"The Natural Philosopher" wrote in message

Very low. Sub 15 degrees with machine made interlocking tiles, however
careful laying is necessary.
I shouldn't think there would be much danger if the new roof is
sheltered by the original building. The problem is that rain may be
blown back up the underside of the tiles.

I would go for the widest possible roof. Then -if there is a failure,
take
the tiles off and put some damp proof membrane in or a couple of lines
of
silicon with each course of tiles.

How many tiles high will the roof be?


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