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July 2008
Page 1 of 13
METAL ROOF SYSTEMS
Insureds of FM Global should contact the local FM Global office
before beginning any roofing work.
Table of ContentsPage
1.0 SCOPE
...................................................................................................................................................
2
1.1 Changes
..........................................................................................................................................
2
2.0 LOSS PREVENTION RECOMMENDATIONS
.......................................................................................
2
2.1 Introduction
......................................................................................................................................
2
2.2 Construction and Location
...............................................................................................................
2
2.2.1 General
..................................................................................................................................
2
2.2.2 Re-cover of Metal Roof Systems
..........................................................................................
3
2.2.3 Metal Roof Systems Used for Re-cover
...............................................................................
5
2.3 Operation and Maintenance
............................................................................................................
63.0 SUPPORT FOR RECOMMENDATIONS
...............................................................................................
6
3.1 Additional Information
......................................................................................................................
6
3.1.1 Structural Design
...................................................................................................................
6
3.1.2 Oriented Strand Board (OSB)/Composite Systems
..............................................................
6
3.1.3 Re-cover of Metal Roof Systems
..........................................................................................
7
3.1.4 Metal Roof Systems Used for Re-cover
...............................................................................
8
3.1.5 Roof Areas Needing Increased Fastening
............................................................................
8
4.0 REFERENCES
......................................................................................................................................
11
4.1 FM Global
.......................................................................................................................................
11
4.2 Others
..............................................................................................................................................
11
APPENDIX A GLOSSARY OF TERMS
.......................................................................................................
11
APPENDIX B DOCUMENT REVISION HISTORY
.....................................................................................
11
APPENDIX C SUPPLEMENTARY INFORMATION
...................................................................................
12
C.1 Metal Panel Types
........................................................................................................................
12
C.1.1 Standing Seam and Lap Seam Roofs
................................................................................
12
C.1.2 Insulated Roof Deck Panels
...............................................................................................
13
C.2 OSB/Composite Systems
.............................................................................................................
13
C.3 Re-cover of Metal Roof Systems
..................................................................................................
13
C.4 Metal Roof Systems Used for Re-cover
.......................................................................................
13
List of FiguresFig. 1. Typical re-cover of existing standing
seam roof.
................................................................................
4
Fig. 2. Standing seam roof in re-cover construction.
.....................................................................................
5
Fig. 3. Standing seam roof applied to OSB/composite insulation.
................................................................
7
Fig. 4. Attachment utilizing bar secured to existing metal
panel. Courtesy of Goodyear Tire & Rubber Co.. 10
Fig. 5. Clip secured to purlinCourtesy of Vic-West Steel Co.
..................................................................
10
Fig. 6. Standing seam clipCourtesy of Vic-West Steel Co.
.....................................................................
12
List of TablesTable 1. Recommended Rating of Field, Perimeter,
and Corner Areas (Zones 1, 2, and 3)
for Enclosed Buildings3
....................................................................................................................
9
FM GlobalProperty Loss Prevention Data Sheets 1-31
2008 Factory Mutual I nsurance Company. All rights reserved. No
part of this document may be reproduced,stored in a retrieval
system, or transmitted, in whole or in part, in any form or by any
means, electronic, mechanical,photocopying, recording, or
otherwise, without written permission of Factory Mutual Insurance
Company.
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1.0 SCOPE
This data sheet provides recommendations for the installation
and maintenance of metal roof systems.Information is included on
new construction, re-cover of existing metal roof systems, and use
of metal roofsystems in re-covering existing low-sloped roofs. The
generic termmetal roof system is used throughout this
data sheet when discussing all three types of systems (standing
seam and lap seam roof systems andinsulated roof deck panel
systems), except where noted. Guidance is also given for those
situations whereFM Approved (see Appendix A for definition)
products are unavailable.
Information and recommendations are applicable to all three
types of metal roof systems unless notedotherwise. Refer to the
Approval Guide(a publication of FM Approvals) and RoofNav
(web-based softwareby FM Approvals) for additional details and
ratings on these systems.
1.1 Changes
July 2008. Table 1 was made consistent with revisions in Data
Sheet 1-28, Wind Design, and Data Sheet1-29,Roof Deck Securement
and Above-Deck Roofing Components. This change raised the safety
factor inthe perimeter and corner areas to 2.0. Prescriptive
perimeter and corner enhancements remain unchanged.Recommendation
2.2.4 relating to gravity loads was added.
2.0 LOSS PREVENTION RECOMMENDATIONS
2.1 Introduction
The recommendations in this data sheet are not intended to
supersede the requirements of any priorFM Approval. They should be
used to supplement the RoofNav listings. For all applications,
follow the generalrecommendations (Section 2.2.1). If applicable,
follow the specific recommendations (Sections 2.2 and 2.3).
