Direct Answer
LOD (Level of Development, or Level of Detail) in BIM defines how much information and geometry a model element contains at each project phase. For steel, LOD 300 means members are modeled with accurate geometry and location; LOD 350 adds connection elements (bolts, plates, welds); LOD 400 is full fabrication detail — what the detailer produces. Understanding LOD prevents mismatched expectations between what your detailer delivers and what the owner requires.
Full Explanation
The American Institute of Architects defines LOD 100–500 in the BIM Forum LOD Specification. LOD 100 is conceptual massing. LOD 200 is approximate geometry. LOD 300 is accurate member geometry, suitable for coordination. LOD 350 includes connection interfaces — critical for MEP coordination at structural penetrations. LOD 400 is full fabrication-level detail, including piece marks, hole patterns, and weld symbols. LOD 500 is as-built. A typical structural steel detailing scope delivers LOD 400 for all members.
What This Means for Your Shop
If an owner's BIM requirement specifies LOD 350 or 400, verify your detailer's contract explicitly includes that level. LOD 400 models take significantly longer to produce than LOD 300 — the difference is meaningful in schedule and cost.
Common Mistakes
Assuming LOD 300 will satisfy all coordination requirements. MEP trades routing through structural members need LOD 350 or higher to properly coordinate penetration locations. An LOD 300 model shows where the beam is but not where the web openings are.
Recommended Process
At project kickoff, confirm the LOD requirement with the BIM manager. Include it in your detailing contract. Verify at mid-project that the model is on track to meet the specified LOD.