1/2 or 3/4 PEX for a pipe feeding a washing machine and tub/shower?

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Canada_DIY_Plumber

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I'm doing a bathroom reno and adding a washer/dryer. The pipe feeding the bathroom is a mix of 1/2" copper and 3/4" PEX. It enters the bathroom as 3/4 PEX and I am installing two shut-off valves in an access panel for the whole bathroom. After these shut-off valves, I need go up into the attic and then down into a plumbing wall to feed the washing machine and a tub/shower. I will feed the lav and toilet using a 1/2" PEX branch.

My options for the run to the washing machine and tub/shower plumbing wall:
A) 3/4" PEX and then split off to 1/2" PEX inside the plumbing wall for the washing machine and shower.
B) 1/2" PEX to the plumbing wall and to each fixture.
C) Two separate 1/2" PEX lines from the shut-off valve that go up through the attic to the washer/dryer and the tub/shower.

My thought process:
This space is for seasonal use only and will often go unoccupied for weeks or months. I like having one line to the plumbing wall that supplies the washer and tub/shower because then I can run the tub for a few minutes to thoroughly flush out most of that line after it has gone unused for a long period of time.

Given that, running 3/4 seems wise because I imagine a 1/2 line would be more susceptible to dramatic pressure drops if someone is running a load of laundry while having a shower (even with the fancy pressure balancing valves of today.)

Aside from a negligible increase in cost, the downside is that the 3/4 line will take longer to supply hot water for the shower in the morning.

I'm leaning to option A but would appreciate any second set of eyes.
 

Terry

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water-sizing-chart-terrylove-40-60.jpg


The chart for PEX below.

ipc_water_size_50.jpg
 

Canada_DIY_Plumber

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Thanks. In that second chart...
I will have 6 fixture units for this run (shower + clothes washer).
So it looks like it is saying my developed length will need to be less than 40 feet if I go with 1/2" and could be more than 40 feet if I go with 3/4"?
This stuff will probably be within 30 feet developed length of the entry to the house.
 
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