2.2 Construction and Location
2.2.1 General
2.2.1.1 Install appropriate wind uplift rated, FM Approved metal
roof systems, where available. Secure thesystem in the roof field
in accordance with RoofNav and the Approval Guide, a publication of
FM Approvals.Use components that are FM Approved for use together.
Use of FM Approved components and systems
is universally recommended and is implied for all applicable
assemblies whether or not specifically stated.
2.2.1.2 Do not accept materials without proper FM Approval
labeling. All FM Approved materials are requiredto have the FM
Approval mark on the packaging or the material itself.
2.2.1.3 Determine design and factored (rated to include safety
factor) field of roof wind uplift pressure inaccordance with Data
Sheet 1-28.
2.2.1.4 Use Table 1 to determine the FMApproved wind uplift
rating for the roof system, including the perimeterand corner
areas, as higher uplift forces on these areas result in the need
for additional securement overthat FM Approved for the field of the
roof. Alternatively, use prescriptive perimeter and corner
enhancementsper Section 3.1.5. Refer to Data Sheet 1-28, Wind
Design, for corner/perimeter definitions, dimensions,
andexamples.
Provide increased deck securement to the next purlin support
and/or deck seam where the perimeter/cornerwidth falls between
purlin supports or deck rib seams.
2.2.1.5 Ensure metal roof systems are designed for snow and rain
loading and drainage in accordance withData Sheet 1-54, Roof Loads
for New Construction.
2.2.1.6 Ensure metal roof systems have a minimum slope of 14
in./ft (21 mm/m). Steeper minimum slopesmay be recommended by the
roof system manufacturer, particularly for lap seam roofs.
2.2.1.7 For lap seam and standing seam metal panel roofs
installed over oriented strand board/foam plasticcomposite
(OSB/composite) insulation, use only FM Approved standing or lap
seam roof systems. Currently,there are no FM Approved combinations
of metal roofs over OSB/composite; however, such installationsmay
be acceptable if installed in accordance with Recommendations
2.2.1.7, 2.2.1.8, and 2.2.1.9.
2.2.1.8 Use only FM Approved OSB/composite insulation with lap
seam and standing seam metal roof. Ensureit secured to the
supporting roof deck per the Approval Guide. Ensure the OSB layer
is a minimum of 58
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in. (16 mm) thick. Determine the spacing of the FM Approved
metal roof system fasteners applied over the
OSB/composite from pull-out tests as outlined in Section
3.1.2.
2.2.1.9 For lap seam and standing seam roofs, when the
supporting roof deck for OSB/composite insulation
is steel, ensure it is FM Approved, 18-22 ga (0.0474-0.0295 in.
[1.204-0.749 mm]), installed per theApproval
Guideand Data Sheet 1-28, Wind Design.2.2.1.10 For protection of
new or re-cover construction of metal roof systems installed
adjacent to Maximum
Foreseeable Loss (MFL) fire walls, refer to Data Sheet 1-22,
Criteria for Maximum Foreseeable Loss Fire
Walls and Space Separation.
2.2.1.11 Do not use perforated liner panels in metal roof
systems where the occupancy uses or produces
a considerable amount of dust, oil, or oil mist. There have been
cases where the dust or oil has collected inside
the panels, greatly increasing the fire spread potential.
2.2.1.12 Provide roof-top walkways in areas subject to frequent
foot traffic to avoid damage to the roof system.
2.2.1.13 Provide thorough supervision by the building owners
qualified representative during all roofconstruction to ensure
quality of workmanship and adherence to FM Global data sheets and
project
specifications.
2.2.2 Re-cover of Metal Roof Systems
2.2.2.1 If the existing metal roof deck is aluminum, consider it
Class 2 when re-covered (an exception is
an existing glass fiber insulated Class 1 aluminum system
re-covered with another metal panel system). When
the roof deck is aluminum, (not necessary with steel roof decks)
remove any existing batt-type insulation
(standing and lap seam roofs) or have it held in place with
steel liner panels (do not use expanded metal or
wire mesh) to avoid shielding of sprinkler water.
Provide automatic sprinklers below all Class 2 deck. Ensure the
existing batt insulation is tight to the underside
of steel decks, with no significant air space (2 in., 50 mm, or
less).
See Data Sheet 1-29,Above-Deck Roof Components, for additional
information on Class 2 roof decks. Follow
the manufacturers instructions as to whether the fasteners
should be driven into or through aluminum forthis purpose. Ensure
the manufacturer confirmed that the fastener/aluminum combination
is not susceptible
to galvanic corrosion.
