Background

Space boundaries are special relationship objects in IFC that connect a space to its bounding elements (walls, doors, windows, slabs). The relationship also has a 2D geometry that represents the 'boundary plane' between the space and the bounding element. If a side of a space does not have a bounding element a virtual space boundary is used.

Architectural design applications, such as ArchiCAD and Revit can export space boundaries to IFC, but the data has very uneven quality.

Space boundaries are used primarily by energy and indoor condition analysis applications.

Functionality of the Add-on

• All existing space boundary objects are first deleted from the model each time the add-on is run
• All included space objects are processed
• The Space Boundary add-on creates space boundary objects based on the geometry of the space objects that exist in the model.
  • No new space objects are created
  • The geometry of the space objects is not modified but taken as-is
• The space boundary objects are created such that they cover each side of the space object's geometry
  • The space boundaries do not necessarily create an air-tight cover around the space because small space boundaries that are caused by modeling inaccuracies can be filtered out
• The generated space boundaries are so-called 1st level boundaries and are created according to the BuildingSmart specification for space boundaries
  • The boundaries are created purely based on the space object's geometry and the bounding elements of the space. No consideration is given to what is behind the bounding element.
  • In accordance with the specification space boundaries for walls and slabs do not contain openings. The space boundaries for doors, and windows are overlapping with the wall and slab space boundaries.

Preparing Models

It is important to make sure the model is suitable for space boundary generation before any space boundaries are generated. The add-on allows for a fair amount of modeling inaccuracy, for example a space and wall do not have to meet each other perfectly accurately, but it can't do miracles.

• Exclude all space objects that don't represent rooms, i.e. for which you want to create space boundaries. You should exclude for example gross/net area spaces and apartments.
• Run the Exclude Duplicates tool. Duplicate objects make the results of the space boundary unpredictable.
• Run the Find Overlapping Objects tool. This tool tells you visually how badly spaces and walls are overlapping with each other. If the result looks bad you should report the issues to the model author and wait for a new version.

Resolving internal/external for building elements

Space boundaries contain information whether the boundary is for a internal or external building element. The add-on gives the following options for determining this status.

• Instance Only = the information is only queried from the object in question
• Host Only = the information is queried from the host (for example a wall can be the host of a window) if the object in question has a host
• Instance then Host = Only use information from host if a host exists and the information is not defined for the object in question
• Host then Instance = Only use the information from the object in question if it does not have a host or the information is not defined for the host

Installing and Running

1. Download the installer from simplebim.com/downloads
2. Run the installer. Please note that you need administrator rights for running the installer
3. Import your model
4. Take the steps for preparing your model as described above
5. Run the Create Space Boundaries tool. You find instructions for running tools here.
6. Set the tolerance and create the space boundaries
7. Export the model into a new IFC file. 

Known Limitations

• The space boundaries for doors are not according to the IFC implementation agreements if the door does not make a clear opening into the wall. For making a clear opening the door must be located inside the wall and not at the edge of the wall, which unfortunately is the most common case.
• There is no preview for the space boundaries in Simplebim, but we plan to add a preview. Currently you can import the exported IFC model into a separate IFC viewer for checking the space boundaries.