The Roof Cleaning Institute Of America Training & Certification Forum
"Find A Certified Roof Cleaner Directory"

Dawn is your surfacant or "sticky juice". It makes the solution sticky, so you add more for steeper roofs and it is something you come to just kinda understand as you do no pressure roof cleaning. I buy 32oz bottles and always use at least one for a 40-50 gallon mix, sometimes I use up to 3 bottles. If you try and add much more you may find it too soapy or foamy. So just keep in mind what it does and always remember you can adjust your mix after you start to use it. If it is running off the roof too fast or drying too fast, add more. It is really something you should just keep simple in your mind and try not to worry about it too much. After you have done a few you will have a "feel" for how much you need. I would suggest to start with one 32oz bottle to 40 gal mix and add more if necessary. If you use too much, It will really foam up at the gutters when it rains. Just don't over complicate it and it will all be good.
Also always add your water before you add the TSP, ISP and Dawn. Most of us pre-mix our TSP in a bucket to not have a bunch of undiluted powder in the bottom of the tank. So leave room for the amount of water/tsp in the bucket for the mix.

Ultra concentrated Dawn is thicker than Ajax.

If you add TSP to your mix you don't need as much Dawn.

1/2 ounce/gallon - 1-1/2 ounces/gallon depending on the pitch of the roof works for me.

Like Bill said, it doesn't have to be exact. You'll get a feel for it from experience.

For walkable roofs we use 1 oz of Ajax/Dawn per Gal of mix keeps the math simple for us and for steeper pitch roofs we start with 2oz per Gal.

we are going with ultra con dawn.  1 oz to 1 gallon. 1st job!  Thanks for all the info everyone!