Roof slope percentage

Follow

Shanglin Li

November 22, 2021 00:03

Hi guys,

I'm studying the book Building Construction, under Chapter 34, which states roof slope recommended underlayment for tile roofs is from 4:12 to 21:12. 

I'm wondering if I convert 21:12 to a percentage, does it sounds right if that's 175%?

Thanks,

0

• 

  aagangchen November 22, 2021 05:21 (Edited November 22, 2021 05:23)

  21/12=1.75

  Arctan(1.75)=60.26 degrees slope:

  https://www.gigacalculator.com/calculators/arctan-calculator.php

  That is a 60.26-degree slope for the roof, not too bad.

  Gang Chen, Author, AIA, LEED AP BD+C (GreenExamEducation.com)

  1

  Comment actions Permalink
• 

  rebekkak November 22, 2021 21:41

  Hi Shanglin,

  You are correct that the % slope would be 175%.  Roof slopes are not usually expressed in % unless they are nearly flat roofs, and 1/4" per foot rise (which is 2%) is minimum.  Rise:12 inches is how it's typically expressed for sloped roofs.  

  Hope this helps!

  Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses

  1

  Comment actions Permalink
• 

  Shanglin Li November 24, 2021 17:20

  Thank you Gang & Rebekka!

  0

  Comment actions Permalink

Please sign in to leave a comment.