Don't make things up. Recommended slope for drainage on concrete and asphalt is .25-.5:12, or 1/4" to 1/2" over 1' of length. Recommended slope for wheelchair

Don't make things up. Recommended slope for drainage on concrete and asphalt is .25-.5:12, or 1/4" to 1/2" over 1' of length. Recommended slope for wheelchair ramps are 1-1.5:12, or 1" to 1.5" over 1' of length.