fixing an old barn roof !!

hi
im just about to put a new roof on an old barn.
i am wanting to place 1/2" ext ply on top of the rafters.
the question is do i have to put a waterproof membrane directly on top of the ply and then cross baton on top of the membrane.
and then fix normal roofing felt before fixing the slate baton.
i think this is called a scotch guard style roof.

if so what membrane should i use directly on top of the ply ?
and what is the best roofing felt i could use before fixing the slate batons ?

Or does anyone have any other ideas !
any help would be great.
charlie

Does it need to be this weatherproof? It is a barn, after all (as in the old question "were you born in a barn?" to someone who leaves the door open).

Ply, felt, battens & tile would be good enough for me. Doesn't even need to be breathable felt.

Or are you converting the barn to some other use?... I think we should be told...

(PS. It's not Speke Hall is it? I think you'll need listed consent for that!)

hi thanks for the reply.

yes i am converting a very large old barn.
in to a very large dwelling
and i do have all the paper work in order.

i have already converted 1 section of the property
and have been living in it for about 5 years.
and i am now doing the rest of the property.

im not a builder, im a scaffolder
but i have done most of the work my self. ill have a go at most things
ive been rebuilding slate and beach stone walls for the last 4 months.
i cant wait to finish them !
and i am very much a belt and braces sort of fella.
this is why i want to use the ply on rafter method.

i have spoken with someone from the builders Center.
he has said the best thing would be to
ply, then
cross baton, then
breather membrane, then
slate baton, then slate.

this sounds about write to me.
what do you lot think ?

THAT WAS PERFECT
THANKS VERY MUCH FREDDY.
THIS HAS ALL THE INFO FOR ME TO NOW FEEL I CAN MAKE THE RIGHT CHOICES.

THIS SITE ROCKS !!!

IN THE WORDS OF ARNOLD S
I'LL BE BACK !
(THE NEXT TIME I GET STUCK)

THANKS AGAIN
CHARLILE