What is the logic behind IPC 715.1 "Backwater Valves"?

[WeWillFigureItOut]

The code reads:
715.1 Sewage Backflow

Where plumbing fixtures are installed on a floor with a finished floor elevation below the elevation of the manhole cover of the next upstream manhole in the public sewer, such fixtures shall be protected by a backwater valve installed in the building drain, or horizontal branch serving such fixtures. Plumbing fixtures installed on a floor with a finished floor elevation above the elevation of the manhole cover of the next upstream manhole in the public sewer shall not discharge through a backwater valve.

Can anyone shed some light on the rationale for this code? Why should the fixtures on the upper floors of a building not drain through a backwater valve?

 

[cda]

Not into poo poo

Does this help::

https://www.townofcary.org/home/showpublisheddocument?id=1651

 

[steveray]

That way the sewer utility for filling up your basement with sewage when they have a problem in the street.....

Because they are mechanical and prone to failure, they don't want fixtures that don't need them to use them....

 

[WeWillFigureItOut]

That way the sewer utility for filling up your basement with sewage when they have a problem in the street.....

Because they are mechanical and prone to failure, they don't want fixtures that don't need them to use them....

So the idea is that you should limit the number of fixtures running through the BWV because the more use that it gets the faster it will wear out?

 

[classicT]

So the idea is that you should limit the number of fixtures running through the BWV because the more use that it gets the faster it will wear out?

Sort of... not wear out, but more likely to clogging.

They are a flapper valve that opens when sewage is moving downstream. Sewage moving upstream, it shuts.

 

[steveray]

That way they just clog "on your side" and it is not the responsibility of the sewer provider.....

 

[ICE]

I have never seen a backwater valve installed in a building drain. It has always been installed in a building sewer.

Hypothetical: You discover that the first floor of a two story dwelling is below the next uphill manhole cover after the slab is in....or even later like after drywall...or worse...at final....and there is no backwater valve. It's a given that a backwater valve is going to be required....but what about two separate building drains?

 

[steveray]

They have given some leeway in existing buildings, this is huge when finishing a basement....

P3008.1 Sewage backflow. Where the flood level rims of
plumbing fixtures are below the elevation of the manhole
cover of the next upstream manhole in the public sewer, the
fixtures shall be protected by a backwater valve installed in
the building drain, branch of the building drain or horizontal
branch serving such fixtures. Plumbing fixtures having flood
level rims above the elevation of the manhole cover of the
next upstream manhole in the public sewer shall not discharge
through a backwater valve.
Exception: In existing buildings, fixtures above the elevation
of the manhole cover of the next upstream manhole in
the public sewer shall not be prohibited from discharging
through a backwater valve.