Design, Construction and Maintenance Guidelines for Galvalume® Sheet

Roofing panels made of Galvalume sheet will provide many years of trouble-free service when properly installed and maintained. Bethlehem works closely with its customers to monitor product performance through roof inspections over a wide range of designs and environments. As a result, we have developed a number of guidelines which may be helpful to builders in achieving a good-looking, long-lasting Galvalume sheet roof.

Standing Water:

Standing water conditions should be avoided by providing free drainage of water from the roofing panels. In multislope roofs, where it may be impossible to avoid creating ponding areas, a valley gutter or other device should be incorporated into the design to aid water drainage.

Accessory Materials:

Copper, lead and unprotected steel should not be used with Galvalume sheet. Galvalume sheet should also not come into direct contact with wet wood or uncured concrete. Wood retains moisture for long periods of time and can shorten the life of a panel in direct contact. Uncured concrete is extremely alkaline and may dissolve the protective coating. Many flashing, parapet and fascia designs are fabricated from galvanized steel. Galvanized, however, does not provide the long-term durability of Galvalume sheet and can cause run-down rust stain onto the Galvalume sheets.

Fastener Selection:

Bethlehem has found that the following fastener materials offer the compatibility and long-term corrosion resistance necessary for use with a Galvalume sheet roof: 300 series stainless steel, zinc alloy cast heads, plastic heads, aluminum or steel heavily coated (> 1 mil) with zinc or cadmium, both with a dichromate topcoat. The best fastener recommendations are available from your supplier or fastener manufacturers.

Fastener Installation:

When installing screws, whether they be self drillers or self tappers, use only as much pressure as necessary to seat the fastener seal. Excessive pressure can cause depressions of panel joints and drip edges. These indentations collect dirt and debris which interfere with free water drainage. Overdriving fasteners can also destroy the sealing washer. If screws are installed at an angle, the sealing washer may not seat and the roof could leak.

Sealants Selection:

When selecting a sealant for panel lap joints or other areas, use a premium material that provides the long-term resiliency and flexibility necessary to effectively seal the joints for the life of the Galvalume sheet roof. The best selection advice would come from a sealant supplier or manufacturer. Careful attention should be paid as well to the compatibility between the sealant and Galvalume sheet with regard to both its adhesion and corrosivity of the curing by-products. Some RTV sealants, for example, will release acetic acid which is corrosive to the coating.

Sealant Application:

Sealants and caulks should be applied only in amounts necessary to make an effective seal. Some sealant materials can discolor as they weather and, although they may not be corrosive or harmful to the Galvalume sheet, have an unappealing appearance that may distress a building owner. Excess or smeared sealant should be removed with recommended solvents.

Lockseaming:

For standing seam roofs, the portable lockseamer must be properly aligned and maintained to insure that the rolls do not cut through the protective Galvalume sheet coating. A misaligned lockseamer can fail to properly close the seam, resulting in leaks.

Roof Structures:

Roof-mounted equipment, such as air conditioning units, are often mounted on small, uncoated steel channels or I-beams. Any uncoated steel used on a Galvalume sheet roof should be given proper surface preparation, then painted with a high-quality maintenance primer and compatible top coat. If left unprotected, the rust will bleed onto the Galvalume sheet panels, resulting in an unsightly stain.

Air Conditioner Drains:

Air conditioner drains should be fabricated from plastic pipe of suitable diameter and extended at least to the rain gutter, and preferably well past the gutter. Drain water from air conditioners contains dissolved copper from the condensation coils that can cause rusting of Galvalume sheet panels in a very short time.

Clean-up:

After erection has been completed, the roof panels and gutters should be swept to remove dirt and debris such as unused fasteners, metal filings, pop-rivet stems, and pieces of flashing. For instance, the shank of a fastener left lying on a roof will rust very quickly and will run down onto the panel causing an unsightly stain.

Mud and dirt tracked onto the roof panels, as well as greasy hand and footprints, can be removed by washing with a cleaner consisting of 1/3 cup mild detergent (e.g., Tide) in one gallon of water applied with a mop or soft broom. The roof should then be thoroughly rinsed with water. High pressure spray application and strong alkaline detergents should not be used.

If washing with a detergent solution is found to be inadequate, solvents such as mineral spirits or Stoddard solvent can be used to remove more stubborn stains. More aggressive and highly volatile solvents such as acetone or toluene should be avoided for safety reasons, as well as their incompatibility with many paint systems used on building panels. The compatibility of any solvent on paint should be tested or known prior to its use.

Periodic Maintenance:

At least once a year, the building owner should have the following roof maintenance performed:

• Check panels, rain gutters and downspouts to ensure they are clear and allow free drainage of rainwater from the roof. Valley gutters and grates should be cleaned, also.
• Remove accumulations of leaves, branches and other debris at ridge caps and in corners.
• Check the condition of auxiliary equipment such as air conditioner supports, drains and housings. Any exposed metal that can rust or has rusted should be painted.
• Remove any trash that has been thrown on the roof that can clog drains or cause silt buildup.

Galvalume is a registered trademark of BIEC International, Inc.