External wall
Yttervägg
A climate-separating wall: the build-up, not the finish, decides almost everything downstream.
Walls category, a wall type with a compound layer structure; the Function parameter set to Exterior
IfcWall / IfcWallStandardCase, typed by IfcWallType; layers in IfcMaterialLayerSet
walls
Net area (m²) per layer, taken from the exact extracted model version; volume (m³) for cast layers
Where this element is normally designated in each Swedish reference system. Code values stay with their publishers.
| System | Designated in | What it establishes |
|---|---|---|
| CoClass | Functional systems, then Constructive systems | The functional table says it encloses and separates; the constructive table says how — timber-framed, steel-stud, concrete sandwich. Only the second one constrains a recipe. |
| BIP | Object designation for the wall type, plus property designations for fire, sound and U-value | Makes the type name and its performance properties readable across disciplines. It does not verify a single one of those values. |
| BK04 | Group and sub-group, per layer material — boards, insulation, studs, membranes | Reached only after material requirements exist. A wall as a whole has no BK04 group; its layers do. |
Identity → system classification → contract → recipe. The recipe expands the build-up into one material requirement per layer, and products are selected per layer, never per wall.
- A wall type named 'Yttervägg 250' is a claim about the build-up, not proof of it. The compound layer structure is the evidence.
- Stacked walls and curtain walls are separate identities and are refused as ordinary walls, not silently absorbed.
- Exterior function in Revit is evidence towards an external-wall classification; room-bounding and geometry also contribute.
BIM data is evidence, not authority
A parameter in a model is a claim made by whoever typed it. Treating claims as authority is how wrong numbers get inherited across an entire project.
Decision receipts: proving why a construction choice was made
A receipt is not a report. It is the reconstructable record of one decision: its scope, its evidence, the rules applied, and the exact versions in force.