2.2.2.2 Ensure the new roof cover (single-ply membrane or
liquid-applied coating system) is specifically FMApproved for
re-cover construction on the existing type of metal roof system
(standing seam, lap seam, or
insulated metal panel).
2.2.2.3 Where constructions specified in recommendation 2.2.2.2
are not available, it is acceptable to re-cover
a metal roof system with a row-attached (batten bars or in-seam
fasteners), FM Approved single-ply roof
cover, provided the following is done:
a. For standing seam roofs: Apply two layers of FM Approved
insulation. Use perlite or polyisocyanurate
insulation for the lower layer. Ensure the thickness is the
height of the seams (see Fig. 1). Do not use
other insulation types unless specifically FM Approved for this
use. Ensure the upper layer is specifically
FM Approved for use with the roof cover. In the case of a
polyisocyanurate lower layer, ensure the top
layer is either FM Approved wood fiber or a FM Approved
thickness of the same polyisocyanurate. Ensure
the total insulation thickness does not exceed the maximum FM
Approved thickness of the
polyisocyanurate insulation.
b. For lap seam roofs: Apply FM Approved polyisocyanurate
insulation over the roof. Ensure the insulation
thickness is sufficient to span the rib openings (See Data Sheet
1-28). If the profile is similar to a standing
seam roof, install the insulation per aabove. Ensure the
insulation is specifically FM Approved for usewith the roof
cover.
c. For FM Approved foam plastic insulated panels: To maintain
the Class 1 rating, cover the panel with
a maximum of 1 in. (25 mm) of FM Approved insulation that is
specifically FM Approved for use with the
roof cover.
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d. Have the insulation(s) pre-secured in the field of the roof
with FM Approved insulation fasteners (through
both layers, if applicable) at 1.5 times the rate recommended
for 22 ga (0.0295 in., 0.749 mm) steel deck
(i.e., the rate is three fasteners per board for boards up to 4
4 ft [1.2 1.2 m], and six fasteners per
board for boards up to 4 8 ft [1.2 2.4 m]).
e. Have the rows of roof cover fasteners run over and driven
directly into the purlins. Use a self-drillingtype, adequate for
the thickness of the purlin flange. Apply the fasteners in the
field of the roof at the
spacing FM Approved for 22 ga (0.0295 in., 0.749 mm) steel
deck.
2.2.2.4 For all re-roofing applications, the new roof will add
additional weight to the structure. Have the
structure analyzed to ensure that it can support the anticipated
loads without reducing the live load capacity
below acceptable limits.
2.2.2.5 For liquid-applied coating re-cover systems, complete
surface preparation of the existing metal roof
with strict adherence to the coating manufacturers
specifications. To meet FM Approval requirements,minimum/maximum
slope requirements and coating application rates must be
observed.
2.2.2.6 Do not apply spray-applied polyurethane foam directly to
the top of metal roof systems unless a
Class 2 deck can be tolerated. Ensure the following are true
before accepting a Class 2 deck:
a. The building is sprinklered.
b. There are no Class 2 roof deck MFL considerations.
c. Batt insulation below the deck is removed or held in place
(tight to the deck underside, with no air
space) with steel liner panels (expanded metal or wire mesh is
not acceptable).
Refer to Data Sheet 1-29, Above Deck Roof Components, for
additional information on Class 2 roof decks.
Refer to Data Sheet 1-57, Plastics in Construction, for details
on the installation of polyurethane foam.
2.2.2.7 Provide roof areas that have increased uplift pressures
with increased fastening as outlined in Section
3.1.5.
Fig. 1. Typical re-cover of existing standing seam roof.
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2.2.3 Metal Roof Systems Used for Re-cover
Insulated roof deck panel systems are not usually used for this
application. Hence, the recommendations
in this section are not applicable to these systems.
2.2.3.1 When a metal roof system is installed over an existing
built-up roof (BUR), a combustible concealed
space can be formed (Fig. 2). Therefore, do one of the
following. Also, use noncombustible framing for thenew roof, except
as noted.
a. If the existing BUR has an American Society for Testing and
Materials (ASTM) E 108 Class A-rated
mineral surfaced cap sheet or is gravel surfaced and the gravel
will remain, no other protection is needed.
