Update: I used to think a 2-inch main line was enough for a small office building

Last month, I was working on a retrofit in a three-story building in Tacoma. The specs called for a 2-inch main, but after mapping out all the new fixtures, the flow rate was way too low. I ran the numbers again and saw we needed a 2.5-inch line to handle the peak demand from the restrooms and kitchenette. It cost more upfront, but it saved a callback for low pressure. Has anyone else had to upsize a main line after the initial plan?

2 comments

2 Comments

the_robert2mo ago

You mentioned mapping out the new fixtures. How detailed was that map? I've seen guys just count heads for fixture units, but they miss the real peak when a whole floor flushes after a meeting. Did you actually walk the planned layout with the owner to time the real use?

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leohart2mo ago

We made a full map with fixture counts and marked every drain line. Counting heads is lazy. You gotta figure out the real flow when a bunch of people use the bathrooms at the same time. We talked to the building manager about their meeting schedule to guess those peaks. Just using the book numbers gets you in trouble every single time.