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Galvalume® Steel Roofing: Good Practices Guide

The following Guide to Good Practices covers the basics of what architects, contractors and building owners need to know about GALVALUME steel roofing — from initial project planning, through construction, and after completion. Properly designed and maintained GALVALUME roofs can provide 30+ years of trouble-free service in most environments.

Long-term Benefits

The Long-Term Benefits Of GALVALUME Steel Roofing Are In Your Hands.

Properly Designed, Installed and Maintained GALVALUME Roofs Can Provide 30+ Years of Trouble-Free Service.

The popularity of steel roofing continues to reach new heights. Today, its weather-tight performance tops off all types of buildings, all around the world.

When GALVALUME sheet steel was introduced in the U.S. in 1972, all bets were on its high-performance characteristics that feature an alloy coating of 55% aluminum-zinc to provide outstanding corrosion resistance.

Time has proven that GALVALUME steel roofs last longer, require less maintenance and offer exceptional value. It"s that combination that has made GALVALUME steel roofing the ideal alternative to traditional non-metallic roof systems.

Your Guide To Good Practice covers the basics of what architects, contractors and building owners need to know about GALVALUME steel roofing — from initial project planning, through construction, and after completion.

Design, installation and maintenance practices developed over the past 25 years ensure that GALVALUME roofs provide long, trouble-free life.

During periodic building inspections, observations were documented of practices that can affect the life of GALVALUME roofs. The good news is that these problems, which typically affected only a few panels on relatively small areas of the roof, can be avoided by using the accepted and recommended practices detailed in this guide.

The recent 25+ year roof inspection showed that properly designed, installed and maintained GALVALUME roofs can provide 30 years or more of trouble-free service in most environments. Use this information to your advantage, because the long- term results are in your hands.

GALVALUME steel roofing covers buildings worldwide today, totaling an estimated 40 billion square feet.

Download the "25+ year roof inspection"

Today"s Top Element Of Design For Architects

At the initial project planning stage, roof slope is a key consideration for architects incorporating GALVALUME roof systems into their designs.

A minimum slope of 1/4:12 is required to ensure sufficient drainage of water and good long-term performance of GALVALUME roof panels. Roof design will dictate the minimum slope for weather tightness. A standing seam roof can be used at the minimum slope of 1/4:12. Its weather tight seams are sealed, interlocked together, and raised above the roof"s drainage plane. "Screw down" roofs are installed at steeper slopes because panels are overlapped at sides and ends, and attached with exposed fasteners.

Atmospheric and climate conditions are also key elements to consider. Corrosive microenvironments from local industrial operations can exist that influence the performance of GALVALUME steel roofing. Likewise, marine exposures can be severe, making the location of the GALVALUME steel roof with respect to the shore line an important consideration.

Installation Is Key To Performance For Contractors

The most popular of all GALVALUME roof systems is the standing seam roof system. It"s made up of metallic-coated steel sheet panels joined together at their sides with standing seams and fastened to the roof substructure with concealed fasteners and clips.

On new roofs, structural GALVALUME steel panels are typically installed directly on purlins. Concealed clips are attached to the purlins, and the panels and clips are joined together by forming, crimping or snapping at the seams.

For most retrofit applications, panels are installed on a sub-framing system which, in turn, is attached to the existing roof structure.

To provide positive water drainage and maximize performance, the recommended minimum slope for GALVALUME roofs is 1/4:12 — otherwise, water collects to form ponds.


Some panels on this 20-year-old standing seam roof were installed with a slope less than the 1/4:12 minimum. Water collected at low areas and caused corrosion of the Al-Zn coating.

Compatible accessories are important to ensure that a GALVALUME roof achieves maximum life. Fasteners and flashings should always be made from material designed to last as long as the GALVALUME roof. Incompatible or substandard accessories can lead to failure of one or more components.


Neutral cure sealants should be applied at end laps to prevent moisture from entering panel lap joints. Crevice corrosion has occurred on this 20-year-old "screw down" GALVALUME roof, near the Gulf of Mexico in Florida, due to poor end lap sealing. The light zinc-electroplated fasteners were also rusted.