If the existing roof is Class 1 insulated steel deck, add no
more than 1 in. (25 mm) of additional
noncombustible insulation (glass fiber, mineral wool, FM
Approved noncombustible board stock) over the
existing graveled BUR; otherwise, the Class 1 rating may be
compromised.
b. Remove the existing BUR, insulation, and adhesive down to the
bare steel deck. Note: if the existing
deck is wood, have it covered with minimum 12in. (13 mm) thick
gypsum board (ordinary gypsum boardis acceptable) prior to
installation of the framing system.
c. If the existing BUR is smooth surfaced and the deck is Class
2 insulated steel deck or concrete, protect
the roof cover with a minimum of 6 in. (152 mm) of unfaced glass
or mineral fiber batts. Do not use thisoption if the existing deck
is Class 1 insulated steel deck, as the additional insulation would
probably
cause the deck to be Class 2.
d. Provide dry-pipe, automatic sprinklers can in the space.
Consider this option only if there will be
sufficient access (e.g., hatchways in the existing roof) to the
sprinkler system. Also, the new and existing
framing must be capable of supporting the additional weight.
Ensure the new framing does not obstruct
the flow of sprinkler water to the existing roof drains.
Combustible framing can be used.
2.2.3.2 Fill the expansion joints in the existing roof with
ceramic or mineral fiber and cover with minimum
22 ga (0.0295 in., 0.749 mm) sheet steel fastened in place.
Ensure the steel is designed to allow for
movement.
Fig. 2. Standing seam roof in re-cover construction.
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2.2.3.3 Ensure framing for the metal roof system is adequately
supported by the existing bar joists. That is,
it is not supported by the steel deck at midspan.
2.2.3.4 Remove all wet insulation in the existing roof system.
For details on wet insulation see Data Sheet
1-29,Above Deck Roof Components.
2.2.3.5 The new roof system and framing will add additional
weight to the structure. The increase may beoffset by removing any
existing gravel surfacing or above-deck components (see
recommendation 2.2.3.1
above). In all cases, analyze the structure to ensure it can
support the anticipated loads.
2.2.4 For new construction of standing seam metal roof systems
on cold-formed steel C or Z purlins, ensure
the design is in accordance with the 2007 version of the
American Iron and Steel Institute (AISI) standard,
North American Specification for the Design of Cold-formed Steel
Structural Members. For locations outsidethe United States,
comparable local specifications may be followed, provided the
design of purlins considerestheir lateral support using one of the
following methods:
1. The purlin capacity used in the design accounts for unbraced
length between purlin braces.
2. The purlin capacity used in the design is based on testing
that similates the lateral resistance provided
by the actual deck and clip assembly.
2.3 Operation and Maintenance
2.3.1 Provide regular maintenance of gutters and parapets to
keep them clear of snow, ice, and debris
accumulations. Use open-channel (three-sided) conductors
(leaders, downspouts) in areas where multiple
snow storms can be expected in any given winter season. Another
option is to truncate down-spouts above
potential snow banks or points of possible vehicle impact
(parking areas, truck docks, etc.). Remove snow
and ice accumulations around closed conductors. Use heat tracing
and/or open-channel conductors for
gutters and conductors with a history of ice blockage.
3.0 SUPPORT FOR RECOMMENDATIONS
3.1 Additional Information
3.1.1 Structural Design
The wind-load design of metal roof systems built to other
specifications may not be as stringent as thoseconforming to FM
Approval requirements and the recommendations in this data sheet.
The design uplift
pressures for each installation should be per Data Sheet 1-28,
with enhancements as recommended in this
document.
Roof deck and purlins or bar joists are typically designed for
uniformly distributed loads. Constructing a
framing system above the existing deck to support a re-cover
system may load the structure with point
(concentrated) loads. This loading is usually a more critical
case. The analysis must take into account any
concentrated live, snow, wind, and dead loads from the new
standing seam system, plus the distributed dead
loads from the existing roof.
When designing a new metal roof system, it may be prudent to
include an allowance for future dead loads
due to possible re-cover construction. Otherwise, future
re-cover options may be limited to coating systems
or panel replacement. If, however, these future options are
deemed sufficient, an additional allowance would
not be cost effective.
3.1.2 Oriented Strand Board (OSB)/Composite Systems
Most OSB/composite insulations (see Fig. 3) listed in the
Approval Guideare FM Approved for use with BUR
covers. With regard to internal firespread, a standing seam or
lap seam metal roof is less critical than a BUR.
Hence, if one of these systems is installed directly over an FM
Approved OSB/composite on steel deck, the
construction can be considered Class 1.
To ensure adequate wind uplift resistance, secure the
OSB/composite to the deck as FM Approved for BUR
construction with the appropriate wind uplift rating. The FM
Approved metal roof system is then secured to
the OSB top surface. It is necessary to run pull-out tests of
the metal roof system fasteners driven into the OSB
board to determine the necessary fastener spacing. This is
because the pull-out resistance of the OSB board
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would most likely be less than that of steel purlins for which
the FM Approved metal roof system was designed.
