Does a drain pipe have to be in the floor/wall or can it run on top of floor underneath cabinets?

I'm renovating my kitchen on the second floor of my duplex, so there is a finished ceiling directly below it. The kitchen sink will be moved about 7 feet horizontally from where it is now. In the current location of the kitchen sink, there will be cabinets and the cabinets will extend all the way until the new sink location.

Since kitchen cabinets have 4 inches of empty space under them, I was wondering if instead of placing the new horizontal drain line in the wall or under the floor, I could simply run it under the cabinets on the floor. Maybe my Google-fu is failing me (or the answer is obvious), but I couldn't find anything referencing doing this. It would save a lot of time and it would be nice not having to destroy my studs or joists. And in the future if it needs repair (knock on wood), I won't be tearing apart my tenant's ceiling or the back of my cabinets.

Is there any reason why this is a bad idea? If it's against code, I'd still like an explanation of why it's a bad idea - I like to learn. Thanks in advance for any advice.

• 4" of height may not give you enough fall over the given run per code. Mar 20, 2015 at 14:41
• Drain pipe 2 1/2" and less requires 1/4"/foot slope, so over 7 feet that's 1 3/4" (`7 * 0.25 = 1.75"`). 1 1/2" schedule 40 PVC has an outside diameter (O.D.) of 1.9". Which means if you round the pipe up to 2" O.D., you'll need 3 3/4" just to slope the pipe properly(`2" + 1.75" = 3.75"`). Mar 20, 2015 at 16:56
• Is it 1/4" per foot slope overall after the sink trap to the main line? Mar 20, 2015 at 17:23
• I never see it as a bad idea if you can get to it for repair at some time in the future. It does make for a bad choice to store things you can eat, or eat from in the same location. Mar 21, 2015 at 22:52