If your historic house has a metal roof, you have one of the longest-lasting, most durable roofs that exist. Some of the advantages of metal roofing include:

• Easy shedding of ice and snow
• Fire-retarding properties
• Light weight
• Long life
• Wind and hail resistance

Your metal roof is also a character-defining feature of your historic house. Regular maintenance will ensure that your metal roof will continue to last for decades.

Historic Use of Metal Roofing

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Dane County. Shown here is a new standing seam metal roof. This type of roof can be installed when an original terne metal roof fails. Source: WHS - State Historic Preservation Office.

Metal roofing has been used for centuries to shed water off homes and buildings. Metal was laid on bay windows, porch roofs and other semi-flat roofs. Metal was also formed into ridge caps for wood-shingled roofs and used to line built-in box gutters. In the late 1800s, steel roofs began to be coated with terne metal: a mixture of around 15% tin and 85% lead. The terne metal coating created a corrosion-resistant surface. However, terne-coated metal roofs must be painted regularly. Copper roofing was used on higher-end homes.

The most common metal roofs are standing-seam and flat-seam roofs. Standing-seam roofs have an interlocking seam between each metal panel that projects up 1/2 to 2 inches from the seam joint. Flat-seamed roofs are small metal panels soldered together without a standing seam.

Repair Your Leaking Metal Roof

Your metal roof can leak if the following damage has occurred:

• Areas of metal have eroded.
• A tree limb or other object has poked through the metal.
• The soldered or standing seams have come apart.
• The flashing has failed.

If you want to keep your metal roof, you should hire a professional to repair your roof with metal patches or repair flashings. Often terne metal or copper repairs will require soldering. You can make temporary repairs with clear, silicone-based caulk. Avoid using tar-based materials to patch holes and erosion, because tar is much more difficult to remove than caulk.

Repair Failing Paint on Your Metal Roof

If you maintain the paint on your terne metal roof, you can expect it to last more than 100 years. You can address some paint maintenance issues yourself, but you should hire a professional if the paint on your main roof is failing. Professionals have the experience and tools to operate on slick metal roofs. However, if the paint on your porch roof or bay windows is wearing off or peeling, you can safely make some spot repairs.

Follow these steps to make spot repairs to painted metal roofs:

1. Remove the old paint by applying a non-methylene chloride based paint stripper to the affected area. Follow the manufacturer's directions for application and safety. You can also wet scrape the paint by lightly misting the surface with water and scraping it with a house scraper. You'll need to be careful that the scraper doesn't damage the metal.
   CAUTION: Do not remove peeling paint with any tool or method that can generate paint dust, including sanders, grinders, wire wheels, pressure washing or any pressurized blasting. The surface may contain lead paint.
2. Clean the entire roof with 1/8 cup of synthetic trisodium phosphate (TSP) powder mixed in a two-gallon bucket of water. TSP is one of the oldest cleaning agents around. Synthetic TSP is more environmentally sound than original TSP and cleans just as well. Hand-scrub the entire roof with a stiff nylon brush and then rinse it thoroughly with clear, cool water from your garden hose.
3. Allow your roof to dry out completely.
4. Follow the paint manufacturer’s instructions to paint all the affected areas. Metal must be painted with oil-based paint. Many companies make an oil-based direct-to-metal (DTM) exterior paint specifically designed for this type of job.

Coat Your Failed Metal Roof

If your metal roof is failing, you can stabilize your roof by applying an elastomeric coating. However, this coating will not be reversible, so this approach would not be the preferred preservation practice over repair. If you must apply an elastomeric coating, you will find many different companies that produce and install elastomeric coating products. These liquid coatings are thicker than paint and tend to be made with recycled rubber. Elastomeric coatings have no vapor permeability, so water cannot penetrate them. You should pick a light color that will reflect the sun’s light away from your roof.

Elastomeric coatings can be applied with brushes, rollers or spray equipment. Elastomeric coatings are usually applied over a mesh sheeting installed on the cleaned metal prior to the final coating. The roof will need to be re-coatedevery 10 to 20 years. Eventually your coated metal roof will have too many layers of elastomeric coating and will need to be replaced.

Replace Your Metal Roof

If your original metal roof must be replaced, you should consider replacing it with a new metal roof. The distinctive architectural look and long life of a metal roof can pay you back by creating a higher sale price. In addition, you won’t have to replace asphalt shingles every 15 to 20 years. Replacing a metal roof is not a do-it-yourself project; you should hire a professional with experience installing metal roofs.

If your historic house never had a metal roof, you should not install a metal roof on it. In most cases, a metal roof would look out of place. It is always best to use a roofing material that was original to your house or one that mimics the original.

The cost for replacing an original metal roof will run quite a bit higher than standard asphalt shingle roofs or EPDM rubber membrane roofing. However, metal should cost less than high-end traditional roofing materials like slate, clay tile and cement roof tiles. The two most popular and cost­-effective modern metal roofing materials are factory-painted, galvanized steel and aluminum. Other metals available today include copper, zinc, terne-coated steel and terne-coated stainless steel.

Most modern manufactured metal roofing materials are factory painted in a wide variety of colors. The best affordable finishes are silicone-modified polyester (SMP) resins and fluoropolymers. They offer good protection from fading due to ultraviolet light exposure, are maintenance free and come with a 30- to 50-year warranty. Avoid simple polyester resins, which tend to lose their color sharpness and gloss.

The information presented here is not intended to provide comprehensive technical advice or instructions on solving historic preservation issues. Any information contained or referenced is meant to provide a basic understanding of historic preservation practices. Read full disclaimer.