Once the pull-out resistance is known, field-of-roof fastening
density can be determined as outlined below.
In no case should the metal roof fastener spacing be less than
the FM Approved spacing for direct securement
to purlins. By limiting these constructions to FM Approved metal
roof systems, failure modes other than
fastener pull-out are already accounted for. Hence, fastener
spacing can be based on fastener pull-out
resistance. As an option, pull-out tests can be run in the
laboratory on representative samples. The procedure
for determining the roof clip fastening density for this
construction using FM Approved metal roof systems
is as follows:
1. Factored wind uplift pressure is determined from Data Sheet
1-28 or applicable design guideline,
whichever is more stringent.
2. Fastener pull-out resistance from the OSB board is obtained.
A minimum of three tests are run with the
average value taken as the resistance.
3. Allowable area/fastener is calculated by dividing pull-out
strength by the factored uplift pressure per Data
Sheet 1-28 as follows:maximum area per fastener = (pull-out
strength)/(factored uplift pressure).In no case
should the spacing be less than that FM Approved for roof
securement direct to purlins.
4. The roof corner/perimeter/peak fastener density is increased
over the field density per Section 3.1.5.
3.1.3 Re-cover of Metal Roof Systems
Not all FM Approved insulation types are recommended in re-cover
construction of metal roof systems
because testing has shown that some insulations (even if
Approved with 22 ga [0.0295 in., 0.749 mm] deck)
can create a Class 2 roof when used to re-cover metal roof
systems. Use only insulations noted in the
recommendations, specifically FM Approved for re-cover of metal
roof systems, or qualified via FM Global
Construction Materials Calorimeter testing. However, if a Class
2 roof is tolerable ( per Data Sheet 1-29), any
insulation compatible with the roof cover can be used. In all
cases, the external fire spread potential (ASTM
E 108 rating) should be known or determined. See Data Sheet 1-29
for information regarding E 108 ratings.
Single-ply roof cover fasteners FM Approved for conventional
re-cover systems are designed for use in
minimum 22 ga (0.0295 in., 0.749 mm) steel deck. Adequate
pull-out resistance would not be obtained if
they were driven into thinner 24-26 ga (0.0237-0.018 in.,
0.607-0.457 mm) metal roof systems. Installing the
fasteners into the thinner panels at a density greater than that
for 22 ga (0.0295 in., 0.749 mm) steel deck
based on static pull-out tests alone is not reasonable. The thin
metal panels may allow excessive fastener
fatigue (back-out or pull-out) due to roof cover fluttering in
mild winds. Adequate securement can be obtained
by driving the roof cover fasteners into the purlins.
Fig. 3. Standing seam roof applied to OSB/composite
insulation.
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The fastening density for securing insulation to these thinner
decks with mechanically-secured, single-ply
roof covers should be 50% greater than that recommended for 22
ga (0.0295 in., 0.749 mm) steel deck. The
reason for the higher density is that fastener pull-out
resistance in the thinner metal panels is less than that
obtained with 22 ga (0.0295 in., 0.749 mm) steel deck. Fastener
fatigue is not considered a major concern
for insulation fasteners because the insulation is not subject
to the same cyclic loading as the mechanically
secured roof cover.
FM Approved liquid-applied coatings and polyurethane foam
systems FM Approved for spray-applied,
direct-to-steel deck may be used to re-cover existing metal roof
systems. For coatings, re-tightening the
fasteners, reinforcing the joints with fabric, wire brushing
rusted areas, and power washing the roof are usually
needed (and required by the coating manufacturer) prior to
coating application. Some coatings have minimum
and maximum slopes for which they are FM Approved. The minimum
slope requirement is needed as some
coatings are not tolerant of ponded water. The maximum slope
requirement is needed to limit exterior flame
spread.
Non-Approved polyurethane foam spray-applied directly to
existing metal roof systems could constitute a
Class 2 roof deck. If a Class 2 deck is tolerable, this may be
acceptable. Refer to Data Sheet 1-29 for
information on Class 2 roof decks.
3.1.4 Metal Roof Systems Used for Re-cover
The additional insulation over existing Class 1 steel and wood
decks is limited to 1 in. (25 mm) because
tests have shown that greater thicknesses can cause the deck to
be Class 2. Filling the existing expansion
joints with mineral fiber is intended to reduce fire spread
through the roof deck in either direction.
