My husband recently passed away unexpectadely and we were in the process of installing new smart siding. We currently have wood siding and there doesn't seem to be any type of tyvek underneath. I pulled a piece of existing siding off and found some kind of board with the words PS-57. My husband was very organized and tyvek was not ordered. I don't think he thought of doing that otherwise it would have been ordered. Do I absolutely need some type of sealant underneath the smart siding. With hopes of a clear answer.