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Is 20" low enough for a kitchen sink drain?

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Forum Discussion: Is 20" low enough for a kitchen sink drain?

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Is 20" low enough for a kitchen sink drain?
Author: sum(FL) Started work on my kitchen. The plumber measured the existing sink drain (the part that sticks out of the wall), the center of the drain is 20" above the slab. So after thinset and tiles it will probably be 19.5" above the finished floor. He said this is too high, there is no way the sink would be able to empty into a garbage disposal and then from there hook to this drain. It needs to be lowered several inches. I told him the existing sink and cabinets I ripped out was working with that drain and it was ok, he said no way, your wife will want a deep sink, your existing sink is probably very narrow. The problem is the vent is five feet away along that exterior concrete wall, and the vent pipe is next to a window, I know it's solidly poured concrete with rebar there (hurricane windows). There will be major difficulty to chase across that wall and cut a five foot horizontal opening then break up that solid concrete, just to lower the drain a couple of inches. So I told him I need to think about it. Then I came home to my existing house, I measured the drain going out of the garbage disposal unit and into the wall is 19.5" above the tiles. My sink is about 8" deep and my wife said it's ok. So why should I lower the drain?

Is 20" low enough for a kitchen sink drain?

Author: sum(FL) Started work on my kitchen. The plumber measured the existing sink drain (the part that sticks out of the wall), the center of the drain is 20" above the slab. So after thinset and tiles it will probably be 19.5" above the finished floor. He said this is too high, there is no way the sink would be able to empty into a garbage disposal and then from there hook to this drain. It needs to be lowered several inches. I told him the existing sink and cabinets I ripped out was working with that drain and it was ok, he said no way, your wife will want a deep sink, your existing sink is probably very narrow. The problem is the vent is five feet away along that exterior concrete wall, and the vent pipe is next to a window, I know it's solidly poured concrete with rebar there (hurricane windows). There will be major difficulty to chase across that wall and cut a five foot horizontal opening then break up that solid concrete, just to lower the drain a couple of inches. So I told him I need to think about it. Then I came home to my existing house, I measured the drain going out of the garbage disposal unit and into the wall is 19.5" above the tiles. My sink is about 8" deep and my wife said it's ok. So why should I lower the drain?

Re: Is 20" low enough for a kitchen sink drain?
Author: PlumberManDan(IA) I would not rough it in at 20" especially since there are a LOT of DEEP sinks, 18" would be tops and then only if I knoew the spec's of the sink before hand. PlumbCat TM 2003 Plumbermandan

Re: Is 20" low enough for a kitchen sink drain?
Author: sum(FL) The existing drain is at 20" already that was from 1970. To lower it I would need to break 5 feet of solid concrete. Is there any creative approach?

Re: Is 20" low enough for a kitchen sink drain?
Author: PlumberManDan(IA) I bet you will not have to break up SLAB, a Picture of the stubout including a little wall and floor would help greatly. PlumbCat TM 2003 Plumbermandan

Re: Is 20" low enough for a kitchen sink drain?
Author: sum(FL) sorry I was not clear, there is no slab involved. The stubout is 20" above the slab. It runs five feet across inside an exterior concrete wall to meet a cast iron vent pipe which is also inside that wall. That wall is solid, poured concrete wall with steel rebars in it. To lower the drain by a couple of inches, I need to break that wall and chase the pipe horizontally across the wall for five feet, then break the vent pipe enough to connect the pipe at a lower spot. I would rather not do that because this will be a big mess. I will snap a picture tomorrow right now I am not at the job site.

Re: Is 20" low enough for a kitchen sink drain?

Author: sum(FL) sorry I was not clear, there is no slab involved. The stubout is 20" above the slab. It runs five feet across inside an exterior concrete wall to meet a cast iron vent pipe which is also inside that wall. That wall is solid, poured concrete wall with steel rebars in it. To lower the drain by a couple of inches, I need to break that wall and chase the pipe horizontally across the wall for five feet, then break the vent pipe enough to connect the pipe at a lower spot. I would rather not do that because this will be a big mess. I will snap a picture tomorrow right now I am not at the job site.

