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# RE: Wind load on sloped roof with parapet

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Wind load on sloped roof with parapet
• From: "Conrad Harrison" <sch.tectonic(--nospam--at)bigpond.com>
• Date: Mon, 1 Dec 2008 16:41:08 +1030

```Jeff,

The air mass coming off the top edge of the parapet will experience
turbulence. Below the turbulence zone is likely to be a stagnant pocket or
zone of suction.

Barring any additional information the best guess of the magnitude of this
suction is the pressure coefficient on the roof without the parapet. The
parapet is like a wall, and has a roof side pressure coefficient equivalent
to that from the adjacent roof surface.

There is thus no shielding of the roof from the wind, it is loaded as if the
parapet wasn't there.

It may be possible to use the simplified method. But I suggest it is simpler
to use pressure coefficients rather than pressures. The pressure
coefficients provide an indication of the relative difference in pressure
between surfaces and as move from one surface to another. For example look
at multi-span and saw-tooth roofs, to get an idea of airflow as moves from
one roof surface to another or over the roof and up against a wall
(parapet).

Thus use the shapes tested and provided in the code to get a best guess of
the pressure coefficients on proposed building.

ASCE7-05 is not the code I use, so cannot give a more specific requirement.
Using AS1170.2 that is how I would work out the coefficients. As long as
provide explanation as to how arrived at pressure coefficients adopted, then
shouldn't have problems getting approval.

Regards
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic(--nospam--at)bigpond.com
South Australia

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