diff --git a/CHANGELOG.md b/CHANGELOG.md
index 37b6917d..4c98226e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Added `Element.compute_elementgeometry()`.
 * Added `Element.compute_modelgeometry()` to replace `Element.compute_geometry()`.
 * Added `Element.compute_modeltransformation()` to replace `Element.compute_worldtransformation()`.
+* Added `Element.is_dirty`.
 
 ### Changed
 
diff --git a/src/compas_model/elements/element.py b/src/compas_model/elements/element.py
index e217128e..17f2d4ee 100644
--- a/src/compas_model/elements/element.py
+++ b/src/compas_model/elements/element.py
@@ -92,6 +92,8 @@ class Element(Data):
         Scaling factor to inflate the AABB with.
     inflate_obb : float
         Scaling factor to inflate the OBB with.
+    is_dirty : bool
+        Flag to indicate that modelgeometry has to be recomputed.
 
     """
 
@@ -140,6 +142,8 @@ def __init__(
         self.inflate_aabb = 0.0
         self.inflate_obb = 0.0
 
+        self._is_dirty = True
+
     # this is not entirely correct
     def __repr__(self) -> str:
         return f"Element(frame={self.frame!r}, name={self.name})"
@@ -177,6 +181,19 @@ def parent(self) -> "ElementNode":
     def features(self) -> list[Feature]:
         return self._features
 
+    @property
+    def is_dirty(self):
+        return self._is_dirty
+
+    @is_dirty.setter
+    def is_dirty(self, value):
+        self._is_dirty = value
+
+        if value:
+            elements = list(self.model.elements())
+            for neighbor in self.model.graph.neighbors_out(self.graphnode):
+                elements[neighbor].is_dirty = value
+
     # ==========================================================================
     # Computed attributes
     # ==========================================================================
@@ -290,7 +307,18 @@ def compute_modelgeometry(self) -> Union[Brep, Mesh]:
         :class:`compas.datastructures.Mesh` | :class:`compas.geometry.Brep`
 
         """
-        raise NotImplementedError
+        graph = self.model.graph
+        elements = list(self.model.elements())  # noqa: F841
+        xform = self.modeltransformation
+        modelgeometry = self.elementgeometry.transformed(xform)
+
+        for neighbor in graph.neighbors_in(self.graphnode):
+            for interaction in graph.edge_interactions((neighbor, self.graphnode)):
+                pass  # TODO: apply interaction
+
+        self.is_dirty = False
+
+        return modelgeometry
 
     def compute_aabb(self) -> Box:
         """Computes the Axis Aligned Bounding Box (AABB) of the geometry of the element.
diff --git a/src/compas_model/models/model.py b/src/compas_model/models/model.py
index 831d6d55..efafaba9 100644
--- a/src/compas_model/models/model.py
+++ b/src/compas_model/models/model.py
@@ -379,6 +379,8 @@ def add_interaction(self, a: Element, b: Element, interaction: Optional[Interact
             interactions.append(interaction)
             self.graph.edge_attribute(edge, name="interactions", value=interactions)
 
+        self._guid_element[str(b.guid)].is_dirty = True
+
         return edge
 
     def remove_element(self, element: Element) -> None:
@@ -397,6 +399,9 @@ def remove_element(self, element: Element) -> None:
         guid = str(element.guid)
         if guid not in self._guid_element:
             raise Exception("Element not in the model.")
+
+        self._guid_element[guid].is_dirty = True
+
         del self._guid_element[guid]
 
         self.graph.delete_node(element.graphnode)
@@ -419,6 +424,9 @@ def remove_interaction(self, a: Element, b: Element, interaction: Optional[Inter
         if interaction:
             raise NotImplementedError
 
+        elements = list(self.elements())
+        elements[b.graphnode].is_dirty = True
+
         edge = a.graphnode, b.graphnode
         if self.graph.has_edge(edge):
             self.graph.delete_edge(edge)
diff --git a/src/compas_model/viewers/blockmodelviewer.py b/src/compas_model/viewers/blockmodelviewer.py
index a94e9426..b4925102 100644
--- a/src/compas_model/viewers/blockmodelviewer.py
+++ b/src/compas_model/viewers/blockmodelviewer.py
@@ -6,6 +6,10 @@
 from compas_model.elements import BlockGeometry
 from compas_model.interactions import ContactInterface
 from compas_model.models import Model
+from compas_viewer import Viewer
+from compas_viewer.components import Button
+from compas_viewer.components.slider import Slider
+from compas_viewer.scene import GroupObject
 
