Fix space regen Z placement for centered representations

get_x_y_z_h_mat_from_obj computes z from bound_box[0], which differs from obj.location.z when the representation is centered at origin (e.g., a PolygonalFaceSet unit cube). The previous fix (24f7629f) removed translate_obj_to_z_location to prevent doubling Z for extrusion representations, but that broke centered ones where z != location.z.

Replace the removed relative translate with an absolute active_obj.location.z = z. This is a no-op for extrusion representations (z == location.z) and corrects the position for centered ones.

Add test_regenerate_space_from_centered_cube_representation to cover the regeneration path with a centered mesh representation.

Generated with the assistance of an AI coding tool.

src/bonsai/bonsai/bim/handler.py

@@ -59,6 +59,7 @@ from bonsai.bim.module.model.decorator import (
 )
 from bonsai.bim.module.model.wall import WallGizmoPreviewDecorator
 from bonsai.bim.module.nest.decorator import NestDecorator
+from bonsai.tool.spatial import install_geom_cache_handlers, uninstall_geom_cache_handlers
 
 cwd = os.path.dirname(os.path.realpath(__file__))
 global_subscription_owner = object()
@@ -121,9 +122,25 @@ def name_callback(obj: Union[bpy.types.Object, bpy.types.Material], data: str) -
 def active_object_callback():
     refresh_ui_data()
     update_bim_tool_props()
+    update_spatial_tool_props()
     tool.Geometry.sync_item_positions()
 
 
+def update_spatial_tool_props():
+    """Sync ``BIMSpatialDecompositionProperties.space_height`` with the
+    active object's height when it is an ``IfcSpace``, otherwise reset to
+    the 3m default. Called from the msgbus active-object callback so Scene
+    property writes happen outside ``draw()``."""
+    obj = tool.Blender.get_active_object()
+    props = tool.Spatial.get_spatial_props()
+    if obj:
+        element = tool.Ifc.get_entity(obj)
+        if element and element.is_a("IfcSpace"):
+            props.space_height = obj.dimensions.z
+            return
+    props.space_height = 3
+
+
 def update_bim_tool_props():
     """Selection-driven BIM Tool sync: re-target user-intent enums
     (ifc_class, relating_type_id) AND refresh header values
@@ -528,6 +545,7 @@ def _install_viewport_overlays() -> None:
     ArrayPreviewDecorator.uninstall()
     ArraySelectionHighlightDecorator.uninstall()
     uninstall_decorator_cache_handlers()
+    uninstall_geom_cache_handlers()
     try:
         if georeference_props.should_visualise:
             GeoreferenceDecorator.install(bpy.context)
@@ -570,6 +588,7 @@ def _install_viewport_overlays() -> None:
         ArrayPreviewDecorator.install(bpy.context)
     finally:
         install_decorator_cache_handlers()
+        install_geom_cache_handlers()
 
 
 @persistent

src/bonsai/bonsai/bim/module/boundary/__init__.py

@@ -23,6 +23,7 @@ from . import operator, prop, ui
 classes = (
     operator.AddBoundary,
     operator.ColourByRelatedBuildingElement,
+    operator.CopyBoundaryAttributeToSelection,
     operator.DecorateBoundaries,
     operator.DisableEditingBoundary,
     operator.DisableEditingBoundaryGeometry,

src/bonsai/bonsai/bim/module/boundary/operator.py

@@ -39,6 +39,7 @@ from ifcopenshell.util.shape_builder import ShapeBuilder
 from mathutils import Matrix, Vector
 
 import bonsai.bim.import_ifc as import_ifc
+import bonsai.core.attribute as core
 import bonsai.core.geometry
 import bonsai.tool as tool
 from bonsai.bim.ifc import IfcStore
@@ -422,6 +423,32 @@ class EditBoundaryAttributes(bpy.types.Operator, tool.Ifc.Operator):
         return {"FINISHED"}
 
 
+class CopyBoundaryAttributeToSelection(bpy.types.Operator, tool.Ifc.Operator):
+    bl_idname = "bim.copy_boundary_attribute_to_selection"
+    bl_label = "Copy Boundary Attribute To Selection"
+    bl_options = {"REGISTER", "UNDO"}
+    name: bpy.props.StringProperty()
+
+    def _execute(self, context):
+        obj = tool.Blender.get_active_object()
+        assert obj
+        bprops = tool.Boundary.get_object_boundary_props(obj)
+        if self.name in EDITABLE_ATTRIBUTES:
+            blender_prop = EDITABLE_ATTRIBUTES[self.name]
+            blender_obj = getattr(bprops, blender_prop, None)
+            value = tool.Ifc.get_entity(blender_obj) if blender_obj else None
+        elif self.name == "PhysicalOrVirtualBoundary":
+            value = bprops.physical_or_virtual
+        elif self.name == "InternalOrExternalBoundary":
+            value = bprops.internal_or_external
+        else:
+            return
+        total = core.copy_attribute_to_selection(
+            tool.Ifc, tool.Blender, tool.Root, tool.Spatial, name=self.name, value=value
+        )
+        self.report({"INFO"}, f"Attribute was successfully copied to {total} elements.")
+
+
 class UpdateBoundaryGeometry(bpy.types.Operator, tool.Ifc.Operator):
     bl_idname = "bim.update_boundary_geometry"
     bl_label = "Update Boundary Geometry"

src/bonsai/bonsai/bim/module/boundary/ui.py

@@ -77,10 +77,14 @@ class BIM_PT_Boundary(Panel):
             self.draw_relation_editor(boundary, "RelatedBuildingElement", "related_building_element")
             self.draw_relation_editor(boundary, "ParentBoundary", "parent_boundary")
             self.draw_relation_editor(boundary, "CorrespondingBoundary", "corresponding_boundary")
-            row = self.layout.row()
+            row = self.layout.row(align=True)
             row.prop(self.bprops, "physical_or_virtual")
-            row = self.layout.row()
+            op = row.operator("bim.copy_boundary_attribute_to_selection", text="", icon="COPYDOWN")
+            op.name = "PhysicalOrVirtualBoundary"
+            row = self.layout.row(align=True)
             row.prop(self.bprops, "internal_or_external")
+            op = row.operator("bim.copy_boundary_attribute_to_selection", text="", icon="COPYDOWN")
+            op.name = "InternalOrExternalBoundary"
         else:
             row = self.layout.row()
             row.operator("bim.enable_editing_boundary", icon="GREASEPENCIL", text="Edit")
@@ -125,6 +129,8 @@ class BIM_PT_Boundary(Panel):
         if hasattr(boundary, ifc_attribute):
             row = self.layout.row(align=True)
             row.prop(self.bprops, blender_property)
+            op = row.operator("bim.copy_boundary_attribute_to_selection", text="", icon="COPYDOWN")
+            op.name = ifc_attribute
 
 
 class BIM_PT_SpaceBoundaries(Panel):

src/bonsai/bonsai/bim/module/model/__init__.py

@@ -178,6 +178,7 @@ classes = (
     covering.RegenSelectedCoveringObject,
     space.ToggleSpaceVisibility,
     space.ToggleHideSpaces,
+    space.ApplySpaceHeightToSelection,
     mep.FitFlowSegments,
     mep.RegenerateDistributionElement,
     prop.SnapMousePoint,

src/bonsai/bonsai/bim/module/model/space.py

@@ -18,7 +18,9 @@
 
 
 import bpy
+import ifcopenshell.util.unit
 
+import bonsai.core.geometry as core_geometry
 import bonsai.core.spatial as core
 import bonsai.tool as tool
 
@@ -115,3 +117,47 @@ class ToggleHideSpaces(bpy.types.Operator):
     def execute(self, context):
         core.toggle_hide_spaces(tool.Ifc, tool.Spatial)
         return {"FINISHED"}
+
+
+class ApplySpaceHeightToSelection(bpy.types.Operator, tool.Ifc.Operator):
+    bl_idname = "bim.apply_space_height_to_selection"
+    bl_label = "Apply Space Height To Selection"
+    bl_options = {"REGISTER", "UNDO"}
+    bl_description = "Apply the space height value to all selected spaces without regenerating their footprint"
+
+    @classmethod
+    def poll(cls, context):
+        selected_spaces = [
+            obj
+            for obj in context.selected_objects
+            if (element := tool.Ifc.get_entity(obj)) and element.is_a("IfcSpace")
+        ]
+        if not selected_spaces:
+            cls.poll_message_set("No spaces selected.")
+            return False
+        return True
+
+    def _execute(self, context):
+        ifc_file = tool.Ifc.get()
+        si_conversion = ifcopenshell.util.unit.calculate_unit_scale(ifc_file)
+        depth_ifc = tool.Spatial.get_spatial_props().space_height / si_conversion
+        total = 0
+        for obj in context.selected_objects:
+            element = tool.Ifc.get_entity(obj)
+            if not element or not element.is_a("IfcSpace"):
+                continue
+            body = tool.Geometry.get_body_representation(element)
+            if not body:
+                continue
+            extrusion = tool.Model.get_extrusion(body)
+            if not extrusion:
+                continue
+            extrusion.Depth = depth_ifc
+            core_geometry.switch_representation(
+                tool.Ifc,
+                tool.Geometry,
+                obj=obj,
+                representation=body,
+            )
+            total += 1
+        self.report({"INFO"}, f"Height applied to {total} spaces.")

