Check of Existing Roof to Support New Mechanical Load

by Jim Houlette on October 1, 2015

EVstudio was asked to help a new client determine if the existing structure can support a new heavier mechanical unit load.   Within a day of the client’s first contact, we had visited the site, reviewed the loading conditions and provided a letter of recommendations with a detail for additional support as needed.

For many of the situations where a new heavier load is placed on the existing structure additional support is not needed.  This is because the IBC allows new loads of less than 5% to be added without any calculations needed and even then many structural components are originally “over-engineered” allowing for additional loading.   The IBC section that addresses the new loads on existing structures is 3403.2.

For this project a 300 lb mechanical unit is being replaced with a 800 lb unit.  The new load on the open web joists is less than 5%, but the existing metal deck needed additional support.  The existing opening in the steel deck had no additional support to begin with and probably should have been placed when first constructed. With our design solution the 800 lb unit can be supported.

Originally posted 2010-01-18 00:32:48. Republished by Blog Post Promoter

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