ABS pipe - contractor question

[newhomediy]

Hi,

I am doing a remodeling (adding 2 more bathrooms + 2 rooms) and my contractor is suggesting a change order (optional) to replace the current 3 inch ABS pipe to a 4 inch ABS pipe + install new cleanout. current house is 3br. 2ba and it would get upgraded to 6Br. 4Ba. - please share your thoughts on whether iI should go ahead with the change order or not a big deal to do this?

appreciate your help from this forum!

Mike

 

[breplum]

Plumbing code has always been fairly over protective and said in my 2016 CPC copy:
"only four WC allowed on any vertical pipe or stack and not to exceed three WC on any horizontal branch or drain."

I have notes taken by me that newer code says "up to 5 WCs on 3" "
On a practical basis, 3" is better related to carry of solids. And the 1.28 or less GPF toilets (which may have not been around in 2003 much) benefit from being able to carry solids better with less water.
Plus, unless you were in a simultaneous flush situation it is not an issue to go with 4". Always: adhere to decent clean-out locations for the first floor...