diff --git a/src/bonsai/bonsai/bim/module/material/operator.py b/src/bonsai/bonsai/bim/module/material/operator.py
index 8e2fdc5701..307047af4a 100644
--- a/src/bonsai/bonsai/bim/module/material/operator.py
+++ b/src/bonsai/bonsai/bim/module/material/operator.py
@@ -371,10 +371,6 @@ class AddLayer(bpy.types.Operator, tool.Ifc.Operator):
             },
         )
 
-        unit_scale = ifcopenshell.util.unit.calculate_unit_scale(tool.Ifc.get())
-        thickness = 0.1  # Arbitrary metric thickness for now
-        layer.LayerThickness = thickness / unit_scale
-
 
 class ReorderMaterialSetItem(bpy.types.Operator, tool.Ifc.Operator):
     bl_idname = "bim.reorder_material_set_item"
diff --git a/src/bonsai/bonsai/bim/module/model/handler.py b/src/bonsai/bonsai/bim/module/model/handler.py
index f513017eef..824d93e989 100644
--- a/src/bonsai/bonsai/bim/module/model/handler.py
+++ b/src/bonsai/bonsai/bim/module/model/handler.py
@@ -49,6 +49,12 @@ def load_post(*args):
         "type.assign_type", "Bonsai.DumbWall.RegenerateFromType", wall.DumbWallPlaner().regenerate_from_type
     )
 
+    ifcopenshell.api.add_post_listener(
+        "material.add_layer", "Bonsai.DumbSlab.RegenerateFromLayer", slab.DumbSlabPlaner().regenerate_from_layer
+    )
+    ifcopenshell.api.add_post_listener(
+        "material.remove_layer", "Bonsai.DumbSlab.RegenerateFromLayer", slab.DumbSlabPlaner().regenerate_from_layer
+    )
     ifcopenshell.api.add_post_listener(
         "material.edit_layer", "Bonsai.DumbSlab.RegenerateFromLayer", slab.DumbSlabPlaner().regenerate_from_layer
     )
diff --git a/src/bonsai/bonsai/bim/module/model/slab.py b/src/bonsai/bonsai/bim/module/model/slab.py
index 1ddeee0b19..43337f090e 100644
--- a/src/bonsai/bonsai/bim/module/model/slab.py
+++ b/src/bonsai/bonsai/bim/module/model/slab.py
@@ -197,27 +197,42 @@ class DumbSlabGenerator:
 class DumbSlabPlaner:
     def regenerate_from_layer(self, usecase_path, ifc_file, settings):
         self.unit_scale = ifcopenshell.util.unit.calculate_unit_scale(ifc_file)
-        layer = settings["layer"]
-        thickness = settings["attributes"].get("LayerThickness")
-        if thickness is None:
+
+        try:
+            # Called from materil.edit_layer
+            layer = settings["layer"]
+            thickness = settings["attributes"].get("LayerThickness")
+            if thickness is None:
+                return
+            layer_set = layer.ToMaterialLayerSet[0]
+
+        except:
+            # Called from materil.add_layer or material.remove_layer
+            obj = bpy.context.active_object
+            element = tool.Ifc.get_entity(obj)
+            if not element:
+                return
+            material = ifcopenshell.util.element.get_material(element)
+            material_set_usage = tool.Ifc.get().by_id(material.id())
+            layer_set = material_set_usage.ForLayerSet
+
+        total_thickness = sum([l.LayerThickness for l in layer_set.MaterialLayers])
+        if not total_thickness:
             return
-        for layer_set in layer.ToMaterialLayerSet:
-            total_thickness = sum([l.LayerThickness for l in layer_set.MaterialLayers])
-            if not total_thickness:
+
+        for inverse in ifc_file.get_inverse(layer_set):
+            if not inverse.is_a("IfcMaterialLayerSetUsage") or inverse.LayerSetDirection != "AXIS3":
                 continue
-            for inverse in ifc_file.get_inverse(layer_set):
-                if not inverse.is_a("IfcMaterialLayerSetUsage") or inverse.LayerSetDirection != "AXIS3":
-                    continue
-                if ifc_file.schema == "IFC2X3":
-                    for rel in ifc_file.get_inverse(inverse):
-                        if not rel.is_a("IfcRelAssociatesMaterial"):
-                            continue
-                        for element in rel.RelatedObjects:
-                            self.change_thickness(element, total_thickness)
-                else:
-                    for rel in inverse.AssociatedTo:
-                        for element in rel.RelatedObjects:
-                            self.change_thickness(element, total_thickness)
+            if ifc_file.schema == "IFC2X3":
+                for rel in ifc_file.get_inverse(inverse):
+                    if not rel.is_a("IfcRelAssociatesMaterial"):
+                        continue
+                    for element in rel.RelatedObjects:
+                        self.change_thickness(element, total_thickness)
+            else:
+                for rel in inverse.AssociatedTo:
+                    for element in rel.RelatedObjects:
+                        self.change_thickness(element, total_thickness)
 
     def regenerate_from_type(self, usecase_path, ifc_file, settings):
         relating_type = settings["relating_type"]
diff --git a/src/ifcopenshell-python/ifcopenshell/api/material/add_layer.py b/src/ifcopenshell-python/ifcopenshell/api/material/add_layer.py
index 3b33ffa745..d20fff9533 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/material/add_layer.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/material/add_layer.py
@@ -80,10 +80,11 @@ def add_layer(
         # Great! Let's assign our material set to our wall type.
         ifcopenshell.api.material.assign_material(model, products=[wall_type], material=material_set)
     """
+    unit_scale = ifcopenshell.util.unit.calculate_unit_scale(file)
     settings = {"layer_set": layer_set, "material": material}
 
     layers = list(settings["layer_set"].MaterialLayers or [])
-    layer = file.create_entity("IfcMaterialLayer", **{"Material": settings["material"], "LayerThickness": 1.0})
+    layer = file.create_entity("IfcMaterialLayer", **{"Material": settings["material"], "LayerThickness": 0.1 / unit_scale})
     layers.append(layer)
     settings["layer_set"].MaterialLayers = layers
     return layer