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Sloped Roof snow load

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In ASCE7-05 it seems the sloped roof snow load is the same as the flat roof snow load except for a few extreme roof slopes no reduction for the typical 6:12.  Is this what others are finding?
 
Tim Rudolph
Pinyon Engineering
Bishop CA
 
 
From: "Scott Maxwell" <smaxwell(--nospam--at)umich.edu>
To: <
seaint(--nospam--at)seaint.org>
Subject: RE: ASCE 7-05 Section 12.14.8.1 (#4) clarification needed

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I interpret this as if the flat roof snow load (Psubf) exceeds 30 psf, =
then
you take 20% of the FLAT roof snow load (Psubf) and add that to the =
seismic
mass.  You do NOT take 20% of the SLOPED roof snow load (Psubs)...that =
is
the "regardless of actual roof slope" part.  And you do NOT take 20% of =
the
portion that exceeds 30 psf.
=20
Thus, if you have a 40 psf flat roof snow load and a 12:12 roof pitch on =
a
non-slippery roof such that the sloped roof snow load is 24 psf, then =
you
would add 8 psf (20% of 40 psf) to the seismic mass...NOT 4.8 psf (20% =
of 24
psf).
=20
Regards,
=20
Scott
Adrian, MI

-----Original Message-----
From: Dennis Wish [mailto:dennis.wish(--nospam--at)verizon.net]=20
Sent: Saturday, July 19, 2008 9:56 PM
To:
seaint(--nospam--at)seaint.org
Subject: ASCE 7-05 Section 12.14.8.1 (#4) clarification needed



I need an interpretation to note number 4 of ASCE 7-05 Section 12.14.8.1
which states:

=93Where the flat roof snow load, Pf, exceeds 30 psf (1.44 kN/m^2), 20 =
percent
of the uniform design snow load, regardless of actual roof slope.=94

=20

This seems to conflict with itself. My first interpretation is that if =
the
snow load for a flat roof (say =BC=94 in 1-foot) slope or a shed roof =
exceeds 30
psf then you would add 20% or 6 psf to the roof dead load. However, the =
last
section of the statement reads =93regardless of actual roof slope=94 in =
which
case I would interpret the 20% of the Snow Load exceeding 30-psf to be =
added
to any sloped roof.=20

=20

How do others interpret this statement. If the roof is flat should 20% =
of
any Snow Load be considered whereas only 20% of the Snow load exceeding
30-psf be used if the roof is pitched?

=20

Dennis S. Wish, PE

=20

Dennis S. Wish, PE

California Professional Engineer

Structural Engineering Consultant

La Quinta, CA 92253

dennis.wish(--nospam--at)verizon.net

http://structuralist.wordpress.com

http://www.structuralist.net

=20