3.1.5 Roof Areas Needing Increased Fastening
As noted in Data Sheet 1-28, increased fastening of roof systems
is needed at the roof corners and perimeter
due to the higher uplift pressure in these areas. Higher uplift
pressure also occurs at the roof peak on roofs
sloped greater than 7(1.5 in./12 in. [38 mm/305 mm]). Use the
methods outlined below to increase fasteningdensity in the specific
areas recommended in Data Sheet 1-28.
Data Sheet 1-29 outlines the recommended methods of increasing
the fastening density of mechanically
secured single-ply roof covers. The basic recommendation is that
increased fastening is achieved by
decreasing the distance between fastener rows rather than
between fasteners in each row. This method
allows a reduced and more even distribution of fasteners; it
also reduces the membrane span. It is not apractical method for
some metal roof systems, however, so other means are used.
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Use one of the following three methods for increasing the
securement of the roof system in the roof perimeter
and corners:
1. Use a roof system with the appropriate FM Global wind uplift
rating in each area per Table 1, or
Table 1. Recommended Rating of Field, Perimeter, and Corner
Areas (Zones 1, 2, and 3) for Enclosed Buildings3
Roof Field Area Design
Pressure, p, (psf)2
Minimum Wind Rating for FM Approved Deck/Above-Deck/Entire1
Assembly
Roof Field Area Enclosed
Bldg.
Roof Perimeter Area
Enclosed Bldg.
Roof Corner Area Enclosed
Bldg.
P 30 60 105 150
30 < p 37.5 75 120 180
37.5 < p 45 90 150 225
45 < p 52.5 105 180 270
52.5 < p 60 120 195 300
60 < p 67.5 135 225 330
67.5 < p 75 150 255 360
75 < p 82.5 165 270 405
82.5 < p 90 180 300 435
90 < p
97.5 195 315 48097.5 < p 105 210 345 510
105 < p 112.5 225 360 540
112.5 < p 120 240 390 585
120 < p 127.5 255 420 615
127.5 < p 135 270 435 660
1 Base the minimum wind rating on the roof field area rating
when perimeter/corner areas are enhanced per this data sheet and
other pertinentFM Global data sheets (1-29, 1-31, etc.). Base the
minimum wind rating on the respective area rating (field,
perimeter, corners) whenperimeter/corner area enhancements in this
document are not proposed, or are not acceptable.2 For roofs with
higher field area design pressures, or to interpolate needed
perimeter and corner ratings when the field requirements arebetween
levels, multiply the needed field area design pressure from Table
3, 4 or 5 (of DS 1-28) by a safety factor of 2.0 and the
respectivepressure coefficient for perimeter and corner areas (see
Table 6), and round up to the next highest 15 psf rating interval.3
Ratings above apply to roof slopes 7 and roof heights 60 ft (19
m).
2. Use the FM Approved proprietary perimeter and/or corner
fastening method, (if one exists), listed for the
manufacturer, or
3. Use the appropriate prescriptive recommendation listed below.
Note: The increase in fastening is applied
to the field of roof fastening listing in the Approval
Guide.
A. Single-Ply Re-cover System Secured Through Existing Metal
Panel Roofs Directly to Purlins
It is not practical to provide additional rows of fasteners for
re-cover systems in which the mechanically-
attached, single-ply roof cover is secured directly to the
purlins because the existing purlins usually are a
fixed distance of 4 to 6 ft (1.2-1.8 m) on center. For these
cases, it would be acceptable to increase the
fastening density of the new single-ply roof cover by decreasing
the spacing between fasteners along each
fastener row or batten bar in the noted areas. The fastener
spacing is a maximum of 60 percent and 40
percent of the FM Approved spacing (for the field of roof) in
the perimeter and corners respectively, but no
closer than 3 in. (76 mm). If there are additional purlins in
the areas needing increased fastening, the fastening
of the single-ply membrane can be increased per Data Sheet 1-29.
Increase pre-securement of the insulation
(Recommendation 2.2.2.3, item d) by 50% in these areas.
B. Proprietary Single-Ply Re-cover System Attached Directly to
Existing Metal Roof System Panels
For FM Approved proprietary re-cover systems in which the new
single-ply roof cover is secured to bars
(rails) attached to the metal roof (Fig. 4), decrease the
distance between fastener rails per Data Sheet 1-29
in the noted areas. In these systems, the base rails are
attached to the metal panels directly over the standing
seams. Hence, where necessary, round spacing down to the next
standing seam. Increase pre-securement
of the insulation (Recommendation 2.2.2.3, item d) by 50% in
these areas.
