I have a 1/2 bath in my basement (toilet and sink). House built in 1964. I would like to add a fiberglass shower/tub combo, however, there is no drain for a shower or tub. How difficult is it to cut the slab to allow installation of the drain line?

-The shower/tub drain would be 6 ft. from the toilet drain (toilet up against ext. wall)
-The shower/tub drain would be 6.5ft. (v-line for the sink)
-The sink and toilet are 4.5ft. Apart

1.) Should I connect to the toilet line or sink line? What is preferred?
2.) What size pipe (dia.) is used under the slab and connecting to the toilet or sink pipes?
3.) Should venting be a problem?
4.) How do I know where the two lines connect (toilet and sink) since they are under the concrete? Most likely the pipes do not connect in a diagonal line. I don’t want to cut the floor up and find out I need to cut elsewhere because other pipes are in the way.
5.) Typically, how far below the concrete do I need to dig to install the p-trap?
6.) How wide of a cut should I make in the concrete to make room for the pipes?
7.) One end of the shower/tub will be pushed up against an outside wall, should I install the shower head/drain on the other end (interior wall) so I can have an access panel to get at the pipes in case of a leak? Otherwise, the shower head would be on the outside wall and exposed to a cooler wall. I live in Minnesota.
8.) How long would it take a plumber to do this? (cut concrete and install pipe under the slab)
9.) How much would something like this cost me if I have the plumber cut the concrete and install the pipes under the slab and to the drain location?
10.) Any tips for installing the fiberglass shower/tub and the framing for it?

Wow! What a way to start my morning. A ten,(count them!) ten part question. Here goes!


1.) Should I connect to the toilet line or sink line? What is preferred?
Connect to the lavatory drain line. This will not only drain the tub/shower but will wet vent it as well.
2.) What size pipe (dia.) is used under the slab and connecting to the toilet or sink pipes?
2" drainage pipes should be used.
3.) Should venting be a problem?
Answered in #1
4.) How do I know where the two lines connect (toilet and sink) since they are under the concrete? Most likely the pipes do not connect in a diagonal line. I don't want to cut the floor up and find out I need to cut elsewhere because other pipes are in the way.
Every plumber worth his salt can take a look at a basement 1/2 bath and just from knowing where the sewer leaves the house can figure out the way he would do the job and be mighty close to where the pipes are under the cement. If you don't wish to call in a plumber for advice then your best bet would be to cut a lateral trench to locate the pipes.
5.) Typically, how far below the concrete do I need to dig to install the p-trap?
It depends upon how far the lavatory drainline's is under the cement. You will take off from there with 1/4" to the foot slope,(1/8ths acceptable if the jobs tight.) and position the trap and raiser in a 14X14" square tub dap out.
6.) How wide of a cut should I make in the concrete to make room for the pipes?
Six inches should give you room enough to work in.
7.) One end of the shower/tub will be pushed up against an outside wall, should I install the shower head/drain on the other end (interior wall) so I can have an access panel to get at the pipes in case of a leak? Otherwise, the shower head would be on the outside wall and exposed to a cooler wall. I live in Minnesota.
By all means, install the pipes and shower head on a interior wall. Make a access panal so you can get at the tub waste and trap if you have to service them.
8.) How long would it take a plumber to do this? (cut concrete and install pipe under the slab)
9.) How much would something like this cost me if I have the plumber cut the concrete and install the pipes under the slab and to the drain location?
in 8 you're asking how good will the plumber be that I contract to do the job,
and in 9 you're asking me to estimate a job I've never seen , don't know what the labor rates are or how much material will be used.
10.) Any tips for installing the fiberglass shower/tub and the framing for it?
The manufacture will have installation and framing instructions with the unit.
good luck on your project. Tom