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There are a lot of things that need to be taken into consideration in 
determining what roof slope to use.  Basically, the minimum roof slope should 
adequately drain water without ponding.  Let's say (hypothetically) that that 
slope is 1:12.  For a building 200 feet wide, the ridge will be 100 inches 
(8'-4") higher than the eave.  However, if you raise the slope to 4.25:12 to 
take advantage of the lower live load permitted, the ridge will now be 425 
inches (35'-5") higher than the eave.  Columns near the ridge would need to 
be similarly longer (and much bigger), more sheathing at the end will be 
required and 6 percent more roof sheathing would be required.

Sometimes "optimum" in one respect will not result in other aspects being 
optimum.  One needs to look at the project as a whole, rather than piecemeal 
"optimize" it.


A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Juan Jo wrote:

. > Dear Sirs,

. > What is the "optimum" slope on a industrial building roof (truss and/or 
. > rigid frame)?  I know from certain slope and down, codes demand a bigger 
. > live load. If that is the only point, then a slope slightly above this 
. > one is the "optimum". Am I right?  Obviously the size of what goes inside 
. > counts but, what else?

. > Thank you,

. > Juan Jo

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