Adding a bathroom to a finished basement greatly improves
the livability of the space, though at first glance it appears
to have gravity working against it. After all, in most
basements the main drainpipe exiting the house is closer to the
ceiling than to the slab below. Actually, this is an easy
opportunity to triumph over client misgivings and
There are two ways to connect a toilet to an existing
overhead drain line: an in-floor ejector system or an
above-floor system. The above-floor system uses a sealed pump
tank, to which the bathroom fixture drains are connected. The
tank can be concealed in an enclosure or closet, and requires
little or no demolition of the concrete floor. On the down
side, you’ll have to build a raised platform, about 6
inches high, to accommodate the waste pipe. This means that
access to the toilet requires a step up. The platform may also
impinge on headroom requirements.
prefer the in-floor system, and customers are usually happier
with it because it provides a normal appearance and easy access
to the toilet. In one recent job, I converted a raised-platform
toilet to an in-floor installation (see Figure 1).
1. A basement toilet on a platform (top)
installs easily but is awkward to use. Using an
in-floor basin with a sewage grinder pump creates a
normal appearance and doesn’t impinge on headroom
In-floor installation requires some concrete demolition to
install the sump basin and underfloor piping. The basin is a
sealed unit, typically made of polyethylene, high-density
polyethylene structural foam, or fiberglass, and contains a
powerful grinder-ejector pump. These are rugged units that
rarely require maintenance, although foreign objects may resist
grinding and jam the works.
Depending on the unit, the basin measures a minimum of 18
inches wide by 30 inches deep. It can be located anywhere in
the basement floor, but it’s important to allow floor
space for the basin and all of the related piping, with access
for maintenance. I try to install the basin outside the
bathroom, close to the point where it connects to the existing
sewer line. This also eliminates anything unfamiliar in the
look of the new bathroom.
To install the
in-floor system, I remove an area of the concrete floor about
24 inches square for the basin, and cut a trench about 8 inches
wide for the waste piping from the bathroom fixtures. Concrete
demolition is dusty work, but I keep the mess to a minimum by
using an electric jackhammer instead of pneumatic tools.
Normally, the amount of concrete to be removed is fairly small.
I remove the concrete and subsoil, then dig the basin pit to a
depth of about 30 inches, so that only the top of the tank will
be exposed. The hardest part of the job is now done, and my
plumber can take over.