What kind of board is it?

[mh1988]

Hello,

I am wondering what kind of board was used in houses from the 60s.

It's on the rafters (under battens and roof tiles). Could it be minerit/eternit board or some other type of mixture used in 60s houses instead of tongue and groove boards.

 

[Gabbe1]

That definitely looks like a fiber cement board.
It was not uncommon in the past to put a thin (about 1-2mm) fiber cement board on the outside of the wall construction but under the surface layer/façade. As an alternative to today's weather protection, like outdoor gypsum or asfaboard.
I have not seen it on roofs before, but it might also have been used as a roof underlay.

 

[mh1988]

That definitely looks like an eternity board.
It was not uncommon in the past to put a thin (about 1-2mm) eternity board on the outside of the wall construction, but under the surface/facade. As an alternative to today's wind protection, such as exterior gypsum board or asfaboard.
I haven't seen it on roofs before but it could probably also be used as an under-roof.

Thanks for the answer.