Section 1611 — California Building Code (Title 24, Part 2)

1611.1 Design rain loads.¶

Each portion of a roof shall be designed to sustain the load of rainwater that will accumulate on it if the primary drainage system for that portion is blocked plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow. The design rainfall shall be based on the 100-year hourly rainfall rate indicated in Figure 1611.1 or on other rainfall rates determined from approved local weather data.

R = 5.2( ds + dh ) (Equation 16-35)

For SI: R = 0.0098( ds + dh ) where: d h = Additional depth of water on the undeflected roof above

the inlet of secondary drainage system at its design flow (in other words, the hydraulic head), in inches (mm). d s = Depth of water on the undeflected roof up to the inlet

of secondary drainage system when the primary drainage system is blocked (in other words, the static head), in inches (mm). R = Rain load on the undeflected roof, in psf (kN/m2). Where

the phrase “undeflected roof” is used, deflections from loads (including dead loads) shall not be considered when determining the amount of rain on the roof.

1611.2 Ponding instability.¶

Susceptible bays of roofs shall be evaluated for ponding instability in accordance with Section 8.4 of ASCE 7.

1611.3 Controlled drainage.¶

Roofs equipped with hardware to control the rate of drainage shall be equipped with a secondary drainage system at a higher elevation that limits accumula

26 2019 CALIFORNIA BUILDING CODE

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TABLE 1610.1 LATERAL SOIL LOAD

STRUCTURAL DESIGN

DESCRIPTION OF BACKFILL MATERIALc	UNIFIED SOIL CLASSIFICATION	DESIGN LATERAL SOIL LOADa (pound per square foot per foot of depth)
DESCRIPTION OF BACKFILL MATERIALc	UNIFIED SOIL CLASSIFICATION	Active pressure	At-rest pressure
Well-graded, clean gravels; gravel-sand mixes	GW	30	60
Poorly graded clean gravels; gravel-sand mixes	GP	30	60
Silty gravels, poorly graded gravel-sand mixes	GM	40	60
Clayey gravels, poorly graded gravel-and-clay mixes	GC	45	60
Well-graded, clean sands; gravelly sand mixes	SW	30	60
Poorly graded clean sands; sand-gravel mixes	SP	30	60
Silty sands, poorly graded sand-silt mixes	SM	45	60
Sand-silt clay mix with plastic fines	SM-SC	45	100
Clayey sands, poorly graded sand-clay mixes	SC	60	100
Inorganic silts and clayey silts	ML	45	100
Mixture of inorganic silt and clay	ML-CL	60	100
Inorganic clays of low to medium plasticity	CL	60	100
Organic silts and silt clays, low plasticity	OL	Note b	Note b
Inorganic clayey silts, elastic silts	MH	Note b	Note b
Inorganic clays of high plasticity	CH	Note b	Note b
Organic clays and silty clays	OH	Note b	Note b

For SI: 1 pound per square foot per foot of depth = 0.157 kPa/m, 1 foot = 304.8 mm. a. Design lateral soil loads are given for moist conditions for the specified soils at their optimum densities. Actual field conditions shall govern. Submerged or

saturated soil pressures shall include the weight of the buoyant soil plus the hydrostatic loads. b. Unsuitable as backfill material. c. The definition and classification of soil materials shall be in accordance with ASTM D2487.

Agency in an engineering report entitled “The Flood Insurance Study for [INSERT NAME OF JURISDICTION],” dated

[INSERT DATE OF ISSUANCE], as amended or revised with the accompanying Flood Insurance Rate Map (FIRM) and Flood Boundary and Floodway Map (FBFM) and related supporting data along with any revisions thereto. The adopted flood hazard map and supporting data are hereby adopted by reference and declared to be part of this section.

Exception: [OSHPD 1R, 2 & 5] The flood hazard map shall include, at a minimum, areas of special flood hazard as identified by the Federal Emergency Management Agency’s Flood Insurance Study (FIS) adopted by the local authority having jurisdiction where the project is located.

1612.3.1 Design flood elevations. Where design flood elevations are not included in the flood hazard areas established in Section 1612.3, or where floodways are not designated, the building official is authorized to require the applicant to do one of the following:

Obtain and reasonably utilize any design flood elevation and floodway data available from a federal, state or other source.
Determine the design flood elevation or floodway in accordance with accepted hydrologic and hydraulic engineering practices used to define special flood hazard areas. Determinations shall be undertaken by a registered design professional who shall document that the technical methods used reflect currently accepted engineering practice.

tion of water on the roof above that elevation. Such roofs shall be designed to sustain the load of rainwater that will accumulate on them to the elevation of the secondary drainage system plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow determined from Section 1611.1. Such roofs shall be checked for ponding instability in accordance with Section 1611.2.