Is there a recommendation for the maximum roof area to be drained by 4"
plastic gutter?

Building regulations were a distant dream when my Victorian barn was
built and the twin down pipes discharge through shoes onto the narrow
strip of verge next to the lane. There has been some local subsidence of
the foundations as a result.

I am currently building a single story *end* extension and will make
provision to pipe collected rainwater to an existing surface water
system. However, underground piping from the original down pipes is not
practicable.

Could I route the barn water along the new gutter without annoying
building control? The total area drained would be 35m2 in plan.

regards
--
Tim Lamb