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OSB Size For Covering Wooden Frame (Outdoor Workshop)

Discussion in 'Wood / Woodwork / Carpentry' started by Skavenger, 7 Sep 2017.

  1. Skavenger

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    OK so I am building a workshop in my garden (project here). The block base is completed and I am now building the frame work.
    The wooden frame will be covered with OSB, waterproof membrame, battens and then clad with something?

    So for the OSB (which is now getting expensive!!) is 9mm OK - I am trying to work out and mark my stud spacing so the size of the OSB is critical so that I can get the OSB joins flush at the corners.

    Thanks
     
  2. Skavenger

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    Just found this which, although from a company selling a product, seems to suggest that the OSB is dependent upon the centre spacing:
    600mm = 11mm OSB
    400mm = 9mm / 11mm OSB

    Mmm any advice would be appreciated?

    Or should I OSB the inside and just waterproof batten and clad on the outside?

    Slightly confused?
     
  3. foxhole

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    The wider the supporting timber spacing it the more likely the osb will warp, cheaper to use 11mm as less timber needed to support, I would fit it internally then you have decent surface to fix shelving etc too.

    Please login (registration is free!) to view this link.
    http://www.timberclick.com/south_west/sheet-materials/osb-boards.html
     
  4. Skavenger

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    Thanks for the link - much cheaper than locally.

    I was going to OSB on the outside but now I am not sure having looked at several different build options. My only concern with just membrane and cladding on the outside is vermin and insects getting into the insulation?
     
  5. foxhole

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    Insects can't get thru membrane , rats can chew thru anything so not a consideration .
     
  6. Skavenger

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    So looks like I am going to OSB on the inside and insulate between the OSN and the cladding.

    I am looking at Celotex and Rock Wool but I can only find Celotex 50mm as the smallest Rock Wool is 100mm (to thick to fit between my 70mm studs, also may work out more expensive?
     
  7. big-all

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    you can get thinner rock wool i have been helping a mate fit 70mm a few weeks ago
    but remember the 18-25mm air gap between outside cladding and insulation
     
  8. Skavenger

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    Is that 18 - 25mm between the insulation and the membrane or between the membrane and the cladding?
    If it's between the insulation and the membrane then I am not sure how I can hold it in place.
     
  9. big-all

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    rockwool will sit where you put it vertically just cut it about 10mm wider to grip the sides
    outside cladding membrane airgap then insulation
     
  10. Skavenger

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    Here is a cross section of how I understand the structure / insulation:
    [​IMG]

    11mm OSB 3 fitted to the inside of the timber frame.
    50mm Rockwool / Celotex or Kingspan fitted up against the back of the OSB.
    20mm Air Gap (Due to 70mm wide timber frame)
    Breathable Membrane stapled to the outside of the timber frame
    Battens screwed / nailed through the membrane into the timber frame
    Cladding fitted to the battens (Either wood or plastic TBC).
     
  11. big-all

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    yes exactly right
    rockwool is easier to work with as its more giving so accurate cut and gripping with a complete seal will work with +5-15mm where as kingspan nearer +2-7mm
     
  12. Mr Chibs

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    Celotex is twice the performance of rockwool... so 50mm celo/100mm rocky
     
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  13. Skavenger

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    Thanks

    I can't seem to find 50mm rockwool in rolls, it comes in slabs but it's designation is sound insulation. Looks like I may have to go with Celotex?
     
  14. Skavenger

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    Switching back to the original question ref OSB. I am using OSB3 18mm for roof and 11mm for internal walls. Comparing prices OSB3 18mm is cheaper from wickes than TimberClick £21.50 v £16.99 (when you buy 3 sheets).
    wickes don't do 11mm OSB 3 TimberClick do for £13.99. wickes do do 11mm OSB 2 (Non Structural) - do I need structural on this timber frame? If so looks like I'll get the 18mm from wickes and the 11mm from TimberClick?

    TP are extortionate!
     
  15. Mr Chibs

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    I'd get the 18mm, with a load of screws in, it will be pretty strong.
    PS, don't think they do 50mm rockwool, I was just commenting on thermal values.
     

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