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Skillsifc-errors-spatial-structure

ifc-errors-spatial-structure

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Updated 10-15 22:18

About this skill

IFC Spatial Structure Errors

Diagnose and fix the errors that break the spatial structure of an IFC file : an element with no spatial container (an orphan), an element contained twice, an element placed at the wrong level, a deprecated proxy abused as a placeholder, and a spatial tree that is missing levels or never reaches IfcProject. These errors leave a file that may still pass EXPRESS schema checks, yet elements vanish from viewers, quantity take-off, and facility-management exports.

For the spatial-structure MODEL (how the tree is built correctly) see ifc-core-spatial-structure and ifc-impl-spatial-decomposition. For abstract WHERE-rule and global-RULE errors in general see ifc-errors-schema-validation. For dangling #id references see ifc-errors-broken-references.

Quick Reference

The mandatory spatial skeleton

Every physical element MUST be locatable through one acyclic tree rooted at IfcProject. The tree levels differ by version:

Level IFC2x3 IFC4 IFC4.3
Context root IfcProject IfcProject IfcProject
Site IfcSite IfcSite IfcSite
Facility IfcBuilding IfcBuilding IfcFacility (IfcBuilding, IfcBridge, IfcRoad, IfcRailway, IfcMarineFacility)
Sub-level IfcBuildingStorey IfcBuildingStorey IfcFacilityPart (IfcBuildingStorey)
Space IfcSpace IfcSpace IfcSpace

IfcProject is NOT a spatial element. It is an IfcContext subtype. The tree attaches BENEATH it via IfcRelAggregates.

The three structuring relationships

Relationship Connects Direction Use for
IfcRelAggregates spatial level to spatial level, project to site, whole to parts RelatingObject (whole) to RelatedObjects SET Building the tree itself : IfcProject to IfcSite to IfcBuilding/IfcFacility to storey to IfcSpace
IfcRelContainedInSpatialStructure a spatial level to physical elements RelatingStructure (one level) to RelatedElements SET OF IfcProduct Placing a wall, beam, door into exactly ONE spatial level
IfcRelReferencedInSpatialStructure a spatial level to elements (IFC4, IFC4.3 only) RelatingStructure to RelatedElements SET A SECONDARY, non-hierarchical reference for an element spanning levels

Core rules

  • ALWAYS attach a physical element to its spatial level with IfcRelContainedInSpatialStructure. NEVER use IfcRelAggregates for that : IfcRelAggregates builds the tree, it does not place elements in it.
  • ALWAYS give every physical IfcElement occurrence exactly ONE IfcRelContainedInSpatialStructure link. Zero links is an orphan ; two links violate the IfcElement.ContainedInStructure inverse, declared SET [0:1].
  • Double containment is NOT a WR31 violation. WR31 forbids putting a SPATIAL STRUCTURE element into RelatedElements. ALWAYS name the correct rule.
  • ALWAYS aggregate every IfcSpatialStructureElement up to IfcProject or another spatial element (WR41). A site with no path to IfcProject breaks the tree.
  • NEVER leave IfcProject.Decomposes populated : the NoDecomposition WHERE rule forbids anything aggregating the project.
  • IFC4.3 : NEVER use IfcBuildingElementProxy as a void or clearance placeholder. ALWAYS use IfcVirtualElement instead.

Decision Trees

Which spatial-structure error is this

Symptom ?
├─ element absent from viewer tree / quantity take-off / FM export
│   └─ count its IfcRelContainedInSpatialStructure links
│       ├─ zero links  -> ORPHAN element. Pattern 1.
│       └─ one link    -> not orphaned ; check the level. Pattern 3.
├─ validation flags IfcElement.ContainedInStructure cardinality
│   -> DOUBLE containment (two links). Pattern 2.
├─ validation flags WR31 on IfcRelContainedInSpatialStructure
│   -> a spatial element is wrongly listed in RelatedElements. Pattern 4.
├─ element is in the tree but under the wrong level (door under IfcSite)
│   -> WRONG containment level. Pattern 3.
├─ a proxy is used as a void / clearance / virtual placeholder
│   -> PROXY-as-placeholder misuse. Pattern 5.
└─ no IfcSite, WR41 fails, NoDecomposition fails, or multiple IfcProject
    -> MISSING or BROKEN spatial tree. Pattern 6.

