Slab vent

[damadake]

I have a master bath with dead space behind the existing wall (used to be an old closet). The current bath is ~6'x7' but could be 12'x7' when the dead space is utilized.The bath has only a shower and the vent pipe runs up the back wall of the shower. There is sufficient room to install a tub in place of the shower, even looks like the drain is just right where it needs to be, but the vent pipe either has to be moved or re-routed.

Could the tub be raised so the vent could be rerouted through the new wall, or must it be moved by breaking up the slab?

Any help would be greatly appreciated. Thanks!

 

[Jimbo]

Not clear why the vent has to be moved, but here are a couple of considrations: the shower drain by code must be 2" whereas the tub was 1½". If you are lucky, only the waste/overflow and trap were 1½ and went immediately into 2". Also, the vent must run vertical until it is approx. at least 42" above the floor. Certainly there could not be vent lines in the slab.

 

[Sponsor]

 

[damadake]

The vent is midway between the back wall and the back of the shower, but the tub would extend the entire length.

The vent runs from the slab (cast iron) through the ceiling and out the roof. A picture would probably help, but I'm not sure how to upload one here.

Thanks for taking time to respond!

 

[hj]

vent

To do it correctly the tub might have to be raised beyond what would be pleasing to look at, or easy to get in and out of. Break the concrete/

 

[damadake]

breaking the concrete seems a scary thing to me, so I'd probably have someone else do that.

So the drain size is also an issue? Can it be reduced with a fitting, or is there more demo required for the drain.

Here's my (really poor) attempt at showing the layout.

+-----------+---------+---------------------+
|           |         |                     |
|           |         |                     |
|           |drain>o  |                     |
|           |         |                     |
|   vent-->o|         |                     |
|           |         |                     |
|           |         |                     |
|           +---------+                     |
|                                           |
|                                           |
|                                           |
|                                           |
|                                           |
+-------------------------------------------+

 

[Dunbar Plumbing]

You will have to bust that floor up to change the size of the piping for the shower and properly redirect the vent without causing code violations.

Otherwise I'd hang up the idea of this project if you have no intentions of doing it right.

 

[damadake]

I suppose breaking the concrete is a common practice in these circumstances? Are there any long term slab risks associated with this? Last but not least, what kind of $ am I looking at to have this done?

I appreciate all of the feedback. Thanks!

 

[Jadnashua]

The only time breaking the slab up for mods where it is a big deal is if it is constructed with post-tensioned cables. This is not that common, but is used in CA and other places. If you cut one of the cables in this type of construction, then you will have problems. If it is a typical reinforced (or not) poured slab, it's not that big of a deal.

Since your shower is probably 2" and you want to change it to a tub (which requires 1.5" drain), you should be able to use an adapter, but you might need to still break out things as getting the (probably new) drain and adapter to make it 1.5" will almost certainly require some wiggle room. Also, depending on the age, it would make sense to evaluate and probably change that drain from CI to PVC while you are in there.

Moving the vent line will have to take into consideration the max distances from the trap, but should not be too big of a deal other than that you will have to tear up more floor. Do you know where the drain goes? My guess is that it runs from the current shower drain towards the vent line. You'd have to tear out the floor further back along that line to install the new vent. It can go up and then jog to reattach to the portion above the ceiling. Picking a good path for it is hard without seeing the thing excavated first, though.

 

[damadake]

great information, thank you! I'm in TX, and the house is a 1960's vintage. My thought on movement was to move the vent forward to the new partition wall, rather than back to the slab edge. I would think staying away from the edge of the slab would be a good thing when tearing it up. Is there any problem doing that? The vent would move ~30" forward and would still be ~17" from the drain, just on the other side. Then the vent could go up the new wall partition and with a jog in the attic go back out the existing vent hole.

Is this realistic? Any potential violations in my thought process?

I'll probably have a real plumber do the busting. I can do lots of things, and could probably do this, but I'd rather have some experience with me on it.

Thanks again lots of good information and I really appreciate it!

 

[rudytheplbr]

Re: Shower/to tub vent

From your drawing it looks like you would not have to move the vent to stay within UPC guidelines for sidearm distances from vent to trap weir. That said, if the vent (in present locale) is in the way of tub installation, I think I would build a false floor for under the tub and re-route the vent under the raised floor, and do like you said in the 2nd post.

