The word “metal” covers a lot of ground. Several metals are used for roofing materials: steel, stainless steel, aluminum, copper, and zinc alloys. Each has different properties that affect durability, price, and appearance.

Steel, used for most metal roofing, is heavier and sturdier than aluminum. Manufacturers have settled on a number of durable coatings and finishes that protect steel from rust and corrosion. It’s usually zinc-coated for corrosion protection and then sealed. A coating of epoxy primer offers adhesion and a baked-on acrylic top coating adds color and protection. Because sheet systems are designed for commercial applications, they generally are given highly durable paint finishes. One popular fluorocarbon coating used on many products is called Kynar.

Stainless steel, a very expensive roofing material, won’t rust or corrode. Terne coating can give it a natural matte-gray finish.

Aluminum, extremely lightweight, is used in much residential metal roofing. It won’t rust, but it must be painted or coated for appearance. Coatings are similar to those used on steel. Environmentalists have expressed concerns about using this precious resource for purposes such as roofing.

Copper (shown at right), rooted in centuries of use, will not rust, has no “finish” to scratch or peel, is soft enough to easily tool, and weathers naturally to a beautiful verdigris patina. Unfortunately, it’s very expensive.

Alloys are formulated for strength, graceful weathering, and durability. Cost depends on the specific material, but, as a group, they are pricey.