Re: Is 20" low enough for a kitchen sink drain?
Author: steve_g(CA) You would know for sure if you knew what sink you were going to use - which you're going to have to figure out sooner or later. If it's a double-bowl you'll need some extra room for the continuous waste. Then spec the disposal, and you will know for a fact how high you want the drain. And I bet you'll find that 20" is too high. You may have finally found a good plumber.

Re: Is 20" low enough for a kitchen sink drain?
Author: packy(MA) you could raise the height of the base cabinets.

Re: Is 20" low enough for a kitchen sink drain?
Author: e-plumber(NY) Before you break out the jack-hammer... You have a few options but first get the cut sheet from the disposer, the exact dimension of the kitchen sink, the exact height of the counter-top and do some simple calculations. Since 1995 (3 years before Google started) www.frankenthalerfoundation.org has been THE best plumbing supplier on the web.

Re: Is 20" low enough for a kitchen sink drain?
Author: mjb1962853(NY) You never want water to SIT in the garbage disposal so its outlet must be higher than the wall pipe. The manufacturer usually specs a recommended height difference. Per E's advice, get all the specs for your sink and garbage disposal and do some calcs BEFORE you start cracking concrete walls. I'd bet it would work IF you skip the garbage disposal. Do you really NEED one? I've had one in every place I've lived for the last 30 years, but I rarely use them to actually grind anything. All critter waste goes into the solid trash and vegetable waste to a compost bin. If you absolutely MUST have a GD, pick a double sink with a shallow side and use that side for mounting the GD. That might work fine with your existing rough-in. Good luck!

Re: Is 20" low enough for a kitchen sink drain?

Author: mjb1962853(NY) You never want water to SIT in the garbage disposal so its outlet must be higher than the wall pipe. The manufacturer usually specs a recommended height difference. Per E's advice, get all the specs for your sink and garbage disposal and do some calcs BEFORE you start cracking concrete walls. I'd bet it would work IF you skip the garbage disposal. Do you really NEED one? I've had one in every place I've lived for the last 30 years, but I rarely use them to actually grind anything. All critter waste goes into the solid trash and vegetable waste to a compost bin. If you absolutely MUST have a GD, pick a double sink with a shallow side and use that side for mounting the GD. That might work fine with your existing rough-in. Good luck!

Re: Is 20" low enough for a kitchen sink drain?
Author: hj(AZ) I believe he is saying the WALL is concrete block with all the cells grouted.

Re: Is 20" low enough for a kitchen sink drain?
Author: hj(AZ) If the drain from the wall is lower than the oulet of the disposer after it is mounted in the sink, and you will have to have them there to measure it, then the plumber should be able to use a "Y", or double "Y" and two traps to connect the drains. IF the drain is not lower than the outlet, then there is no "creative" method that will work. Edited 1 times.

Re: Is 20" low enough for a kitchen sink drain?
Author: hj(AZ) And the range, and get platform shoes for his wife.

Re: Is 20" low enough for a kitchen sink drain?
Author: sum(FL) OK I am not there right now, I did find a photo I took during demolition that will explain the situation. Here is it: Unfortunately I did not pay a whole lot of attention when things were ripped out and trashed during demo, so I am trying to guess a bit here. First, there is a window that looks out to the pool, the old counter top extends outside to the courtyard for about 8" and is used as a small counter on the outside. For this reason, the counter height is fixed. I could may be raise it a bit, built up the bottom of the window frame, but this may cause a problem with the dishwasher which is on that side, as well as turn a "standard hurricane window" into a "custom sized hurricane window" which about double or triple the cost. There is a door to the right, this door is now gone and changed into a window. Between the door and window there is a narrow stip of wall about 10" wide, the vent pipe goes through it. This is poured solid concrete. We had to install rebars in it to reinforce the hurricane proof windows. To examine closer the drains, I put a few labels... a - I don't know why it is there. I don't remember how it was connected before. I think may be it is a separate drain for each side of the double sink? I just don't remember. b - water supply for the dish washer? but I think this is a cold supply, so why not two hot supplies? c - the drain where it is 20" above the floor. d - electrical MC cable for dishwasher power. The old sink was a double SS sink. I think the right side has a disposal unit, the dishwasher ties into it? or the dishwasher use the other drain? may be each sink drains independently? Both drains travels to the right and connect to the vent to the right of the window. I have to pick out a sink and disposal then...I was hoping to wait on that. Edited 1 times.

