[Greenbuilding] roof replacement asphalt versus steel

[Bruce Donelson]

> I have seen lots of exposed fastener roofs where the fasteners wiggle
> out, especially on the lower part of the roof. This is more prevalent
> with
> lengths longer than about 20' (6 meters)



Thanks for expanding upon your first statement, Bruce.

I'd have to say that I too have seen exposed fastener roofs where the
fasteners have been "wiggled out".

But I'd also have to say that in most cases, they were very old roofs that
used nails ("lead-heads").

I'd also have to say that in those cases, the skip sheathing into which
the nails were driven weren't what one would call "solid" material and
walking around on those roofs was not unlike walking around on top of a
mattress.

On exposed-fastener roofs where screws were used, driven into solid
purlins, I'd have to say that the instances of wiggled-out screws is rare
- the exception rather than the rule -with perhaps one or two errant
fasteners at most in the entire roof.

That would seem to indicate that the problem is due to a defect in the
purlin (assuming that they weren't just driven into something like 1/2"
sheathing) at that point or perhaps a problem of work(wo)manship rather
than a characteristic that is inherent to exposed-fastener systems.

If the errant fasteners, when they do occur, are most often found at the
lower part of the roof, then this could be viewed as a Good Thing in that
that part of the roof is the most accessible and hence, the "problem"
(such as it is),  is easy to fix.

> The concealed fastener metal roofs seem to be immune to this fastener
> loosening, maybe because of the restricted space between the two metal
> sheets

Since the material, length of sheet, screw shank/thread profile, climatic
conditions etc are the same for both types, then any wiggling-out
forces/mechanisms should also be the same, or so reason would suggest, the
only difference being with concealed fasteners, one would not see the
misbehaving fasteners because they're ... concealed ?

Good Points All

I had a shop in a barn with 2x6 purlins and pans about 25' long. Almost all
of the screws in lower two purlins had wiggled out. I replaced them (age
about 15 years) and had "raised" a new crop the next year, when a high wind
tore off a pretty good section. Admittedly a light gauge steel. I replaced
fasteners on that roof at least three years running.

Another job I worked on had exposed fasteners in pans about 20 to 25 feet
long. It was 1 year old and had exposed fasteners into 5/8" OSB. Most of the
lower fasteners were loose, and some had already backed out nearly an inch.
This is a very common occurence.

I've never seen this occur with zip-lock panels. I think it may have to do
with the sheets being so close together. The better panels also have some
process where they can expand along the fasteners. This is either done with
slots in the panel, (my favorite) or with clips that can slide along the
steel. If the screws were backing out, they would show bumps in the roof
where the pans were being lifted up. Snap-lock roofs which I have
disassembled have never shown any loose screws.

Errant fasteners have not been a problem with loosened screws. Every loose
screw I have ever dealt with has been embedded in solid wood purlins or OSB
or plywood. Errant fasteners will often leak, because the neoprene isn't
compressed at all, but it doesn't tend to get the screws to back out a long
distance.

Bruce Donelson
A Better Builder