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RE: Factory Mutual Span

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As I recall, an FM Class 1-90 rating applies restrictions on the deck type,
gage, and fastener spacing.  The primary concern is the wind uplift.  I've
changed companies and don't have access to a copy, but I think the relevant
document is:

1-28 Wind Loads to Roof Systems and Roof Deck Securement

FMRC sells their standards through their web site at:

I've worked on roofs for which the insurance requirments were tougher than
the building code requirements, so it might be wise to verify what is

Rex Donahey
Composite Technologies Corp

-----Original Message-----
From: Brian K. Smith [mailto:smitheng(--nospam--at)]
Sent: Monday, March 27, 2000 12:46 PM
To: seaint(--nospam--at)
Subject: RE: Factory Mutual Span

If you look a little further up in the chart, you will see the maximum SDI
clear spans for the same deck.  Unless the insurance carrier for your client
is specifying that you meet factory mutual ratings, I would stick with the
SDI clear spans.

Brian K. Smith, P.E.

> -----Original Message-----
> From: Richard Lewis [mailto:rlewis(--nospam--at)]
> Sent: Monday, March 27, 2000 10:15 AM
> To: seaint(--nospam--at)
> Subject: Factory Mutual Span
> I am looking for information on the maximum Factory Mutual span for 22 ga.
> 1-1/2" wide rib roof deck.  My United Steel Deck catalog gives a 6'-0" max
> span for the FMS span.  The footnote tells me this is for  class 1
> construction.  It refers to FMRC Approval Guide.
> Can anybody elaborate of what this means?
> __________________________________________________
> Richard Lewis, P.E.
> Missionary TECH Team
> rlewis(--nospam--at)