Introduction
Protective Coating
Factors and Benefits
Weight
Fire Protection
Noise
Weather Resistance
Longevity
Colorfastness
Cost
Walkability
Lightning Susceptability
Maintenance
Conclusion
Chart

Introduction:

Tired of costly roof repairs?  Cracked, curling, and peeling shingles?  Rotting shakes or broken tiles?  Metal roofing is a compelling alternative in today's search for a durable, maintenance-free roofing solution that stands up to severe environmental hazards like earthquakes, wind-driven rains, hail, fire and intense heat.  An excellent choice for both residential applications, today's metal roofing comes in a dizzying array of choices.  Some styles mimic more traditional looks like shake, tile and slate -- at a fraction of the weight.

In the past, metal roofing was used primarily on agricultural and commercial structures.  However, during the 1940's, significant advances in base metal and coatings accelerated the use of metal into more and more residential applications.

According to the Metal Roofing Alliance, an estimated 5 to 8 million U.S. households enjoy the benefits of metal roofs.  Growing at over 150,000 new installations per year, metal roofs are projected to account for over 10% of the total North American roofing market by 2003, up from just over 4% in 2000.  This exponential adoption is a result of improved styling and color choice, proven long-term performance and durability, increased consumer and contractor education, and growing emphasis on fire and seismic risk reduction.

The most common metals used today in new installations include treated steel, aluminum and copper.  Copper has been used for centuries.  The variegated green patina of centuries-old copper roofs can be seen on villas and churches across Europe.  In fact, copper can last 500 years or more -- protected by the thin film of oxide that shields it from the elements. Today, copper is popular on bay and bow windows as well as rain gutters, downspouts and even entire roofs.
Top

Protective Coatings:

To increase longevity and protect against rust or corrosion, metals such steel undergo special factory surface treatments. Contractor's Guide points out three common steel surface preparations, including:

galvanized
aluminized
Galvalume TM (combination of the above two)

The galvanizing process, proven for nearly 300 years, is formed by a thin layer of molten zinc on the steel surface. The galvanized zinc topcoat bonds metallurgically to the steel's surface, forming a tough barrier that delays corrosion. Without this coating, steel would rust as it oxidizes from exposure to moisture and oxygen in the air.  As an added bonus, zinc is more electronegative than steel, providing what's known as "sacrificial protection." This means that steel -- which under normal circumstances would be compromised by surface scratches or small nail holes -- actually repairs itself as zinc molecules migrate to protect exposed steel. The combined zinc-iron finish creates a practical, durable, long lasting surface. This is one reason that galvanized steel is commonly used in rain gutters exposed to frequent moisture and acid build up from fallen leaves and pine needles. 

Aluminized steel is a more recent development, becoming commercially available in the 1950's.  Similar to the galvanizing process, aluminum is metallurgically bonded to the steel surface, providing excellent heat reflectivity and corrosion protection.  However, unlike zinc, aluminum lacks the "sacrificial protection" property discussed earlier. Therefore, scratches or exposed edges are likely to rust sooner compared to galvanized steel. For this reason, extra care is required in the handling and installation of aluminized steel panels to avoid damage to the protective surface.

Galvalume TM - the process of galvanizing steel with a zinc-aluminum alloy - offers the best of both worlds. Developed and trademarked by Bethlehem Steel, it was first sold commercially in 1972 according to U.S. Patent and Trademark records. The alloy is roughly 80 percent aluminum and 20 zinc by volume (or 55/45 by weight, respectively). The resulting surface coating is about 1 mil thick (0.001 inches) and provides the excellent corrosion protection and heat reflectivity of aluminum with the sacrificial self-healing properties of zinc.

Galvanized, aluminized, or Galvalume steel can optionally be coated with a layer of paint or a granular topcoat to provide even greater protection and lasting beauty. This gives architects total flexibility in color and textures to match a given design theme or style.
Top

Factors & Benefits:

When comparing metal roofing to alternatives, several factors must be considered.  This section examines properties of metals roofs and provides a comparison to other roofing products.  In addition, several myths about metal roofs are dispelled.
Top

Weight:

Metal roofs shine in this category, offering one of the lowest weight-per-square-foot metrics of any roofing material on the market. Typical installed weights range from 1.25 to 1.75 lbs. per square foot (psf).  Since metal does not absorb moisture, its weight is the same in both dry and wet conditions (excluding snow or ice build up).  By contrast, heavy shake can weigh a few psf or more when wet.  Clay and concrete tiles can weigh as much as 10 psf, requiring super sub-structures to support this added mass.  Lightweight metal helps to reduce worker fatigue since heavy lifting is significantly reduced.

The reduced weight is of particular importance in high seismic zones -- such as California -- where roofs can experience severe vertical and horizontal forces during an earthquake.  The lightweight metal roof significantly reduces the chances of catastrophic failure or collapse of the roof structure during a massive quake.
Top

Fire Protection:

Since metal is non-combustible, it will not burn or support the spread of fire.  Most roofing materials, except clay or concrete tiles, have fire resistance protection on one side only (usually the top side). During an internal fire, a heavy roof could experience premature collapse as the internal support members give way.  A wood roof generally accelerates the spread of fire, as the wood provides increased dry fuel for the fire itself.  A metal roof can help to preserve the integrity of the roof structure long enough to ensure a safe escape.
Top

Noise:

Concern about noise of metal roofs has kept otherwise eager  consumers away from the product.  While it is true that metal can resonate unlike tile or wood, studies confirm that a properly installed metal roof yields no significant increase in noise compared to other roofing alternatives.  Attic insulation and double-pane windows  -- combined with the fact that many metal roofs are mounted flush on a solid decking -- all contribute to acceptable noise performance of metal roofing.  In addition, the embossed textures of new metal roofs help to disperse rain, reducing noise even further.
Top

Weather Resistance:

Metal offers superior weather resistance, including exposure to extreme heat and cold.  According to studies by the Florida Solar Commission, metal roofs reflect as much as 70% of the sun, thereby reducing solar gain by as much as 34%.  This helps to keep attics cooler in the summer, translating into energy savings and improved interior occupant comfort.

