New sewer 4" or 6"?

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DavidTu

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Single family 4+ baths. Will have two 4" building drains coming together and then out to sewer. Original sewers around here are sometimes 6" terracotta. We'll have not only sanitary drainage but also gutters (allowed by city) on 5000 SF house (1200-1500 SF footprint)

Thoughts on 4" vs 6" from building drains wye? Guess I'm looking to find out if it's a bad idea to have 6", which I lean towards.
 

Cacher_Chick

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My biggest concern would be what happens if there is a blockage when the rainwater is deluging the system?
Despite gravity, I see potential for a real mess.
 

Reach4

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So, the rainwater falling on your house will have to be run through the sewage plant?
Usually.
CSOSign_500x390.ashx

https://www.kingcounty.gov/services/environment/wastewater/cso-status.aspx
 

DavidTu

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We're renovating a 100+ year old home, not new construction so our options in storm water may be practically limited. I'll look into it further based on feedback. The main thrust of my inquiry is not in regards to storm water, but really size of the sewer pipe.

Therefore, I would really like any useful feedback on advisability or inadvisability of using a 6" side sewer rather than 4". Would there be any issues of not carrying waste adequately? I'm assuming it would be unlikely to have a blockage which is attractive. Any other pros or cons?
 

Reach4

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Do you have a basement? Which does the city recommend?
 

Michael Young

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Single family 4+ baths. Will have two 4" building drains coming together and then out to sewer. Original sewers around here are sometimes 6" terracotta. We'll have not only sanitary drainage but also gutters (allowed by city) on 5000 SF house (1200-1500 SF footprint)

Thoughts on 4" vs 6" from building drains wye? Guess I'm looking to find out if it's a bad idea to have 6", which I lean towards.


Obviously, bigger is always better. So if the connection at the street will allow you to use 6", then I would also lean towards 6". However, like others have expressed, there is a concern with combining rainwater with wastewater. You've probably seen where after an exceptional strong rainstorm, the water is actually spewing up and out of the storm drains. This is because the storm drains are not keeping up with the demand. So in the situation you describe (mixing rainwater with sewage), you put yourself at risk of having RAW SEWAGE spewing up inside your house that same way you've seen water spewing out of storm drains. It's not permitted by code to combine the two systems. However, there may be an exception in your municipality or it may be grandfathered in for older buildings. Just make sure you get it inspected and be absolutely 100% positive that you (or your plumber) installs a backwater valve. http://www.homeservicestriad.com/

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