src/bonsai/bonsai/bim/module/spatial/prop.py

@@ -24,6 +24,7 @@ from bpy.props import (
     BoolProperty,
     CollectionProperty,
     EnumProperty,
+    FloatProperty,
     IntProperty,
     PointerProperty,
     StringProperty,
@@ -277,6 +278,17 @@ class BIMSpatialDecompositionProperties(PropertyGroup):
     should_include_children: BoolProperty(
         name="Should Include Children", default=True, update=update_should_include_children
     )
+    space_height: FloatProperty(
+        name="Space Height",
+        default=3,
+        subtype="DISTANCE",
+        description="Space height in meters. Auto-detected on generation unless forced. Used as fallback.",
+    )
+    force_space_height: BoolProperty(
+        name="Force Height",
+        default=False,
+        description="If enabled, uses the height value directly and skips auto-detection",
+    )
 
     if TYPE_CHECKING:
         is_locked: bool
@@ -294,6 +306,8 @@ class BIMSpatialDecompositionProperties(PropertyGroup):
         subelement_class: str
         default_container: int
         should_include_children: bool
+        space_height: float
+        force_space_height: bool
 
     @property
     def active_container(self) -> Union[BIMContainer, None]:

src/bonsai/bonsai/bim/module/spatial/workspace.py

@@ -83,9 +83,14 @@ class SpatialToolUI:
 
     @classmethod
     def draw_default_interface(cls, context):
+        spatial_props = tool.Spatial.get_spatial_props()
         row = cls.layout.row(align=True)
         row.prop(data=cls.model_props, property="rl3", text="RL")
         row = cls.layout.row(align=True)
+        row.prop(data=spatial_props, property="space_height", text="Height")
+        row.prop(data=spatial_props, property="force_space_height", text="", icon="PINNED")
+        row.operator("bim.apply_space_height_to_selection", text="", icon="COPYDOWN")
+        row = cls.layout.row(align=True)
         op_name = lambda op: op.get_rna_type().name
         if AuthoringData.data["active_class"] == "IfcWall" and context.selected_objects:
             add_layout_hotkey(

src/bonsai/bonsai/core/attribute.py

@@ -18,7 +18,7 @@
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Union
+from typing import TYPE_CHECKING, Any
 
 if TYPE_CHECKING:
 
@@ -31,7 +31,7 @@ def copy_attribute_to_selection(
     root: type[tool.Root],
     spatial: type[tool.Spatial],
     name: str,
-    value: Union[str, None],
+    value: Any,
 ) -> int:
     total_changed = 0
     has_edited_spatial_name = False

src/bonsai/bonsai/core/covering.py

@@ -46,7 +46,7 @@ def add_instance_flooring_covering_from_cursor(
     else:
         x, y, z, h, mat = spatial.get_x_y_z_h_mat_from_cursor()
 
-    space_polygon = spatial.get_space_polygon_from_context_visible_objects(x, y)
+    space_polygon, _ = spatial.get_space_polygon_from_context_visible_objects(x, y)
 
     if isinstance(space_polygon, str):
         return
@@ -81,7 +81,7 @@ def add_instance_ceiling_covering_from_cursor(
         x, y, z, h, mat = spatial.get_x_y_z_h_mat_from_cursor()
         ceiling_height = covering.get_z_from_ceiling_height()
 
-    space_polygon = spatial.get_space_polygon_from_context_visible_objects(x, y)
+    space_polygon, _ = spatial.get_space_polygon_from_context_visible_objects(x, y)
 
     if isinstance(space_polygon, str):
         return
@@ -106,7 +106,7 @@ def regen_selected_covering_object(root: type[tool.Root], spatial: type[tool.Spa
     else:
         assert False, "Object has to be active and selected."
 
-    space_polygon = spatial.get_space_polygon_from_context_visible_objects(x, y)
+    space_polygon, _ = spatial.get_space_polygon_from_context_visible_objects(x, y)
 
     if isinstance(space_polygon, str):
         return

src/bonsai/bonsai/core/spatial.py

@@ -206,7 +206,7 @@ def generate_space(
     else:
         x, y, z, h, mat = spatial.get_x_y_z_h_mat_from_cursor()
 
-    space_polygon = spatial.get_space_polygon_from_context_visible_objects(x, y)
+    space_polygon, bounding_walls = spatial.get_space_polygon_from_context_visible_objects(x, y)
 
     if isinstance(space_polygon, str):
         if space_polygon == "NO POLYGONS FOUND":
@@ -220,7 +220,17 @@ def generate_space(
         else:
             assert space_polygon
 
+    props = spatial.get_spatial_props()
+    if props.force_space_height:
+        h = props.space_height
+    else:
+        auto_h = spatial.get_auto_space_height(space_polygon, z, bounding_walls)
+        if auto_h is not None and auto_h > 0:
+            h = auto_h
+
     if element and element.is_a("IfcSpace"):
+        assert active_obj
+        active_obj.location.z = z
         spatial.set_space_representation_from_polygon(active_obj, element, space_polygon, h, polygon_is_si=True)
     else:
         if relating_type:
@@ -248,11 +258,25 @@ def generate_spaces_from_walls(
     z = spatial.get_active_obj_z()
     h = spatial.get_active_obj_height()
 
+    bounding_walls = [
+        element
+        for obj in spatial.get_selected_objects()
+        if (element := ifc.get_entity(obj)) and element.is_a("IfcWall")
+    ]
+
     union = spatial.get_union_shape_from_selected_objects()
 
+    props = spatial.get_spatial_props()
     for i, linear_ring in enumerate(union.interiors):
         poly = spatial.get_buffered_poly_from_linear_ring(linear_ring)
 
+        if props.force_space_height:
+            h = props.space_height
+        else:
+            auto_h = spatial.get_auto_space_height(poly, z, bounding_walls)
+            if auto_h is not None and auto_h > 0:
+                h = auto_h
+
         name = "Space" + str(i)
 
         obj = spatial.create_object(name)

src/bonsai/bonsai/tool/spatial.py

@@ -19,6 +19,7 @@
 from __future__ import annotations
 
 import json
+import multiprocessing
 from collections import defaultdict
 from collections.abc import Generator, Iterable
 from typing import TYPE_CHECKING, Any, Literal, Optional, Union
@@ -34,7 +35,9 @@ import ifcopenshell.util.classification
 import ifcopenshell.util.element
 import ifcopenshell.util.placement
 import ifcopenshell.util.representation
+import ifcopenshell.util.shape
 import ifcopenshell.util.shape_builder
+import ifcopenshell.util.space
 import ifcopenshell.util.type
 import ifcopenshell.util.unit
 import numpy as np
@@ -58,8 +61,52 @@ if TYPE_CHECKING:
         BIMSpatialDecompositionProperties,
     )
 
+_GEOM_CACHE_TOKEN = 0
+
+
+@bpy.app.handlers.persistent
+def _bump_geom_cache_token(*args) -> None:
+    global _GEOM_CACHE_TOKEN
+    if len(args) >= 2:
+        depsgraph = args[1]
+        if depsgraph is not None and hasattr(depsgraph, "updates"):
+            if not any(
+                (getattr(u, "is_updated_geometry", False) or getattr(u, "is_updated_transform", False))
+                and hasattr(u, "id")
+                and isinstance(u.id, bpy.types.Object)
+                for u in depsgraph.updates
+            ):
+                return
+    _GEOM_CACHE_TOKEN += 1
+
+
+def install_geom_cache_handlers() -> None:
+    for hook in (
+        bpy.app.handlers.depsgraph_update_post,
+        bpy.app.handlers.undo_post,
+        bpy.app.handlers.redo_post,
+        bpy.app.handlers.load_post,
+    ):
+        if _bump_geom_cache_token not in hook:
+            hook.append(_bump_geom_cache_token)
+
+
+def uninstall_geom_cache_handlers() -> None:
+    for hook in (
+        bpy.app.handlers.depsgraph_update_post,
+        bpy.app.handlers.undo_post,
+        bpy.app.handlers.redo_post,
+        bpy.app.handlers.load_post,
+    ):
+        try:
+            hook.remove(_bump_geom_cache_token)
+        except ValueError:
+            pass
+
 
 class Spatial(bonsai.core.tool.Spatial):
+    _geom_cache: dict = {}
+
     @classmethod
     def get_spatial_props(cls) -> BIMSpatialDecompositionProperties:
         return bpy.context.scene.BIMSpatialDecompositionProperties
@@ -755,29 +802,114 @@ class Spatial(bonsai.core.tool.Spatial):
 
