer - anything from a thin plastic sheet to advanced adaptable membranes - in the inside of the frame. You'll also need a breather membrane on the outside of the osb. So in a way, osb on the inside can be easier. If you're planning to insulate and have it heated, especially with blown cellulose, you need to get the detailing right on the wall buildup to take the pressure of the pumped insulation, but the osb on the inside should be fine. I'd also suggest that if it's to be heated and you insulate with something wooly, I'd counter batten the outisde of the frame with 2x2 and install an extra layer of insulation. Using cheapo glass wool insulation this will be as cheap as chips. It'll take the edge off the cold on winter and help a bit in the summer. So basically you'd end up with a wall build up from the inside: osb stud wall 2x2 cross battens breather membrane battens for cladding cladding. I would line the inside of the roof structure with osb - to act as your vapour barrier, just like with the walls. With the metal roofing sheets you are going to get condensation on the inside. You must make sure you have a ventilation gap between your insulation and the metal roof. So I'd recommend you plan in battens on top of the rafters. With or without insulation, I'd install a breather membrane on top of your rafters, under the battens. Essentially you'd end up with a buildup along these lines from the inside: osb rafters (with insulation) breather membrane battens (forming ventilation gap) roof sheet As with the walls, it's worth considering the thickness of your rafters and the amount of insulation you can get in there. Just make sure your rough opening are straight and true, ? and a bit larger than your windows and doors. 10mm each side/top & bottom usually works fine. There are plenty of sites that'll show you how to frame rough openings but here is one that covers it https://www.jlconline.com/training-the-trades/framing-rough-openings_o The great thing about timber framing is that you can actually still do most of it with hand tools. All you really need is: Hammer Screwdriver Hand saw Pencil Tape measure Square (speed square is ideal) Spirit level Chisel (Stapler for membrane helps) String (for straightening frame and walls) But you'll need a drill for your sole plate and anchors.. Good luck with it!

I completely agree. I have 18mm OSB and density has never been a consideration by anyone. It's only the structural performance of the board that's ever been considered. It's worth keeping in mind that, as @Moonshine suggested, the building regulations aren't entirely prescriptive and you've got detailing options, often provided by materials manufacturers.

To put the board density question into perspective, I've just bought a load of Knauf Aquapanel Outdoor - the given density for this board is 16kg/m2. Is there actually a timber based board that doesn't contain cement that gets up to 15kg/m2 without a silly thickness?

If it helps, we had redwood floorboards in our old house simply varnished with Ecos Paints (I think it's now called Lakeland paints) interior/exterior clear varnish. Over 12 years it all held up better than our engineered oak floor. I'd be surprised if you could buy it for only ~£10/m2. I just got a price for 40m2 of softwood t&g interior wall cladding which came in at about £25/m2 and that's obviously smaller dimension than floorboards. However, you wouldn't need an additional floor cover.

Good decision. GreenCoat PLX is a great product and a million times better than rubber. Can't believe your roofer recommended rubber as an equivalent! In terms of alternatives, I've only seen one example of a roof using GRP where they'd used profiles to recreate the look of the seams. From a distance it looked vaguely similar and okay but from near the difference was pretty obvious.

You need these they feel a bit weird at first but they really do work. Saved my knees many times. BTW what's the tape/membrane you're using at the plinth? Is it just bitumen felt or is it 'fleeced' - hard to tell in the pic. I'm trying to find a fleeced bit of membrane to go between some timber and aluminium flashing, but might just plump with epdm tape.

FWIW, I just got a price on some Birch interior plywood - 1525 x 1525 x 15mm. £44 per sheet plus VAT. In December I paid under £17/sheet.

I've got a Plumbfix account and can't say it has really benefited me that much at all. I tend to get better prices elsewhere, like even Toolstation, and the 10% discount I've found is only on a small number of products I've needed. They've offered to provide a quote service for larger orders but haven't tried that yet. One thing I found a couple of times was that when buying in person I got a better price than ordering online for click and collect, but maybe that's just my imagination or wishful thinking..

I think @nod sums it up. I was recently asked by someone to look over a quote they'd got from a local contractor known in the area. At the bottom of the quote it said the company is fully insured. The next page detailed the insurance cover which amounted to public liability only. No all risks, no professional indemnity. My sister was once getting some extensive renovation and extension work done and the builder who'd quoted and she preferred was adamant he had all risks cover. He told her to ring his insurer if she didn't believe him. Low and behold the insurer told her he didn't have all risks but only public liability. He then replied that he knew he had sufficient cover, she didn't know what she was talking about and wasn't prepared to take out anything else. Obviously he didn't get the job. I do however know a tradesman who did successfully claim after dropping some heavy wall tiles into an expensive new bath and cracking it. The insurer paid out for a replacement but all in all it took about 9 months to get it all fixed. I think if you want to make sure your contractor is fully insured you're gonna have to comb their paperwork ?

