Chopping boards etc are made from hard-woods, oak and similar. Roof timbers are made from softwoods, pine and the like and are not meant to be exposed to weathering because even with preservative treatment, they will eventually rot if they get wet.Wood does not rot after brief contact with water!! Think about it, wooden utensils and chopping boards really wouldn't be a thing if that was in any way possible.
Hard-wood trees grow slowly, they produce dense, heavy, expensive timber very slowly over human generations. Pine trees produce porous, light, cheap, timber relatively quickly. This is the stuff grown by Coillte and investors in tree farms in order to get returns quickly. These trees also blow down very easily in storms, especially when rooted in peat-lands, which has been practice up to recent times.