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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorTimSmall
    • CommentTimeJul 17th 2012
     
    A local architect pointed out to me that OSB is not consistently airtight, so I thought I'd do some "blow up" tests on my roof, since I have my DIY blower door in-place.

    My loft conversion has been done with T+G 18mm OSB3, edges glued with PU wood glue. The test method was to put some 300x300 ish polythene squares on the face of a couple of the boards, with a bead of acrylic around the margin.

    The Smartply square takes about 15 mins to inflate to 25mm or so at 200ish pascals (possibly a bit more), and the Norboard Sterlingboard takes a little longer.

    He dug up a presentation from the Laboratory of Building Physics at The Catholic University of Leuven, (I couldn't find a copy on the net) whereby they did some testing on OSB brands, and the variation between the best and worst brands was about a factor of 50 (unfortunately they don't give brands, just number the manufacturers 1 to 8. Their conclusions included "OSB as air barrier material for Passive House is questionable". Ho-hum.

    I'm wondering what to apply to it to improve matters? I'm thinking of spraying or rollering one of the following:

    PVA.
    PU wood glue.
    Acrylic emulsion paint.
    Nothing (perhaps such relatively uniform leaks don't matter so much?).

    Any opinions as to which is likely to be best, or suggestions for alternatives?
    •  
      CommentAuthorfostertom
    • CommentTimeJul 17th 2012 edited
     
    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).
    • CommentAuthorTimSmall
    • CommentTimeJul 17th 2012
     
    Yep, I did think of that. All of those should be vapour open-ish if applied as a thin coat. I do have 100mm of PIR (non-foil faced) outboard of the OSB/3, so it shouldn't be critical if I end up making it a bit less permeable.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 17th 2012
     
    I edited to add a calc, Tim
    • CommentAuthorTimSmall
    • CommentTimeJul 17th 2012
     
    Thanks for doing the calc Tom, I hadn't got around to that. Worth considering that the figure is at well over 50 pascals (my pressure meter is on the blink, but I estimate around 200 Pa).

    The location is coastal (England+Wales Approved Document C puts it in driving rain zone 3 "Severe"), so I think I'll try to tighten it up a bit further.

    The OSB did get a bit of rain on it during construction, so I think the resultant swelling etc. can't have helped it's tightness... The results in m³/m²/h/Pa were (approx - I'm reading off the graph on a power point presentation):

    A: 0.01 (range 0.0079 to 0.0138)
    B: 0.0003 (range 0.0003 to 0.0003)
    C: 0.0038 (range 0.0024 to 0.0057)
    D: 0.0088 (range 0.0063 to 0.0093)
    E: 0.0020 (range 0.0012 to 0.0024)
    F: 0.0045 (range 0.0030 to 0.0059)
    G: 0.0020 (range 0.0017 to 0.0024)
    H: 0.0020 (range 0.0018 to 0.0024)

    The Leuven results were between 0.01 and approx 0.0003 m³/m²/h/Pa. The presentation proposed a limit of 0.0018 m³/m²/h/Pa, and gave the Canadian limit as 0.00096 m³/m²/h/Pa.

    They didn't state what thickness boards they tested, just that they tested 8 brands in total from Belgium, Germany, France, United Kingdom, Ireland and Luxembourg.


    My calcs (based on somewhat iffy data) suggests that both of mine (in-situ with EWI including adhesive) are doing something on the order of 0.0003 m³/m²/h/Pa - which is pretty good, on that basis.

    For the PassivHaus which they give as a typical example, you could still achieve the required tightness with any of the tested boards, but it'd be pretty difficult with "brand A".
    • CommentAuthorTimSmall
    • CommentTimeJul 17th 2012
     
    I'll see if I can get some more data points for boards which I have tomorrow...
    • CommentAuthorTimSmall
    • CommentTimeJul 17th 2012
     
    •  
      CommentAuthorfostertom
    • CommentTimeJul 17th 2012 edited
     
    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.
    •  
      CommentAuthordjh
    • CommentTimeJul 18th 2012
     
    TimSmall wrote: "He dug up a presentation from the Laboratory of Building Physics at The Catholic University of Leuven, (I couldn't find a copy on the net)"

    The link given in the LinkedIn thread works:

    http://www.linkedin.com/redirect?url=http%3A%2F%2Fwww%2Emendeley%2Ecom%2Fdownload%2Fpublic%2F35879%2F3686773611%2F9b3c4e723d2042867cf783960db3ebd04e66c472%2Fdl%2Epdf&urlhash=vhXo&_t=tracking_disc
    • CommentAuthorGreenPaddy
    • CommentTimeJul 18th 2012
     
    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.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 18th 2012
     
    Calc it in any interstitial condensation software - it's quite proveable.
    • CommentAuthorborpin
    • CommentTimeJul 19th 2012
     
    [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?
    • CommentAuthorTimber
    • CommentTimeJul 19th 2012
     
    Can't see BCO having too much of an issue with it. It is still considered traditional timber frame used in a reverse wall configuration.

