I am finalising my building warrant application information. The original wall build up uses an i-beam frame with a structural wood fibre board on the external face. I had planned to do this on both wall and roof. The structural engineer has now asked me why we're not having sarking boards, but I (perhaps in a slightly misinformed manner) assumed that the fibre board could act as sarking. Clearly I need to discuss this with the engineer.

 

I know a few others on here have made use of wood fibre board on external walls, but has anyone used it to replace traditional timber sarking boards?

Yes I have 100mm wood fibre board on the walls (rendered) and on the roof as the sarking board.  Building control accepted it for the building warrant and the structural engineer had no issues.

 

I am not sure if the wood fibre gives enough racking strength on it's own. Our SE specified an OSB layer on the inside of the roof frame, and 2 layers of OSB on the inside of the wall frames to give the building the required racking strength.

@ProDave thanks, that's helpful.   At the moment we're planning on using structural fibreboard externally that is only ~15mm. I don't need it any thicker as the frame is already wide enough for the target u value. It has the same racking strength as OSB.