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Roof paint work in Norway (C) Daniel FriedmanPaints and Coatings Recommended for Metal Roofing

Metal roof paint choices, application, life: this article discusses choices of metal roof coatings, their properties, application methods, and maintenance.

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Paints and Coatings Recommended for Metal Roofing

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. Our roof top photo shows safety precautions in place while re-coating a roof in Oslo, Norway.

Watch out: one of the quickest ways to fall off of a metal roof is to try walking on it while painting the surface, stepping in wet paint. Speaking from experience in Dunnsville, VA. Also see the page top photo at this article for some rooftop safety precautions including scaffolding and fencing. - Ed.

Rusted corrugated roofing (C) Daniel Friedman

While unpainted metal roofs are common on utility buildings and some rustic homes, most homeowners prefer a painted surface. In addition to improving the appearance, a high-quality factory finish can significantly extend the life of metal roofing.

The corrugated roofing at left (Hudson New York) was never painted.

In general, factory finishes are durable and flexible enough to tolerate factory roll-forming and bending on-site.

The best finishes carry decades-long warranties against cracking and peeling, and “excessive” chalking and fading (as defined by the manufacturer).

The quality of the finish is determined by the type of resin and the stability of the pigments.

Polyester-Resin Roof Paints for Metal Roofing

Polyester-resin paints are the least expensive and are commonly used on exposed-fastener panels. These have a medium to high gloss when applied, but they will fade significantly within 5 to 7 years on surfaces exposed to direct sun. Bright red, for example, may fade to pink. Fading will be less noticeable on light colors, making them a better choice. Warranties are typically for 3 to 5 years and rarely cover fading or chalking.

Silicone-Modified Polyester Roof Coatings

SMPs (siliconemodified polyesters) use polyester resins blended with silicone additives to improve performance. In general, the higher the silicone content, the more durable the finish.

These are available in medium- and high-gloss colors, and they resist fading and chalking much better than standard polyester paints. Warranties against excessive fading and chalking typically run from 10 to 20 years, depending on the formulation.

PVDF Fluoropolymer Resin Roof Paints

Based on a fluorocarbon-based resin called PVDF, these are the most technically advanced and most expensive finishes. Sold under the trade names Kynar 500® and Hylar 5000®, fluorocarbon-based paints provide a smooth and dense medium-gloss finish that offers excellent durability and long-lasting resistance to fading and chalking, even under intense sun exposures.

The Teflon-like coating also resists dirt retention and holds up better in coastal environments than other finishes. The finish is softer than SMPs, however, and can be damaged by the roofing installers, if they are not careful. Typical warranties run 20 years or greater, with 10- to 20-year protection against excessive fading.

Use of Reflective Finishes for Metal Roofs to Reduce Building Air Conditioning Costs

Painted metal roof (C) Daniel FriedmanOur photo (left) shows a very common practice: painting antiqu3e metal roofs with aluminized roof coatings to reduce rusting, improve roof life, and increase reflectivity to reduce heat gain in the building in hot sunny weather.

Watch out: some roof coatings and paints and particularly some roofing cements commonly used to "patch" old rusting or leaky metal roofs may work in the short run, but contain corrosive chemicals that actually speed further metal roof corrosion.

Be sure that the coating or patch material you use on a metal roof is approved for the metal surfaces to which it is being applied. In Newburgh NY we inspected the restoration of an historic home that had made extensive use of copper roof flashing.

The most severe corrosion had occurred where and after a bituminous flashing cement had been blobbed atop of copper flashing joints.

Metal roofing examples (C) Daniel FriedmanWhite metal roofs can reduce cooling loads by as much as 30%, according to tests conducted by the Florida Solar Energy Center. More modest savings are now available with dark colors as well by using metal shingles coated with special paints formulated to selectively reflect the sun’s infrared and ultraviolet radiation.

These “Hi-R” paints are now standard options with Hylar/Kynar® finishes. Tests indicate that aluminum shakes with a reflective brown finish reject 30% to 40% of the total solar radiation compared to 67% for a white metal roof.

Granular Coatings Used on Metal Roof Shingles

Some metal shingles are available with a textured finish consisting of crushed stone or ceramic granules blended into an acrylic resin. These are applied over a special primer and sealed with a clear acrylic sealer.

The multicolored granules give the appearance of an asphalt shingle and protect against scratching from foot traffic. The finishes also help protect against denting from hail and help conceal any small dents.

- - Adapted with permission from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) .

Resources: Roofing Materials & Equipment Suppliers

Manufacturers

Metal Roofing

- - Adapted with permission from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) .


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Continue reading at METAL ROOF EXPOSED FASTENER SYSTEM or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see

LIFE EXPECTANCY of METAL ROOFS

METAL ROOFING - home

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METAL ROOF COATINGS & PAINTS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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