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Flashing & Sealing Specifications for Exposed Fastener Metal Roof Systems
- FLASHING for METAL ROOFS - How to install flashing on barn roofing
- How to seal barn roofing
- Exposed fastener metal roof systems
- Installation guide for agricultural building roofing or "metal barn roofing"
- Flashings and Accessories for Exposed-Fastener Metal Roofs
- Characteristics of metal roofing materials
- Best practices for roofing material installation, flashing, ventilation, nailing, underlayment
- FLASHING on BUILDINGS - separate article, topic home
- Questions & Answers about metal roof flashing & sealing
- References
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
This article describes metal roof flashing and sealing products and installation details for exposed-fastener metal roof systems: barn roofing, or agricultural building roofing systems.
This article series discusses best practices in the selection and installation of residential roofing. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
Also see METAL ROOF EXPOSED FASTENER SYSTEM and METAL ROOF COATINGS & PAINTS and GALVANIC SCALE & METAL CORROSION. See our metal roofing home page, METAL ROOFING and see CORRUGATED ROOFING and COPPER ROOFING.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Flashings and Accessories for Exposed-Fastener Metal Roofs
Adapted/paraphrased with permission from Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES:
Most manufacturers supply
preformed flashings, drip edges, rake moldings, and
ridge caps color-matched to their roofing panels, as well as
color-matched coil stock for fabricating custom pieces onsite.
They also provide rubber closure strips or expandable
foam tapes to seal panel ends against water and insect
intrusion at eaves, valleys, ridges, and other terminations.
Pay particular attention to panel ends at metal roof valleys. Some
manufacturers supply special closures for the angled cuts
through ribs, but closures may need to be fashioned by cutting
up standard closure strips.
Some manufacturers also
provide an expandable foam sealant tape that conforms to
the rib pattern for a tight seal up the valley.
Depending on
the panel profile, the end treatment will vary, but ends
should be fully sealed. Remember to place screws in flat
sections and to use extra screws up the valley (Figure 2-38).
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For plumbing vents, most manufacturers recommend
a moldable aluminum jack bent to conform to the profile
of the roofing (Figure 2-40).
Rectangular openings, such as skylights and chimneys,
typically require both base and counterflashing so
roof panels are free to move with changes in temperature.
Depending on the panel profile, either use a pan flashing
or an L-flashing sealed to the top surface of the roofing
panel with sheet metal screws and butyl tape.
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On large
openings in metal roofs, a cricket is needed on the up slope to divert water
around the penetration. Custom-made, one-piece curbs
with built-in diverters simplify this type of installation. All
flashing joints should be sealed with butyl tape or a manufacturer-
recommended sealant.
Sealing Details for Exposed-Fastener Metal Roofs
For the watertight performance required on
homes (as opposed to barns), metal roofs need careful
sealing around all penetrations, side laps, and end laps. On
side seams and lap joints, the sealant should always go
on the uphill, or “dry,” side of any fasteners (Figure 2-41).
Sealant should also be used at ridge caps, valleys, and
wherever flashings lap over or under the metal roofing.
The preferred sealant for most concealed seams in
metal roof panels is butyl tape, which absorbs movement and
will not shrink. Gunnable terpolymer butyl or urethane
caulk can also be used, as specified by the manufacturer.
But never use acid-cure silicone caulking (the common
type with vinegar odor) or asphalt roofing cement, as they
will damage most metal coatings.
How to Allow for Panel Movement in Exposed Fastener Metal Roof Systems
Metal roof panels were originally designed
for installation on purlins that can absorb the normal
movement as the panels expand and contract from temperature
changes. The thermal movement of a long panel
installed over solid plywood, however, can cause problems.
Typically, either the hole in the metal roofing elongates—creating
a potential leak—or the screw becomes loosened, making
the roof vulnerable to blow-off. The problems are greatest
with aluminum, which has 70% more thermal movement
than steel and less tensile strength. To avoid problems, experts
recommend the following:
- With exposed-fastener panels, avoid lengths over
40 feet for steel or 16 feet for aluminum—less for
climates subject to wide temperature swings. Break
the run into two panels.
- On long runs of painted roofing, choose lighter
shades, preferably white.
- Use screws in the flat part of the panel, not on the ribs.
Screws should penetrate the sheathing fully, plus
1/4 to 1/2 inch.
- Where leak-free performance is critical, fasten the
roofing to Z-shaped metal purlins screwed horizontally
across the plywood sheathing. Or switch to a
concealed fastener system.