     # HERE STARTS SPATIAL TOOL
 
+    @classmethod
+    def get_or_build_geom_cache(cls) -> dict:
+        """Build or return a cached dict of IFC element shapes for space generation.
+
+        The cache is keyed on ``_GEOM_CACHE_TOKEN`` which is bumped by a
+        ``depsgraph_update_post`` handler when any Object geometry or transform
+        changes, and on undo/redo/load. This means the cache survives space
+        generations (which don't change Object geometry) but is correctly
+        invalidated when a user moves or edits a wall, slab, etc.
+
+        :return: ``{"shapes": {id: {"verts": ndarray, "faces": ndarray, "bottom_z": float, "top_z": float}}, "token": int}``
+        """
+        global _GEOM_CACHE_TOKEN
+        cached = cls._geom_cache.get("current")
+        if cached and cached["token"] == _GEOM_CACHE_TOKEN:
+            return cached
+
+        ifc_file = tool.Ifc.get()
+        include = []
+        for ifc_class in ifcopenshell.util.space.BOUNDING_CLASSES + ifcopenshell.util.space.HEIGHT_DETECTION_CLASSES:
+            include.extend(ifc_file.by_type(ifc_class))
+
+        settings = ifcopenshell.geom.settings()
+        settings.set("disable-opening-subtractions", True)
+        settings.set("use-world-coords", True)
+
+        shapes = {}
+        iterator = ifcopenshell.geom.iterator(settings, ifc_file, multiprocessing.cpu_count(), include=include)
+        if iterator.initialize():
+            while True:
+                shape = iterator.get()
+                verts = ifcopenshell.util.shape.get_shape_vertices(shape, shape.geometry)
+                faces = ifcopenshell.util.shape.get_faces(shape.geometry)
+                zs = verts[:, 2]
+                shapes[shape.id] = {
+                    "verts": verts,
+                    "faces": faces,
+                    "bottom_z": float(zs.min()),
+                    "top_z": float(zs.max()),
+                }
+                if not iterator.next():
+                    break
+
+        cache = {"shapes": shapes, "token": _GEOM_CACHE_TOKEN}
+        cls._geom_cache["current"] = cache
+        return cache
+
     @classmethod
     def is_bounding_class(cls, visible_element: ifcopenshell.entity_instance) -> bool:
-        for ifc_class in ["IfcWall", "IfcColumn", "IfcMember", "IfcVirtualElement", "IfcPlate"]:
+        for ifc_class in ifcopenshell.util.space.BOUNDING_CLASSES:
             if visible_element.is_a(ifc_class):
                 return True
         return False
 
     @classmethod
-    def get_space_polygon_from_context_visible_objects(
-        cls, x: float, y: float
-    ) -> Union[shapely.Polygon, Literal["NO POLYGONS FOUND", "NO POLYGON FOR POINT"]]:
-        boundary_lines = cls.get_boundary_lines_from_context_visible_objects()
-        unioned_boundaries = shapely.union_all(shapely.GeometryCollection(boundary_lines))
-        closed_polygons = shapely.polygonize(unioned_boundaries.geoms)
-        if not closed_polygons:
-            return "NO POLYGONS FOUND"
-        space_polygon = None
-        for polygon in closed_polygons.geoms:
-            if shapely.contains_xy(polygon, x, y):
-                space_polygon = shapely.force_3d(polygon)
-        if space_polygon is None:
-            return "NO POLYGON FOR POINT"
-        return space_polygon
+    def get_boundary_lines_from_ifc_elements(
+        cls,
+        cut_z: float,
+    ) -> tuple[list[shapely.LineString], list[ifcopenshell.entity_instance]]:
+        """Generate boundary lines by bisecting IFC element geometry with a horizontal plane.
+
+        Uses the class-level geometry cache (parallel iterator) instead of
+        iterating Blender visible objects. Works without any Blender objects
+        being loaded.
+
+        :param cut_z: Z elevation of the cutting plane in world coordinates.
+        :return: (boundary_lines, bounding_elements)
+        """
+        cache = cls.get_or_build_geom_cache()
+        return ifcopenshell.util.space.get_boundary_lines(tool.Ifc.get(), cache["shapes"], cut_z)
+
+    @classmethod
+    def get_space_polygon_from_context_visible_objects(cls, x: float, y: float) -> tuple[
+        Union[shapely.Polygon, Literal["NO POLYGONS FOUND", "NO POLYGON FOR POINT"]],
+        list[ifcopenshell.entity_instance],
+    ]:
+        props = tool.Model.get_model_props()
+        calculation_rl = props.rl3
+        container = tool.Root.get_default_container()
+        container_obj = tool.Ifc.get_object(container)
+        cut_z = container_obj.matrix_world.translation.z + calculation_rl
+
+        boundary_lines, bounding_elements = cls.get_boundary_lines_from_ifc_elements(cut_z)
+        polygon, _ = ifcopenshell.util.space.get_space_polygon(boundary_lines, x, y)
+        if isinstance(polygon, str):
+            return polygon, []
+        return polygon, bounding_elements
+
+    @classmethod
+    def get_auto_space_height(
+        cls,
+        space_polygon: shapely.Polygon,
+        base_z: float,
+        bounding_walls: list[ifcopenshell.entity_instance],
+    ) -> Optional[float]:
+        """Auto-detect space height from elements above using IFC geometry.
+
+        Delegates to :func:`ifcopenshell.util.space.get_auto_space_height`.
+
+        :param space_polygon: The space footprint polygon in world XY.
+        :param base_z: The space's base Z in world coordinates.
+        :param bounding_walls: List of IFC wall elements bounding the space.
+        :return: Detected height in SI (meters), or None if nothing found.
+        """
+        cache = cls.get_or_build_geom_cache()
+        return ifcopenshell.util.space.get_auto_space_height(
+            tool.Ifc.get(), cache["shapes"], space_polygon, base_z, bounding_walls
+        )
 
     @classmethod
     def debug_shape(cls, foo: shapely.Polygon) -> None:
@@ -810,7 +942,9 @@ class Spatial(bonsai.core.tool.Spatial):
         bpy.context.view_layer.update()
 
     @classmethod
-    def get_boundary_lines_from_context_visible_objects(cls) -> list[shapely.LineString]:
+    def get_boundary_lines_from_context_visible_objects(
+        cls,
+    ) -> tuple[list[shapely.LineString], list[ifcopenshell.entity_instance]]:
         props = tool.Model.get_model_props()
         calculation_rl = props.rl3
         container = tool.Root.get_default_container()
@@ -818,6 +952,7 @@ class Spatial(bonsai.core.tool.Spatial):
         cut_point = container_obj.matrix_world.translation.copy() + Vector((0, 0, calculation_rl))
         cut_normal = Vector((0, 0, 1))
         boundary_lines = []
+        bounding_elements = []
 
         for obj in bpy.context.visible_objects:
             visible_element = tool.Ifc.get_entity(obj)
@@ -831,6 +966,7 @@ class Spatial(bonsai.core.tool.Spatial):
             ):
                 continue
 
+            bounding_elements.append(visible_element)
             old_mesh = obj.data
             assert isinstance(old_mesh, bpy.types.Mesh)
             if visible_element.HasOpenings:
@@ -870,7 +1006,7 @@ class Spatial(bonsai.core.tool.Spatial):
                 start, end = tool.Drawing.extend_line(start, end, 0.05)
                 boundary_lines.append(shapely.LineString([start, end]))
 
-        return boundary_lines
+        return boundary_lines, bounding_elements
 
     @classmethod
     def get_gross_mesh_from_element(cls, visible_element: ifcopenshell.entity_instance) -> bpy.types.Mesh:

src/bonsai/bonsai/tool/wall.py

@@ -245,16 +245,9 @@ class Wall(bonsai.core.tool.Wall):
     @classmethod
     def iter_wall_slab_connections(cls, wall: ifcopenshell.entity_instance):
         """Yield ``(slab, rel)`` tuples for every ``IfcRelConnectsElements(TOP)``
-        connecting a slab to this wall — the rel kind ``extend_walls_to_underside``
-        creates. Walks ``wall.ConnectedFrom`` because the slab is the relating
-        side of the TOP rel."""
-        for rel in getattr(wall, "ConnectedFrom", []) or ():
-            if not rel.is_a("IfcRelConnectsElements") or rel.Description != "TOP":
-                continue
-            slab = rel.RelatingElement
-            if slab is None:
-                continue
-            yield slab, rel
+        connecting a slab to this wall. Delegates to
+        :func:`ifcopenshell.util.element.iter_top_connections`."""
+        yield from ifcopenshell.util.element.iter_top_connections(wall)
 
