Roof felt

[Jackal]

Hello I wonder if anyone can help.
I live in a Victorian terraced house and there is no roof felt under the slates,all there is is a sort of white powdery stuff which is falling to bits as every time i open my loft ladder i get showered in it.
Do i have to have felt put on or what else do i need to get done.My roof doesn't leak but i reckon it won't be long at this rate.
Any help appreciated.

 

[noseall]

the crumbly white stuff is torching. this was used before felt and helped hold the tiles down and prevent wind lift. your tiles will not leak without it but will be moderately less secure.