Does anybody know if timber treatment is mandatory in Scotland for timber framed buildings?
I usually work with timbers with higher natural durability, but I'm considering a project which involves construction of closed panels in the workshop and I want to use CLS or some other regularised softwood for the studwork etc.
Finding anything like that which is naturally durable or boron treated seems pretty impossible unless on a contract basis and that would be rather expensive (haulage etc....), and I don't want to use wood with conventional more toxic treatments.
The panels are going to be constructed using an NBT specified wall build consisting of Pavatex woodfibre insulations which results in a highly higroscopic breathing wall.
I thought that untreated studs would be ok but on checking (by google search) I can find nothing which says this with certainty.
So I thought the great mine of knowledge at the GBF might be able to reassure me before I dive into the building regs. myself!
Cheers
Justin

Yes the closed panels will make up the walls and roof of a house in Aberdeenshire.
My worry really is whether the building control officer will accept untreated timber for the structural frame.

Not sure how you'd go with closed panels, but with post and beam we kept the BCO happy by dipping the ends of the posts in Pro Bor.

Ah, that last was a reply to Peter not Nick!
Nick I was indeed wondering whether the sole plates might be the only members that really need to be treated. I suppose your BCO was concerned about the bottoms of the posts?

Hello again, here I am with an update and a new request for help.
The plan to produce closed panels using untreated C16 softwood has been slowly grinding along since the last posts above.
I have found that in most cases where untreated timber was used the very common negative response from building control, insurance companies (NHBC etc), engineers etc. were dealt with through the involvement of an architect willing to go the extra mile.
In order to offer a closed panel system that is seen as a solution not a problem, it should not push the project architect outside of their comfort zone, so I’m now in the process of applying for grant aid to do some university based testing of the panels, with the aim of gaining a ‘registered detail’ certificate from building control.
As expected the grant giving bodies require more than the dreams of a chippy turned budding entrepreneur as proof that there is some demand for these things. I am pretty convinced there is a demand out there, from talking to my clients and architects, but they want something closer to what you might call data.
Does anybody here have any ideas of anything that might impress them?
I’m wondering for example if there is any organisation in the uk which promotes healthy living environments in the home (equivalent to the Healthy Building Project in the US), or recycling and reuse of building materials, which might have done some research?
Anything anyone has come across really.
Cheers for now
Justin

http://www.safeguardeurope.com has full specs for liberal brushing or spraying Pro-Bor on untreated timberwork after cut/fit/assembly - which has the advantage of being drawn into the 'capillary' butt joints between members and so soaking right across the cut ends - which pressure treatment doesn't achieve on anything but small section timbers - the core of most timbers is left untreated.

Posted By: Paul in MontrealSo strange. Almost all buildings in this part of Canada are timber framed. None of them use treated timber, except maybe for the sole plate - and even then, it's often not required if the right sort of sill gasket is used.

How much of a problem is rot in old buildings generally in Canada? Does the climate cause lots of it as it does in the UK?

Most of the timber in our house is untreated. I think I did use treated for the bottom of the sole plate structure, even though they're on DPC strips on a slab with a DPM underneath it! Our expectation is that it's pretty dry and is protected further by the hygroscopic properties of the straw. Bottom of the sole plate isn't in contact with straw and will get any leaks flowing over/through it.

Keep timber dry and it won't rot or get eaten

No need for treatment then :)

Posted By: Justin Rwe had a sort of 'mini condo crisis' of our own in the UK, but rather than ingress of water from the outside the problem was condensation due to faulty design and materials

And the solution was - inner VCLs - which we're still ideologically lumbered with.

The inner VCL panacea worked (for a while, until thicker insulations came in), but not, my guess, for the reason assumed.

They thought that water vapour originating from inside was the main (or only) source of water within the construction, and that it was transported by vapour diffusion, so they cut it off by a vapour barrier.

In fact water within the construction originates overwhelmingly from outside; ebbs and flows through the fabric diurnally and annually; and even more significant than vapour diffusion, is transport by bulk air movement through the fabric.

So these (hitherto asbsent) VCLs were succesful not because they were blocking uni-directional water vapour diffusion, but because they also accidentally worked as a crude air barrier (hitherto absent), resisting bulk air ebb-and-flow through the fabric.

Nowadays, with thick insulations, the danger of intersitial condensation has ramped up, beyond the ability of this crude panacea to cope. As an air barrier it's inadequate, gappy, unless done much more perfectly, As a vapour barrier it's a disaster, because thick-insulation constructions rely on being able to re-dry freely both inward as well as outward.

The latter has caused development of premium-price 'intelligent' VCLs which claim to lower their water vapour resistance at times when inward-drying is needed. My messing with WUFI showed clearly that in at least the constructions I was modeling, and at least in southernish UK climate, the walls performed much better with an excellent air barrier but no VCL at all.

These were developed in continental Europe

Posted By: djhwe're the only one with a mild maritime climate instead of a continental one

but IMHO it's a con to sell them (and foolish to specify them) in souhernish UK except maybe over swimming pools or something.

Posted By: Timberheavily insulated timber frame structures using a poly VCL on the inside and a drained and vented cavity on the outside do not suffer from interstitial condensation

But according to WUFI, the outermost part of the insulation (in the order of outer third, quarter, fifth) regularly reaches 95% RH in winter, so condenses more or less, and needs all the re-drying capacity it can get, to make it short lived/intermittent/harmless (so I don't put any timber product within the outer 40% of the sandwich), and as I say, WUFI shows that's best served by no VCL at all (but of course, v gd air barrier). In the weather region and in the construction I tested.

Good - but 120/140 is I'd say top-end of the 'old' (apx current Bldg Regs) insulation regime, where trad VCL does work still. What happens when you double the insulation, or more for full PH?

What about 80mm of rigid foam (fail faced) between studs with 80mm (fail faced) inside of the studs?

I could use less inside and sill get a reasonable u value for the dormer, but I need to use lots of 80mm for IWI on all the brick walls.

Posted By: djhestimates the number of days at a particular RH it will take before mould appears

That sounds more accessible that WUFI which has a module for that.

Fostertom - If you play the numbers, 120mm of rigid foam in a 140mm stud frame with brick cladding and a service zone can get a U-Value of 0.19 W/m2K.

Certainly not barely scraping through old regs! Placed in the coldest part of the UK and modeled with a high internal relative humidity (high occupancy) there is no condensation risk.

I find it hard to understand why there is such a resistance to accepting what works. IN the US and canada thy build using a standard poly VCL on the inside - its cold in Canada! In the last 10 years in the UK, over 100k new build timber frame houses have been constructed using mineral wool and rigid foam insulation with poly VCLs on the inside. These also work!

I am not putting down 'breathing' construction or whatever you want to call it, but it does wind me up when supporters of breathing walls state that normal TF structures don't work. It is just plain wrong.

Anyway, way off topic now. If you want to use untreated timber in a timber frame wall then good for you. Go for it. BUT it is foolhardy to ignore what is a requirement of warranty providers and a recommendation o British Standards (BS 8417). If you can obtain a 3rd party approval, then that should help deal with the warranty provider issues and give customers and clients some comfort.