Is 1 1/2" drain pipe ok for shower drain? and 2nd floor P-trap question...

The bathroom is completely gutted. We're getting ready to put the PVC drain pipe in for the shower and it needs to go through 2 or 3 joists to join the main stack. I notice all the shower drains are designed for 2" pipe. To keep the joist holes as small as possible is it ok to transition from say a 2" P-trap to 1 1/2" pipe, or am I asking for trouble (slow drains) later on?

Also -- this is a 2nd floor bathroom and we don't want to open up the ceiling below for P-trap access -- I assume I need a one-piece P-trap (without the swiveling adjustable thingy) and need to be right on the money for exact center of the shower before we glue it together, before we put the subfloor down?

Thanks.

2 inch

it would be wise on the second floor just to do it right and not
fool around cutting corners....you might pay for it later...

1 1/2 will barely work on a shower situatioin
although I have seen it done that way many times

in many older homes that was what was used.....


but if you have got the walls open , its not that much more trouble to

drill 2 inch holes and not worry about the shower drain getting overwhelmed

someday in the future.....

yes, you really should install a solid pvc trap on the second floor


Wether you are capable of hitting the measurement perfect on
that trap is the big question

if you measure it perfect to center and use the type of PVC shower
drain with the rubber neopreme gasket in it you can glue everything
together but the stand pipe comming up through the floor

of course you can try this without useing the glue to make sure you got it right first.... then mark all the fittings with a majic marker so you stay on the money... and do the final run with glue....


you can set the base in place then measure the stand pipe and
glue it in through the drain hole once the base is in place and you are sure about everything being perfect....if you so wish , that makes things easy

then install that neopreme gasket and tighten it down....




good luck , have fun