I am building a deck (12' wide) and see that deck boards (at least when perpendicular to the house) should be sloped away from the house so water will run away from the house. Seeing numbers for the slope from 1/8" to 1/4":

  • per foot
  • per three feet
  • per twelve feet
  • per (unspecified)

Is there a 'correct' value or range of values as such? What makes it correct?

Does it vary based on (what) conditions?

Perhaps a higher slope for composite decking that tends to sag?

Note: a one degree slope would be 0.209" per foot.

  • 1
    ...but a 1% slope (which is how such things are commonly specified, not in degrees) is within spitting distance of 1/8" per foot (1:96 .vs. 1:100)- and is the slope that pretty much ANY "flat" surface outdoors should have at a minimum. If that flat surface is next to your house, the slope should be away from the house. Otherwise just where you want the water to drain to.
    – Ecnerwal
    Jun 29, 2020 at 3:06

1 Answer 1


I’d use 1/8” per foot slope because 1) it’s enough to actually allow water to run off, and 2) the deck will “appear” flat

  1. You don’t want standing water on your deck. It can cause rot, etc. I live where we get a ton of rain. It’s important to get rid of water on wood, etc. on the exterior of a home.

  2. When you look at the deck, it will appear flat AND your soup bowl will not spill when you place it on a table.

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