Good Luck,
Rudy

EAT "WILD ALASKA SALMON" IT'S GOOD FOR YOU AND YOURS!!

 

[damadake]

You are correct, the vent would be in the middle of the tub.

Raising the tub was my original thought, and would prefer it to hacking the slab. Are there any functional or violation types of issues with just raising it, then adding a stub in front of the tub?

Thanks

 

[Dunbar Plumbing]

What code in what state allows flat venting under 42"


And here's a question to all plumbers:

You know why flat venting under 42 is a code?

 

[damadake]

I'm assuming that means it is a violation, right?

 

[damadake]

I guess this answers the question...

DWV System Design
There is no such thing as a horizontal waste pipe. All waste pipes must run vertically or have enough downward pitch or slope to allow gravity to do its job and pull the water quickly through the pipe. Drainpipes cannot snake around obstacles within walls, either. Twists and turns can cause slowdowns or backups within the system, so be sure there is enough room for drainpipes to drop on their way to the waste stack or main drainpipe. After all, the last thing you need is a drainage system that doesn't drain.

or does it...

Vent pipes from lower floors must join the roof vent above the upper floor appliances to avoid backups in the system. Unlike drainpipes, vent pipes can run horizontally since gas-air pressure is drawn upward by the lower atmospheric pressure outside the house.

 

[Phil H2]

What code in what state allows flat venting under 42"


And here's a question to all plumbers:

You know why flat venting under 42 is a code?

I thought flat venting was when the take off is below the centerline of the drain pipe - code violation.

42" ?? UPC requiires vents to run vertical until 6" above the floodrim of the fixtures served. It also allow vents to run horizontal below the floodrim if structural conditions prevent going above the floodrim first. But, the fittings below the floodrim must be drainage rather than vent fittings.

 

[Dubldare]

Six inches above the fixture's flood level rim means your good to go for horizontal on vents, unless they are washed: AKA wet venting.

The 42" comes in as normally the max height for sinks are 36", although 34" is more of a norm for countertops, and many (non-ADA) lav sinks are set at 31".

36" + 6" = 42"

I'd like to see people stick to the 42", the higher the better IMO.

When tieing two vents together on a vertical, always insure 6"+ elevation above the highest fixtures vent.


I have had to, on occasion, go horizontal lower than 42". On a tank-type closet vent, I've had to go horizontal at 30", due to an electrical panel (in a mech room behind the bathroom). Didn't like to do it, but I was a good 12" above the closets flood rim.

I have cut out and corrected several flat vents. All were packed full of crap/rust/etc.

 

[Dubldare]

Also of note:

Vertical means a vertical pipe, OR one which is within 45° of the vertical, measured off the vertical axis.

Horizontal means a horizontal pipe, OR one which is within 45° of the horizontal, measured off the horizontal axis.

 

[damadake]

I'm easily confused, sorry.

The existing vent only serves the shower, so is it correct or not to run a horizontal vent for 30", then up the other partition? Is this within code, or a violation?

Thanks!

 

[Jadnashua]

My guess is that the drain line runs towards where the vent comes out of the slab and it runs vertically from there. You'd need to know where the actual drain line is...to know where you can go vertically from that and if it was within the max distance from the trap.

 

[Dunbar Plumbing]

I have cut out and corrected several flat vents. All were packed full of crap/rust/etc.

That's one of the primary reasons for no flat venting under 42.

Gravity (less than 45 degree pitch) helps prevent those vents from closing up from situations involving clogs.

Clogs meaning a sudden backup and a flat vent has no way to clear itself.

So turning that vent with 90's is setting that vent up for failure if that system clogs and matter goes into that flat section.

No one will know to run water through that vent....all that will matter is that the shower is draining. Sure enough though over repeated clogs that flat vent seals off and now you have a fixture that is incorrectly designed.

Remember, plumbing is installed in accordance to operate without error. Too often I see those in and out of this plumbing profession dodging the bullet to avoid what "seems" to be more work to do it right.

Better them than me. I just won't install/service/repair plumbing unless it is done right. Have to have pride in one's workmanship to sleep at night without worry or lawyers climbing your bank accounts.

I'd rather be known as pricey and right than cheap and wrong any day of the year.