New close board porch roof....underlay required?

[vards01]

I am in the process of replacing some elements of my rotten porch, and someone suggested using some underlay under the tile battens:

1) Would this be necessary?
2) in todays market what would be a good product to use

Thanks for the pointers in advance,

Untitled

• vards01
• 18 Aug 2011
• 2