ASCE7-05 mean roof height

[AlienMonkey]

Lets say you have a flat roof building with a parapet. Is the mean roof height, h, to the eave of the building, center of parapet, or top of parapet?

 

[JedClampett]

"h" is always the eave height for a flat rrof. But the wind pressures for the parapet are based on the top of parapet.

 

[msquared48]

For roofs greater than 10 degrees in slope, the MRH (h) is the distance from the average roof height (eave height to highest point of roof structure) to the average finish grade line for the direction being considered.

For roofs 10 degrees or less, it is the distance from the average finish grade elevation to the roof eave height. The definition on page 22 of ASCE7 does not refer to any parapets, but to me, it only makes sense to take the top of the parapet for the upper "h" value for the building. Technically, the eave height is where the sloping roof ends. As there is no real exposed eave when there is a parapet, assuming the wall continues past the roof to the top of the parapet, I conservatively interpret the top of the parapet as the "eave". If the parapet varies in height, I use the average top of parapet height in computing "h".

Just my way of doing it.



Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[WillisV]

I use mean roof height for low slope roofs as roof level, not parapet level, as JedClampett says. Parapet pressures are then calculated separately for the q at the top of the parapet.

This has been discussed before, with me and Mike offering the same (opposite) answers =)

thread507-224229

 

[msquared48]

Well, at least we're consistent. (bigsmile)

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[WillisV]

FYI - for some justification of my position, ASCE's Guide to the Wind Load Provisions of ASCE 7-05 (

http://www.asce.org/Product.aspx?id=2147487439)

takes the mean height at the top of the roof for qh, and calculates qz at the top of the parapet separately for the parapet loads only.