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    •  
      CommentAuthorfostertom
    • CommentTimeMar 5th 2017 edited
     
    Here's what the OSB is glued and screwed to - a minimised timber frame, 4x2 studs 6x2 rafters, coupling with the OSB monocoque skin to minimise need for doubled studs, lintols etc that plague typical timber-frame builds with thermal bridging. No noggings to support OSB edges incl vertical corner and horizontal eave angles - instead 0.7mm galv dryliner's flatstrap and adjustable angle sections. Plain plasterboard to wall and soffit, electricians welcome to penetrate as needed. Blown-in cellulose (Warmcel) between the timber framing.
      2011-07-26 040reduced.jpg
    • CommentAuthorMikC
    • CommentTimeMar 5th 2017
     
    Is the flat strap and angled metal continuous over the studwork, or is it applied afterwards in small sections between the studs? I presume it is fixed with small screws so as not to poke through the OSB. I guess you could use sections of OSB offcuts to do the same job, though it would be trickier on the angled part.
    • CommentAuthorgoodevans
    • CommentTimeMar 8th 2017
     
    Here is revision B of an eaves detail

    I have decided to use a small fascia (fixed to the counter-battens) - sitting just proud of the render - this may leave a small channel above the render and behind the fascia - is this an issue.

    Again an osb skin is laid over the rafters as an air barrier - is this useful as part of the roof structure or do I use a membrane instead? I'm thinking that the vertical osb over the rafter ends would be better if replaced by a membrane.

    The underfelt is located between the counter-battens and the battens and is supported on a eaves tray at the bottom. I think ventilation is needed under the felt as condensation may form on the underside of the felt. but no VCL is required.

    The top plate forms part of the air barrier as the barrier passes from outside the rafters to the wall plaster.

    comments criticisms please any issues?
      Eaves rev B.jpg
    •  
      CommentAuthorfostertom
    • CommentTimeMar 8th 2017
     
    Posted By: MikCIs the flat strap and angled metal continuous over the studwork
    Continuous - lightly tacked in place. Bits of OSB would be harder and as you say no good at angles.

    Several manufs used to supply a range of variants to these sections but seem to have drastically pruned their ranges so you have to get one bit here another bit there. No prob - many ways easier to get a local metal shop to slice and fold glav sheet to a 'cutting list' - unequal leg/exact angle etc - 0.7mm steel is impractical to bend/adjust to angle on site. 0.5mm might be good enough - haven't tried.

    Sometimes it cockles and you just have to put in lots of screws to pull it flat - can see a bit of that in the interior pic - of course there's gap filling glue in the interface.
    •  
      CommentAuthordjh
    • CommentTimeMar 8th 2017
     
    Posted By: goodevansThe top plate forms part of the air barrier as the barrier passes from outside the rafters to the wall plaster.

    Just to comment on this point specifically. It's best not to rely on 'raw' timber as part of the airtightness barrier because it can develop cracks over time. Processed products like OSB are fine (modulo the 'is OSB airtight' issue) because they don't crack in the same way. You will in any case want to use some tape to connect the plaster to whatever else (either plastered in to the wet plaster or stuck on to the plaster after it dries. I prefer the former) so if it was me I would continue with tape and perhaps small widths of membrane to connect the plaster to the OSB.

    PS A single red line on the drawing is a good way to indicate that you have a continuous air barrier.
    • CommentAuthorjfb
    • CommentTimeMar 8th 2017
     
    the OSB is pretty useful as something to walk on as you are installing the EPS/counter battens. Not sure I'd want to be walking around on EPS on a membrane (if I think I get your question right) and hoping i'm on a rafter.
    • CommentAuthorgoodevans
    • CommentTimeMar 8th 2017
     
    good point jfb - the osb on the rafters feels like the right thing to do - keeps the rafters in the the place and just locks the roof together.
    • CommentAuthorringi
    • CommentTimeMar 8th 2017
     
    Posted By: fostertom
    Posted By: MikCIs the flat strap and angled metal continuous over the studwork
    Continuous - lightly tacked in place. Bits of OSB would be harder and as you say no good at angles.