Also see "Metal Roofing: 'Fixing' for Thermal Movement", Thomas L. Smith, AIA, CRC
Wavy Metal Panels or Oil-Canning Problems on Metal Roofs: Thermal Expansion
Thermal expansion in light-gauge metal
panels can cause a wavy appearance called “oil-canning”
in the flat areas. In general, this does not signal a performance
problem, but it may be visually objectionable.
Oilcanning
tends to be most visible in bright light from a close
distance, and it is generally more noticeable on shiny metals,
such as Galvalume®, than on colored metal panels.
Oilcanning on metal roofs
is primarily a problem in profiles with few ridges to stiffen
the panels. To reduce the metal roof rippling or oilcanning effect, some manufacturers
provide self-adhesive foam strips that are attached lengthwise
to the bottom of metal panels.
-- Adapted with permission from Best Practices Guide to Residential Construction.
Resources: Roofing Materials & Equipment Suppliers
Manufacturers
Metal Roofing
- Classic Products
www.classicroof.com
Modular metal shingle panels and standing seam panels
- Decra Roofing Systems
www.decra.com
Modular metal shingle, tile, and shake panels
- Dura-Lok Roofing Systems
www.duraloc.com
Modular metal roofing shingles with granular coating
- Fabral
www.fabral.com
Exposed fastener and concealed clip metal roofing
panels
- Gerard Roofing Technologies
www.gerardusa.com
Modular metal shake and tile panels with granular
coating
- Met-Tile
www.met-tile.com
Modular metal roof-tile panels
- Atas International
www.atas.com
Modular metal shingle, tile, and standing-seam panels
- Custom-Bilt Metals
www.custombiltmetals.com
Modular metal shakes and standing seam panels
- Zappone Manufacturing, website www.zappone.com/
Zappone Manufacturing, 2928 North Pittsburg St. Spokane, WA 99207
1-800-285-2677, Washington State Copper Roofing Supplier of
Copper scallop shingles, copper shingles, copper bay windows, vertical walls, aluminum roof shingles
Venting Underlayments
Benjamin Obdyke
www.benjaminobdyke.com
Cedar Breather, a
3/8 -in.-thick matrix-type underlayment
designed to provide ventilation and drainage space under
wood roofing
More Information about Roofing Materials, Methods, Standards
Asphalt Roofing Manufacturers Association (ARMA)
www.asphaltroofing.org
Cedar Shake and Shingle Bureau
www.cedarbureau.org
Metal Roofing Alliance
www.metalroofing.com
Tile Roofing Institute
www.tileroofing.org
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-- Adapted with permission from Best Practices Guide to Residential Construction.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- ASTM - ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, 19428-2959 USA The ASTM standards listed below can be purchased in fulltext directly from http://www.astm.org/
- "Metal Roofing: 'Fixing' for Thermal Movement", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 72, NRCA
- "Metal Roof Systems: Design Considerations for Snow and Ice", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 74, NRCA
- "Steel [Roof] Decks: Issues for the 1990's", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 74, NRCA
- "Steel [Roof] Deck Corrosion Bulletin, NRCA", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 58, NRCA
- "The Many Aspects of Metal [Roof] Shingles", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] NRCA
- Architectural elements: the technological revolution: Galvanized iron roof plates and corrugated sheets; cast iron facades, columns, door and window caps, ... (American historical catalog collection), Diana S Waite, available used out of Amazon.
- "Choosing Roofing," Jefferson Kolle, January 1995, No. 92, Fine Homebuilding, Taunton Press, 63 S. Main St., PO Box 5506, Newton CT 06470 - 800-888-8286 - see http://www.taunton.com/FineHomebuilding/ for the magazine's website and for subscription information.
- [1] Follansbee Roofing, Follansbee WV 26037, Tel: 800-624-6906, website: www.follansbeeroofing.com and http://www.follansbeeroofing.com/products/TerneII.aspx Quoting Follansbee on TerneII properties:
Follansbee Steel is the only manufacturer of a pre-painted or natural Terne roof and is a leading supplier of metal roofs for new and retrofit commercial, institutional, residential and historic preservation projects.
Terne II - Classic Terne-Coated Steel
... is a new and improved version of historic Terne metal, ... Terne II has improved capability for resisting corrosion in all environments ... also has excellent formability, solderability, and affinity for paint ... without compromising mechanical characteristics. It can be used in flatlock, standing seam, vertical wall designs and virtually any other application in which original Terne has been used. It is strong and ductile, having high yield and tensile strengths as well as workability. This new material can easily be formed with conventional roofing tools.
With Terne II roofing, it is advisable to paint the material as soon as conditions permit. Oxide formation is slower than with the original Terne and the wait for proper painting conditions provides substantially less risk. The new material is coated with Follansbee's new ZT® alloy, a combination of zinc and tin. This coating is designed not only as a barrier but also to be anodic to the steel substrate and reduce the potential for oxidation before painting.
