I have a question whether or not building a floor on top of concrete is a viable option to insert plumbing underneath for a half bath.

I am looking to finish a small porch off of my kitchen and turn it into a small powder room and hallway/mud area with an exterior door to the back of the house.

I have had several contractors come out to quote. This porch is a concrete slab located directly over the basement and it is part of the main house footprint (not an addition and it has basement access underneath) the porch is one step DOWN from the kitchen.

One contractor came up with the idea of raising the floor to the level of where the kitchen is so it looks cohesive (an not an add on) and run the plumbing under the new floor level into the wall at the basement ceiling and then tie into the existing plumbing that way. He would add new steps/railing outside to the backyard because raising the floor would essentially add a step into the house from the exterior. The other contractors were just going to leave the step down into the porch and drill through the concrete floor.

Is this a viable option for the plumbing to be placed under a new floor instead of drilling deep down into the porch slab and entering the basement that way? I would love to not have to step down into the bathroom if possible, but i am just curious why no one else thought of this option...so that's why i am questioning if its a normal way to go.

Any insight would be appreciated.



1 Answer 1


I generally prefer the same floor level too, but it sounds like this is separate from the plumbing. If either route would let you get the plumbing installed (to code), I don't see any reason not to. Also keep in mind that you can raise the floor and run the plumbing straight down through drilled holes.

As far as raising the floor goes, the main consideration there wouldn't be the plumbing but whether the ceiling is high enough after you raise your floor 6 inches or so. IBC Section 310.6.1 would require that there be at least 7' clearance to the lowest projection from the ceiling (i.e. the bottom of the light fixture). If space allows and you'd be happier with the result, I'd go for it.

  • Thanks for your input. The ceiling height is 9 1/2 feet so there is room to raise the floor to the same level as the kitchen. He did mention that too. I think it's easier to cut through the bottom of the exterior wall and into the open basement ceiling below than all the way down through the concrete floor mainly b/c the porch is about 4 feet thick before it hits the basement ceiling. I just want to make sure it's 'safe' to install plumbing under a sub floor. The city requires this all to be inspected before the floor/walls are closed in so i would assume its nothing new?
    – Lindsay
    Apr 6, 2014 at 19:48
  • The plumbing code requirements would mainly concern the diameter of the drain, the slope of the drain, and the distance between the drain and the vent. Assuming that all of these can be met by running it between the two floor levels, this wouldn't be any different than having it between any other finished floor and ceiling.
    – Comintern
    Apr 6, 2014 at 20:32
  • Yes, everything has been taken into consideration by all the of the contractors that I met with. I am still waiting for a few more estimates but ultimately I like the idea of having all one level and not a step down into a bathroom/mud room area. Thanks again for the advice!
    – Lindsay
    Apr 7, 2014 at 14:48

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