In article ,
The Natural Philosopher wrote:
Don't boher. it is only there to stop pressure build up blowing
slates/tiles off...

Whilst that may be one factor, it also stops any driven rain reaching the
rafters. And given it's a relatively new idea, how did they stop tiles
blowing off in the old days?

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*Verbs HAS to agree with their subjects *

Dave Plowman London SW 12
RIP Acorn