I have a 4 inch line exiting my basement and then extending across the wall about 16 feet. It then is reduced to 3 inch and it continues horizontal for another 14 feet. It then turns vertical and goes straight out the roof. It is picking up 1 toilet, 2 sinks, 1 tub, 1 shower, and 1 washer.

My question is:
Is it allowed by code to be reduced from 4 inch to 3 inch while running horizontally in the basement?

I have heard these two conflicting things.

1. someone told me that if it enters the house with 4 inch, then it must continue straight through and vent at 4 inch.

2. someone also told me that it may be reduced from 4 inch to three inch as long as that reduction occurs before it goes vertical.

The house is in Philadelphia.

Help is greatly appreciated!

Hi Johnny

In my area, if you start 4" then the pipes must remain 4" up and through the roof.

With that being said, if you are already reduced to 3" why the concern?

Back to you...

Mark

Hi Johnny

In my area, if you start out 4" then the pipes must remain 4" up and through the roof.

With that being said, if you are already reduced to 3" why the concern?

Back to you...

Mark

Thanks Mark,

My concern is not so much about the function, but more about the code.

I'm wondering if it will be an issue when I decide to sell the home.

Or if a plumbing inspector ever happens to be in my basement.

If the work was done on a permit , it would have been inspected. Do you have a CO (certificate of occupancy)? This would have been issued by building dept.

Chuck

Hi Johnny

A home inspector will NOT be looking at things like that. They'll be looking for all the other things they look at:

Foundation, lead, termites, roof, sinks have ptraps and vents, sinks and faucets work and don't leak, boiler/furnace all OK, backflow preventers where required, electrical updated and proper (where required), windows tight, safety issues, etc. etc. etc..

You should be fine with this issue as presented!

Mark

Codes vary greatly from area to area. In my area you merely need to meet the cross sectional area required for the house drain when it comes to venting. You can accomplish this by running the same size vent as the house drain up and out the roof, or with a combination of smaller vents to meet the required venting. Also in my area it goes off "required house drain" which in your case would be three inch (even if it is 4 or even 6 inch, you still only require 3 so you only would need venting for 3" no matter the actual house drain size). Of course no plumber in his right mind would run three inch for underground outside the home for the house sewer, but you could by code here. We always bring in four inch, and reduce to three inch for single and double bath homes. As long as the fixtures units required for all fixtures in the home is low enough for three inch to handle it, you only need enough venting through the roof for the three inch pipe. It can get a bit confusing for sure, especially with code variations from city to city and state to state. Your best bet here is to contact your local plumbing inspector and have them give you the laws of the land in your area. Good luck and please do let us know what they have to say.
Lee.

Believe it or not, there are Home Inspectors that WILL look for things like that. IF this was in the home you are attempting to purchase, I do not think it will be a problem.There are plenty of houses with vent stacks that start as 4" but the pipe through the roof ends up being 2" and they are not condemned for it.