Continuity of air space under cladding

11 Apr 2006
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United Kingdom
I'm building an insulated timber frame outbuilding. It's a fairly standard studword and PIR board design, the outside of which is clad in OSB sheet, then breather membrane, then vertical battens to provide a 25mm breather space, then cladding.

My question: Should the eaves/soffits be design so that the 25mm air gap behind the cladding has continuity in to the 50mm air gap in my roof, all the way up to my ridge vents?


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You would want to seperate the two cavities to stop fire spread, do you care about this in an outbuilding?
No- I don't care about the fire risk. My main concern is in the structure not holding on to moisture and rotting.

To be honest, there won't be that much interstitial moisture anyway - it won't be heated and will just be an occasional room, but I guess the job of the cavity is to also make sure any rain/storm moisture has good chance to disperse.

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