     @classmethod
     def iter_slab_wall_connections(cls, slab: ifcopenshell.entity_instance):

src/bonsai/test/core/test_covering.py

@@ -0,0 +1,112 @@
+# Bonsai - OpenBIM Blender Add-on
+# Copyright (C) 2021 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of Bonsai.
+#
+# Bonsai is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Bonsai is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
+#
+# This file was generated with the assistance of an AI coding tool.
+
+import pytest
+
+import bonsai
+import bonsai.core.covering as subject
+import bonsai.core.tool
+from test.core.bootstrap import Prophecy, ifc, root, spatial
+
+# NOTE: The Prophecy mocking framework serialises call arguments as JSON,
+# which means shapely geometry objects cannot be passed through mocked
+# calls.  We use the plain integer 42 as a serialisable stand-in for the
+# polygon return value; the test verifies the unpack behaviour (that the
+# polygon-like scalar 42 reaches set_covering_representation_from_polygon
+# instead of the tuple (42, []) which old code would have passed).
+
+
+@pytest.fixture
+def covering():
+    prophet = Prophecy(bonsai.core.tool.Covering)
+    yield prophet
+    prophet.verify()
+
+
+class TestAddInstanceFlooringCoveringFromCursor:
+    def test_run(self, ifc, root, spatial):
+        root.get_default_container().should_be_called().will_return("container")
+        spatial.get_active_obj().should_be_called().will_return(None)
+        spatial.get_selected_objects().should_be_called().will_return([])
+        spatial.get_relating_type_id().should_be_called().will_return(0)
+        spatial.get_x_y_z_h_mat_from_cursor().should_be_called().will_return((0, 0, 0, 3, None))
+
+        spatial.get_space_polygon_from_context_visible_objects(0, 0).should_be_called().will_return((42, []))
+        spatial.create_object("Covering").should_be_called().will_return("mock_obj")
+        spatial.set_obj_origin_to_cursor_position_and_zero_elevation("mock_obj").should_be_called()
+        spatial.translate_obj_to_z_location("mock_obj", 0).should_be_called()
+        spatial.assign_type_to_obj("mock_obj").should_be_called()
+        spatial.set_covering_representation_from_polygon("mock_obj", 42, polygon_is_si=True).should_be_called()
+
+        subject.add_instance_flooring_covering_from_cursor(ifc, root, spatial)
+
+    def test_raises_when_no_default_container(self, ifc, root, spatial):
+        root.get_default_container().should_be_called().will_return(None)
+        with pytest.raises(subject.NoDefaultContainer):
+            subject.add_instance_flooring_covering_from_cursor(ifc, root, spatial)
+
+
+class TestAddInstanceCeilingCoveringFromCursor:
+    def test_run(self, ifc, root, covering, spatial):
+        root.get_default_container().should_be_called().will_return("container")
+        spatial.get_active_obj().should_be_called().will_return(None)
+        spatial.get_selected_objects().should_be_called().will_return([])
+        spatial.get_relating_type_id().should_be_called().will_return(0)
+        covering.get_z_from_ceiling_height().should_be_called().will_return(3.0)
+        spatial.get_x_y_z_h_mat_from_cursor().should_be_called().will_return((0, 0, 0, 3, None))
+
+        spatial.get_space_polygon_from_context_visible_objects(0, 0).should_be_called().will_return((42, []))
+        spatial.create_object("Covering").should_be_called().will_return("mock_obj")
+        spatial.set_obj_origin_to_cursor_position_and_zero_elevation("mock_obj").should_be_called()
+        spatial.translate_obj_to_z_location("mock_obj", 3.0).should_be_called()
+        spatial.assign_type_to_obj("mock_obj").should_be_called()
+        spatial.set_covering_representation_from_polygon("mock_obj", 42, polygon_is_si=True).should_be_called()
+
+        subject.add_instance_ceiling_covering_from_cursor(ifc, root, covering, spatial)
+
+    def test_raises_when_no_default_container(self, ifc, root, covering, spatial):
+        root.get_default_container().should_be_called().will_return(None)
+        with pytest.raises(subject.NoDefaultContainer):
+            subject.add_instance_ceiling_covering_from_cursor(ifc, root, covering, spatial)
+
+
+class TestRegenSelectedCoveringObject:
+    def test_run(self, root, spatial):
+        root.get_default_container().should_be_called().will_return("container")
+        spatial.get_active_obj().should_be_called().will_return("active")
+        spatial.get_selected_objects().should_be_called().will_return(["active"])
+        spatial.get_x_y_z_h_mat_from_obj("active").should_be_called().will_return((2, 3, 1, 3, None))
+
+        spatial.get_space_polygon_from_context_visible_objects(2, 3).should_be_called().will_return((42, []))
+        spatial.set_covering_representation_from_polygon("active", 42, polygon_is_si=True).should_be_called()
+
+        subject.regen_selected_covering_object(root, spatial)
+
+    def test_raises_when_no_default_container(self, root, spatial):
+        root.get_default_container().should_be_called().will_return(None)
+        with pytest.raises(subject.NoDefaultContainer):
+            subject.regen_selected_covering_object(root, spatial)
+
+    def test_raises_when_no_active_selected(self, root, spatial):
+        root.get_default_container().should_be_called().will_return("container")
+        spatial.get_active_obj().should_be_called().will_return(None)
+        spatial.get_selected_objects().should_be_called().will_return([])
+        with pytest.raises(AssertionError):
+            subject.regen_selected_covering_object(root, spatial)

src/bonsai/test/tool/test_spatial.py

@@ -24,12 +24,14 @@ import ifcopenshell.api.feature
 import ifcopenshell.api.nest
 import ifcopenshell.api.root
 import ifcopenshell.api.spatial
+import ifcopenshell.util.representation
 import numpy as np
 from mathutils import Matrix
 
 import bonsai.core.tool
 import bonsai.tool as tool
 from bonsai.tool.spatial import Spatial as subject
+from bonsai.tool.spatial import _bump_geom_cache_token
 from test.bim.bootstrap import NewFile
 
 
@@ -258,17 +260,44 @@ class TestSelectProducts(NewFile):
         assert obj in bpy.context.selected_objects
 
 
+class _BlockHelper:
+    """Shared helpers for creating IFC walls/slabs with solid-block representations."""
+
+    @staticmethod
+    def create_wall(ifc, height=10.0):
+        """Create an IFC wall with a 10x10x{height} block representation from z=0."""
+        ctx = ifcopenshell.util.representation.get_context(ifc, "Model", "Body", "MODEL_VIEW")
+        wall = ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcWall")
+        placement_2d = ifc.createIfcAxis2Placement2D(ifc.createIfcCartesianPoint([0.0, 0.0]))
+        profile = ifc.createIfcRectangleProfileDef("AREA", None, placement_2d, 10.0, 10.0)
+        placement_3d = ifc.createIfcAxis2Placement3D(ifc.createIfcCartesianPoint([-5.0, -5.0, 0.0]))
+        extrusion = ifc.createIfcExtrudedAreaSolid(
+            profile, placement_3d, ifc.createIfcDirection([0.0, 0.0, 1.0]), height
+        )
+        shape_rep = ifc.createIfcShapeRepresentation(ctx, "Body", "SweptSolid", [extrusion])
+        wall.Representation = ifc.createIfcProductDefinitionShape(None, None, [shape_rep])
+        return wall, extrusion
+
+    @staticmethod
+    def create_slab(ifc, z=4.0):
+        """Create an IfcSlab with a 12x12x1.0 block representation at bottom_z={z}."""
+        ctx = ifcopenshell.util.representation.get_context(ifc, "Model", "Body", "MODEL_VIEW")
+        slab = ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcSlab")
+        placement_2d = ifc.createIfcAxis2Placement2D(ifc.createIfcCartesianPoint([0.0, 0.0]))
+        profile = ifc.createIfcRectangleProfileDef("AREA", None, placement_2d, 12.0, 12.0)
+        placement_3d = ifc.createIfcAxis2Placement3D(ifc.createIfcCartesianPoint([-6.0, -6.0, z]))
+        extrusion = ifc.createIfcExtrudedAreaSolid(profile, placement_3d, ifc.createIfcDirection([0.0, 0.0, 1.0]), 1.0)
+        shape_rep = ifc.createIfcShapeRepresentation(ctx, "Body", "SweptSolid", [extrusion])
+        slab.Representation = ifc.createIfcProductDefinitionShape(None, None, [shape_rep])
+
+
 class TestGenerateSpace(NewFile):
     def test_generate_space_at_cursor(self):
         bpy.ops.bim.create_project()
         ifc = tool.Ifc.get()
-        scene = bpy.context.scene
-        product = ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcWall")
-        bpy.ops.mesh.primitive_cube_add(size=10, location=(0, 0, 4))
-        obj = bpy.data.objects["Cube"]
-        scene.collection.objects.link(obj)
-        tool.Ifc.link(product, obj)
-        scene.cursor.location = (0, 0, 0)
+        # The wall block spans z=0..10, bisects to a 10x10 polygon at cut_z.
+        _BlockHelper.create_wall(ifc, height=10.0)
+        bpy.context.scene.cursor.location = (0, 0, 0)
 
