The fundamental difference in the three
types of single-family houses shown is
the density at which they can be built—
which is to say the number of units that
can be put on an acre of land in each of
these configurations. The upward limit
of the detached house is about six units
to the acre. The upward limit of the
semidetached house is eight units to the
acre, but this allows for a driveway to be
put between each unit, something that could not be achieved in detached units at six to the acre. Row houses can be
built at an upward limit of 16 units to the acre if one also wishes to pro-
vide off-street parking on a one-to-one basis.