Types of Structural Load on Metal Buildings

Structural loads are the forces a building must resist throughout its service life. Identifying every load type before design begins separates a smooth project from one that needs expensive structural changes after steel has been cut.

Per ASCE 7-22, loads are classified by source and behavior: dead loads, live loads, environmental loads (wind, snow, rain, seismic), and special loads (thermal, soil pressure, impact). This is an organizational framework for design purposes. Each category carries a different load factor, reflecting how predictable that load type is. Understanding why the categories exist — not just their names — is what helps teams ask the right questions at the right project stage.

This page covers all major load types and how each affects metal building design. For dead load vs live load values, see our dead load vs live load guide. For calculation procedures, see our steel building load calculation guide.

Dead Load and Live Load: The Two Primary Gravity Loads

Both are vertical gravity loads. The most common mistake we see at the enquiry stage is treating them as interchangeable. They use different design factors because one is predictable and the other is not.

Dead load is the permanent, fixed weight of everything that does not move: structural members, roof and wall cladding, insulation, HVAC ductwork, sprinklers, electrical conduit, and any equipment anchored to the frame. In metal building practice, this includes what the industry calls collateral loads — fixed non-structural items like suspended ceilings, lighting systems, and interior partitions. These are routinely left off early-stage bills of materials and found during fabrication drawing review. IBC requires dead load design to use actual material weights, not assumed defaults.

Live load is the variable weight from occupancy and use. It must be assigned zone by zone per ASCE 7-22 and IBC 2021, based on each area’s occupancy category. A building with both heavy storage and an office mezzanine cannot use a single live load value. Local amendments and jurisdiction-specific code adoptions should always be verified before design begins. Adopted editions vary by state and region.

Environmental Loads: Wind, Snow, Rain, and Seismic

Environmental loads act on a building from outside. Each one governs a different part of the structural system. We confirm all four against site-specific parameters before any frame design is issued. Using regional defaults without checking local amendments is a consistent source of non-conformance on cross-border projects.

Wind Load

Wind acts inward on windward surfaces and outward on leeward walls and roof. For single-story metal buildings, roof uplift under suction often governs the design of panel-to-purlin fasteners and purlin-to-rafter connections — not just the primary frame. Wind load must be resolved before secondary member selection begins.

Wind design parameters — basic wind speed, exposure category, roof geometry, and internal pressure classification — are site-specific inputs governed by ASCE 7-22 Chapters 26–30. On coastal and high-wind projects we deliver in Southeast Asia and the Middle East, wind uplift controls roof connection design more often than any other load combination.

Snow Load

Snow load is the vertical force from accumulated snow, governed by ASCE 7-22 Chapter 7. The design value depends on ground snow load, roof slope, exposure, and the building’s thermal condition.

The thermal factor in ASCE 7-22 does not always reduce snow load. Cold storage buildings and structures kept near freezing can have thermal factors at or above 1.0. This means the full ground snow load applies — or is amplified. Assuming “heated building equals lower snow load” without checking the thermal factor category is an error we see from warmer-climate teams working on northern projects.

Drift and unbalanced snow at parapets, roof steps, and valleys require checks beyond the basic uniform roof value. These conditions have governed purlin sizing on several projects where initial designs used only the flat roof value.

Rain Load and Ponding

Rain load is among the most frequently overlooked load types in metal building design. ASCE 7-22 Chapter 8 addresses it separately from snow. The requirement is that roofs must support accumulated water if primary drainage is blocked, up to the secondary overflow drain level.

Ponding is a related but distinct concern. On low-slope metal roofs with flexible purlins, water accumulation causes deflection. Deflection deepens the ponding area. More water adds more load. This self-amplifying cycle can lead to progressive collapse if not checked at design stage. We flag ponding risk on any roof with slope below approximately 1:50. Primary and secondary drainage capacity, scupper sizing, and overflow drain elevation must be confirmed alongside structural member sizing — not treated as a plumbing detail separate from the structural design.

Seismic Load

Seismic load is the lateral inertial force a building experiences during ground movement, governed by ASCE 7-22 Chapters 11–16. The seismic design category (SDC) depends on three inputs: the site’s ground motion hazard parameters, the site soil class, and the building’s risk category. All three must be confirmed. Using SDC from location alone — without site soil classification — produces incorrect seismic demand in many cases.

Steel’s ductility is its key advantage in seismic applications. But it depends entirely on connection detailing matching the ductility assumptions in the analysis model. In SDC C and above, AISC 341-22 specifies connection types that cannot be retrofitted after fabrication. We confirm the governing SDC and required connection category before any fabrication drawings are issued.

Special Loads: Thermal, Soil Pressure, and Impact

These load types must be identified at project inception. Omitting them creates structural deficiencies that are expensive to correct after fabrication.

Thermal load comes from temperature-driven expansion and contraction of steel. Whether expansion joints or slotted connections are needed depends on building length, local temperature range, restraint conditions, and connection detailing. There is no single universal length threshold in the code. Long buildings in climates with wide seasonal temperature swings get a thermal movement review as a standard step in our design coordination. The outcome of that review determines what accommodation is needed.

Soil and hydrostatic pressure apply to buildings with below-grade elements — basements, retaining walls, or below-grade mechanical rooms. Lateral earth pressure depends on soil type, density, depth, and water table. In areas with high water tables, foundations must also resist upward hydrostatic pressure. These are separate design checks from the above-grade structural analysis. Geotechnical input is required before foundation design begins.

Impact and dynamic loads apply where overhead cranes, vibrating machinery, or vehicle dock impact are present. Crane runway girders require fatigue design per AISC Design Guide 7. This is separate from static strength checks. Repeated loading cycles from crane operation govern member life in a way that a single static calculation does not capture. For buildings with process equipment, we request equipment load data and mounting details before frame design begins.

Blast load applies to high-security or government facilities. It requires specialist analysis beyond the scope of standard pre-engineered metal building systems.

Load Combinations: Why Load Classification Matters in Practice

Loads are classified into separate categories because they use different design factors and do not all reach their maximum values at the same time. ASCE 7-22 specifies required load combinations under both LRFD and ASD. Each combination represents a credible worst-case scenario. Every structural member must be checked against all applicable combinations to find the governing condition.

The wind uplift combination most consistently surprises project teams on single-story metal buildings. It uses a reduced dead load factor, because dead load acts against uplift. A light steel roof with low dead load offers less resistance to wind suction. This is why roof-to-purlin fastener design is often the critical output of a wind analysis — not just primary frame sizing.

Getting load combinations right requires knowing which load types are present, which combinations apply under the adopted code edition, and which combination produces the highest demand for each member. This is where load type identification at project inception translates directly into fabrication drawing accuracy. Once all applicable load types are confirmed, the next question is how the structure’s members and connections respond to those combined demands — see our structural loading capacity guide for how capacity is verified against design loads.

Conclusion

Every load type governs a different decision in a metal building project. Dead load and collateral load drive foundation and frame sizing. Live load drives mezzanine and floor beam selection. Wind drives bracing layout and roof connection design. Snow and rain drive purlin sizing and drainage confirmation. Seismic drives connection category selection. Thermal drives expansion joint placement. None can be safely assumed to be covered by another.

To confirm all applicable load types for your project, explore our metal building packages to understand the full scope of what we cover — then share your site location, occupancy type, building dimensions, fixed equipment list, roof slope, and any special use requirements. We review these inputs against governing code provisions before structural proposals or fabrication drawings are issued.