osb & plasterboard external walls

[wiss20]

Hi, 

 

I'm going to be boarding out my extension walls soon,, I'm planning on battening then 9mm osb then 12.5mm plasterboard over that (no insulation) some of the walls are external (100mm cavity, brick/wool/block) do I need a vapour barrier behind the osb at all on the external walls??

I'm not keen on dot & dab, also I'm doing this myself so think this will be easier not to make a mess of !!

[Russell griffiths]

Why the 9mm osb, I don’t see what it adds. 

 

How are you planning on providing an air tight layer, you will need to do something 

either wet plaster, or a parge coat, or dot and dab done correctly or a vapour control layer

 

you need to do something or your just building a leaky sieve.

 

So really you need to supply something. 

 

Edited December 27, 2020 by Russell griffiths

[tonyshouse]

Osb may not be dimensionally stable and warp, buckle etc, what centres will the battens be? 
 

you may be building yourself a colander where outdoor air can get in bypassing any insulation in the walls. 

[PeterW]

2 hours ago, wiss20 said:

Hi, 

 

I'm going to be boarding out my extension walls soon,, I'm planning on battening then 9mm osb then 12.5mm plasterboard over that (no insulation) some of the walls are external (100mm cavity, brick/wool/block) do I need a vapour barrier behind the osb at all on the external walls??

I'm not keen on dot & dab, also I'm doing this myself so think this will be easier not to make a mess of !!

is this being skimmed ..? If you are doing it yourself then get some of the board fix foam - Easy to use and you get it tight to the blockwork with very little ability for air to pass around the back of the boards. 

[wiss20]

Yeah going to be skimmed over,, not looked into using foam to fix with actually,, the reason for the osb was to give strength when boarding over battens (300 centers on battens) at least the walls will be solid without the hollows of dat and dab,, so if I do go down the batten route would I be best to put a vapour barrier direct onto the blockwork behind the battens? 

[ProDave]

12.5mm plasterboard is okay spanning 600mm centre joists with no support.  At 300mm battens you do not need the OSB there unless it's specifically to fix something to.

[SuperPav]

Having had an extension in another house with similar construction by an average builder (rendered block, rockwool batts, block internally, with dot and dab plasterboard), I can tell you that the air tightness of the inner leaf of blockwork can be incredibly poor, with a gale blowing behind the PB. I'd be tempted to wrap the wall in membrane before you batten over it.

 

Are you adding battens for a service void, or just to mount the plasterboard to? If the latter, then I can echo the above and recommend the foamy adhesive - much easier to at least create contained pockets behind the boards with less air leakage (also helps reduce fire spread I believe!).

 

Alternatively kill two birds with one stone and just wet plaster onto the blocks?