My understanding is that there are sometimes gaps in cover when a contractor only holds Professional Indemnity and Public Liability insurance and that the part of contractors insurance that's important is cover for unforeseen loss or damage to the construction work. This covers rebuild costs, for example. This part of the insurance is often arranged in joint names between the contractor and client. Contractor's insurance is also referred to as all risks. Not all trades need this as the extent of the work being done doesn't necessitate this type of cover. The problem is that contractor's cover isn't always a uniform policy but can be based on multiple separate policies depending on their operating model, so I'd be inclined to go back to the insurer and ask them to clarify exactly what they mean and what that level of cover has to cover!

When I look over this detail I'm most troubled by the box gutter arrangement and cavity. I don't think that woodfibre is suited to this situation. With the box gutter sitting on top of the woodfibre as it is here, there's too much risk of moisture damage as it needs at least 2 or three layers of protection.For example, flashing and membrane/aluminium tape/epdm tape on top of the woodfibre. As far as I'm aware, woodfibre is also not suitable for use in wall cavities, only as external or internal wall insulation, or behind a ventilated rain screen. There doesn't seem to be any ventilation provision here which would need to be in place for the woodfibre. You also don't have easy access if there is a problem at any point. I think in this instance, you'd be better off looking at a mineral wool like Rockwool, for example. This would be cheaper than the woodfibre. HTH

Hi Ollie, Yes, ideally you want to insulate the front of the block wall. This should be down to a minimum of 215mm below the top of your floor beams. EPS would be fine, or XPS. It's common to find EPS 200 or 300 rather than 70 detailed here for the perimeter board. As @Mr Punter suggests you might want to look at your insulation thickness all over and also consider whether rigid insulation is the best option for you in a timber frame - it's more difficult to fit and detail between the studs compared to flexible insulation materials.

Did this detail come from the timber frame company? I think the design is problematic. You don't have necessary bottom ventilation gap for the cladding and you are lining yourself up for water problems both at the bottom of the cladding on the outside and because any water ingress behind the cladding has no way to get out. You can completely remove the 'splash' course as it doesn't appear to serve any particular purpose and will only cost you extra money in both labour and materials. Is your cladding to be installed vertical or horizontally? If it's vertical you need counter battens. You also apper to have a cold bridge problem at your wall-floor junction.

Ah cool. So now I'm itching to ask how you did the curved section? It's very nicely done. I've got curved ceilings which are to be finished with Birch ply too where the curve is created by the glulam beams.

I've just been scanning brochure and installation docs and it does have immersion available. They also sell a PV kit. I haven't read in detail but remains promising.

Is that a plywood finish ceiling? If it is, did you have to use an intumescent treatment?

Great stuff, thanks for the heads up on that. I've been looking for boiler and thermal store setups for a while now and this looks ideal.

That's been my motto too, although I did get some friends over to intall my 200kg and 300kg 1st floor windows. You're actually not too far from me. I've got two hoists, one electric, one chain knocking around. Let me know if you want a hand and when and I'll see if I can make it over. I'm sure we could figure something out. My main problem throughout the whole of my build has been how to get things up inaccessible banking!

Of course, Peter. I used Robbins Timber in Bristol for most of my timber supplies. For my Glulam beams it was Buckland Timber (I needed bespoke curved and straight beams). I actually tried to use Colorcoat Urban. I found that both tech support and sales were so inadequate, that, as you know, I went elsewhere. I'm now very glad I did. There's no way the Tata proposition would have cut the mustard for our project. @Kevin J will no doubt hate me for saying this ?? but I didn't go with Metal Solutions either, even though I did speak to them about my project - they were also kind enough to test whether their snaplock product would work for my roof (sadly it didn't due to curve radius). I used The Metal Roofing Company which supplies the Lindab Greencoat PLX, which is basically rebadged SSAB Greencoat. This, however, is old school either hire in a roofing contractor, who they'll put you in touch with, or DIY from coils. Re toys, I did my entire frame using a Festool HK85 together with a cross cut rail (attaches to saw for all manner of mitres up to 60 degrees) and 2 1400mm rails. I don't think I'll ever go to using chops saws or table saws again as I can just take the tools to the materials and cut everything on the pack..or the floor..or wherever it's lying. I did also use a pheumatic framing nailer, positive placement nailer, hammer, spirit level, and a cheap Erbauer impact driver. Oh, and a tape measure ? Probably most underrated of the toys is my Nilfisk M class extractor which is pretty much permanently attached to my saw - OMG is that one of the best buys I made. That was pretty much it for that part of the build.

Thanks Peter. Is that still the case with cls, blimey. It was an issue when I bought all my cls for partition walls and I bought the last stock from my timber merchants. That was back in December.

Normally the cls comes untreated but I asked for it treated so my timber merchant sent the whole lot off to get treated before devliery. I think a lot of merchants will supply to you treated or untreated.