What Is LOD in BIM? Level of Development vs Level of Detail

At LOD 100 an element may be a symbol or a mass. You can use it for early studies, not for measurement. At LOD 200 the element has approximate size, shape, location, and orientation. You can use it to reserve space, with the understanding it will move. At LOD 300 the quantity, size, shape, location, and orientation are specific enough to coordinate and to measure from, within the uses the plan allows.

LOD 350 models the interfaces: supports, connections, and the parts needed to show how the element meets its neighbors. That is the level coordination meetings often need and design models often lack. LOD 400 adds the detail a fabricator needs to make the piece. LOD 500 records a field-verified element. It is not automatic at the end of the job. Someone has to verify it.

Level of detail describes how much geometry is shown. Level of development describes how much thought and authorization sit behind it. A manufacturer’s highly detailed family dropped into a schematic model does not become LOD 400 because the mesh is dense. If the engineer has not designed that connection, nobody should fabricate from it.

The practical test is a sentence: may the coordinator dimension from this, may the estimator count it, may the detailer build it? Those can be three different answers for the same element. Write the authorized uses next to the LOD. The number alone gets misread.

ISO 19650 does not use level of development. It uses level of information need, which states what geometric information, alphanumeric information, and documentation a deliverable must contain for a given purpose and milestone. The shift moves the question from a number on the element to a requirement the appointing party sets for each exchange.

In practice, projects in ISO 19650 markets and projects in AIA and BIMForum markets talk past each other. A US contractor asking for LOD 350 and a UK appointing party issuing a level of information need are asking for the same kind of thing in different words. Translate between them in the BIM execution plan rather than assume the terms match.

A BIM execution plan attaches target LODs to phases. Structural framing might be LOD 300 at CD issue and still LOD 200 in early DD. MEP mains might reach LOD 350 only in the trade coordination model, after award. Expecting fabrication reliability from a design model because the software can display it is how owners think they bought shop drawings in the design fee.

Different elements in one model sit at different LODs at the same time. Equipment may be a specific product while the duct connecting it is still approximate. Reports that say the model is LOD 300 without an element matrix are marketing. Ask for the matrix.

Clash detection on LOD 200 ductwork produces clashes that move when the duct is sized. That can still be useful if the meeting treats them as space reservations. Treating them as field issues wastes the trades. The coordination plan should say which LOD is in the federated model this month.

When a contractor takes over a design model for VDC, the first task is to learn what the author authorized. IFC export does not raise the LOD. It only carries what was in the source, sometimes with parameters renamed or dropped. Verify the fields you intend to rely on after the exchange.

A LOD matrix is only useful if someone checks the delivered model against it. The check has two halves. One is geometric: whether the element is where, and as big as, the LOD allows someone to rely on. The other is data: whether the properties the matrix requires, such as fire ratings, classification codes, and manufacturer fields, are populated.

The data half can be done without opening the authoring tool. An IFC export can be opened in a browser viewer, its property sets queried, and the results compared with the drawings and specifications that say what the element should be. The geometric half usually stays in a model-checking tool with a rule set.