I'm going to build a non-load bearing half wall in the kitchen to create a
peninnsula. The wall will conceal the water and electric for the sink
I'm wondering what the maximum size schedule 40 PVC pipe is that I can run
up through the floor plate of the half-wall. If I frame the wall using
2x4s, then a 3 inch PVC pipe will practically cut the plate in half. I'd
prefer to avoid building the wall out of 2x6s, just to keep the wall size
down. (I'm required to use a 3 inch pipe, but nothing was said about the
I'm also going to put down 1/4 inch bc plywood underlayment over an
existing vinyl floor. Should I put the underlayment down first, then build
the wall, or put the wall right on the old flooring. (Don't want to pull
up the old floor because of asbestos.)
Anyone have any input?
Only your local inspector can tell you if he'll pass it, but since
it's not a bearing wall, and not supporting a great load, you should
be OK to run the 3". You'll have to put metal nail protector plates
on the sides of the plate where the pipe comes up so you don't nail or
screw through the pipe when you drywall or mount cabinets.
Can you just run the pipe up through the cabinet base instead?
IIWM, I'd do the underlayment first, then build the wall. Less
cutting and fitting.
I already planned to use the nail plates, but thanks for the heads up. I
thought about running the pipe up through the cabinet, but it's kind of a
PITA to install the cabinet then, and it would be so much "cleaner" to
have everything coming out of the wall. Perhaps I'm worrying too much?
I'm not sure you understand the purpose of a vent. In your situation
a 2" pipe with an air admittance valve would work better than what
you're planning and be easier and cheaper to build.
There are two typical methods of venting an island/peninsula - this
article covers both methods:
I found that very article before...thanks. Unfortunately, cheater vents
are not legal in my state.
As for a true vent, I would have to rip up two lathe and plaster walls,
create three floor penetrations, and put a hole in the roof just to vent
the sink. I have no access to the attic, so it would prove difficult to
get the pipe through to the roof in the first place. I would also be
required to re-plumb the entire house to be vented, as adding a vent
would change the plumbing arrangement too much for "grandfathered"
As it is, I'm merely moving the sink a few feet...much easier and
Cheater vent...yep, and I guess that GUI is a cheater interface. ;)
Maybe I'm not understanding you. You said your existing system is
completely unvented. I got the impression that you weren't going
through the inspection process. Maybe I'm wrong on that, but it's
really odd that an inspector would insist that you conform to some
ancient plumbing method so your house stays 'consistent' instead of
doing what you can to upgrade it. Around here if you start messing
around with the plumbing they'll make you add venting as required. If
it's a lot of work - tough.
No inspector is directly involved...yet. I asked a few questions during
the planning phase. As you say, if you mess around with the plumbing,
they make you update it, even if it's a lot of work. However, merely
moving a sink can be interpreted as not really messing with the plumbing.
The bottom line is, if I don't want to re-plumb the entire house, I have
to keep it as is. I'd probably put in an AAV if I wasn't going to sell
Thanks for your thoughts on this.
I don't want to belabor the point...points, I'll be bringing up
another one in a minute, but your code is behind the times regarding
an AAV. It's not illegal, it simply doesn't conform to the existing
code. Your whole plumbing _system_ doesn't conform to the current
code! So what do you think you're really doing by sticking with 3"
pipe? Please explain a single benefit of going with a 3" pipe.
The other point...there will be cabinets against this new knee wall,
and freestanding cabinets don't need additional support, so why does
attaching cabinets require stiffening the knee wall at all?
I know...thanks. I've checked with TWO plumbing friends, three books, the
Internet, and the inspector. AAVs are not code legal in my state. As long
as I'm really just /moving/ a sink, I don't have to re-plumb the entire
Why not treat it as two half walls with a 3" pipe between them? If it's
non-load bearing the floor plate can be split.
When I have built half walls and I have access to them from the basement
I place all-thread rods spaced at perhaps 2 ft intervals. I recess a
nut and heavy washer into the header and pass the rod down through the
floor plate and into the basement where another washer and nut allow me
to tension the wall. This keeps the wall from loosening with time. I
find that I can tighten up on the nut in the basement several times over
the first couple of years as the wood dries. The top nut that is buried
in the wall should be staked, or have Loktite applied so that it won't
That's an interesting approach. I'll have one end of the wall anchored
to blocking in the adjacent wall, and the other end will go through the
floor to blocking in the joists. It's an L-shaped wall, so it should be
solid. It's also running perpendicular to the joists, so I will be able
to nail the plate to the joists.
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