I own a property that has a brick chimney that extends maybe 10 feet or so
above where it comes through the roof at the back of the house. The
property that I own is a "twin" home -- meaning two single family homes that
are attached with a common wall in between -- I own the home on one side and
my neighbor owns the home on the other side. My side is a rental property
that I have rented out to a family, and my neighbor on the other side owns
his half and lives there.

The chimney is actually two chimneys in one. It goes up along the inside of
the back wall along the party wall line, and my half of the chimney is for
my home and the other half is for the neighbor's home. The combined chimney
was originally brick and it now has stucco over the brick on all four sides.
The stucco is starting to deteriorate in a few places and the chimney looks
like it may be leaning a little. So, I am going to have a chimney person
look at it and tell me what he thinks it needs etc. It may just need to
have the stucco repaired or redone or it may need a lot more than that.

What I am wondering is, if it turns out that the best thing to do is to take
down the existing chimney and replace it, are there other types of chimney
construction that could be used for the replacement other than brick or
block? Both houses have aluminum siding and no brick, and the chimneys in
the back, so there is no need for a new chimney to be made of brick or
anything fancy. Even metal chimneys would be fine with me (and probably my
neighbor) if there is such a thing for this type of application.

The heaters for both houses are gas-fired steam radiator heat and the hot
water heaters are gas hot water.

I found the following link that gives some guidelines for how high the
chimney is typically supposed to be in relation to the roof:
http://www.solidflue.com/concerns.htm#Common . I didn't do any measuring,
but if it needs a new chimney and it is legal and safe to have the new
chimney be less high than the existing one, I would go with that.

I'll be asking the chimney person these same questions, but I thought I'd
also post the questions here beforehand to get any ideas or suggestions
anyone may have.

Thanks.