    Just google 'timber frame reverse wall' and load of links pop up from various sources.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 19th 2012
     
    Posted By: borpinWhat exactly is bubble-glue?
    polyurethane gap filling adhesive - will tell you what make we use when an02ew gets back from hol.
    • CommentAuthorborpin
    • CommentTimeJul 20th 2012 edited
     
    Posted By: TimberCan't see BCO having too much of an issue with it. It is still considered traditional timber frame used in a reverse wall configuration.
    I thought we were talking about a standard TF with external insulation?
    • CommentAuthorTimber
    • CommentTimeJul 20th 2012
     
    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.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 20th 2012
     
    Posted By: Timberfrom 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
    Wha? If there's one thing a plywood dinghy has, it's racking resistance - a monocoque. Rings like a bell!
    • CommentAuthorTimber
    • CommentTimeJul 20th 2012 edited
     
    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.
    •  
      CommentAuthordjh
    • CommentTimeJul 21st 2012
     
    Posted By: TimberYes, 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.

    Tie a rope to one corner; tie the other end of the rope to a Land Rover and gun the motor? Are you allowed to provide constructive proof of racking resistance?
    •  
      CommentAuthorfostertom
    • CommentTimeJul 22nd 2012
     
    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'.
    • CommentAuthoran02ew
    • CommentTimeAug 3rd 2012
     
    Posted By: TimberOh and the glue, AFAIK is a polyurethene D4 adhesive. Google and you will find suppliers. The Americans have a product called Gorilla Glue.



    Gorilla glue, i found to be very expensive, probably due to the brand name. google search "D4 adhesive" a good price should be £12-£15 pL
    •  
      CommentAuthorjoe90
    • CommentTimeAug 3rd 2012
     
    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
    • CommentAuthorTimSmall
    • CommentTimeAug 3rd 2012
     
    I've used this:

    http://www.toolstation.com/shop/Adhesives+Sealants/Wood+Adhesive+PVA/Polyurethane+Wood+Adhesive+750g+30+Minute/d180/sd3198/p52489

    but have found that if you are using a lot, then it's cheaper to buy Apollo Speedbond PU Adhesive A9900:

    http://www.sheffins.co.uk/show_prod.asp?ProdID=2287&CatID=36&SubCatID=79

    which appears to be identical - I bought mine from my local roofing supplier - 6 litres for £40 or so (if I remember correctly) - so around half price that you pay for the little bottles. This comes in a can tho', so we use it to refill the toolstation squeezy bottles.


    This from Screwfix looks similar BICBW (and they only stock the 5 minute version - I've been using the 30 minute because I assume it'll soak in better).

    http://www.screwfix.com/p/joiners-mate-adhesive-1ltr/67369
    • CommentAuthoran02ew
    • CommentTimeAug 4th 2012
     
    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:cry: 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.
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 4th 2012
     
    Posted By: an02ewavoid 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


    Think you need this:
    http://www.paintstrip.com/cold.htm

    What we used to clean the PU machines with. Comes is 40 gallon barrels too :bigsmile:
  1.  
    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
    • CommentAuthoran02ew
    • CommentTimeAug 7th 2012
     
    I have read with great interest all the comments on this discussion, and have now come up with a plan whereby i can protect the structure of my 12mm OSB3 smart ply from the rain almost until it has been covered, i will also not only bubble glue on metal flat strip all joint( the Tom Foster method) but also tape all joints and maybe evan seal the outer surface of the osb. The Bib & Brace approach
  2.  
    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.
    • CommentAuthoran02ew
    • CommentTimeAug 9th 2012
     
    Posted By: Cav8andrewan02ew, 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.


    Is 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.
    • CommentAuthorborpin
    • CommentTimeAug 9th 2012
     
    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).
   
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