On Nov 6, 5:08*pm, "Ed Huntress" wrote:
...
Second, here's US Steel on the subject of using weathering steel for roofs:
http://www.ussconstruction.com/metal/metal/corten.shtml
Ed Huntress

They do say it can rust through though not by pitting. However this
lot may be surplus due to poor chemistry.

I have galvanized roofing from Home Depot on the flat wood shed roof
where it collects rust-promoting oak leaves and branches over the
winter. A few of the sheets had started to corrode from trapped water
when I bought them (at a discount) and a couple of those spots lost
all the zinc and began to rust after exposure. LPS-3 applied yearly
has almost stopped them from growing although one tiny leak did
develop.

It's a serious nuisance to spray a large surface I can't walk on. Most
of the wood shed roof panels are weighted down rather than screwed so
I can remove them for maintenance or replacement when a large fallen
branch dents them. I can reshape a crumpled panel fairly well with a
rubber hammer and pipe anvil but it needs to overlap by several
corrugations afterwards to be watertight.

I roofed half of my storage shed with the galvanized steel, angled 45
degrees which sheds snow once the weather warms. The northern side is
clear SunTuf polycarbonate, over PalRuf PVC which falling acorns soon
punctured. To allow rapid repair I made two of the six panels on each
side removable hatches and put a strip of PT decking along the lower
edge to support a ladder.

My grandparents on a hill farm in Alabama had tin roofs on the house
and outbuildings and being the lightweight kid I had the job of fixing
them when we visited. They didn't have road salt or oak leaves and the
metal had only a light coat of rust, mostly the wind caused damage
there. I'm sure it was higher quality roofing than the 29 Gauge that
HD and Lowes sells.

Another discussion on accelerated rusting;
http://greenisles.com/objectio.htm

Jim Wilkins