Chapter 16 load requirements, load combinations, dead loads, live loads, soil loads, rain loads.
3
hours
0.3
CEUs
Codes and Standards
1.7.3
This course covers material relevant to the following ICC certification exams:
Chapter 16 load requirements, load combinations, dead loads, live loads, soil loads, rain loads.
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On-Demand Online
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Self-Paced
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Certificate of Completion
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Contact our support teamDetermine appropriate dead and live loads for different occupancies and uses
Every structural requirement in the code, and every decision an engineer or reviewer makes about member sizing, connections, and foundations, starts from a single question: what does the building actually have to resist? Get that question wrong at the outset and every downstream calculation inherits the error, no matter how carefully the rest of the design is executed. That is why gravity and environmental load determination sits at the very front of structural design and structural plan review — before load combinations are applied and before load paths are traced to the ground, the individual loads themselves have to be identified correctly for the specific occupancy and use in front of the reviewer.
Dead load is the most conceptually straightforward of the load types: it is the permanent, unmoving weight of the structure itself and everything built into it — framing, floor and roof assemblies, permanent partitions, fixed mechanical and electrical equipment, and finishes that do not change over the life of the building. Because dead load reflects what was actually built, it is largely a matter of correctly accounting for the materials and assemblies shown on the drawings, rather than judgment about how people will use the space.
Live load is different in kind, not just in weight. It represents the load produced by occupancy and use — people, furnishings, movable equipment, stored materials — and it is inherently variable because it depends on how a space is actually occupied rather than on what was physically constructed. This is precisely why live load assumptions are tied to occupancy classification and specific use rather than a single blanket assumption: a storage area, an assembly space, an office, and a mechanical room impose fundamentally different demands in concept, because the activities and loading patterns in each are different. A reviewer's first job with live load is not to check a number in isolation but to confirm the occupancy and use assumed for the load determination actually matches the occupancy and use shown elsewhere in the construction documents.
Consider a permit application for a tenant space where the intended use shifts partway through design from open office space to an assembly use — a training or gathering area with denser, less predictable occupant loading than a typical office layout. That kind of change does not just affect egress capacity; it directly affects the live load the floor and its supporting members need to resist, because the two occupancies represent genuinely different loading concepts, not just different labels.
A careful reviewer treats this as a structural coordination issue, not solely a life-safety one, confirming the structural general notes and calculations reflect the occupancy and use actually intended for the space rather than an earlier design iteration. Determining and applying the specific loads is the responsibility of the engineer of record, who owns the structural calculations; the plans examiner's role is to verify the documented assumptions are consistent, complete, and code-compliant, not to independently re-derive the engineering. In the field, an inspector encountering a completed space used differently than approved is looking at the same underlying issue from the opposite direction: the as-built condition may no longer match the load assumptions the structure was designed for.
The most common failure is treating occupancy classification and structural load assumptions as two separate, unrelated checklist items rather than recognizing that one drives the other — confirming an occupancy is coded correctly on the cover sheet without ever checking that the structural calculations actually agree with it. A related mistake is accepting a late-stage use change without confirming the structural documents were updated to match, on the assumption that "it's just a use change" rather than a live load change in different language.
The correction is the same discipline every time: treat occupancy and use as the starting input to load determination, verify that input is consistent across every discipline's documents, and require a documented update to the structural calculations whenever occupancy or use changes.
Code Reference: IBC Sections 1603, 1604, and 1607 - Defines required structural information and gravity/live load criteria.
Apply load combinations and safety factors in structural design
No single load type acts on a building in isolation. Dead load is always present, but live load, snow, wind, and seismic forces combine with it — and with each other — in different ways depending on what is actually happening to the building at a given moment. Rarely does a structure need to be checked against every possible load type at its individual maximum simultaneously, because some combinations are physically unrealistic. Load combinations exist to solve this problem: they define which loads must be checked together, and in what realistic pairings, so a design accounts for genuine simultaneous demand without either ignoring real combined effects or over-designing for combinations that could never occur together.
