Abstract The collapse of roof structures under extreme snow loads can harm building occupants, leave building owners burdened by costs of repairs, and lead to loss of income, equipment or merchandise. This study investigates the reliability of two types of steel roofs: those supported by open web steel joists, and those supported by wide-flange steel sections. The reliability assessment considers uncertainty in snow and dead loading and in the capacity of the two types of roof systems through Monte Carlo simulation. Nonlinear models are used to quantify the capacity of the open web steel joist roofs. Reliability for both safety and serviceability is investigated. Results show that the reliability for the studied roof types is highly dependent on the location and seasonal snowfall patterns at the building location and the inclusion of serviceability deflection limits in design. Building geometry is not found to strongly influence the reliability assessments.