By John W. Gordon, PhD

Investigating a metal roof seldom comes up for a home inspector, and doing so has its pluses and minuses. The metal roof is invariably well built, appealing, and a low maintenance component; however, it tends to be perilous to traverse and it challenges the investigator significantly. Standards of Practice indicate that inspectors must traverse the roof if possible and must report the reasons if it isn’t traversed. The danger of traversing steep roofs is reason enough. Another is that the inspector may incur some liability of damage; manufacturers of slate, clay, or metal roofing materials recommend avoiding walking on them lest the roof’s integrity be compromised.

A metal roof is generally considered a high-quality product, perhaps inferior only to clay and slate roofs. It is costly, which alone is reason enough for inspectors to be tentative about traversing it. Yet the inspector’s client has to decide whether his investing in this higher-priced house is worthwhile, and he expects the investigation to be thorough.

There are several advantages to roofs made of metal. They weigh no more than conventional asphalt or wood roofs, freeing the investigator from having to assess the structure to determine if it provides adequate support. (This based on the assumption that some other material was used to construct the original roof.) Metal is rigid, strong, and smooth; hence, snow is more easily shed and less likely to cause damage or leaks.

Rigidity and strength also imply resistance to deformation, obviating the need to investigate problems characteristic of shingle and shake roofs (immaterial if made of cedar or asphalt), such as splitting, curling, and cupping. Other advantages of metal are that it doesn’t combust and that such roofs do not exhibit many joints. This latter characteristic implies less chance of leaks.

What the investigator needs to key in on are the disadvantages of metal roofs. The biggest drawback is rusting. Care is taken to coat the components with protectants against corrosion, but rusting still happens. Another drawback is denting. Most important, the inspector needs to check for buckling, which metal is susceptible to because it expands and contracts so much in response to temperature changes. Thus, manufacturers usually limit panel widths to twenty inches and installers must allow for these thermal movements.

The two standard configurations for metal roofs are shingles and panels. This doesn’t concern the investigator as much as the material itself and what are used for flashing, fasteners, and joints. Shingles come in a wide range of appearances, frequently emulating wood shingles, shakes, or clay tile. However, unlike conventional shingles, these are hardly overlapped so that exposure is almost 100%. Shingles are usually made from aluminum or treated steel and often coated with stone granules, acrylic, or paint. The fasteners are screws, clips, or nails.

A greater variety of materials are used to make metal panels, including zinc, copper, galvanized or un-galvanized steel, aluminum, and alloys. Joints most often vertically run down the roof surface. Seams might be stood upright, laid flat, or battened. Fasteners are screws or clips.

Other than checking for buckling, dents, and rust, the investigator should estimate the roof’s remaining life. This is one of the assets of metal roofs; they have life spans in the range of twenty-five to fifty years, clearly lasting longer than the more traditionally constructed roofs.

About the Author: John W. Gordon is licensed by Washington State to

provide pest and home inspection services

in the north Puget Sound area. You can follow his regular blogs about metal roofs and other subjects at

HomeInspectionWA.net/blog

. The URL for John’s homepage is

HomeInspectionWA.net

.

Source:

isnare.com

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