Wind and seismic forces deserve their own conceptual understanding, because they behave differently from gravity loads and from each other, even though both must eventually be combined with gravity effects. Wind load is fundamentally a pressure phenomenon: air moving against and around a building creates pressure and suction on its surfaces, and how significant that pressure is in concept depends on the building's exposure to open terrain, its height above ground, and its overall shape. Seismic force, by contrast, is generated by the building's own mass resisting sudden ground motion, not something pushing on the building from outside. Because the two arise from such different mechanisms, a structure that performs well against one does not automatically perform well against the other, which is part of why both are combined with gravity loads independently rather than treated as interchangeable "lateral load" items.
The code also recognizes two broad, named approaches to applying loads and their combinations: allowable stress design and load and resistance factor design, more commonly called strength design. Both rest on the same underlying idea — that a structure's capacity must exceed its realistic combined demand by a margin sufficient to account for uncertainty in the loads and the materials resisting them — but they organize that margin differently. An engineer of record selects and applies one methodology consistently; a reviewer does not redo that selection, but needs to recognize which approach a set of calculations uses so the results can be evaluated on consistent terms.
IBC Chapter 16 does not develop all of this methodology from scratch. For much of the detailed load and load-combination methodology, Chapter 16 scopes and references the nationally recognized ASCE 7 loading standard, incorporating its provisions by reference rather than restating them in the building code itself — which is why structural calculations for a building cite both the IBC and that referenced standard by name. Buildings are also not all held to the same load requirements regardless of the consequences of failure: the code groups structures into risk categories, recognizing that a warehouse with few occupants does not carry the same acceptable risk, in concept, as a hospital or a facility meant to stay operational during a disaster. That grouping scales how load requirements are applied, which is why a reviewer needs to confirm the risk category assumed in the structural documents actually matches the building's occupancy and function.
Consider a plan review for an emergency response facility intended to remain operational during and after a significant wind or seismic event. If the structural general notes classify the building using assumptions appropriate to an ordinary, lower-consequence occupancy, the entire load combination and design methodology built on that classification is out of alignment with what the building is actually intended to do — even if every calculation downstream is performed correctly. A careful reviewer checks the risk category assumption against the building's actual function early in review, because catching a misclassified risk category after calculations are complete means the entire analysis has to be redone. The same discipline applies to wind and seismic assumptions: the reviewer is not re-deriving the forces the engineer of record calculated, but is confirming that exposure, height, and shape characteristics shown on the architectural and site documents are consistent with the structural calculations, and that both wind and seismic combinations were addressed rather than only whichever load type dominates in that region.
A frequent error is treating load combinations as a black-box result rather than a set of assumptions a reviewer can sanity-check — accepting that "combinations were checked" without confirming which risk category, methodology, and realistic load pairings were actually used. Another failure is letting a risk category assumption go unverified because it is buried in general notes, even though it scales essentially every subsequent load requirement. The correction is to make risk category and design methodology an explicit, early checkpoint, and to confirm wind and seismic assumptions are individually consistent with the building's actual exposure, height, shape, and function.
Code Reference: IBC Section 1605 with related Chapter 16 provisions - Applies load combinations and design methodology selection.
Understand soil, roof, and rain load calculations and requirements
Snow, rain, and soil loads share a feature that dead and live loads do not: they originate outside the building and depend heavily on where it sits, not just on how it is used. Snow load starts as a ground-level condition translated into a roof-level design load, accounting for the fact that a roof rarely accumulates snow uniformly — wind and roof geometry cause snow to drift into deeper accumulations in some areas and slide off entirely in others, so a design must address both the general roof snow condition and more concentrated drift and sliding conditions at roof shape changes. Rain load, and the related concept of ponding, addresses what happens when water is not properly and continuously drained from a roof: standing water adds weight, and on a roof with limited stiffness or drainage capacity, that added weight can deflect the roof further and allow more water to collect — a feedback pattern that has caused real roof failures where drainage was inadequately designed or maintained.