Which spatial level should contain this element

What is the element ?
├─ a physical building element (wall, beam, slab, column, pipe)
│   -> contain in the storey it physically belongs to (IfcBuildingStorey).
├─ furniture, sanitary, a sensor, equipment inside a room
│   -> contain in the IfcSpace if the room is modelled, else the storey.
├─ a site element (fence, terrain feature, external pavement)
│   -> contain in IfcSite.
├─ an element spanning two storeys (a stair, a tall facade panel)
│   -> contain in ONE storey ; reference the other storey with
│      IfcRelReferencedInSpatialStructure (IFC4, IFC4.3 only).
└─ a spatial level itself (IfcSpace, IfcBuildingStorey)
    -> NEVER use IfcRelContainedInSpatialStructure. Aggregate it with
       IfcRelAggregates. Putting it in RelatedElements breaks WR31.

Proxy or virtual element : placeholder decision

Need a non-physical placeholder (provision for void, clearance, imaginary boundary) ?
├─ file schema is IFC4.3
│   -> use IfcVirtualElement. NEVER IfcBuildingElementProxy : the proxy is
│      deprecated for this use in IFC4.3.0.0.
├─ file schema is IFC2x3 or IFC4
│   -> IfcVirtualElement is preferred for imaginary space boundaries.
│      IfcBuildingElementProxy with PredefinedType PROVISIONFORVOID is the
│      legacy provision-for-void pattern still accepted in these versions.
└─ the object is genuinely a physical, unclassifiable construction element
    -> IfcBuildingElementProxy is correct (any version). It is NOT a misuse here.

Patterns

Pattern 1 : detect and fix an orphan element

An orphan is a physical IfcElement occurrence whose ContainedInStructure inverse resolves to zero IfcRelContainedInSpatialStructure instances. The SET [0:1] inverse cardinality ALLOWS zero, so the file can pass EXPRESS schema validation, yet the element is unreachable by spatial traversal : viewers omit it from the model tree and quantity take-off skips it.

Detect : for each physical element, check whether any IfcRelContainedInSpatialStructure lists it in RelatedElements.

Fix : add ONE IfcRelContainedInSpatialStructure whose RelatingStructure is the correct spatial level (see the level decision tree) and whose RelatedElements includes the orphan. NEVER attach it with IfcRelAggregates. The buildingSMART normative SPS rule family flags missing containment ; ALWAYS re-validate after the fix.

Pattern 2 : fix double containment

Double containment is one element listed in RelatedElements of TWO different IfcRelContainedInSpatialStructure instances. It violates the inverse attribute IfcElement.ContainedInStructure, declared SET [0:1] OF IfcRelContainedInSpatialStructure FOR RelatedElements. The compliance check reports an inverse-cardinality error.

Fix : decide the ONE spatial level that owns the element and keep that single IfcRelContainedInSpatialStructure link. Remove the element from the RelatedElements of every other containment relationship. If the element genuinely relates to a second level (a stair across two storeys), express that second link with IfcRelReferencedInSpatialStructure (IFC4, IFC4.3). NEVER keep two ...ContainedInSpatialStructure links to satisfy both levels.

Pattern 3 : fix a wrong containment level

The element has exactly one containment link, so it is not an orphan, but the RelatingStructure is the wrong level : a door contained directly in IfcSite, a wall contained in IfcProject (impossible : IfcProject is not spatial), or room furniture contained in the storey when the IfcSpace exists.

This is schema-valid but semantically wrong : downstream consumers group by spatial level, so the element lands in the wrong room schedule or floor plan.

Fix : edit the single IfcRelContainedInSpatialStructure so RelatingStructure points at the correct level per the level decision tree. ALWAYS contain a physical building element in its IfcBuildingStorey ; contain room-scoped contents in the IfcSpace when that space is modelled.

Pattern 4 : fix a WR31 violation

WR31 on IfcRelContainedInSpatialStructure states verbatim : "The relationship object shall not be used to include other spatial structure elements into a spatial structure element. The hierarchy of the spatial structure is defined using IfcRelAggregates." The rule is identical in IFC2x3, IFC4, and IFC4.3.