 try:
     from compas_viewer import Viewer
diff --git a/tests/test_element.py b/tests/test_element.py
new file mode 100644
index 00000000..4edc0c11
--- /dev/null
+++ b/tests/test_element.py
@@ -0,0 +1,163 @@
+from compas_model.models import Model
+from compas_model.elements import Element
+from compas_model.interactions import Interaction
+from compas.datastructures import Mesh
+from typing import Optional
+
+from compas.geometry import Frame
+from compas.geometry import Box
+from compas.geometry import Transformation
+
+
+class MyElement(Element):
+    """Class representing an element for testing."""
+
+    def __init__(
+        self,
+        size: float = 0.1,
+        frame: Frame = Frame.worldXY(),
+        transformation: Optional[Transformation] = None,
+        name: Optional[str] = None,
+    ) -> "MyElement":
+        super().__init__(frame=frame, transformation=transformation, name=name)
+
+        self.size: float = size
+
+    def compute_elementgeometry(self) -> Mesh:
+        """Element geometry in the local frame.
+
+        Returns
+        -------
+        :class:`compas.datastructures.Mesh`
+
+        """
+
+        return Box(self.size, self.size, self.size, self.frame).to_mesh()
+
+
+def test_is_dirty_setter():
+    model = Model()
+    a = MyElement(name="a")
+    b = MyElement(name="b")
+    c = MyElement(name="c")
+    d = MyElement(name="d")
+    model.add_element(a)
+    model.add_element(b)
+    model.add_element(c)
+    model.add_element(d)
+    model.add_interaction(a, c, interaction=Interaction(name="i_a_c"))  # a affects c
+    model.add_interaction(a, b, interaction=Interaction(name="i_b_c"))  # a affects b
+    a.is_dirty = False
+    b.is_dirty = False
+    c.is_dirty = False
+    d.is_dirty = False
+
+    elements = list(model.elements())
+
+    assert not elements[0].is_dirty
+    assert not elements[1].is_dirty
+    assert not elements[2].is_dirty
+    assert not elements[3].is_dirty
+
+    elements[0].is_dirty = True
+
+    assert elements[0].is_dirty
+    assert elements[1].is_dirty
+    assert elements[2].is_dirty
+    assert not elements[3].is_dirty
+
+
+def test_is_dirty_add_interaction():
+    model = Model()
+    a = MyElement(name="a")
+    b = MyElement(name="b")
+    c = MyElement(name="c")
+    d = MyElement(name="d")
+    model.add_element(a)
+    model.add_element(b)
+    model.add_element(c)
+    model.add_element(d)
+
+    model.add_interaction(a, b, interaction=Interaction(name="i_a_b"))  # c affects a
+    for element in model.elements():
+        element.modelgeometry  # All elements is_dirty is set to False
+    model.add_interaction(a, c, interaction=Interaction(name="i_a_c"))  # c affects b
+
+    elements = list(model.elements())
+    assert not elements[0].is_dirty
+    assert not elements[1].is_dirty
+    assert elements[2].is_dirty
+    assert not elements[3].is_dirty
+
+
+def test_is_dirty_remove_interaction():
+    model = Model()
+    a = MyElement(name="a")
+    b = MyElement(name="b")
+    c = MyElement(name="c")
+    d = MyElement(name="d")
+    model.add_element(a)
+    model.add_element(b)
+    model.add_element(c)
+    model.add_element(d)
+    model.add_interaction(a, b, interaction=Interaction(name="i_a_b"))  # a affects b
+    model.add_interaction(a, c, interaction=Interaction(name="i_a_c"))  # a affects c
+
+    for element in model.elements():
+        element.is_dirty = False
+    model.remove_interaction(a, b)  # a affects b
+    model.remove_interaction(a, c)  # a affects c
+
+    elements = list(model.elements())
+    assert not elements[0].is_dirty
+    assert elements[1].is_dirty
+    assert elements[2].is_dirty
+    assert not elements[3].is_dirty
+
+
+def test_is_dirty_remove_element_0():
+    model = Model()
+    a = MyElement(name="a")
+    b = MyElement(name="b")
+    c = MyElement(name="c")
+    d = MyElement(name="d")
+    model.add_element(a)
+    model.add_element(b)
+    model.add_element(c)
+    model.add_element(d)
+    model.add_interaction(a, b, interaction=Interaction(name="i_a_b"))  # a affects b
+    model.add_interaction(a, c, interaction=Interaction(name="i_a_c"))  # a affects c
+
+    for element in model.elements():
+        element.modelgeometry  # All element is_dirty is set to False
+
+    model.remove_element(a)  # b and c is_dirty is set to True
+
+    elements = list(model.elements())
+    assert elements[0].is_dirty
+    assert elements[1].is_dirty
+    assert not elements[2].is_dirty
+
+
+def test_is_dirty_remove_element_1():
+    model = Model()
+    a = MyElement(name="a")
+    b = MyElement(name="b")
+    c = MyElement(name="c")
+    d = MyElement(name="d")
+    model.add_element(a)
+    model.add_element(b)
+    model.add_element(c)
+    model.add_element(d)
+    model.add_interaction(a, b, interaction=Interaction(name="i_a_b"))  # a affects b
+    model.add_interaction(a, c, interaction=Interaction(name="i_a_c"))  # a affects c
+
+    for element in model.elements():
+        element.modelgeometry  # All element is_dirty is set to False
+
+    model.remove_element(b)  # b and c is_dirty is set to True
+
+    elements = list(model.elements())
+    assert not elements[0].is_dirty
+    assert not elements[1].is_dirty
+    assert not elements[2].is_dirty