In certain areas of the world where hail is prevalent, metal roofs have performed exceptionally well.  For example, Dura-Loc metal roofs have passed a class 4 UL hail test.  In similar situations, other roofing materials would be destroyed, leading to premature leaking. In extreme cases, it is possible for "baseball sized" hail to deform a metal surface leading to cosmetic damage.  However, the integrity of the roof remains intact while continuing to provide protection against the elements.  Depending on the surface treatment of the metal roof, minor cosmetic damage may be camouflaged by variegated surfaces.
Top

Longevity:

Some metal roofs, such as copper, can outlast the structure itself.  It's no coincidence that most metal roofing manufacturers stand behind their products with 50-year transferable warranties.  Some companies, such as Classic Products even offer lifetime warranties for the original owners.  Assuming proper maintenance, a quality metal roof could last 50 years, though this is the upper range of what homeowners should reasonably expect.
Top

Colorfastness:

Depending on the coating used, metal roofs exhibit excellent colorfastness and gloss retention.  Among the best performing finishes is Polyvinylidene Fluoride (PVDF), known in the trades as Kynar-500 or Hylar-5000.  Important properties of PVDF finishes include:

High mechanical strength and toughness
High abrasion resistance
Chemical and solvent resistance
Weathering resistance
High thermal stability
High dielectric strength
UV light and radiation resistance
Fungi resistance

PVDF is so tough it is used extensively in commercial and medical applications where high reliability is essential even in caustic and highly corrosive environments. PVDF is also used on many commercial-grade window frames including Pella Clad windows.

Other coatings include urethane, plastisol, acrylic and silicone.  However, while most of these surface treatments lose the majority of their gloss retention after three to five years, PVDF maintains stable gloss retention for nine to ten years, after which a gradual drop off begins to occur.

With respect to actual color retention of PVDF, Taiyo Steel in Japan conducted a study comparing PVDF to the aforementioned coatings.  Ten-meter high steel panels facing a southern exposure were erected.  Over the 14-year period, only PVDF maintained near original appearance -- confirming again the high-performance of PVDF-treated substrates.

Cost:

Metal roofs come in an infinite variety of styles, colors, shapes and qualities.  However, metal roofs have an installation cost comparable to tile or high-quality shake.  Composition or asphalt shingles are generally the lowest-cost roofing material, while traditional slate is the most expensive.

Installation cost is only one component of the total lifecycle cost of a roof.  Due to metal's durability and nearly maintenance-free performance, a good metal roof will not require replacement during the life of the structure.  Even though its up front cost may be more, the net-present value of a metal roof over a 50-year period means that its true cost is in line with even the least expensive roofing materials.  Furthermore, a quality roof adds value to the home and neighborhood which isn't accounted for in this analysis.

Many other forms of roofing, such as wood and even tiles, require periodic maintenance, including replacement of broken, split, or cracked pieces, as well as fire preservative treatments and pressure washing to remove algae and fungus build up.  Even concrete tile roofs can begin to show signs of significant fungus build up after just a few years -- particularly on the shady sides of a roof that receive less sun exposure.  Pressure washing and sealing a tile roof can cost several thousand dollars, not to mention the dangers associated with walking on a roof prone to breakage.
Top

Walkability:

Walkability is a factor on most roofs, and metal roofs are not immune.  In cases where metal roofs -- such as panels -- are laid flat on a solid plywood decking, the risk of damage is low.  However, if the roof is laid on battens, such as metal tiles and shingles, care must be taken to walk on the supported areas only.  Excessive weight on the unsupported sections can potentially deform the surface, requiring replacement.  Some metal roof manufacturers offer a foam filler on the backside if frequent walking is expected.  Generally, a properly installed metal roof should require virtually no maintenance, mitigating the need to walk on it at all.
Top

Lightning Susceptibility:

Contrary to popular belief, a metal roof is no more likely to attract lightning than any other type of roof.  Consider trees (made of wood) which frequently attract lightning.  Studies prove that lightning is attracted to the highest surrounding objects, regardless of their composition.  In the event lightning were to strike a metal roof, it will not combust like wood.  Rather, it will help to disperse the electrical charge over a larger surface area.  Some municipalities may require grounding of the roof, however, this is the exception rather than the rule.
Top

Maintenance:

Metal roofs are virtually maintenance-free.  Period rinsing with a hose or pressure washer can help keep the surface clean and free of corrosive residue, such as bird droppings and acid rain.  Generally, the surface of metal roofs do not support the growth of algae.
Top

Conclusion:

Metal roofing is rapidly gaining acceptance as a flexible, creative, lightweight, long-lasting roofing alternative to traditional products like shake, asphalt shingles, and tile or slate. Modern manufacturing techniques permit almost any size, shape, and style in an unlimited choice of colors and patterns. The competitive lifecycle costs of quality metal roofing provide an economical, virtually maintenance-free surface that resists fire, earthquakes, heavy winds, large temperature swings, and other environmental hazards.

Top