Building Loading – Rain Load

(Revised: 06/17/2024)

The Rain Load tab defines design-related information regarding the building’s Rain loads.

Rain loading only applies to the 2023 Florida code and 2024 IBC projects (i.e., codes requiring ASCE 7-22).

Rain loads need not be considered when the Rain load is less than the roof Snow load or the roof Live load.

Downspout Quantity, Rainfall Intensity:

The input Rainfall Intensity value is used for checking the external gutter size and the downspout spacings for primary drainage.

Is ASCE 7-22 Section 8.2 Rain Loading Applicable?

· Yes = Rain Design Loading will be required if any primary or secondary drainage system could be blocked from allowing rainwater to drain from the roof

· No = If the Building Condition does not have an “Eave With Parapet” or a “Valley condition”

Building Condition:

There are two building conditions that may result in Rain Load needing to be applied to a roof surface:

· Eave With Parapet, or a

· Valley

Primary Drainage:

The primary drainage options are:

· Parapet Gutter, or

· Valley Gutter

Secondary Drainage:

The secondary drainage options are:

· Rectangular scupper

· Channel scupper

· Round standpipe

· Round scupper

15-min Duration, Rainfall Intensity:

The second Rainfall Intensity value is needed for roof Rain Design Loading to be calculated and applied:

In the same Rain tab, when Rain Design Loads are required to determine the size of roof drainage using scuppers, drainpipes, and secondary drains, this second Rainfall Intensity value is needed:

This second Rainfall Intensity value is from a 15-minute duration over the following Mean Recurrence Intervals:

· 100-year MRI for Risk Category I or II

· 200-year MRI for Risk Category III

· 500-year MRI for Risk Category IV

Conductor Tributary:

In the building length direction, the Conductor Tributary “length” is the spacing of the secondary drains.

Static Head:

Static Head is the elevation difference between the secondary drain and the bottom of the primary drain.

· When the secondary drain is a scupper, this would be to the bottom of the scupper

· When the secondary drain is a standpipe, this would be to the top of the standpipe

· A typical gutter system is the primary drain

Standard Controls:

§ OK, Cancel, Apply, Help

See also:

§ Building Loading - Building Codes

§ Building Loading - Live Load

§ Building Loading - Wind Load

§ Building Loading - Snow Load

§ Building Loading - Seismic Load

§ Building Loading - Tornado Load

§ Building Loading - Deflection Conditions