The violation : a spatial structure element (an IfcSpace, IfcBuildingStorey, IfcBuilding, IfcSite, ...) appears in the RelatedElements SET of an IfcRelContainedInSpatialStructure. The author used containment where aggregation was required.

Fix : remove the spatial element from RelatedElements and connect it to its parent level with IfcRelAggregates instead (RelatingObject = parent level, RelatedObjects includes the spatial element). WR31 is NOT about double containment ; NEVER report it as such.

Pattern 5 : replace a proxy-as-placeholder with IfcVirtualElement

IfcBuildingElementProxy is the escape hatch for genuinely unclassifiable PHYSICAL construction elements. It is misused when it stands in for a non-physical placeholder : a provision for void, a clearance zone, an imaginary space boundary.

IFC4.3 made this explicit. The IFC4.3.0.0 change note states virtual elements "can now be used for void provisions and clearance to replace existing functionality on IfcBuildingElementProxy". IfcVirtualElement gained a PredefinedType of IfcVirtualElementTypeEnum : BOUNDARY, PROVISIONFORVOID, CLEARANCE, USERDEFINED, NOTDEFINED.

Fix (IFC4.3) : replace each placeholder IfcBuildingElementProxy with an IfcVirtualElement, set PredefinedType to PROVISIONFORVOID, CLEARANCE, or BOUNDARY as appropriate, and keep the element in the spatial structure with the SAME IfcRelContainedInSpatialStructure link. In IFC2x3 and IFC4 the legacy proxy-with-PROVISIONFORVOID pattern still validates ; ALWAYS migrate it when upgrading a file to IFC4.3.

Pattern 6 : repair a missing or broken spatial tree

A broken tree has one or more of : no IfcSite, a spatial element with no aggregation path to IfcProject, more than one IfcProject, or IfcProject itself being aggregated by something.

Checks and fixes:

  • WR41 on IfcSpatialStructureElement : "All spatial structure elements shall be associated (using the IfcRelAggregates relationship) with another spatial structure element, or with IfcProject." A site or building with an empty Decomposes inverse fails WR41. Fix : add the IfcRelAggregates link to its parent.
  • NoDecomposition on IfcProject : IfcProject.Decomposes MUST be empty. Nothing aggregates the project. Fix : remove any IfcRelAggregates whose RelatedObjects contains the IfcProject.
  • IfcSingleProjectInstance global RULE (IFC4, IFC4.3) : SIZEOF(IfcProject) <= 1. Fix : keep exactly one IfcProject and re-aggregate every site beneath it.
  • A missing intermediate level (elements containment-linked to IfcBuilding with no IfcBuildingStorey) is accepted by some tools but breaks storey-based views. ALWAYS model the full chain Project to Site to Building/Facility to Storey to Space and contain physical elements at the storey or space level.

ALWAYS run the buildingSMART validation service after the repair : the SPS normative rule family checks basic spatial structure for buildings.

Reference Links

  • references/methods.md : entity and attribute signatures, the ContainedInStructure inverse, WR31, WR41, NoDecomposition, IfcSingleProjectInstance, IfcVirtualElementTypeEnum, version differences.
  • references/examples.md : verified STEP fragments : a correct tree, each error and its fix.
  • references/anti-patterns.md : the spatial-structure mistakes and why each one is wrong.

Related skills

  • ifc-core-spatial-structure : how the spatial tree is built correctly.
  • ifc-impl-spatial-decomposition : the authoring workflow for the tree.
  • ifc-core-relationships : the objectified IfcRel* pattern, relating vs related.
  • ifc-errors-schema-validation : WHERE-rule, global-RULE, abstract-entity errors.
  • ifc-errors-broken-references : dangling #id and missing INVERSE links.
  • ifc-errors-version-mismatch : deprecated and removed-entity errors per schema.

Verified sources

All entity declarations, attribute types, WHERE-rule text (WR31, WR41, NoDecomposition), the ContainedInStructure inverse cardinality, and the IfcVirtualElement change note verified 2026-05-20 via WebFetch against the buildingSMART sources in SOURCES.md : the IFC 4.3.2 specification, the IFC4 ADD2 TC1 specification, and the IFC2x3 TC1 specification.