Lack of Standards

Post date: Jun 21, 2015 6:43:52 AM

I was reading the architect's specification for the sheet metal used to line the canales (scuppers) where he calls for “26 ounce” copper. Oh? I have seen fabric and paper graded by density (weight per unit area), but never sheet metal. Here are two size descriptions from Basic Copper:

• 16 MIL (.016 inches thick) 26 gauge: The 16 mil is approximately 1.5 times thicker than the 10 MIL . It would take approximately 62.5 sheets of 16 MIL stacked on top of each other to make an inch. Also called 26 gauge, the 16 mil copper weighs approximately 12 ounces per square foot. It is significantly more rigid and less pliable that the thinner material, but will also hold weight and can be bent/ formed into shape by hand or with tools. It is a very durable. It can be cut with tin snips, shears or a utility knife with a heavy duty blade. 16 mil is often used for sculptures, jewelry-making and other arts and crafts projects. Our customers have used the 16 mil for backsplashes, bar tops, countertops, and range hoods as well as roofing projects (see the photo gallery for information about creating acupola from 16 mil copper) and other outdoor structural projects where the durability of the material outweighs the need for more pliability.
• 22 Mil/16 Ounce Copper (.0216") 24 gauge: 16 ounce copper sheeting is a heavy weight copper often referred to as "roofing copper" or "roofing flashing." It weighs approximately 1 pound per square foot. It's often used for roofing and flashing, various art and craft projects, DIY projects such as backsplashes, countertops and range hoods, electrical applications, research and development and much more. 16 ounce copper can be bent and formed by hand but is very durable. Metals snips are needed to cut this thickness.

Ach, du lieber! I find from Storm Copper that for roofing applications, “To make matters even more confusing, the roofing industry measures copper thickness in ounces per square foot. 16 oz. copper sheet is a very common size of roofing copper. Listed below are product links that cross reference inches to gauge.” However they don’t cross-reference density vs. thickness.

Alaskan Copper and Brass does have a density vs. thickness vs. Birmingham Wire Gauge (BWG) chart, but 26 ounce seems not to be shown:

• 24 oz 0.0320” 21 BWG
• 32 oz 0.0430” 19 BWG

I do wish the Americans had switched to the metric system a few decades ago.

The Copper Development Association gives a table:

It looks as though that industry has a ‘nominal’ measure but actually delivers much less (‘minimum’).

Again, there is no ’26 ounce’ material. It seems that 24 and 26 gauge are used for roofing.

It turns out that the same number gauge means very different thickness, depending upon which metal you are measuring. “US Standard”, Galvanized Steel, Stainless Steel, Aluminum, Copper, and Zinc all use variants of the same set of number gauges, as explained by Riverside Sheet Metal.

This is about as rational as many of the other things our legislators do.