diff --git a/city_model_structure/attributes/surface.py b/city_model_structure/attributes/surface.py
index ecd9efcb..f38a571a 100644
--- a/city_model_structure/attributes/surface.py
+++ b/city_model_structure/attributes/surface.py
@@ -49,6 +49,7 @@ class Surface:
     self._shared_surfaces = []
     self._global_irradiance = dict()
     self._ground_coordinates = (self.min_x, self.min_y, self.min_z)
+    self._is_planar = None
 
   def parent(self, parent, surface_id):
     """
@@ -480,3 +481,17 @@ class Surface:
   @property
   def convex(self):
     return pn.Polygon.is_convex(self.polygon.points)
+
+  @property
+  def is_planar(self) -> bool:
+    if self._is_planar is None:
+      self._is_planar = True
+      vectors = []
+      for i in range(1,len(self.points)):
+        vectors.append(self.points[i] - self.points[0])
+      for i in range(2, len(vectors)):
+        product = np.dot(np.cross(vectors[0], vectors[1]), vectors[i])
+        if math.fabs(product) > 1e-4:
+          self._is_planar = False
+          break
+    return self._is_planar