Timber frame workshop

Discussion in 'Trade Talk' started by Bcjoiner, 2 Jun 2014.

  1. Bcjoiner

    Bcjoiner

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    I'm building a timber frame workshop, starting off with a 4" concrete block layed around the perimeter then a 4"x2" wall.
    I'm still to decide whether or not il do a shallow pitch or flat roof.
    I have 100mm celotex to put inbetween walls then was planning to put a 9mm osb, tyvek, batten and then clad.

    Is this a correct process?? I've been unsure whether celotex was to thick & how I go about air flow in the wall??

    I got all the insulation off a building site & a lot of it is paper lined with tiny pin like holes, think it's used for roofing. Is this ok?
     
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  3. Nekkid

    Nekkid

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    Why are you putting osb between the insulation and the cladding?
     
  4. foxhole

    foxhole

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    I would put the tyvek behind the cladding.
     
  5. AronSearle

    AronSearle

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    You are not supposed to do this.

    Cladding / battens / membrane.
     
  6. AronSearle

    AronSearle

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    You need a VCL on the warm side of the wall.

    The insulation is fine, when you say paper lined, do you mean foil faced?

    Either way its fine, but with foil facing a VCL is more important.

    When fitting the rigid either make the panels up so that you can push the studs up to the insulation (so make as panels rather than a stick built frame), or use squirty foam to fill in the gaps betwen insulation and studs (and their will be gaps..
     
  7. Nekkid

    Nekkid

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    Hi Aron,
    Would the foil on foil faced insulation not act as a vcl in itself? If you have a vcl on the warm side of the wall and foil facings on the outside, you effectively have 2 vcls which i have learnt is a big no no as moisture will get trapped between them.or have i misunderstood the function of a vcl?
    The reason i ask is i live and work in Sweden at the moment and the way we build here ( all timber frame, obviously!) is, from the inside out, sheetrock or osb etc, plastic sheeting ( ie total moisture barrier) insulation, wind proof sheeting (but NOT moisture proof) , battens, cladding ( usually timber).
    Im moving back to the uk soon and am trying to get a handle on the uk terms and products!
    Thanks!
     
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  9. AronSearle

    AronSearle

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    With foil faced insulation fitted between the studs, the concern is that water vapour can only pass through the studs., or if poorly fitted through gaps between the insulation and studs, as you say it's foil faced on both sides so the studs are the only breathable material.

    There is a little contention on this issue, but mainstream thinking is that a VCL on the warm side will stop the moisture "concentrating" through the studs and causing condensation within the face of the stud or those gaps.

    This is based upon the UK climate where vapour movement is mostly inside > out, other countries in more southern climes can see the reverse, in fact specific membranes have been made to deal with the potential for reverse condensation (I.E Intello membranes), though they are not relevant here.

    Remember the main point of a VCL is to maintain a 5x1 ratio of breath ability, with rigid foam the argument is that with a VCL, or with a taped joint over the studs, moisture can escape 5x times more easily through the studs and gaps around the insulation than it can get in.
     
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  10. Nekkid

    Nekkid

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    Thanks Aron.
    So the vcl is not a total moisture barrier? Here we use plastic sheeting which is obviously totaly moisture proof. Maybe because there are stricter rules about ventilation. Am i right in thinking that the only requirement of building regs re ventilation is that you have ventialtion in the windows ( the little slider thing)?
     
  11. AronSearle

    AronSearle

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    All models assume it is not, moisture gets through gaps/laps and punctures (no workmanship is perfect, british builders even less so).

    I'm not quite sure on building regs, I think if the building achieves an air tightness rating of 2 or less, you have to have some kind of mechanical air ventillation. To put that into context most well built timber frames with a VCL should achieve less than 10 without any struggle, and 5 with somewhat relative ease if care is taken, 2 or less and you are talking passive house type stuff.
     
  12. Nekkid

    Nekkid

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    Of course we Swedish builders make far fewer holes in our vcls than our british counterparts! ;) what i was getting at though is the actual material the vcl is made of, is it totaly moisture resistant? Ie in an ideal world the vcl should let no moisture at all pass in either direction.....true or false? Or is it supposed to be permeable to some extent? I can qualify my previous comment about plastic by saying that the goal is to have a 100% moisture barrier. Obviously its true what you say there are always punctures and joints.

    Which leads me to wonder, if you build pasive, how do you avoid puncturing the vcl when you screw your sheetrock??

    Man ive got a lot to learn! Its a bizarre thing not being able to talk about what i do for a living in my native tongue!
     
  13. AronSearle

    AronSearle

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    VCL's technically have a vapour resistivity value so high they are practically impermeable, but some gaps are inevitable no matter the workmanship and that's what models assume.

    With passive its not unusual for the board materials to also provide air tightness as well as a VCL (or to not even have a VCL), for instance OSB/plywood is sometimes used, expanding glue at all joints with a coat of vapour resistance paint, this gets around the issue of screw-holes.
     
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