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Re: Premanufactured Metal Buildings

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> From: "Brian S Bossley" <bsbossley(--nospam--at)>

> Can you design a premanufactured metal building with no slope?


> What is the minimum slope allowed?

"Allowed" is a question that you have to answer.
"Possible" is 0:12.
Slope is a serviceability issue. What is appropriate for the project? Do
you want to use typical profile steel cladding or will you apply a
conventional BUR? Profile steel cladding can only shed water in one
direction, making a flat roof difficult to drain, IF required.

Even conventional roofs are not "flat". Tapered insulation and natural
deflection help to shed water. Nobody seems to have a problem with that.

> From: "David Maynard" <davemaynard(--nospam--at)>

> Why wouldn't you want a slope to your roof?

Sales people complain that some customers (and municipalities) do not
like the gable appearance. This can be hidden with parapets or even
modified with gambrels to keep the slope.

> From: "Bruce Holcomb" <bholcomb(--nospam--at)>

> I worked for a metal building mfr. for 5 years.  We used a minimum roof
> slope of 1/2" per foot for screw-down roof panels and 1/4" per foot for
> standing seam roof panels.  This is in agreement with section 1507.4.2
> of the IBC (and probably older codes as well). =20

I'll have to check that one.

> I remember another engineer designing a project with 1/8" per foot roof
> slope, but that was pretty unusual and IIRC, there was discussion about
> voiding the warranty.  Of course, the flatter your roof, the longer it
> takes for water to run off and that gives it more time to find a hole to
> leak into the building. =20

> Ponding becomes more of an issue for lower slope roofs also.

True, but not more than a conventional roof. L/240 doesn't distinguish
between cold-formed Zs and OWSJ.

> From: "Jason W. Kilgore" <jkilgore(--nospam--at)>

> > Can you design a premanufactured metal building with no slope?
> > What is the minimum slope allowed?
> Yes, and the minimum slope is whatever is required for drainage.

So, any roof that is as "flat" as a "conventional" roof is fine.

> Also, different manufacturers can do different things.  Some manufacturers
> are only capable of designing the "classic" PEMB with some minor changes,
> and some can design pretty much anything you can dream up.

I like your attitude!

> The most interesting PEMB I saw leave there was a church that looked like
> the starship Enterprise (NC-1701, no bloody "A", "B", or "C") in plan.  The

> Typically, though, the more you deviate from the "classic" system the more
> your PEMB costs.

At that point, you could also say that the more you deviate from a
classic "conventional" structure, the more your building will cost. It
is all relative.

> From: (Sorry, I lost the attribution and the posting wasn't archived
>        at SEAINT)

> Zero slope is not PEMB

Possibly not 100% "PEMB", maybe. But PEMB is not defined JUST by the
roof system.

> - it's a conventional system and you'd be hard
> pressed to get a PEMB manufacturer to go that route.

True. But you can get anything if you wave money.

> 1/4 in 12 is the minimum slope allowed and at that point it needs to be
> a standing seam roofing system.

See "allowed", above.

Standing seam roof is not a panacea and is not the limiting aspect. Some
"standing seam" roof panels should be more appropriately called
"standing overlap" panels.

One of my specialties is to deal with the butt-ugliest, messiest
concepts that anybody would want to build ... using a PEMB. Want to
house an operation supporting a 100T crane; a 100' tall process
building; a church for the Gene Roddenberry followers; an indoor soccer
stadium; a mine complex in Siberia; a green roof; a PEMB with 0:12? Call

There's no secret: know the product and the manufacturer's capabilities;
write fully developed generic spec; review the competitive quotes with
knowledge; insist on seeing a fully disclosed deflection criteria with
the quote; if a manufacturer can't meet your requirements, is unwilling
to try or can't provide a realistic alternative, move on to the next or
use a different approach.

If the owner is advised of "extra" cost, tell them the trade-offs that
the "savings" will create for the project (e.g. lights swaying under
moderate wind loads, future maintenance, etc.). Ultimately, it is their
decision where the money goes and your decision to work with that or

There is no reason that you could not seal a roof and hold water to
depth on a PEMB. There is no reason that you must use only the materials
that a PEMB manufacturer wants to supply. Of course, the manufacturer
wants to sell as much as possible to any project but they can't prevent
you from doing your own Mix & Match.

Paul Ransom, P. Eng.
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)> <>

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