Facts Your Father Never Told You About Metal Roofing

(Dear old dad … what were you thinking?)

Did he mention anything about corrosion of steel panels?

  • Use a felt marker on panels during constructions not pencils. Pencils contain graphite and graphite is corrosive to steel panels.
  • Water run off from copper coming from plumbing pipes, electrical or air conditioning units will cause roof corrosion. Copper and steel do not get along. Roof failure can occur in just a few short years.
  • Some silicone caulks are corrosive to steel. If the tube does not specifically say “for use on steel” do not use it. As a general rule if the silicone caulk has a strong odor, it is corrosive to metal.
  • Treated lumber in contact with metal roof panels used to support air conditioning units or other equipment will cause corrosion of steel roof panels.
  • When different metals are in contact with each other an electro chemical reaction takes place which adds to corrosion and to the break down of metals. This process is known as galvanic reaction; the result of dissimilar metals in contact with each other.

Did he talk to you about installation and things you should not do?

  • It has been shown that the use of electric impact drivers substantially increases the probability of improper placement of screws; so don’t use them.
  • Do not remove sheathing from a roof and install standing seam or install a roof on a new building with open purlins unless the system is rated structural. Most standing seam systems are not rated structural and do not provide diaphragm strength. Lexington and Concord are not structural panels. Failure to follow this rule will likely lead to the collapse of your building.
  • It is not recommended to touch up minor paint scratches, even though All American Steel™ carries touch up kits. Weather XL and Kynar 500 performance cannot be duplicated with field applications. The newly applied paint will fade faster than the factory finish and eventually will be more pronounced than the original scratch; sounds like something Dad would say…..had he remembered.
  • Never cut panels with an abrasive blade. Panel damage will occur and hasten the corrosive process and will void your warranty. The red hot shards will damage the 40 year paint finish. For exposed fastener panels a full width shears is recommended and is available from All American Steel™ for rent. Standing seam panels should be cut with hand shears or a power nibbler.
  • Galvalume roof panels such as Lexington and Concord should not come in direct contact with new mortar or concrete. The high alkaline content will cause rapid corrosion. In old mortar or concrete, the level of alkaline decreases dramatically and diminishes the degree of concern of this phenomenon.

How about things you should do?

  • Use butyl sealants for metal. The sealant should be applied concealed. Exposure to sunlight will breakdown butyl.
  • Use high temperature synthetic roof felt and high temperature ice and water shield over roof sheathing. Temperatures between metal roofing and roof decks can exceed 200° F.
  • Lower roof pitches have greater wind uplift than steeper pitched roofs. As a general rule fastener spacing should be closer on lower pitched roofs.
  • Standard 15# or 30# asphalt underlayment, because of the heat, will adhere to the underside of the roof panels and will constrict the normal daily expansion and contraction of the panels, enhancing the “oil canning effect.”
  • If you are going to put snow guards on your roofs be sure to place panel fastening screws on a direct screw down a minimum of 12” on center on the bottom 1/3 of the roof.
  • Use only stainless steel fastening screws.
  • Oil canning is inherent in all metal roofing from all manufacturers and is not cause for rejection. Through the course of a day, depending on the time of the year, observable deflection (oil canning) of the panels can be exacerbated for a short time and then not appear for the balance of the day. If this is of great concern perhaps a metal roof is not the right roof for you.
  • To lessen oil canning we recommend going to a crinkle finish with striations. Besides adding to the beauty of your roof the suns rays are refracted and oil canning is dramatically reduced.
  • Placing a small backer rod in the middle of your standing seam panels lessens the effect of oil canning.
  • Rib tab closures are a small expense but provides a craftsman look to your roof.

If Dad didn’t tell you about the other stuff, he sure the heck didn’t say anything about this general information.

  • Todays metal roofs are not significantly noisier than other roofs. Metal roofs received that reputation years ago when homes were sheathed with boards and quite often the boards were spaced to save money and promote ventilation. The spacing produced a “drum effect” and a loud roof when it rained or hailed. Some people enjoyed the sound and found it soothing and others found it objectionable. Roofs today are sheathed with plywood or OSB with synthetic felt and ice and water shield. The “drum effect” no longer exists.
  • All American Steel™ roofs carry a 40 year finish warranty, but how long will they last before they fail; a long long time.
  • There are standing seam roofs well into their second hundred years and the galvalume roofs of today are far superior to the metal roofs of yesteryear.
  • Metal roofs have no greater chance of being hit by lightening than any other type of roof.
  • You do not normally need to remove existing shingles to install a new metal roof.
  • 26 gauge metal is thicker than 29 gauge. It is important to remember metal thickness increases as metal gauges decrease.

Your Father didn’t tell you the difference between the substrates galvalume and galvanized because frankly he probably didn’t know the difference … as luck would have it we do.

Substrate Facts

Galvalume coating

  • Galvalume is a hot-dip process in aluminum, zinc and silicon. AZ55
  • 55% aluminum, 43.5% zinc, 1.5% silicon by weight.
  • 80% aluminum, 19% zinc, 1% silicon by volume.
  • Zinc bonds with steel to create a barrier to corrosion caused by moisture.
  • Aluminum is a metal that naturally resists corrosion and reflects heat.
  • Silicon enhances the adhesion of the coating.
  • Galvalume under normal environmental conditions is at least 2-4 times as resistant to corrosion compared to galvanized.
  • Galvalume should not be used in contact with concrete or mortar. The high alkaline content will cause rapid corrosion.
  • Galvalume panels are not warrantied when used in animal containment buildings.
  • Galvalume carries a 25 year 6 month warranty from the steel mill on rust perforation.

GALVANIZED coating

  • Galvanized is a hot-dip process in zinc. G100
  • A chemical bond occurs between the zinc and the carbon sheet steel.
  • Galvanized coating is measured in ounces per 100 square feet.
  • G100 has 100 oz. of zinc per 100 square feet; includes both sides.
  • The greater the amount of zinc, the greater the protection against corrosion.
  • Galvanized panels perform better in animal containment buildings than galvalume but still are not warrantied.
  • The zinc in the two substrates actually sacrifices itself to protect the underlying steel from rust when panel damage occurs. Since galvanized has more zinc this phenomenon is more pronounced in galvanized panels. After 10 years this action seems to equalize between the two substrates.
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