Restoration Guide: Metal Roofing
Editor's Note: This is article 10 of 13 in the Roofs Chapter of the Old House Web's Home Restoration Guide. This guide was developed and edited for old homes from original material in the U.S. Housing and Urban Development (HUD) Rehab Guide.
10. Metal Roofing
While metal roofing has been in the United States in one form or another since the 18th Century, it's only been lately that advancements have made it desirable and practical as quality residential roofing.
Corrugated galvanized steel sheets were used in the early 1900s, but primarily for rural housing and outbuildings; it often corroded and leaked and was unattractive. At that time, copper was available, but was far too expensive for all but top-end houses.
Since World War II, a number of factors have made metal roofing a more viable option:
- Zinc/aluminum alloys have increased corrosion resistance
- New methods of coating have reduced fading and chalking
- Better sealants keep out moisture
- Fastening clips allow more roof movement
- Installers can fabricate longer panels on site
- Buyers have a wider choice of options with metal tiles that simulate traditional materials, such as slate, clay and wood
Methods and Materials
- Repairing Metal Roofs
- New Standing Seam Metal Roof
- New Metal Shakes and Tiles
- New Flat Metal Shingles
Weathering, wind, hail, corrosive air pollution, ultraviolet light and rapid expansion and contraction all work against metal roofs, and they will eventually fail. Replacing damaged panels with the same material will take care of small problems--steel or aluminum panels can be attached with screws and sealant; zinc or copper can be soldered in place. Other patch methods, such as asphalt patches or acrylic repairs, are ugly and have limited lifetimes. A roof may be entirely recoated with some types of acrylic or polyurethane, but their life expectancy is only one to five years. They are ugly, suitable only for low-slope use where they are not visible.
Spot repair is cost effective for small areas, though replacement panels probably will not match the weathered panels on your old house. If your damage is extensive, you had better undertake the major home renovation of reroofing.
Standing seam metal roofing is popular for high-end houses and multifamily housing for both its high performance and its appearance. It comes in preformed sheets, or it can be made on site in sheets up to 100 feet long. A variety of metals are used, including aluminum, galvanized steel (and trademarked versions Galvalume and Zincalume), painted steel, stainless steel, copper and zinc.
Panels for residential standing seam roofs, designed to shed water very rapidly, usually have ribs ¾" to 1 ½" high (the standing seams) and are a foot to 16" wide.
The National Roofing Contractors Association (NRCA) recommends ventilation under the metal panels because of the potential for condensation.
Standing seam roofing is lightweight and easy to install. In some cases, it can be installed over existing roofing. It is not combustible and resists decay and mildew. It does cost more than many roofing systems and some types are not warranted if within a quarter mile of saltwater. Warranties for standing seam metal roofing vary widely and should be carefully read.
Lightweight metal panels made to simulate shakes or S-tiles have gained popularity because of their fire and wind resistance. They usually are galvanized steel, coated with a smooth covering to look like tile or textured granules to simulate shakes. They are easy and fast to install and come with long-term warranties; however, they often look like coated steel, rather than the shakes or tiles they are meant to mimic.
Some manufacturers are making specialty metal shingle panels (including copper), usually 12"x48", that are designed to look like individual shingles. One manufacturer makes a scalloped "Victorian" edge designed to be used in old house restoration projects.
Metal shingles can be installed over conventional roof sheathing and have high resistance to wind and weather. They are durable and not combustible. They are light and easy to install, though installation is a little more involved than other metal roofing products. They can also be costly--especially copper.
Jim Mallery, a semi-retired journalist and onetime registered contractor, has extensive experience remodeling, repairing, and rebuilding homes.