Streak lines, big time. Because its cleaning twice as it runs ,kinda like you said.
Edit: exactly like you said
SH on steroids 
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Liar. 
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Not a big deal for SH unless on wood or any other materials that might leave a faint streak mark. When doing red mud removal or other works that involves acid it is a must.
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If you wanna strip it all off …
If you wanna just prep for paint, I would DS HF @100 % then DS HCS at 20:1. Turbo nozzle all metal.@firefighter4hire
This is said but if its all clean, there shouldnt be any streaks
This is what I was told when I worked for the school district as a janitor. It was also on the head custodian civil service test as a question.
I do bottom to top
It helps me get under the siding lip. gravity takes care of the rest.
also prevents streaks.
also by rinsing from bottom to top you are ensuring a more through cleaning, since chemicals are “retouching”
yes it might be a BIT longer, cause you working “against gravity” but then again you using a 8gpm.
I foam so I save on chems, although we all know SH is dirt cheap
Potato, patatoe, Ford/Chevy…
do what works for you
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The one instance where I see top to bottom application being a potential issue, is when it’s hot, sunny, and you’re washing siding that can discolor. The heat will make the water evaporate out of your solution as it hits the siding, allowing more concentrated solution to drip down and cause streaking.
Apart from washing darker siding, I now soap top to bottom. It does save time and chemical. Maybe not a whole lot, but every bit counts 
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Honestly it applies more when working with wood. The theory behind it is when applying something to a roof or siding, the solution running down will alter the colour of the wood in drip patterns. I’ve actually seen this in person a few times as well. When it comes to vinyl siding I have done top down on one side of the house and bottom up on another side… no difference.
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Thanks Bear. Very insightful. I appreciate that!
Yeah, noticed the ‘clean streaks’ a few times myself when starting at the top. I just be sure to hit it again real quick.
Or just start from the bottom and not worry about it
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Yepper.