         bpy.ops.bim.generate_space()
         space = bpy.data.objects["IfcSpace/Space"]
@@ -292,13 +321,8 @@ class TestGenerateSpace(NewFile):
     def test_regenerate_space_preserves_z_location(self):
         bpy.ops.bim.create_project()
         ifc = tool.Ifc.get()
-        scene = bpy.context.scene
-        product = ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcWall")
-        bpy.ops.mesh.primitive_cube_add(size=10, location=(0, 0, 4))
-        obj = bpy.data.objects["Cube"]
-        scene.collection.objects.link(obj)
-        tool.Ifc.link(product, obj)
-        scene.cursor.location = (0, 0, 0)
+        _BlockHelper.create_wall(ifc, height=10.0)
+        bpy.context.scene.cursor.location = (0, 0, 0)
 
         bpy.ops.bim.generate_space()
         space = bpy.data.objects["IfcSpace/Space"]
@@ -307,8 +331,158 @@ class TestGenerateSpace(NewFile):
 
         bpy.context.view_layer.objects.active = space
         space.select_set(True)
-        obj.select_set(False)
 
         bpy.ops.bim.generate_space()
 
         assert np.isclose(space.location.z, 5), f"Expected z=5, got {space.location.z}"
+
+    def test_auto_space_height_from_slab_above(self):
+        bpy.ops.bim.create_project()
+        ifc = tool.Ifc.get()
+        _BlockHelper.create_wall(ifc, height=10.0)
+        _BlockHelper.create_slab(ifc, z=4.0)
+        bpy.context.scene.cursor.location = (0, 0, 0)
+
+        bpy.ops.bim.generate_space()
+        space = bpy.data.objects["IfcSpace/Space"]
+        assert np.isclose(space.dimensions.z, 4, atol=0.1), f"Expected height ~4, got {space.dimensions.z}"
+
+    def test_forced_space_height(self):
+        bpy.ops.bim.create_project()
+        ifc = tool.Ifc.get()
+        _BlockHelper.create_wall(ifc, height=10.0)
+        bpy.context.scene.cursor.location = (0, 0, 0)
+
+        spatial_props = tool.Spatial.get_spatial_props()
+        spatial_props.force_space_height = True
+        spatial_props.space_height = 5
+        bpy.ops.bim.generate_space()
+        space = bpy.data.objects["IfcSpace/Space"]
+        assert np.isclose(space.dimensions.z, 5, atol=0.1), f"Expected height 5, got {space.dimensions.z}"
+
+    def test_auto_space_height_fallback_no_slab(self):
+        bpy.ops.bim.create_project()
+        ifc = tool.Ifc.get()
+        _BlockHelper.create_wall(ifc, height=10.0)
+        bpy.context.scene.cursor.location = (0, 0, 0)
+
+        spatial_props = tool.Spatial.get_spatial_props()
+        spatial_props.force_space_height = False
+        bpy.ops.bim.generate_space()
+        space = bpy.data.objects["IfcSpace/Space"]
+        assert space.dimensions.z > 0, f"Expected positive height, got {space.dimensions.z}"
+
+    def test_apply_space_height_to_selection(self):
+        bpy.ops.bim.create_project()
+        ifc = tool.Ifc.get()
+        _BlockHelper.create_wall(ifc, height=10.0)
+        bpy.context.scene.cursor.location = (0, 0, 0)
+
+        bpy.ops.bim.generate_space()
+        space = bpy.data.objects["IfcSpace/Space"]
+
+        spatial_props = tool.Spatial.get_spatial_props()
+        spatial_props.space_height = 6
+        bpy.context.view_layer.objects.active = space
+        space.select_set(True)
+
+        bpy.ops.bim.apply_space_height_to_selection()
+        bpy.context.view_layer.update()
+        assert np.isclose(space.dimensions.z, 6, atol=0.1), f"Expected height 6, got {space.dimensions.z}"
+
+    def test_cache_survives_second_generation(self):
+        bpy.ops.bim.create_project()
+        ifc = tool.Ifc.get()
+        _BlockHelper.create_wall(ifc, height=10.0)
+        bpy.context.scene.cursor.location = (0, 0, 0)
+
+        bpy.ops.bim.generate_space()
+        space1 = bpy.data.objects["IfcSpace/Space"]
+        height1 = space1.dimensions.z
+
+        bpy.ops.bim.generate_space()
+        space2 = bpy.data.objects["IfcSpace/Space"]
+        height2 = space2.dimensions.z
+
+        assert np.isclose(height1, height2, atol=0.1), f"Cache changed height: {height1} vs {height2}"
+
+    def test_regenerate_after_wall_height_change(self):
+        bpy.ops.bim.create_project()
+        ifc = tool.Ifc.get()
+        wall, extrusion = _BlockHelper.create_wall(ifc, height=10.0)
+        bpy.context.scene.cursor.location = (0, 0, 0)
+
+        bpy.ops.bim.generate_space()
+        space = bpy.data.objects["IfcSpace/Space"]
+        original_height = space.dimensions.z
+
+        # Modify the IFC representation to change the wall height.
+        extrusion.Depth = 15.0
+        _bump_geom_cache_token()
+
+        bpy.context.view_layer.objects.active = space
+        space.select_set(True)
+
+        bpy.ops.bim.generate_space()
+        new_height = space.dimensions.z
+        assert new_height != original_height or new_height > 0
+
+    def test_regenerate_space_from_centered_cube_representation(self):
+        bpy.ops.bim.create_project()
+        ifc = tool.Ifc.get()
+        _BlockHelper.create_wall(ifc, height=10.0)
+        scene = bpy.context.scene
+        scene.cursor.location = (0, 0, 0)
+
+        # Create a space with a unit cube PolygonalFaceSet centered at local origin.
+        ctx = ifcopenshell.util.representation.get_context(ifc, "Model", "Body", "MODEL_VIEW")
+        points = ifc.createIfcCartesianPointList3D(
+            [
+                (-0.5, -0.5, -0.5),
+                (-0.5, -0.5, 0.5),
+                (-0.5, 0.5, -0.5),
+                (-0.5, 0.5, 0.5),
+                (0.5, -0.5, -0.5),
+                (0.5, -0.5, 0.5),
+                (0.5, 0.5, -0.5),
+                (0.5, 0.5, 0.5),
+            ]
+        )
+        faces = [
+            ifc.createIfcIndexedPolygonalFace([1, 2, 4, 3]),
+            ifc.createIfcIndexedPolygonalFace([3, 4, 8, 7]),
+            ifc.createIfcIndexedPolygonalFace([7, 8, 6, 5]),
+            ifc.createIfcIndexedPolygonalFace([5, 6, 2, 1]),
+            ifc.createIfcIndexedPolygonalFace([3, 7, 5, 1]),
+            ifc.createIfcIndexedPolygonalFace([8, 4, 2, 6]),
+        ]
+        face_set = ifc.createIfcPolygonalFaceSet(points, closed=True, faces=faces)
+        shape_rep = ifc.createIfcShapeRepresentation(ctx, "Body", "Tessellation", [face_set])
+
+        space_element = ifcopenshell.api.root.create_entity(ifc, ifc_class="IfcSpace")
+        space_element.Representation = ifc.createIfcProductDefinitionShape(None, None, [shape_rep])
+
+        bpy.ops.mesh.primitive_cube_add(size=1, location=(0, 0, 5))
+        obj = bpy.data.objects["Cube"]
+        scene.collection.objects.link(obj)
+        tool.Ifc.link(space_element, obj)
+        bpy.context.view_layer.update()
+        obj.name = "MySpace"
+
+        # Check the cube's world bottom Z before regeneration.
+        bottom_z = (obj.matrix_world @ Vector(obj.bound_box[0])).z
+        assert np.isclose(bottom_z, 4.5), f"Expected bottom_z=4.5, got {bottom_z}"
+
+        # Regenerate the space.
+        bpy.context.view_layer.objects.active = obj
+        obj.select_set(True)
+        bpy.ops.bim.generate_space()
+
+        mesh = obj.data
+        assert isinstance(mesh, bpy.types.Mesh)
+        verts = [v.co.z for v in mesh.vertices]
+        min_z = min(verts)
+        max_z = max(verts)
+        assert min_z >= 0, f"Expected extrusion to start at local z>=0, got min_z={min_z}"
+        assert max_z > 0, f"Expected extrusion to have positive height, got max_z={max_z}"
+        assert np.isclose(obj.location.z, 4.5, atol=0.01), f"Expected location.z=4.5, got {obj.location.z}"

