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When it comes to supporting a house with columns in a basement, the International Residential Code (IRC) offers minimal prescriptive guidance. While the code includes fastening requirements for floor framing (R502.9) and mandates lateral restraint for columns (R407.3), it does not provide explicit requirements for how much bearing a girder must have on a column. This lack of specificity is not an oversight—it's a necessity due to the sheer number of variables involved.
Consider an LVL beam designed to span a large basement opening. If the original plan calls for four lally columns but is modified to use only one, the column must now support four times the weight. The required bearing at that connection must be significantly larger than if four columns were used. In contrast, a built-up girder made of multiple wood members raises the question: Is a small 4x4 bearing plate adequate, or should it be larger? The answer depends entirely on the load calculations.
For building professionals, the takeaway is clear: When in doubt, get an engineer involved. The IRC sets the framework, but proper structural design requires expertise beyond what the prescriptive code provides.
Why the IRC Cannot Be Prescriptive on Required Bearing
Several factors influence the amount of bearing required for a girder resting on a column:- Point Loads on the Girder: A beam carrying significant point loads—such as those concentrated at a single lally column—requires more bearing than one evenly supported by multiple columns.
- Column Spacing: A girder spanning a greater distance with fewer columns will impose a higher load per column, affecting the necessary bearing area.
- Live and Dead Loads: The total weight a column must support depends on the structure above it, including floors, walls, furniture, and occupants.
- Material and Beam Type: A built-up nominal beam (such as five 2x10s forming a 7-1/2” wide girder) distributes loads differently than a single LVL or steel beam.
- Bearing Plate Size and Distribution: If a column is supporting substantial weight, a small bearing plate—such as a 1/4" x 4" x 5" steel plate—may be insufficient, creating excessive pressure at the connection point.
Fasteners Aren't the Only Missing Requirement
Discussions on The Building Code Forum have raised concerns about the lack of prescriptive fastening requirements for beam-to-column connections. But beyond fasteners, the IRC is also silent on the required bearing area itself. The reason is the same—there is no one-size-fits-all solution.Consider an LVL beam designed to span a large basement opening. If the original plan calls for four lally columns but is modified to use only one, the column must now support four times the weight. The required bearing at that connection must be significantly larger than if four columns were used. In contrast, a built-up girder made of multiple wood members raises the question: Is a small 4x4 bearing plate adequate, or should it be larger? The answer depends entirely on the load calculations.
The Role of Architects and Engineers
Because of these complexities, the design of beam-to-column connections must be left to an architect or structural engineer. These professionals calculate the loads, determine the necessary bearing area, and specify fastener requirements based on the unique conditions of the structure. This is the same reason why, in many cases, residential basement columns come with pre-manufactured steel bearing plates welded to the top—because they have been engineered for common loading scenarios.Why Hasn't the Code Caught Up?
While building codes evolve to address emerging construction practices, they often remain silent on fundamental structural elements like beam-to-column bearing. The IRC provides general guidance, but it does not attempt to regulate every variable in load-bearing design. Instead, it relies on engineering principles and standard design practices to ensure structural integrity.The Building Code Forum Summary
The absence of prescriptive requirements for beam-to-column bearing in the IRC is not a flaw—it's an acknowledgment that each situation is unique. While the code specifies that connections must prevent uplift and lateral displacement, it does not dictate how much bearing is required because that calculation depends on too many factors. The safest and most code-compliant approach is to defer to architectural and engineering design, ensuring that load distribution and bearing requirements are properly addressed.For building professionals, the takeaway is clear: When in doubt, get an engineer involved. The IRC sets the framework, but proper structural design requires expertise beyond what the prescriptive code provides.
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