Believe it or not, old dog in the bar jokes withstanding, not everyone knows what they’ve got on top of their house.
It’s metal? It’s terne? It’s a standing seam roof- or it’s painted with something and no one knows. We’ve even seen where people have banged the standing seems over and then hot-mopped a metal roof.
In America metal roofs started to appear in the mid 1800′s. The age of the “Fireproof roof” was beginning, and hot rolling process for metal were becoming more common as part of the industrial revolution. A lot of these roofs were thicker than what we install today- just because they weren’t able to draw the steel as thin.
In the 1860′s, the options for metal roofs were copper, lead, tin-coated iron, and terne-coated steel. Tin-coated malleable iron was disappearing at the time. Copper and terne rolled roofs were very popular during that vintage–terne more so because it was less expensive.Terne is an alloy of lead and tin that provides excellent corrosion protection for steel. It was recently taken off the market due to the politics of lead, although no specific health threat was ever established. Terne roofs can last a very long time. A lot of terne roofs are a good 100 years old. To say a terne roof would last 170 years might be optimistic, but it’s not out of the question if the roof has been well maintained over the years–especially if it’s located in a benign climate like that in some of the drier western states.
via Terne Metal Roofs on Historic Houses – Fixing Our Historic House.
Here is a bit more on terne:
When terne was first used, during the colonial era, it contained roughly 80 percent lead and 20 percent tin. However, in the latter half of the 20th century, as lead was found to have potentially detrimental health effects, the lead/tin alloy had to be replaced. Seven years of metallurgic research and development produced a new and superior zinc/tin alloy in the mid-1990s. This new alloy, proven through ASTM corrosion resistance testing, provides improved performance and aesthetics over the original, minus potential risk to health.
via Terne Roofing > Types of Metal > Metal Building Construction | TheMetalInitiative.com.
Many of these lead based roofs were later painted- with anything from a silver metal paint to an asphalt based tar. Either way, if there is lead in it- you probably want to replace it- as the runoff isn’t exactly great for your garden (getting a little extra iron in the Tomatoes is good- getting lead in them is not).
The good thing about replacing an old metal roof is that you probably won’t be spending days on a tear-off. Metal roofs come off a lot faster than a 3 in 1 shingle roof- and go on a lot quicker.
So now you know what the old term “terne” means, and the dog in the bar sill gets it right when asked what’s on top of the building- “Roof, Roof”