Following some part Q housing development here, I re-gained possession
of a 60' x 15' steel frame lean-to.
Having already erected it twice, once as originally intended and a
second time after an exciting barn fire, (pics. available) I felt
invested in a further use:-)
I acquired a neighbouring yard in 1983 which had a range of buildings
blown together from materials available to the demolition contractor
owners at that time. One 55' x 16' blockwork wall barn build with an
almost flat tarred felt roof seemed an ideal location as the existing
roof was sagging badly and leaking.
Some free steel I beam and 20' steel purlins salvaged from the housing
job came my way and I was able to fabricate the extra 4 legs needed.
Last week was part fit the roof week and today was the first opportunity
to observe the impact of light rain.

Hmm. Not good:-( Agricultural roofing meeting BS5502 class 2 can slope
at 12.5 degrees which mine does. The roof sheets are 18' long insulated
steel sheet coated with a plastic finish. What appears to happen is that
water droplets gather on the surface, eventually two neighbours mingle
and start a run: gathering more droplets as they go and reaching the
drip with sufficient energy to partly overshoot the 6"gutter!

Gutter position was always going to be an issue as the thickness of
insulation and the 4" cut back drip are well across even a 6" gutter.
The situation worsens as there is only one suitable place for the soak
preventing a dual slope gutter and access is very restricted due to a
lean-to glasshouse along most of the wall:-(

Current thinking is to see how it performs in different rain patterns
with a fall back plan to fit a 90degree deflector to the roof edge. Need
to avoid splash/mist gathering on the exposed insulation.
--
Tim Lamb