src/ifcopenshell-python/ifcopenshell/util/element.py

@@ -2007,3 +2007,24 @@ def get_material_profiles(element: ifcopenshell.entity_instance) -> list[Priorit
         )
         for material_profile in material.MaterialProfiles
     ]
+
+
+def iter_top_connections(
+    element: ifcopenshell.entity_instance,
+) -> Generator[tuple[ifcopenshell.entity_instance, ifcopenshell.entity_instance], None, None]:
+    """Yield ``(connected_element, rel)`` tuples for every
+    ``IfcRelConnectsElements`` with ``Description == "TOP"`` connecting
+    to this element.
+
+    Walks ``element.ConnectedFrom`` because the connecting element (e.g. a
+    slab) is the relating side of the TOP relationship.
+
+    :param element: The IFC element (typically a wall).
+    :return: Generator of ``(connected_element, rel)`` tuples.
+    """
+    for rel in getattr(element, "ConnectedFrom", []) or ():
+        if not rel.is_a("IfcRelConnectsElements") or rel.Description != "TOP":
+            continue
+        connected = rel.RelatingElement
+        if connected is not None:
+            yield connected, rel

src/ifcopenshell-python/ifcopenshell/util/shape.py

@@ -752,3 +752,81 @@ def get_total_edge_length(geometry: W.triangulation) -> float:
     vertices = get_vertices(geometry)
     vertices = vertices[get_edges(geometry)]
     return np.linalg.norm(vertices[:, 1] - vertices[:, 0], axis=1).sum().item()
+
+
+def _extend_line(start: np.ndarray, end: np.ndarray, distance: float) -> tuple[np.ndarray, np.ndarray]:
+    """Extend a line segment by a fixed distance on both ends.
+
+    :param start: (x, y) or (x, y, z) array.
+    :param end: (x, y) or (x, y, z) array.
+    :param distance: Distance to extend on each end.
+    :return: (new_start, new_end) arrays.
+    """
+    direction = end - start
+    norm = np.linalg.norm(direction)
+    if norm == 0:
+        return start, end
+    offset = distance * (direction / norm)
+    return start - offset, end + offset
+
+
+def bisect_mesh_plane_vf(
+    verts: npt.NDArray[np.float64],
+    faces: npt.NDArray[np.int32],
+    plane_z: float,
+    *,
+    precision: int = 3,
+    extend: float = 0.0,
+) -> list:
+    """Intersect a triangulated mesh with a horizontal Z plane.
+
+    All faces are processed at once via numpy broadcasting for performance.
+
+    :param verts: (n, 3) array of vertices in world coordinates.
+    :param faces: (m, 3) array of triangle vertex indices.
+    :param plane_z: Z elevation of the horizontal cutting plane.
+    :param precision: Decimal places to round intersection point coordinates to.
+    :param extend: Distance to extend each segment on both ends, to ensure
+        overlap with neighbouring segments for polygon closure.
+    :return: List of (start_xy, end_xy) tuples where each coordinate is (x, y).
+    """
+    if len(faces) == 0:
+        return []
+    v0 = verts[faces[:, 0]]
+    v1 = verts[faces[:, 1]]
+    v2 = verts[faces[:, 2]]
+    d0 = v0[:, 2] - plane_z
+    d1 = v1[:, 2] - plane_z
+    d2 = v2[:, 2] - plane_z
+    straddle = ~((np.minimum(np.minimum(d0, d1), d2) > 0) | (np.maximum(np.maximum(d0, d1), d2) < 0))
+    if not np.any(straddle):
+        return []
+    idx = np.where(straddle)[0]
+    d0s, d1s, d2s = d0[idx], d1[idx], d2[idx]
+    v0s, v1s, v2s = v0[idx], v1[idx], v2[idx]
+
+    def _edge_intersections(va, vb, da, db):
+        mask = da * db < 0
+        diff = da - db
+        diff = np.where(diff == 0, 1.0, diff)
+        t = np.where(mask, da / diff, 0.0)
+        pts = va + t[:, np.newaxis] * (vb - va)
+        return pts, mask
+
+    p01, m01 = _edge_intersections(v0s, v1s, d0s, d1s)
+    p12, m12 = _edge_intersections(v1s, v2s, d1s, d2s)
+    p20, m20 = _edge_intersections(v2s, v0s, d2s, d0s)
+
+    segments = []
+    for i in range(len(idx)):
+        pts_xy = []
+        for pt, mask in ((p01[i], m01[i]), (p12[i], m12[i]), (p20[i], m20[i])):
+            if mask:
+                pts_xy.append((round(float(pt[0]), precision), round(float(pt[1]), precision)))
+        if len(pts_xy) == 2 and pts_xy[0] != pts_xy[1]:
+            if extend > 0:
+                s, e = _extend_line(np.array(pts_xy[0]), np.array(pts_xy[1]), extend)
+                segments.append((s.tolist(), e.tolist()))
+            else:
+                segments.append(pts_xy)
+    return segments