Soil load and hydrostatic pressure work below grade the way wind and rain work above it, describing forces from the surrounding environment pressing on foundation and below-grade walls — lateral earth pressure and groundwater pressing against a wall it can reach. Special and impact loads round out the picture: forces from equipment operation, vehicle impact, or other conditions unique to a building's function.
None of these site-specific loads can be determined from general knowledge alone. Ground snow conditions, wind characteristics, and seismic parameters for a given location come from location-specific maps and data referenced by the code and the nationally recognized loading standard, not a reviewer's memory or a rule of thumb carried over from another project. Plan review here is a verification function, not a re-calculation function: the plans examiner's job is to confirm the design team used the correct site-specific inputs for the actual project location, not to independently supply those values during review.
That verification depends entirely on the design criteria being stated somewhere the reviewer can find them. A construction document set should include a design criteria or general notes sheet stating the loads and site-specific parameters the design is based on — occupancy and risk category, the governing snow, wind, and seismic assumptions, and the design methodology used — in one place, clearly enough that a reviewer can confirm those criteria are present, appropriate for the project's occupancy and location, and consistent with the rest of the document set. From there, the load path — the continuous chain of structural elements carrying loads from where they originate down through the building to the foundation and into the ground — is what actually puts those criteria into practice, which is why structural plan review depends on tracing that path through the drawings rather than checking isolated members in isolation.
Consider a submittal where the architectural and structural sheets are otherwise complete and well-coordinated, but the design criteria sheet is missing the design loads and site-specific parameters entirely — no stated snow, wind, or seismic design basis, no stated risk category, nothing establishing what the structural calculations were actually based on. Even if individual member sizes appear reasonable at a glance, a reviewer cannot verify code compliance without knowing what the design was designed for, because reasonable-looking members sized for the wrong site conditions or risk category are merely coincidentally similar to what a compliant design might look like. The correct response is not to guess at what the criteria probably are, or approve conditionally and chase the information down later. The submittal should be returned specifically for the missing design criteria, with the reviewer identifying exactly what needs to be stated — governing environmental loads, occupancy and risk category, and design methodology — so the engineer of record can supply a complete design-basis sheet the rest of the review can be checked against.
A recurring mistake is reviewing individual structural details thoroughly while never confirming a design criteria sheet exists — checking the parts without confirming the stated basis those parts are supposed to satisfy. A related failure is accepting a design criteria sheet listing loads inconsistent with the site or occupancy, as if copied from an unrelated prior project. Snow drift and wind uplift conditions at roof-level transitions and parapets are also commonly overlooked because they require examining roof geometry specifically, rather than assuming the general roof condition covers every detail. The correction is to make the design criteria sheet a first-pass checkpoint before detailed review begins, verify its parameters against the actual site and occupancy, and specifically check roof geometry for drift and uplift-prone conditions.
Code Reference: IBC Sections 1608, 1609, and 1611 - Integrates environmental loading considerations into complete design assumptions.
IBC Structural Design Loads and Load Combinations is ultimately about getting the inputs right before anything downstream can be trusted. Dead and live loads have to reflect what was actually built and how the space is actually occupied; environmental loads — snow, wind, seismic, rain, soil, and any special or impact conditions — have to reflect where the building sits, using correct site-specific data rather than assumptions carried over from elsewhere; and load combinations have to capture realistic simultaneous demand without ignoring genuine combined effects or over-designing for combinations that could not occur together.
Plan review and inspection in this area function as verification, not re-engineering. The engineer of record determines and applies the specific loads, methodology, and combinations; the reviewer confirms those assumptions are complete, internally consistent, appropriate for the actual occupancy, risk category, and site, and clearly documented on a design criteria sheet the rest of the structural drawings can be checked against. When that verification habit is applied consistently, structural design load review becomes a reliable safeguard, and the load path from roof to foundation stays traceable and defensible from design through construction.