Home>Discussions>EXTERIORS>Can you put sheathing over celotex fibreboard?
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Can you put sheathing over celotex fibreboard?


My parents recently bought a 30 year old 2 bedroom bungalow in order to downsize for retirement. The exterior walls are sheathed with celotex fibreboard (also known as black board, buffalo board, donna conna in some places).

My father is not a fan of having just the celotex as his exterior walls (doesn't hold a nail for vinyl siding application and does not provide as much wall rigidity as other sheathing). It has gotten soft some small areas like around the bath/shower, but appears to be fine everywhere else. We were planning on resheathing with OSB, then adding 1 inch XPS, and then tyvek.

The question is can we just sheath over the celotex with the OSB or does the celotex have to be removed? Would putting the OSB over the celotex cause moisture issues?

It would seem if you put the OSB over the celotex you would just be creating a wall with higher R-value but would it cause any problems that you can think of?

Your input would be very appreciated. Thanks.

Re: Can you put sheathing over celotex fibreboard?

i can think of a couple things right off the bat,

by not stripping it off you wont be able to find out if the soft spots are do to leaks and if its causing rot to structure which needs to be attended to if so

your also going to require longer fasteners for the osb to go up and nail to the studs. and the same goes for installing the vinyl siding.

strip it down, start from scratch and makes sure its structurely sound and weather tight, from there the siding is just lipstick and mascara

Re: Can you put sheathing over celotex fibreboard?

I would tear the celotex down too, inspect for water damage, correct if necessary. Then continue with new OSB or plywood.

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