WFCM Wind Loads for hip type roof

[PT999]

I am looking at a standard 2 story house with hips on all four sides meeting at the center.

WFCM for wind loads has two tables for wind loads, one for wind perpendicular to the ridge, and one for wind parallel to the ridge, with wind parallel to ridge loads less than the perpendicular to ridge loads.

Which wind load table applies to my no ridge, all hip roof?

 

[JAE]

You have 4 ridges - each at 45 deg. from the mid point. Wind can be perp to the ridges (approximated by perpendicular to any of the four edges) or parallel to the ridges (at any 45 deg. angle in plan). That's how I'd look at it anyway.

 

[PT999]

I guess by that reasoning, use the larger wind force in all directions.

 

[cap4000]

I have the 1998 WFCM and on page 41 footnote 6 indicates that an attic floor or ceiling are NOT required for hip roof systems. However, with the new ASCE 2005 on page 57 under Components and Cladding depending on your roof area and roof angle Cp equals 0.5 to 0.3 for pressure and -0.9 to -0.8 for suction. What is your roof angle and Wind Speed and I will give the ASCE 2005 values for both suction and pressure from page 42. Go with ASCE on this one and play it safe. Along the hips and overhangs the numbers are almost tripled. Nice thread. Good Luck.

 

[PT999]

Roof Angle 45 degrees, and wind speed = 110 mph (NY State, Long Island area).

 

[cap4000]

I believe you are Exposure C a very severe category. Assuming your building at 30 feet high the multiplier is 1.40. Hip Roofs Diagrams at 45 degrees are not shown in the ASCE 2005, only up to 27 degrees. But in the specs on page 24 it indicates hip roofs up to 45 degrees. Yet Another Conflict in this recently issued code. The new ASCE code now has 2 load cases to design for essentially changing the uplift values at the roof for each case. I beleive in New York you are using IRC and IBC 2000?? Is this correct?? Typical pressures vary from 12 to 20psf and suction from -5 to 13psf depending on where you are on the structure. C&C loads are doubled and some tripled x 1.40 multiplier.Good Luck and go conservative on your design.