C. New Construction Standing Seam Roof Secured to Purlins
For new construction of standing seam roofs secured directly to
purlins, the clips are installed at each
purlin/seam intersection (Fig. 5). Therefore, it would not be
possible to increase the number of clips without
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increasing the number of purlins or using narrower panels. Using
narrower panels on only the perimeter or
corners of the roof is not practical. Increased fastening can be
accomplished by installing additional purlins
in the noted areas. Space these purlins a maximum of 12 and 1/3
times the spacing in the field of the roof inthe perimeter and
corners respectively.
Example: Field of roof purlin spacing of 5 ft (1.5 m) would have
perimeter spacing of 2.5 ft (0.76 m) andcorner spacing of 1.67 ft
(0.5 m).
Fig. 4. Attachment utilizing bar secured to existing metal
panel. Courtesy of Goodyear Tire & Rubber Co.
Fig. 5. Clip secured to purlinCourtesy of Vic-West Steel Co.
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D. New ConstructionStanding Seam and Lap Seam Roof Secured to
OSB/Composite
For metal roof systems secured to OSB/composite board, ensure
the spacing between clips along the panel
joints is a maximum of 12 and 1/3 times the spacing in the field
of the roof in the perimeter and cornersrespectively. Increase the
fastening of the OSB/composite board per Data Sheet 1-29, assuming
a fully
adhered roof cover has been installed.E. Lap Seam Roof
Systems
With lap seam roofs, it may be acceptable to have constant
purlin spacing across the entire roof and reduce
the spacing between fasteners in the perimeter and corners to no
more than 60% and 40%, respectively,
of that needed for the field of the roof along each purlin.
Another option is to fasten the panels to intermediate
purlins or sub-purlins in the noted areas per Cabove. For new
construction, ensure the panel span doesnot exceed that allowed by
the manufacturer for the design wind load (one half that of Table
1)
F. New Construction Insulated Roof Deck Panels
Treat systems using clips per Cabove. Treat systems using
through-bolting per Eabove.
4.0 REFERENCES
4.1 FM Global
Data Sheet 1-22, Maximum Foreseeable Loss Limiting Factors.
Data Sheet 1-28, Wind Design.
Data Sheet 1-29, Roof Deck Securement and Above-Deck Roof
Components.
Data Sheet 1-54, Roof Loads for New Construction.
Data Sheet 1-57, Plastics in Construction.
4.2 Others
American Iron and Steel Institution (AISI)
American Iron and Steel Institute (AISI). AISI Cold-Formed Steel
Design Manual. AISI TS-8-02, Base Test
Method for Purlins Supporting a Standing Seam Roof System.
Latest edition.
American Iron and Steel Institute (AISI). North American
Specification for the Design of Cold-Formed Steel
Structural Members. Latest edition.
APPENDIX A GLOSSARY OF TERMS
Also see Data Sheet 1-28 for additional explanation of teams
related to wind design.
FM Approved: References toFM Approved in this data sheet mean
the products or services have satisfiedthe criteria for FM
Approvals. Refer to the Approval Guide, a publication of FM
Approvals, for a complete
listing of products and services that are FM Approved.
Metal roof system(MRS): As used in this document, the term
refers to standing seam and lap seam roof
systems, and insulated roof deck panel systems.
APPENDIX B DOCUMENT REVISION HISTORY
July 2008. Table 1 was made consistent with revisions in Data
Sheet 1-28, Wind Design, and Data Sheet
1-29,Roof Deck Securement and Above-Deck Roofing Components.
This change raised the safety factor in
the perimeter and corner areas to 2.0. Prescriptive perimeter
and corner enhancements remain unchanged.
Recommendation 2.2.4 relating to gravity loads was added.
May 2003. Clarifications were made to recommendations in the
Section 2.2.3,Metal Roof Systems Usedfor Re-cover.
May 2002. Clarification was made to recommendation 2.2.2.1 under
Section 2.2.2, Re-cover of Metal Roof
Systems.
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January 2000. That revision of the document was reorganized to
provide a consistent format and to
consolidate related Engineering Bulletins.
January 1999. Table 1 was completely revised.
June 1996. Editorial changes were made.
June 1992. First edition of Metal Roof Systems.
APPENDIX C SUPPLEMENTARY INFORMATION
C.1 Metal Panel Types
There are three basic types of metal roof systems: lap seam,
standing seam, and insulated roof deck panel
systems.
C.1.1 Standing Seam and Lap Seam Roofs
These metal roof systems are formed using 22-26 ga (0.0295-0.018
in., 0.749-0.457 mm) steel. Copper and
aluminum may also be used for standing seam panels. Steel panels
are usually coated with zinc or
zinc-aluminum alloys and/or painted to minimize corrosion.
Standing seam panels are usually 12-24 in.
