In this post, I will provide a brief overview of determining thermal factors, C_{t}, for calculating flat roof snow loads on structures per ASCE 7-10, Table 7-3. The thermal factors are based on the thermal condition of the roof.

## Thermal Factors for Structures Based on Thermal Conditions

Structures kept just above freezing and other with cold, ventilated roofs in which the thermal resistance (R-value) between the ventilated space and the heated space exceeds 25 °F x h x ft^{2}/Btu (4.4 K x m^{2}/W), C_{t} = 1.1

Unheated and open air structures, C_{t} = 1.2

Structures intentionally kept below freezing, C_{t} = 1.3

Continuously heated greenhouses with a roof having a thermal resistance (R-value) less than 2.0 °F x h x ft^{2}/Btu (0.4 K x m^{2}/W), C_{t} = 0.85

All other structures, C_{t} = 1.0

## ASCE 7-10, Table 7-3