src/ifcopenshell-python/ifcopenshell/util/space.py

@@ -0,0 +1,246 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2026 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Blender-independent utilities for space geometry generation.
+
+These functions operate on IFC geometry data (vertices, faces, element
+relationships) without requiring any Blender objects to be loaded. They are
+used by Bonsai's space generation pipeline but can also be used standalone
+for IFC analysis.
+"""
+
+from __future__ import annotations
+
+from typing import Optional, Union
+
+import ifcopenshell
+import ifcopenshell.util.element
+import ifcopenshell.util.shape
+import shapely
+
+BOUNDING_CLASSES = ("IfcWall", "IfcColumn", "IfcMember", "IfcVirtualElement", "IfcPlate")
+HEIGHT_DETECTION_CLASSES = ("IfcSlab", "IfcRoof")
+
+
+def get_boundary_lines(
+    ifc_file: ifcopenshell.file,
+    shapes: dict,
+    cut_z: float,
+    bounding_classes: tuple = BOUNDING_CLASSES,
+) -> tuple[list[shapely.LineString], list[ifcopenshell.entity_instance]]:
+    """Generate boundary lines by bisecting IFC element geometry with a horizontal plane.
+
+    :param ifc_file: The IFC file.
+    :param shapes: Dict of element shapes keyed by element id, as produced by
+        a geometry cache. Each entry must have ``verts`` (n,3 ndarray),
+        ``faces`` (m,3 ndarray), ``bottom_z`` (float), ``top_z`` (float).
+    :param cut_z: Z elevation of the cutting plane in world coordinates.
+    :param bounding_classes: IFC classes to treat as space-bounding elements.
+    :return: ``(boundary_lines, bounding_elements)`` where boundary_lines is a
+        list of shapely LineString segments and bounding_elements is a list of
+        IFC entity instances that intersect the cutting plane.
+    """
+    boundary_lines: list[shapely.LineString] = []
+    bounding_elements: list[ifcopenshell.entity_instance] = []
+
+    for element_id, shape_data in shapes.items():
+        element = ifc_file.by_id(element_id)
+        if not any(element.is_a(cls) for cls in bounding_classes):
+            continue
+        if cut_z <= shape_data["bottom_z"] or cut_z >= shape_data["top_z"]:
+            continue
+        bounding_elements.append(element)
+        segments = ifcopenshell.util.shape.bisect_mesh_plane_vf(
+            shape_data["verts"], shape_data["faces"], cut_z, precision=3, extend=0.05
+        )
+        for start, end in segments:
+            boundary_lines.append(shapely.LineString([start, end]))
+
+    return boundary_lines, bounding_elements
+
+
+def get_space_polygon(
+    boundary_lines: list[shapely.LineString],
+    x: float,
+    y: float,
+) -> tuple[Union[shapely.Polygon, str], list]:
+    """Assemble boundary lines into closed polygons and find the one containing (x, y).
+
+    :param boundary_lines: List of shapely LineString segments forming a planar graph.
+    :param x: X coordinate of the point to test.
+    :param y: Y coordinate of the point to test.
+    :return: ``(polygon, [])`` on success, or ``("NO POLYGONS FOUND", [])`` /
+        ``("NO POLYGON FOR POINT", [])`` on failure. The second element is
+        reserved for bounding elements (returned by the caller from
+        :func:`get_boundary_lines`).
+    """
+    unioned = shapely.union_all(shapely.GeometryCollection(boundary_lines))
+    closed_polygons = shapely.polygonize(unioned.geoms)
+    if not closed_polygons:
+        return "NO POLYGONS FOUND", []
+    for polygon in closed_polygons.geoms:
+        if shapely.contains_xy(polygon, x, y):
+            return shapely.force_3d(polygon), []
+    return "NO POLYGON FOR POINT", []
+
+
+def get_auto_space_height(
+    ifc_file: ifcopenshell.file,
+    shapes: dict,
+    space_polygon: shapely.Polygon,
+    base_z: float,
+    bounding_walls: list[ifcopenshell.entity_instance],
+) -> Optional[float]:
+    """Auto-detect space height from elements above using IFC geometry.
+
+    Detection priority:
+    1. ``IfcRelConnectsElements`` (TOP) connections on bounding walls
+    2. ``IfcSlab`` / ``IfcRoof`` elements above with XY overlap to the space polygon
+    3. Minimum wall top Z of bounding walls
+
+    :param ifc_file: The IFC file.
+    :param shapes: Dict of element shapes keyed by element id (see :func:`get_boundary_lines`).
+    :param space_polygon: The space footprint polygon in world XY.
+    :param base_z: The space's base Z in world coordinates.
+    :param bounding_walls: List of IFC wall elements bounding the space.
+    :return: Detected height in meters, or ``None`` if nothing found.
+    """
+    height = get_height_from_top_connections(ifc_file, shapes, bounding_walls, base_z, space_polygon)
+    if height is not None and height > 0:
+        return height
+
+    height = get_height_from_elements_above(ifc_file, shapes, space_polygon, base_z)
+    if height is not None and height > 0:
+        return height
+
+    height = get_height_from_wall_tops(shapes, bounding_walls, base_z)
+    if height is not None and height > 0:
+        return height
+
+    return None
+
+
+def get_height_from_top_connections(
+    ifc_file: ifcopenshell.file,
+    shapes: dict,
+    bounding_walls: list[ifcopenshell.entity_instance],
+    base_z: float,
+    space_polygon: shapely.Polygon,
+) -> Optional[float]:
+    """Find the lowest bottom face of elements connected to bounding walls via IfcRelConnectsElements(TOP).
+
+    :param ifc_file: The IFC file.
+    :param shapes: Dict of element shapes keyed by element id.
+    :param bounding_walls: List of IFC wall elements.
+    :param base_z: The space's base Z in world coordinates.
+    :param space_polygon: The space footprint polygon in world XY.
+    :return: Height in meters, or ``None``.
+    """
+    lowest_min_z: Optional[float] = None
+    for wall_element in bounding_walls:
+        for connected_element, _rel in ifcopenshell.util.element.iter_top_connections(wall_element):
+            if not (connected_element.is_a("IfcSlab") or connected_element.is_a("IfcRoof")):
+                continue
+            shape_data = shapes.get(connected_element.id())
+            if not shape_data:
+                continue
+            min_z = shape_data["bottom_z"]
+            if min_z <= base_z:
+                continue
+            verts = shape_data["verts"]
+            element_box = shapely.box(
+                float(verts[:, 0].min()),
+                float(verts[:, 1].min()),
+                float(verts[:, 0].max()),
+                float(verts[:, 1].max()),
+            )
+            if not element_box.intersects(space_polygon):
+                continue
+            if lowest_min_z is None or min_z < lowest_min_z:
+                lowest_min_z = min_z
+    if lowest_min_z is not None:
+        return lowest_min_z - base_z
+    return None
+
+
+def get_height_from_elements_above(
+    ifc_file: ifcopenshell.file,
+    shapes: dict,
+    space_polygon: shapely.Polygon,
+    base_z: float,
+    height_classes: tuple = HEIGHT_DETECTION_CLASSES,
+) -> Optional[float]:
+    """Find the lowest IfcSlab / IfcRoof above whose XY bbox overlaps the space polygon.
+
+    :param ifc_file: The IFC file.
+    :param shapes: Dict of element shapes keyed by element id.
+    :param space_polygon: The space footprint polygon in world XY.
+    :param base_z: The space's base Z in world coordinates.
+    :param height_classes: IFC classes to consider as ceiling elements.
+    :return: Height in meters, or ``None``.
+    """
+    lowest_min_z: Optional[float] = None
+    for ifc_class in height_classes:
+        for element in ifc_file.by_type(ifc_class):
+            shape_data = shapes.get(element.id())
+            if not shape_data:
+                continue
+            min_z = shape_data["bottom_z"]
+            if min_z <= base_z:
+                continue
+            verts = shape_data["verts"]
+            element_box = shapely.box(
+                float(verts[:, 0].min()),
+                float(verts[:, 1].min()),
+                float(verts[:, 0].max()),
+                float(verts[:, 1].max()),
+            )
+            if not element_box.intersects(space_polygon):
+                continue
+            if lowest_min_z is None or min_z < lowest_min_z:
+                lowest_min_z = min_z
+    if lowest_min_z is not None:
+        return lowest_min_z - base_z
+    return None
+
+
+def get_height_from_wall_tops(
+    shapes: dict,
+    bounding_walls: list[ifcopenshell.entity_instance],
+    base_z: float,
+) -> Optional[float]:
+    """Find the minimum wall top Z among bounding walls.
+
+    :param shapes: Dict of element shapes keyed by element id.
+    :param bounding_walls: List of IFC wall elements.
+    :param base_z: The space's base Z in world coordinates.
+    :return: Height in meters, or ``None``.
+    """
+    lowest_top_z: Optional[float] = None
+    for wall_element in bounding_walls:
+        shape_data = shapes.get(wall_element.id())
+        if not shape_data:
+            continue
+        max_z = shape_data["top_z"]
+        if max_z <= base_z:
+            continue
+        if lowest_top_z is None or max_z < lowest_top_z:
+            lowest_top_z = max_z
+    if lowest_top_z is not None:
+        return lowest_top_z - base_z
+    return None

src/ifcopenshell-python/test/util/test_element.py

@@ -1392,3 +1392,47 @@ class TestCopyDeepIFC4(test.bootstrap.IFC4):
         element2 = subject.copy_deep(self.file, element)
         assert element2.Segments[0][0] == (1, 2)
         assert element2.Segments[1][0] == (3, 4)
+
+
+class TestIterTopConnections(test.bootstrap.IFC4):
+    def test_yields_top_connected_element(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        slab = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcSlab")
+        rel = self.file.createIfcRelConnectsElements(
+            GlobalId=ifcopenshell.guid.new(),
+            RelatingElement=slab,
+            RelatedElement=wall,
+            Description="TOP",
+        )
+        results = list(subject.iter_top_connections(wall))
+        assert len(results) == 1
+        assert results[0][0] == slab
+        assert results[0][1] == rel
+
+    def test_returns_empty_when_no_connections(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        assert list(subject.iter_top_connections(wall)) == []
+
+    def test_filters_non_top_description(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        slab = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcSlab")
+        self.file.createIfcRelConnectsElements(
+            GlobalId=ifcopenshell.guid.new(),
+            RelatingElement=slab,
+            RelatedElement=wall,
+            Description="BOTTOM",
+        )
+        assert list(subject.iter_top_connections(wall)) == []
+
+    def test_filters_non_rel_connects_elements(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        slab = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcSlab")
+        self.file.createIfcRelConnectsPathElements(
+            GlobalId=ifcopenshell.guid.new(),
+            RelatingElement=slab,
+            RelatedElement=wall,
+            Description="ATPATH",
+            RelatingConnectionType="ATPATH",
+            RelatedConnectionType="ATPATH",
+        )
+        assert list(subject.iter_top_connections(wall)) == []

src/ifcopenshell-python/test/util/test_shape.py

@@ -0,0 +1,97 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2026 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import numpy as np
+
+import ifcopenshell.util.shape as subject
+
+
+def _cube_verts_faces(size=2.0, z_offset=0.0):
+    """Build a triangulated cube as (verts, faces) numpy arrays."""
+    s = size / 2
+    verts = np.array(
+        [
+            [-s, -s, -s + z_offset],
+            [s, -s, -s + z_offset],
+            [s, s, -s + z_offset],
+            [-s, s, -s + z_offset],
+            [-s, -s, s + z_offset],
+            [s, -s, s + z_offset],
+            [s, s, s + z_offset],
+            [-s, s, s + z_offset],
+        ],
+        dtype=np.float64,
+    )
+    faces = np.array(
+        [
+            [0, 1, 2],
+            [0, 2, 3],
+            [4, 6, 5],
+            [4, 7, 6],
+            [0, 4, 5],
+            [0, 5, 1],
+            [1, 5, 6],
+            [1, 6, 2],
+            [2, 6, 7],
+            [2, 7, 3],
+            [3, 7, 4],
+            [3, 4, 0],
+        ],
+        dtype=np.int32,
+    )
+    return verts, faces
+
+
+class TestBisectMeshPlaneVf:
+    def test_bisect_at_mid_height(self):
+        verts, faces = _cube_verts_faces(size=2.0)
+        segments = subject.bisect_mesh_plane_vf(verts, faces, plane_z=0.0)
+        assert len(segments) >= 4
+        for start, end in segments:
+            assert len(start) == 2
+            assert len(end) == 2
+
+    def test_bisect_above_mesh_returns_empty(self):
+        verts, faces = _cube_verts_faces(size=2.0)
+        segments = subject.bisect_mesh_plane_vf(verts, faces, plane_z=10.0)
+        assert segments == []
+
+    def test_bisect_below_mesh_returns_empty(self):
+        verts, faces = _cube_verts_faces(size=2.0)
+        segments = subject.bisect_mesh_plane_vf(verts, faces, plane_z=-10.0)
+        assert segments == []
+
+    def test_bisect_with_extend(self):
+        verts, faces = _cube_verts_faces(size=2.0)
+        segments_no_extend = subject.bisect_mesh_plane_vf(verts, faces, plane_z=0.0, extend=0.0)
+        segments_extend = subject.bisect_mesh_plane_vf(verts, faces, plane_z=0.0, extend=0.05)
+        assert len(segments_extend) == len(segments_no_extend)
+        for (s_ext, e_ext), (s_no, e_no) in zip(segments_extend, segments_no_extend):
+            assert abs(s_ext[0] - s_no[0]) >= 0.04 or abs(s_ext[1] - s_no[1]) >= 0.04
+
+    def test_bisect_empty_faces(self):
+        verts = np.array([[0, 0, 0], [1, 0, 0], [0, 1, 0]], dtype=np.float64)
+        faces = np.array([], dtype=np.int32).reshape(0, 3)
+        assert subject.bisect_mesh_plane_vf(verts, faces, plane_z=0.0) == []
+
+    def test_bisect_precision(self):
+        verts, faces = _cube_verts_faces(size=2.0)
+        segments = subject.bisect_mesh_plane_vf(verts, faces, plane_z=0.0, precision=6)
+        for start, end in segments:
+            for coord in start + end:
+                assert round(coord, 6) == coord

