Slope Ratio Confusions

[Lance Millar]

My co-worker and I are confused over the expression of slope ratios.  In the DOJ’s ADA standards they express the slope ratios as the rise first and the horizontal dimension is second, for example, 1:12 maximum slope for a ramp (405.2, Chapter 4).  However in Hopper’s Landscape Architectural Graphic Standards book, he explains that traditionally the first number is the horizontal dimension and the rise is second as explained on page 187.

Can anyone enlighten us as to why they are written both ways?  They both seem to be correct but could also so easily be confused if it’s not previously understood which number comes first in a specific situation.

Thanks in advanced!

[Fred Besancon]

I don’t know an official answer, but the first thing that came to mind is that roof pitches are typically measured where the first number is the vertical number.  Most of the building codes are architecturally focused (as the name implies).  Perhaps this is the reason why…

[Jonathan P. Williams, RLA]

I was always taught rise over run. 

[Andrew Garulay, RLA]

It is strange. I see the same thing as Lance.

When dealing with cut and fill slopes it seems that the ratio is horizontal:vertical.  Massachusetts uses this convention in defining a wetland resource area called a Coastal Bank.

My understanding is that H:V is a US convention when dealing with contours and the opposite is true in Europe.

When dealing with ADA it is vertical:horizontal. I have no idea why it is opposite, or why the other is opposite.

Percent of slope is always rise/run as far as I have ever seen it.

[Author]

Posts