Davis Square Building Structural Roof Assessment
Commercial Associates | Raleigh NC
About 10 years ago, the existing built-up roof was recovered with a membrane system. Roof leaks have been reported and ponded water occurred on several parts of the roof.
Atlas Engineering, Inc. visited Davis Square multi-tenant commercial building on September 7, 2022 to perform study and structural assessment of the existing roof system.
Atlas Engineering took measurements of the building perimeter, roof system, and elevation of the roof surface. It was determined that the low-sloped roof system had no consistent slope for drainage and appeared to have been installed in the flat condition, which may have induced ponding issues to occur. An isolated area of severely corroded and failing roof decking was observed in the back of one of the unit. Atlas Engineering immediately called Commercial Associates about the issue and marked the hazardous area on the roof membrane and advised that no one should step in the area until repairs are made.
Based on field measurements, couple found identification tags, and guidelines provided by the Steel Joist Institute (SJI), existing joists' types were identified as 24H8. Atlas utilized SJI tables and various structural methods (structural analysis & RISA 3D) to determine bar joists' sectional properties, load rating, and anticipated deflection under existing loads.
Atlas utilized 2018 North Carolina Building Code and ASCE 7-10 to find minimum required loading. In addition, (2) 12"x12" roof cuts were made to document what layers of roofing exist and to estimate current dead loads. Roof cuts were repaired the same day. As a result, the required minimum loads combined with the dead load of the roof and the weight ponding water rendered bending moment that exceeded the maximum allowable bending moment capacity of the joists. Atlas believes the the recovered built-up roof and ponding water were the main reasons for overload in the roof structure.
Atlas Engineering issued report recommending the replacement of existing roof system with either the low slope roof with tapered insulation or the retrofit metal decking. This would mitigate two current issues, the excessive weight and ponding. In addition, the deteriorated roof decking area must be replaced with new structural metal roof decking.