Re: Is 20" low enough for a kitchen sink drain?

Author: sum(FL) OK I am not there right now, I did find a photo I took during demolition that will explain the situation. Here is it: Unfortunately I did not pay a whole lot of attention when things were ripped out and trashed during demo, so I am trying to guess a bit here. First, there is a window that looks out to the pool, the old counter top extends outside to the courtyard for about 8" and is used as a small counter on the outside. For this reason, the counter height is fixed. I could may be raise it a bit, built up the bottom of the window frame, but this may cause a problem with the dishwasher which is on that side, as well as turn a "standard hurricane window" into a "custom sized hurricane window" which about double or triple the cost. There is a door to the right, this door is now gone and changed into a window. Between the door and window there is a narrow stip of wall about 10" wide, the vent pipe goes through it. This is poured solid concrete. We had to install rebars in it to reinforce the hurricane proof windows. To examine closer the drains, I put a few labels... a - I don't know why it is there. I don't remember how it was connected before. I think may be it is a separate drain for each side of the double sink? I just don't remember. b - water supply for the dish washer? but I think this is a cold supply, so why not two hot supplies? c - the drain where it is 20" above the floor. d - electrical MC cable for dishwasher power. The old sink was a double SS sink. I think the right side has a disposal unit, the dishwasher ties into it? or the dishwasher use the other drain? may be each sink drains independently? Both drains travels to the right and connect to the vent to the right of the window. I have to pick out a sink and disposal then...I was hoping to wait on that. Edited 1 times.

Re: Is 20" low enough for a kitchen sink drain?
Author: birddoggiest(ID) If the cabinets are not in yet can you open up the wall where the pipe comes out of the floor add a tee and run it behind the cabinets or maybe through them? I don't know if a Saniflo pump would be an option? A just a thought, that is a tough spot to make work. Edited 1 times.

Re: Is 20" low enough for a kitchen sink drain?
Author: PlumberManDan(IA) If you choose a sink that needs a lower drain line the you will HAVE to bust up concrete, Find the drain line in the 10" section open up that section of poured wall, granted it will not be pleasant. Find the BURIED IN THE WALL TEE, break out all concrete surrounding the tee plus 6" above and 18" below the horizonal protion of the tee clean the pipe and place a NEW santee coming out of the wall at a 45, then using a st 45 of the correct size bring the waste arm OUT of the wall and then continue on the horizonal portion to the placement of the drain, You will have to move the wall out accordingly to hide the waste arm but breaking a little poured wall is better than breaking 5' of it. PlumbCat TM 2003 Plumbermandan

Re: Is 20" low enough for a kitchen sink drain?

Author: PlumberManDan(IA) If you choose a sink that needs a lower drain line the you will HAVE to bust up concrete, Find the drain line in the 10" section open up that section of poured wall, granted it will not be pleasant. Find the BURIED IN THE WALL TEE, break out all concrete surrounding the tee plus 6" above and 18" below the horizonal protion of the tee clean the pipe and place a NEW santee coming out of the wall at a 45, then using a st 45 of the correct size bring the waste arm OUT of the wall and then continue on the horizonal portion to the placement of the drain, You will have to move the wall out accordingly to hide the waste arm but breaking a little poured wall is better than breaking 5' of it. PlumbCat TM 2003 Plumbermandan

Re: Is 20" low enough for a kitchen sink drain?
Author: scottdenny(CA) Pull the angle stops, remove the back wall of the cabinet. Lower the waste to 13", extend the water stub outs, retrace your steps. Better yet, call a plumber.