When installing fiberglass blanket insulation under GALVALUME roofs, be careful to seal all vapor barrier seams and repair punctures, penetrations or holes in the vapor barrier. Condensation of water vapor on the underside of the roof, along with saturation of the insulation,can cause inside-out corrosion. Leaking rainwater at loose fasteners can also saturate insulation and cause corrosion from inside.

Fasteners are used extensively on "screw down" roofs and, to a lesser degree, on standing seam roofs. Quality fasteners with a life matching that of the Al-Zn coating should be used.

Screw Down

The heavy zinc-electroplated steel fasteners on this 17-year-old roof in Florida are in good condition and free of rust.


Insulation should not be exposed where it will be continually wet and in contact with the underside of roof panels. Here wet, exosed insulation at the top wall panels caused corrosion from the underside of a 20-year-old roof on Florida"s Atlantic Coast.

Immediately after installation, make sure panels are swept clean to remove construction debris such as unused fasteners, metal filings, pop-rivet stems and pieces of flashing. The rusting of debris is often mistaken for roof corrosion.

Architectural GALVALUME steel roofing is usually installed on a metal or wood deck fastened to the roof structural system. Concealed clips or screws fix the panels to the deck. It"s recommended that a 30-lb. felt paper be used between the roof and deck.

In all installations, a minimum 1/4:12 slope should be provided for maximum performance over time.

Care must be exercised during unloading, storing and installation of panels to avoid damage by bending, warping, twisting, scoring and corrosion. To avoid storage corrosion, stacks should be stored off the ground on skids-at an angle for drainage-and protected with a loose-fitting waterproof cover.

Roof panels are delivered to the job site in packaged, blocked and banded stacks. The stacks must be handled properly with cranes and fork trucks to avoid kinking.

Roof Panels

The 0.022-inch thick "screw down" roof panels on this 16-year-old building were kinked from careless handling causing water to collect and form ponds.

Maintenance Guarantees Satisfaction For Building Owners

Minimum maintenance of GALVALUME steel roofing is required. The roof should be inspected at least once a year. Any exposed metal that can rust or has rusted should be painted. Leaves, branches, and trash should be removed from gutters, at ridge caps and in corners. Also watch out for discharge from industrial stacks, and particulate matter and high sulfur exhaust from space heaters.

Roof-top ancillaries and air conditioner supports, drains and housings should be checked. Particular attention should be paid to add-on roof ancillaries that create new roof penetrations. Roof-top air conditioners should be installed on GALVALUME curbs designed to avoid ponding water.

Lighter gauge, low slope screw down roofs are susceptible to panel walk-down. As a precaution, workmen should walk on panel areas supported by purlins. Walk-down is generally not a problem on standing seam roofs with a 1/4:12 slope when 0.024-inch thick and heavier panels are used with 5" or less purlin spacing.

Class Lighter Gauge

This 0.022-inch thick screw down roof has a 1/4:12 slope; heavy foot traffic during installation and maintenance caused panels to deflect permanently between the purlins and collect water.

Condensate from air conditioning and refrigeration equipment should never be allowed to drain directly onto the roof panels. The drainage contains copper ions from condenser coils that accelerate corrosion.

In the event of a roof leak, do not indiscriminately plaster the suspected leak area with tar or asphalt or use repair tape. Water can collect under the repair material, causing corrosion. Instead, have an experienced metal roofing contractor locate the leak, identify its cause, and properly repair the roof.

All rooftop equipment should be installed so that water can drain around it. Manufactured curbs and flashings, when used as recommended, will ensure proper drainage.

The air conditioneron this roof is installed using a manufactured curb. Water easily drains around the unit and off the roof.

Do not indiscriminately apply roof repair materials at suspected leak areas. Instead, have an experienced metal roofing contractor locate the leak, identify its cause, and properly repair the roof.

Here is an example of a leak improperly repaired with repair tape on the outside. Water trapped under the repairs caused severe corrosion and rusting.

Condensate from rooftop air conditioners should be discharged through a plastic pipe extended to a rain gutter or vent pipe, but preferably to the ground. The condensate contains dissolved copper from contact with the condensation coils and can cause rapid corrosion if discharged on the roof panels.

Air conditioner condensate is discharged by a plastic tube into a plumbing vent pipe, eliminating drainage and corrosion problems.

On this good-condition 20-year-old roof, condensate from HVAC unit is causing premature rusting of the galvanized curb and the GALVALUME panel.