The traditional oil-based paints long required on original Terne are not recommended for application on Terne II. Follansbee's Rapidri paint with its faster drying time and ease of application is much superior to the old painting system. The Rapidri acrylic paints are aesthetically pleasing while offering enhanced durability and color retention. ...
- Metal Roofing Alliance, E. 4142 Hwy 302, Belfair, WA 98528, Telephone:(360) 275-6164, Customer Support 410-534-6900, Email: support@metalroofing.com,
Website: www.metalroofing.com. Quoting:
The Metal Roofing Alliance was formed in 1998 by a small group of forward-thinking metal roofing manufacturers with the main goal of educating consumers about the many benefits of metal roofing. Since our inception, we've shown millions of people just how beautiful, durable and money-saving metal roofing can be for them. Over the years, our membership has grown to include paint companies, material suppliers, industry publications and more. Be sure to take advantage of all of the great resources our members offer.
- The Metal Initiative, 4700 W. Lake Ave., Glenview, IL 60025, P:847.375.4785 Website: www.themetalinitiative.com/, Email: Louise Ristau lristau@connect2amc.com Quoting:
The Metal Initiative is a coalition of manufacturers, individuals and associations that have come together to provide information on the features and benefits of metal in construction. Carrying its message of metal primarily to the professional building owner community, The Metal Initiative seeks to gather and disseminate useful information for decision-makers.
- Metal Roofing, an Illustrated Guide, R.A. Knowlton , [metal shingle roofs],
- Copper Roofing, by CDA
- Copper Roofing, Master specifications for copper roofing and sheet metal work in building construction: Institutional, commercial, industrial, I.E. Anderson, 1961 (hard to find)
- Corrugated Iron, Building on the Frontier, Simon Holloway
- Problems in Roofing Design, B. Harrison McCampbell, Butterworth Heineman, 1991 ISBN 0-7506-9162-X (available used)
- Grapevine Design Guidelines - Web Search 07/12/2010
- "Copy on file as - /roof/Asbestos-to-Zinc_Metal_Roofing_NPS.pdf - From Asbestos to Zinc, Roofing for Historic buildings, Metals - ", Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
http://www.nps.gov/history/hps/tps/roofingexhibit/metals2.htm
- "Copy on file as - /roof/Asbestos-to-Zinc_Metal_Roofing_NPS_3.pdf - From Asbestos to Zinc, Roofing for Historic buildings, Metals-part II, Coated Ferrous Metals: Iron, Lead, Zinc, Tin, Terne, Galvanized, Enameled Roofs - ", Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
http://www.nps.gov/history/hps/tps/roofingexhibit/metals.htm
- "On file as /roof/Asbestos-to-Zinc_Metal_Roofing_NPS_2.pdf - From Asbestos to Zinc, Roofing for Historic buildings, Metals- Roofing Today - ", Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
http://www.nps.gov/history/hps/tps/roofingexhibit/roofingtoday.htm
- "Copy on file as - /roof/Roofing_Historic_NPS.pdf">Roofing for Historic buildings - ", Sarah M. Sweetser, Preservation Brief 4, Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
http://www.nps.gov/history/hps/tps/briefs/brief04.htm
- "Copy on file as - /exterior/NPS_Preserv_Brief_16_Subs_Mtls.pdf">The Use of Substitute Materials on Historic Building Exteriors - ",
Sharon C. Park, AIA, Preservation Brief 16, Technical Preservation Services, National Park Service, U.S. Department of the Interior, web search 9./29.10, original source:
http://www.nps.gov/history/hps/tps/briefs/brief16.htm
- "Metal Roofing: 'Fixing' for Thermal Movement [ copy on file as /roof/Metal_Roof_Movement_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 72, NRCA
- "Metal Roof Systems: Design Considerations for Snow and Ice [ copy on file as /roof/Metal_Roof_Snow_Ice_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 74, NRCA
- "Steel [Roof] Decks: Issues for the 1990's [ copy on file as /roof/ Steel_Roof_Deck_Corrosion1_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 74, NRCA
- "Steel [Roof] Deck Corrosion Bulletin, NRCA [ copy on file as /roof/Steel_Roof_Deck_Corrosion_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] p. 58, NRCA
- "The Many Aspects of Metal [Roof] Shingles [copy on file as Metal_shingles_NRCA.pdf ] - ", Thomas L. Smith, AIA, CRC., Professional Roofing, [date pending] NRCA
- NRCA - National Roofing Contractors Association - http://www.nrca.net/, 10255 W. Higgins Road, Suite 600,
Rosemont, IL 60018-5607, Tel: (847) 299-9070
- ...
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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