Hmm

If inflating 25mm at centre, say 15mm av over the area, per 300x300 in 15 mins, what's that for say a 12' x 12' x 8' high room, 2 walls and roof exposed? (12x8x2 + 12x12) x .015 x 4 = 20m3/h for a 31m3 room = .65ac/hr. Not disastrous, but there's that 50:1 variability, and I've been using the stuff 9 not 18 thick.

Before rollering stuff on, have to consider water vapour permeability too, if you're looking for airtight but vapour-open(ish).

I edited to add a calc, Tim

I'll see if I can get some more data points for boards which I have tomorrow...

Hey that Linkedin thread is a treasure-trove of real expertise - I need to dig around, see if there's more. Don't know much about Linkedin, Facebook, Twitter, mobile phones and all that precocious stuff - high time I did!

Good to see our Viking House on there, and glad to see his robust defence of 9mm Smartply OSB3, which an02ew and me have standardised on (it's no-added-formaldehyde, too). We don't use silicone - we bubble-glue and screw it to the lightweighted stud frame, like a plywood dinghy, with dryliner's galv angles and flatstrap as board-edge noggings.

Gents,

what information do you put forward in our details to building control, so that they accept the design of timber frame without a "traditional" vapour control layer. I really want to go down this OSB airtightness route, as "traditional" internal membranes is a pain, but I dread the response from the BSO.

[sound of broken record] Icynene in the TF? It pretty much seals in terms of being air tight yet lets the timber breathe in. Get the right thickness (in and out) and you will not get any interstitial condensation.

Posted By: GreenPaddyGents, what information do you put forward in our details to building control, so that they accept the design of timber frame without a "traditional" vapour control layer. I really want to go down this OSB airtightness route, as "traditional" internal membranes is a pain, but I dread the response from the BSO.

A key reason why I did not go that route and instead went for a Light Steel Frame. I am sure in a few years it will be a standard detail though.

Posted By: fostertomwe bubble-glue

What exactly is bubble-glue?

Posted By: borpinWhat exactly is bubble-glue?

polyurethane gap filling adhesive - will tell you what make we use when an02ew gets back from hol.

Ah, ok, my bad.

Hey, if you put enough EPS on the outside, the 5/1 rules may still apply.

You can stray quite a lot from the 5x rule, but there are only a few ways to make it work properly.

Anyway the BCO/3rd party certification thing is a tricky one, but I could see a case being made strongly enough to convince a BCO that is would be OK, subject to a couple of things like a cavity on the outside of the insulation (behind cladding (I know I keep harping on about cavities, but they are important)) and a way to ensure moisture resistance around window and door penetrations (as well as the use of a breather membrane).

The only thing I would say about fostertom's method (and photo) is that you need to ensure that racking resistance is achieved. I like the approach, but from a structural point of view you need to make sure you can prove it works. Screws don't have the same shear capacity as nails, and the glue joint is something that can't be justified if it is a site based opperation (BS 5268 and EC5 don't allow it (to the best of my knowledge)).

Anyway, I will keep quiet now and watch with interest.

Oh and the glue, AFAIK is a polyurethene D4 adhesive. Google and you will find suppliers. The Americans have a product called Gorilla Glue.

Yes, but if you need to submit structural calculations to validate the racking resistance, you can't take contribution from a site applied adhesive (if I remember correctly). It is not a controlled process, so the only 'official' contribution to racking resistance you can take is from the screws. Screws have less shear resistance than a similar sized nail, so they may be needed at closer centres than nails.

In addition, all board edges should be supported on timber noggins or rails. I know you are usin the metal flat strap, and I am not sure if this is 'ok' but most (if not all) racking resistance calcs are based on board supported on timber studs and rails with no intermediate board joints.

I agree that practically it is a very strong build method and is well up to the task, but proving by calculation might be a bit tricky.

Edited to add - Sorry all I must stop being so negative but it is the pesimist in me, plus part of how I do my job!

Second edit to add - something that is more relevant to the thread... It is interesting the leakage of OSB. I had wrongly assumed that it would be a bit more air tight than it appears to be. However, when leakage testing a whole building, surely the leakage from the other areas of the building would be far greater than that through the OSB, as is attested by those who have used this method and achieved excellent air tightness test results.

IN addition, exposure to moisture an swelling of the OSB would reduce its air tightness as the compressed board expands a bit. However, under normal exposure to moisture during construction, OSB/3 doesn't really swell much at all. Only more prolonged wetting without a much chance for the boards to dry results in board swell. So in a normal build program, the exposure to rain shouldn't be an issue.

I'll ask my SE but he's never questioned the soundness of the monocoque box - he has a nice way of saying 'by inspection' in his calcs - which means 'it's obviously OK'.

an02ew,

I thought from the description that "bubble glue" expanded or foamed slightly, could you tell us what product you used, its not advertising if you dont work for the company and a few of us on here would like a recommendation based on your experience.

Ta

Joe90
You thought correct the glue that i use does bubble/foam slightly on curing. I have not stuck (excuse the pun) to one brand or supplier, but for convince and because i think the product has a limited shelf life, i buy as i need usually online, say 4/5 litres at a time in 1l or 750ml bottles. usually paying between £12-15 pl. the product looks like a thick maple syrup when open in the bottle lid, but be careful not to leave opened for long or you’ll waste the whole bottle, also either wear gloves or avoid getting on your hands as i have not found a solvent that will remove it as yet and it just has to be left to gradually rub off once applied a reaction with the air occurs and the glue foams to fill any gaps and dry’s hard. I have also found that it can’t be used on small loose items i.e. stair spindles and infill, as the glue expands it pushes apart the small loose items and one instance all the infill lifted and all the spindles slipped down the string cap to end up in a heap on the floor. despite that it is a very useful adhesive and i will always keep some in the van.

I have used Den Braven Montagefix 750 ml cartridges @ £2.45 + from A one tools & fixings (hope its OK to mention supplier) as my bubble glue.
What does anyone think of this product as an alternative air barrier (to sheet membrane) on OSB, Fastight Airseal Coating @ fastight.com

an02ew, what would you consider sealing the outer surface with and would you have any concern that it might compromise the vapour permeability of the roof and the 5 to 1 ratio. My suggestion for the Fastight Coating was for the inner face of OSB before facing with plasterboard/Fermacell.

Posted By: an02ewIs there any reason why i cannot move the air tight layer(OSB) to mid way throught my wall make-up? as i in my wall make up, from the outside: 200mm EPS on 11mm osb(airtight layer) over 147 timber frame filled with warmcell 500 covered with Plasterboard.

Will you still have a VCL on the inside? I considered much the same but it is not an approved construction method so you may have a battle with the BCO. What is on the outside of the EPS? Most EWI systems are approved if you have a cavity _between_ the EPS and the OSB (which is crazy).