In message , Cursitor Doom
writes
On Sun, 23 Jun 2019 23:39:24 +0100, Jim GM4DHJ ... wrote:

not talking about sarking felt but old fashioned close boarding timber
sarking etc......I think you English are just too tight to use it ,,,and
its requirement for counter battons .....got to build properly in the
near of Scotland .....

I don't think it's anything to do with cost; just that the further north
and west you go, the wilder the weather.

Victorian barn and farmhouse here, mid Herts. have timber sarking.
Relatively small slate (9"x18") roof may be linked.
Interesting boards: about 9" wide and barely 5/8" thick. Unwarped so
must have been carefully cut.

--
Tim Lamb