Robert Allison wrote:
mm wrote:
I've looked for a definition on the web and it seems that T1-11 is
hardboard. But I've also seen it called plywood. Which is it?

I thought they were very different. Plywood is iiuc 3 or more layers
of wood, where each layer comes from putting a log on a big lathe and
taking off a continuous strip of wood, each layer deeper into the log
for every rotation of the lathe. That's why one sees a repetitive
pattern on plywood, because if that part of the tree is 16 inches in
circumference, every 16 inches one sees a different level of the same
branches, etc.
Hardboard otoh in wikipedia is described "Hardboard, also called
high-density fiberboard, is a type of fiberboard, which is an
engineered wood product. It is similar to particleboard and
medium-density fiberboard, but is denser and much stronger and harder
because it is made out of exploded wood fibers that have been highly
compressed. Consequently, the density of hardboard is 31 lbs. or more
per cubic foot[1] and is usually about 50-65 lbs. per cubic foot. It
differs from particle board in that the bonding of the wood fibers
requires no additional materials,[2] although resin is often added.
Unlike particleboard, it will not split or crack. It is used in
construction and furniture."

I think T1-11 is heavier than plywood of the same thickness. It seems
to be hardboard. Right?

Thanks.

As others have said, T1-11 is plywood. It comes in 3/8" or 5/8"
thicknesses and either 4" or 8" wide options. Hardboard siding has been
manufactured to look like T1-11, but it is in fact, hardboard siding
with a finish "like" T1-11. Even Hardipanels come with a T1-11 finish,
although they call it Sierra 8. That doesn't make it T1-11.

OK. so what do you call the stuff on my house , a tract home built
in 1971, which has siding that "looks" like T-111 but is
definitely not plywood (like the other posters picture). It is
some kind of composition I would compare to thick cardboard. If
allowed to get wet, it swells like a roll of paper towels would.
And it does not hold a screw very well at all.