src/ifcopenshell-python/test/util/test_space.py

@@ -0,0 +1,186 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2026 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import ifcopenshell.api.geometry
+import ifcopenshell.api.root
+import ifcopenshell.geom
+import ifcopenshell.guid
+import ifcopenshell.util.shape
+import ifcopenshell.util.space as subject
+import pytest
+import shapely
+import test.bootstrap
+
+
+def _build_shapes_dict(ifc_file, elements):
+    """Build a shapes dict as expected by ifcopenshell.util.space functions."""
+    settings = ifcopenshell.geom.settings()
+    settings.set("disable-opening-subtractions", True)
+    settings.set("use-world-coords", True)
+    shapes = {}
+    for element in elements:
+        shape = ifcopenshell.geom.create_shape(settings, element)
+        verts = ifcopenshell.util.shape.get_shape_vertices(shape, shape.geometry)
+        faces = ifcopenshell.util.shape.get_faces(shape.geometry)
+        zs = verts[:, 2]
+        shapes[element.id()] = {
+            "verts": verts,
+            "faces": faces,
+            "bottom_z": float(zs.min()),
+            "top_z": float(zs.max()),
+        }
+    return shapes
+
+
+def _add_extruded_body(ifc_file, element, coords_2d, depth, z_offset=0.0):
+    """Add a body representation (extruded polyline) to an element."""
+    if not ifc_file.by_type("IfcProject"):
+        ifcopenshell.api.root.create_entity(ifc_file, ifc_class="IfcProject")
+    ctx = ifc_file.createIfcGeometricRepresentationContext(
+        ContextType="Model",
+        CoordinateSpaceDimension=3,
+        Precision=1e-5,
+        WorldCoordinateSystem=ifc_file.createIfcAxis2Placement3D(
+            ifc_file.createIfcCartesianPoint((0.0, 0.0, 0.0)),
+            ifc_file.createIfcDirection((0.0, 0.0, 1.0)),
+            ifc_file.createIfcDirection((1.0, 0.0, 0.0)),
+        ),
+    )
+    sub_ctx = ifc_file.createIfcGeometricRepresentationSubContext(
+        ContextIdentifier="Body",
+        ContextType="Model",
+        ParentContext=ctx,
+        TargetView="MODEL_VIEW",
+    )
+    pts = [ifc_file.createIfcCartesianPoint((float(x), float(y))) for x, y in coords_2d]
+    polyline = ifc_file.createIfcPolyline(pts)
+    profile = ifc_file.create_entity("IfcArbitraryClosedProfileDef", ProfileType="CURVE", OuterCurve=polyline)
+    placement = ifc_file.createIfcAxis2Placement3D(
+        ifc_file.createIfcCartesianPoint((0.0, 0.0, z_offset)),
+        ifc_file.createIfcDirection((0.0, 0.0, 1.0)),
+        ifc_file.createIfcDirection((1.0, 0.0, 0.0)),
+    )
+    direction = ifc_file.createIfcDirection((0.0, 0.0, 1.0))
+    solid = ifc_file.createIfcExtrudedAreaSolid(profile, placement, direction, depth)
+    rep = ifc_file.create_entity(
+        "IfcShapeRepresentation",
+        ContextOfItems=sub_ctx,
+        RepresentationIdentifier="Body",
+        RepresentationType="SweptSolid",
+        Items=[solid],
+    )
+    ifcopenshell.api.geometry.assign_representation(ifc_file, product=element, representation=rep)
+
+
+class TestGetBoundaryLines(test.bootstrap.IFC4):
+    def test_returns_segments_for_intersecting_walls(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        _add_extruded_body(self.file, wall, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 3.0)
+        shapes = _build_shapes_dict(self.file, [wall])
+        lines, bounding = subject.get_boundary_lines(self.file, shapes, cut_z=1.0)
+        assert len(lines) > 0
+        assert wall in bounding
+
+    def test_skips_elements_not_intersecting_plane(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        _add_extruded_body(self.file, wall, [[-1, -1], [1, -1], [1, 1], [-1, 1]], 1.0)
+        shapes = _build_shapes_dict(self.file, [wall])
+        lines, bounding = subject.get_boundary_lines(self.file, shapes, cut_z=10.0)
+        assert lines == []
+        assert bounding == []
+
+    def test_skips_non_bounding_classes(self):
+        slab = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcSlab")
+        _add_extruded_body(self.file, slab, [[-1, -1], [1, -1], [1, 1], [-1, 1]], 1.0)
+        shapes = _build_shapes_dict(self.file, [slab])
+        lines, bounding = subject.get_boundary_lines(self.file, shapes, cut_z=0.5)
+        assert slab not in bounding
+
+
+class TestGetSpacePolygon(test.bootstrap.IFC4):
+    def test_finds_containing_polygon(self):
+        lines = [
+            shapely.LineString([(0, 0), (10, 0)]),
+            shapely.LineString([(10, 0), (10, 10)]),
+            shapely.LineString([(10, 10), (0, 10)]),
+            shapely.LineString([(0, 10), (0, 0)]),
+        ]
+        polygon, _ = subject.get_space_polygon(lines, 5, 5)
+        assert not isinstance(polygon, str)
+        assert polygon.area == pytest.approx(100)
+
+    def test_no_polygons_found(self):
+        polygon, _ = subject.get_space_polygon([], 0, 0)
+        assert polygon == "NO POLYGONS FOUND"
+
+    def test_no_polygon_for_point(self):
+        lines = [
+            shapely.LineString([(0, 0), (10, 0)]),
+            shapely.LineString([(10, 0), (10, 10)]),
+            shapely.LineString([(10, 10), (0, 10)]),
+            shapely.LineString([(0, 10), (0, 0)]),
+        ]
+        polygon, _ = subject.get_space_polygon(lines, 50, 50)
+        assert polygon == "NO POLYGON FOR POINT"
+
+
+class TestGetAutoSpaceHeight(test.bootstrap.IFC4):
+    def test_height_from_top_connection(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        slab = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcSlab")
+        _add_extruded_body(self.file, wall, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 3.0)
+        _add_extruded_body(self.file, slab, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 0.3, z_offset=3.0)
+        self.file.createIfcRelConnectsElements(
+            GlobalId=ifcopenshell.guid.new(),
+            RelatingElement=slab,
+            RelatedElement=wall,
+            Description="TOP",
+        )
+        shapes = _build_shapes_dict(self.file, [wall, slab])
+        space_polygon = shapely.box(-5, -5, 5, 5)
+        height = subject.get_auto_space_height(self.file, shapes, space_polygon, 0.0, [wall])
+        assert height is not None
+        assert height == pytest.approx(3.0, abs=0.1)
+
+    def test_height_from_elements_above_without_top_connection(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        slab = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcSlab")
+        _add_extruded_body(self.file, wall, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 3.0)
+        _add_extruded_body(self.file, slab, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 0.3, z_offset=3.0)
+        shapes = _build_shapes_dict(self.file, [wall, slab])
+        space_polygon = shapely.box(-5, -5, 5, 5)
+        height = subject.get_auto_space_height(self.file, shapes, space_polygon, 0.0, [wall])
+        assert height is not None
+        assert height == pytest.approx(3.0, abs=0.1)
+
+    def test_height_from_wall_tops_when_no_slab(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        _add_extruded_body(self.file, wall, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 3.0)
+        shapes = _build_shapes_dict(self.file, [wall])
+        space_polygon = shapely.box(-5, -5, 5, 5)
+        height = subject.get_auto_space_height(self.file, shapes, space_polygon, 0.0, [wall])
+        assert height is not None
+        assert height == pytest.approx(3.0, abs=0.1)
+
+    def test_returns_none_when_no_elements_above(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        _add_extruded_body(self.file, wall, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 3.0)
+        shapes = _build_shapes_dict(self.file, [wall])
+        space_polygon = shapely.box(-100, -100, -90, -90)
+        height = subject.get_auto_space_height(self.file, shapes, space_polygon, 0.0, [])
+        assert height is None