"Before sheet metal, ductwork was made out of wood. Nowadays, sheet
metal
ductwork is being replaced by the flexible "dryer vent" type stuff; I
expect
this is a major reason for their demise. I expect 10 years from now,
copper
plumbing will be pretty rare. "

Actually there is a larger trend in the works that should scare the
heck out of the construction trade....manufacturing housing modules on
an assembly line.

There is no reason why China could not manufacture modules of a house
and ship them to the United States for assembly...each module would fit
inside a container.

The assembly would be quick, efficient and could be done by McDonald
skill level labor.

In relation to ductwork, it would be preinstalled and would just snap
together at the module interfaces.

Even the site preparation would be minimized by a standard...do you
want a slab or a basement?

Considering that single owner homes are the bulk of income for
construction, it is just a matter of time before it happens on a large
scale.

And considering that most people live in a house for less than seven
years, a "throwaway house" would not be a hard concept to sell.

TMT