(305-610 mm) wide. Lap seam panels are generally wider, about 48
in (1.2 m). The limiting factor for panellength is usually
transportation restrictions.
For new construction, the panels are usually secured to
supporting members called purlins. The purlins are
CorZshaped cold-rolled members. They are usually 12-16 ga
(0.105-0.059 in., 2.667-1.500 mm) steel.In some cases, bar joists
are used.
Lap seam roofs are cold-formed steel panels that are fastened
directly to the purlins with self-drilling fasteners.
The fasteners are driven through the panels into the purlins.
The fasteners include a washer under the head
to seal against leakage. A sealant may be applied within the
laps to provide waterproofing. FM Approved
systems are listed in the Approval Guide within the Protected
Metal Panel and/or Panel Roof Covering
sections. Lap seam roofs are usually corrugated but can be
formed with large flat areas between the ribs,
resembling standing seam panels.
A potential problem with this type of roof is that movement
caused by thermal expansion can induce stress
on the fasteners and panel joints. Screw holes can become
elongated and the sealants in the panel jointscan crack. Both
situations can cause leaks.
Standing seam roofs also consist of cold-formed metal panels,
but they are not through-fastened to the purlins.
Instead, clips (Fig. 6) are fastened to the purlins. The panel
is then secured to the clips within the panel joints
(Fig. 5). The edges of the panels form a tight seal, 2-4 in.
(51-102 mm) above the flat portion of the roof.
Some systems include a sealant in the joint. Under usual
conditions, this keeps the seam above the level of
water on the roof and maintains water tightness. However, if
gutters or downspouts become blocked, leakage
can occur. The concealed clips do not penetrate the panel and
allow for movement caused by thermal
expansion.
Fig. 6. Standing seam clipCourtesy of Vic-West Steel Co.
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The standing seam panels can be joined using a proprietary
machine or hand tools. These seams are formed
in one of two ways: panel edges can be folded over each other,
or a separate strip (batten) can be put over
the two edges and crimped together. A third type of joint does
not incorporate crimping. The panels simply
snap together when installed. Currently, there are no
snap-together systems FM Approved. The end laps of
all types are usually simple overlaps and are screwed together
with a sealant applied between the layers.
Adequately sized and fastened clips can provide the necessary
wind uplift resistance while allowing the panels
to move in the longitudinal direction. To accommodate this
movement, only one end of the panels is
restrained. Typically, the panels are secured with
through-fasteners at the eave line and clip fasteners in the
field of the roof. This allows the roof to expand at the ridge.
Ridge caps are designed to accommodate this
movement.
Both roof types are usually insulated on the underside with
glass fiber batts and a vapor retarder. A metal
liner panel may also be installed on the underside. The liner is
usually of thinner gage than the roof panel.
In most systems, the liner does not add uplift strength to the
assembly.
C.1.2 Insulated Roof Deck Panels
A variation of the above systems is the insulated metal sandwich
panel that consists of metal skins with a
foam plastic or paper and/or aluminum foil honeycomb core. These
are typically factory assembled. They can
be attached with clips, similar to standing seam roofs or
through fastened. FM Approved panels are listedin the Approval
Guideunder the Panel Roof Coverings category.
C.2 OSB/Composite Systems
A common installation for standing seam roof systems consists of
an OSB/composite insulation mechanically
secured to standard FM Approved deep steel roof deck. The
standing seam clips are then fastened to the
OSB top surface of the insulation. Typical OSB/composites have a
7/16 in. (11 mm) thick OSB top surface that
offers considerably less fastener pull-out resistance than steel
purlins. The minimum recommended OSB
thickness for this application is 58 in. (16 mm).
Currently, there are no FM Approved combinations of metal panels
and OSB/composite insulations.
C.3 Re-cover of Metal Roof Systems
Metal roof systems are commonly re-covered with coatings or
single-ply roof cover systems. Many existingmetal roofs are 24-26
ga (0.607-0.457 mm); hence, adequate mechanical securement to the
roof panel itself
is difficult. Single-ply systems specifically FM Approved for
re-cover over existing metal roof systems should
be installed and fastened as FM Approved in the field of the
roof and enhanced as outlined at the corners
/perimeter/peak.
C.4 Metal Roof Systems Used for Re-cover
Metal roof systems may be used to re-cover existing low sloped
BUR systems. For these installations, a
framing system is constructed over the existing BUR (Fig. 2). It
may be necessary to remove the gravel
surfacing to reduce the dead load to the structure. The framing
supports are secured through the existing roof
covering to the deck. The new metal roof system is then secured
to the framing. This installation allows for
improved drainage as the new standing seam system can (and
should) be sloped.
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