    Have you tried using GRP with roles of reinforcement tape for these joints?
    •  
      CommentAuthorfostertom
    • CommentTimeMar 8th 2017 edited
     
    You mean applied internally after board fixing? Aren't we back to adhesion without mechanical restraint, and getting into impossible corners?
    •  
      CommentAuthordjh
    • CommentTimeMar 9th 2017
     
    Posted By: goodevansgood point jfb - the osb on the rafters feels like the right thing to do - keeps the rafters in the the place and just locks the roof together.

    It's also watertight, and provides good support for a tarp if you want to mollycoddle it.
    • CommentAuthorringi
    • CommentTimeMar 9th 2017
     
    Posted By: fostertomYou mean applied internally after board fixing? Aren't we back to adhesion without mechanical restraint, and getting into impossible corners?


    No I was thinking of on the outside of the OSB and JUST on the joints that are not over a glued stud.
    •  
      CommentAuthorfostertom
    • CommentTimeMar 9th 2017
     
    Aha - maybe
    • CommentAuthorgoodevans
    • CommentTimeMar 9th 2017
     
    Revision C

    The fascia now has a small gap behind allowing ventilation and drainage to the underside of the underfelt.

    A single sheet of mechanically fixed membrane from the plaster to the osb sarking is shown. all that is required is to lay the sheet over the wall before the top plate goes on (or between two plates if puncture looks likely). The membrane can be embedded into the plaster and 'stuck' to the osb sarking with a stiff galvanised strap to hold it down for life.

    a vertical piece of osb (as per rev a/b) can be used here to protect the membrane if necessary.

    I'm pleased with this - looks buildable and simple - any comments/improvements

    Will I be forced to use a VCL
      Eaves rev C.jpg
    •  
      CommentAuthordjh
    • CommentTimeMar 10th 2017
     
    Looks good to me. You'll want some glue as well as the galvanised strap to make an airtight joint - it's the kind of use Orcon F is designed for. Or you could use adhesive airtight tape and put the galv strap over the top. There are tapes designed for plastering in; I don't know how well membrane would work. I'd suggest checking with somebody who knows or doing an experiment before the real thing.

    Don't forget there will be fixings and perhaps straps to hold the wall plate and roof trusses down on the wall. Work out in advance how you want to seal the penetrations.
    • CommentAuthorringi
    • CommentTimeMar 10th 2017
     
    How will the wall EPS be fixed near the top?
  1.  
    ''How will the wall EPS be fixed near the top?''

    Through to rafter ends?
    • CommentAuthorgoodevans
    • CommentTimeMar 13th 2017
     
    Latest incarnation...
    a) Vertical OSB back in - fixed to sarking OSB via angled galvanised plate as per Toms detail
    b) To avoid a split in the top plate destroying the barrier - barrier tape placed either over or under the plate
    c) Top plate to plaster barrier use of osb or membrane.

    onto gable detail next. - new thread.
      Eaves rev D.jpg
    • CommentAuthorlineweight
    • CommentTimeMar 13th 2017 edited
     
    Just on the subject of making airtight joint between sheets of OSB without a timber stud behind... my solution, although this was for internal angles on the *inside* of a roof buildup was to use DPC strip. I put beads of sealant between the DPC strip and the OSB, and then a timber batten (in my case actually a strip of OSB) on top of the DPC, one each side of the "corner". Then screws through batten>DPC strip>sealant>OSB sheathing. I reckoned that DPC strip ought to have a decent lifespan (assuming it does the job its designed for), is pretty tough, and will allow a little bit of movement where necessary. Also, cheap, and easily adaptable to any angle.

    In fact I also used DPC strip where I wanted an airtight seal between OSB roof sheathing and crappy old brickwork party wall. Either "cutting it in" to mortar joints where convenient or using a variation of the timber-batten-screwed-through approach. On these cases the intention was to allow for some movement over time. It was quite fiddly and possibly completely overkill but I did it and feel it ought to stay working for a good number of years.
      Screen Shot 2017-03-13 at 16.38.38.jpg
    • CommentAuthorlineweight
    • CommentTimeMar 13th 2017
     
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      Screen Shot 2017-03-13 at 16.38.53.jpg
    • CommentAuthorlineweight
    • CommentTimeMar 13th 2017
     
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      Screen Shot 2017-03-13 at 16.39.20.jpg
    • CommentAuthorlineweight
    • CommentTimeMar 13th 2017
     
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      Screen Shot 2017-03-13 at 16.39.29.jpg
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