Re: Is 20" low enough for a kitchen sink drain?
Author: sum(FL) Scott, I can't. I already did all that except lower it to 13". Basically that cannot be done without demolishing a lot more, and the plumber agreed with it.

Re: Is 20" low enough for a kitchen sink drain?
Author: scottdenny(CA) Is the waste tee behind the cabinet or is it remote? If it is behind the cabinet, I see no reason why it can't be lowered.

Re: Is 20" low enough for a kitchen sink drain?
Author: sum(FL) Scott, The stub out is inside the concrete wall under the window, travels to the right and ties into a 3" cast iron vent pipe that runs through the narrow space between the window and the door. The vent pipe is embedded in solid concrete with steel rebar at each corner for hurricane protection, and to the right there is a commercial heavy gauge metal door jamb that was set in place when the concrete was poured with it penetrating deep into the ground with metal flippers on it's side to eat into the concrete wall. My concrete contractor took out a huge saw and was not able to get the door jamb out so we left the jamb in the wall. The jamb "protects" the vent pipe from the right. There are also about three metal EMT pipe that runs up that narrow space. Basically I don't see a way to open up the vent pipe to do a lower connection. Well not impossible, but I will have to explore all other means before doing it.

Re: Is 20" low enough for a kitchen sink drain?

Author: sum(FL) Scott, The stub out is inside the concrete wall under the window, travels to the right and ties into a 3" cast iron vent pipe that runs through the narrow space between the window and the door. The vent pipe is embedded in solid concrete with steel rebar at each corner for hurricane protection, and to the right there is a commercial heavy gauge metal door jamb that was set in place when the concrete was poured with it penetrating deep into the ground with metal flippers on it's side to eat into the concrete wall. My concrete contractor took out a huge saw and was not able to get the door jamb out so we left the jamb in the wall. The jamb "protects" the vent pipe from the right. There are also about three metal EMT pipe that runs up that narrow space. Basically I don't see a way to open up the vent pipe to do a lower connection. Well not impossible, but I will have to explore all other means before doing it.

Re: Is 20" low enough for a kitchen sink drain?
Author: scottdenny(CA) Sum How do you know which way the drain line travels once it enters the concrete wall? I'm referring to the drain, not the vent.

Re: Is 20" low enough for a kitchen sink drain?
Author: sum(FL) Scott the cabinet backer boards are out now. There is an electrical EMT pipe a bit to the right of the stubout, see the MC cable? That was for the dishwasher, part of that concrete was partially hollow around that EMT pipe and I could see the bottom of drain pipe passing to the right. I am pretty sure the drain lines travel to the right and tie into the red vent pipe there. Now what I cannot say if the two pipes ties into the vent pipe individually or they merge somewhere. Both pipes "bent" to the right. I know they don't go vertically down and travels below if that's what you are wondering. Edited 1 times.

Re: Is 20" low enough for a kitchen sink drain?

Author: sum(FL) Scott the cabinet backer boards are out now. There is an electrical EMT pipe a bit to the right of the stubout, see the MC cable? That was for the dishwasher, part of that concrete was partially hollow around that EMT pipe and I could see the bottom of drain pipe passing to the right. I am pretty sure the drain lines travel to the right and tie into the red vent pipe there. Now what I cannot say if the two pipes ties into the vent pipe individually or they merge somewhere. Both pipes "bent" to the right. I know they don't go vertically down and travels below if that's what you are wondering. Edited 1 times.

Re: Is 20" low enough for a kitchen sink drain?
Author: scottdenny(CA) Sum Remove the trap and look into the waste line going into the wall. Does it elbow to the right or downward?