In this post, I will provide a brief overview of determining exposure factors, Ce, for calculating flat roof snow loads on structures per ASCE 7-10, Table 7-2. The exposure factors are based on the terrain category of the location of the structure and the exposure of the roof.

## Exposure Factors for Terrain Category B

Fully Exposed Roof, Ce – 0.9

Partially Exposed Roof, Ce – 1.0

Sheltered, Ce – 1.2

## Exposure Factors for Terrain Category C

Fully Exposed Roof, Ce – 0.9

Partially Exposed Roof, Ce – 1.0

Sheltered, Ce – 1.1

## Exposure Factors for Terrain Category D

Fully Exposed Roof, Ce – 0.8

Partially Exposed Roof, Ce – 0.9

Sheltered, Ce – 1.0

## Exposure Factors for Terrain Category Above Treeline in Windswept Mountainous Areas

Fully Exposed Roof, Ce – 0.7

Partially Exposed Roof, Ce – 0.8

Sheltered, Ce – N/A

## Exposure Factors for Terrain Category in Alaska, in Areas Where Trees do not Exist Within a 2-mile Radius of the Site

Fully Exposed Roof, Ce – 0.7

Partially Exposed Roof, Ce – 0.8

Sheltered, Ce – N/A

## ASCE 7-10, Table 7-2

In this post, I will provide a brief overview of calculating flat roof snow loads that are specified in ASCE 7-10, Chapter 7. Before diving deeper, it’s a good idea to review the definitions of parameters used in the snow load formula.

## Parameter Definitions

Ce = Exposure Factor, ASCE 7-10 Table 7-2

Ct = Thermal Factor, ASCE 7-10 Table 7-3

Is = Importance Factor, ASCE 7-10 Table 1.5-2

pg = Ground Snow Load, ASCE 7-10 Figure 7-1 and Table 7-1

## Flat Roof Snow Load Formula, ASCE 7-10, Equation 7.3-1

pf = 0.7CeCtIspg

Flat Roof Snow Load = 0.7 times the exposure factor times the thermal factor times the importance factor times the ground snow load

In this post, I will provide a brief overview of the structural deflection limits of structural elements based on loading conditions specified in the International Building Code 2015 (IBC 2015), Table 1604.3.

## Roof Members Deflection Limits

Members supporting plaster or stucco ceiling (Live Load) = L/360

Members supporting plaster or stucco ceiling (Snow or Wind load) = L/360

Members supporting plaster or stucco ceiling (Dead + Live Load) = L/240

Members supporting nonplaster ceiling (Live Load) = L/240

Members supporting nonplaster ceiling (Snow or Wind load) = L/240

Members not supporting ceiling (Live Load) = L/180

Members not supporting ceiling (Snow or Wind load) = L/180

## Floor Members Deflection Limits

Floor members  (Live Load) = L/360

Floor members (Snow or Wind load) = N/A

## Exterior Walls Deflection Limits

Walls with plaster or stucco finishes (Live Load) = N/A

Walls with plaster or stucco finishes (Snow or Wind load) = L/360

Walls with plaster or stucco finishes (Dead + Live Load) = N/A

Walls with other brittle finishes (Live Load) = N/A

Walls with other brittle finishes (Snow or Wind load) = L/240

Walls with flexible finishes (Live Load) = N/A

Walls with flexible finishes  (Snow or Wind load) = L/120

## Interior Partitions Deflection Limits

Partitions with plaster or stucco finishes (Live Load) = L/360

Partitions with plaster or stucco finishes (Snow or Wind load) = N/A

Partitions with plaster or stucco finishes (Dead + Live Load) = N/A

Partitions with other brittle finishes (Live Load) = L/240

Partitions with other brittle finishes (Snow or Wind load) = N/A

Partitions with flexible finishes (Live Load) = L/120

Partitions with flexible finishes  (Snow or Wind load) = N/A

## Farm Buildings Deflection Limits

Farm Buildings (Live Load) = N/A

Farm Buildings (Snow or Wind load) = N/A

## Greenhouses

Greenhouses (Snow or Wind load) = N/A

In this post, I will provide a brief overview of how to reduce uniform live loads using ASCE 7-10, Section 4.7. This post does not cover the reduction of roof uniform live loads. .

## Parameter Definitions

L = Reduced design live load per ft2 (m2) of area supported by the member

Lo = Unreduced design live load per ft2 (m2) of area supported by the member (ASCE 7-10, Table 4-1)

AT = Tributary area in ft2 (m2)

KLL = Live Load Element Factor (Table 4-2)

## Limitations / Conditions for Reducing Live Loads

1. Uniform live loads may only be reduced if the limitations listed in Sections 4.7.3 – 4.7.6 are satisfied
2. Uniform load loads may only be reduced for members for which the product of the live load element factor and tributary area is at least 400 ft(KLL*AT ≥ 400)
3. L  ≥ 0.5L for members supporting one floor
4. L  ≥ 0.4L for members supporting two or more floors

In this post, I will provide a brief overview of the live load element factors,KLL, used in the reduction of uniform live load specified in ASCE 7-10, Table 4-2.

## Live Load Element Factors, KLL, by Element Type

Live load element factor for interior columns, KLL =  4

Live load element factor for exterior columns without cantilever slabs, KLL =  4

Live load element factor for edge columns with cantilever slabs, KLL = 3

Live load element factor for corner columns with cantilever slabs, KLL = 2

Live load element factor for edge beams without cantilever slabs, KLL = 2

Live load element factor for interior beams, KLL = 2

Live load element factor for edge beams with cantilever slabs, KLL = 1

Live load element factor for cantilever beams, KLL = 1

Live load element factor for one-way slabs , KLL = 1

Live load element factor for two-way slabs, KLL = 1

Live load element factor for members without provisions for continuous shear transfer normal to their span, KLL = 1

Live load element factor for all other members not identified, KLL = 1