Understanding Structural Design Criteria for Pre-Engineered Metal Buildings (PEMBs): Part Three

Designing for Roof Loads in Pre-Engineered Metal Buildings

Pre-Engineered Metal Buildings (PEMBs) are designed to handle various loads. These include dead, live, and collateral loads. The International Building Code (IBC) sets minimum requirements. But, to design for real-world conditions, we must understand the building’s specific use. This article is about roof loads.

Dead Loads

Dead loads are static, permanent loads. They are the weight of structural components, like beams, walls, and roofing. When the PEMB provider manufactures all components, they include dead loads in the design. But, the PEMB designer must be told about non-metal wall systems, masonry, or conventional roofing materials to ensure accuracy.

Solar panels, for instance, introduce extra dead loads that vary by anchorage method. A ballasted system needs about 8 psf. Clamp systems, common on metal roofs, need about 5 psf. It’s critical to find these loads in the design process. This will avoid overloading the structure.

Live Loads

Live loads are dynamic loads caused by building use or occupancy. For roofs, these usually come from maintenance or temporary construction loads. The IBC sets a minimum roof live load of 20 psf.

Collateral Loads

Collateral loads are often overlooked in project specifications, yet they hold equal importance. These include any loads hung from the roof, such as HVAC systems, lighting, sprinkler lines, and electrical cable trays. The PEMB designer relies on the project’s engineer of record for these specs.

Uniform collateral loads typically accommodate basic systems, with a standard design load of 5 psf. For industrial uses, this can increase to 10 psf or more. It depends on the complexity of the equipment and systems. Concentrated collateral loads—such as suspended HVAC units or sprinkler mains—should also be identified to ensure proper design.

Key Takeaway

Designing PEMBs for roof loads requires collaboration between the project’s engineer of record and the PEMB designer. Proper communication of all anticipated loads ensures a safe, functional, and efficient structure tailored to the client’s needs.

It’s vital to specify these loads accurately.

Good, early planning avoids costly design changes. It ensures the building works as intended.