diff --git a/CityGML/clause_6_6_CityObjectGroup.adoc b/CityGML/clause_6_6_CityObjectGroup.adoc
index 7edc1c8..2852a00 100644
--- a/CityGML/clause_6_6_CityObjectGroup.adoc
+++ b/CityGML/clause_6_6_CityObjectGroup.adoc
@@ -48,3 +48,19 @@ The CityGML CityObjectGroup XML elements and their corresponding CityGML UML cla
 |===
 
 include::requirements/cityobjectgroup/REQ_CityObjectGroup_Reference.adoc[]
+
+Surface boundaries are constrained by the following requirement:
+
+include::requirements/CityObjectGroup/REQ_CityObjectGroup_Boundaries.adoc[]
+
+<<cityobjectgroup-boundaries-table>> lists the surfaces that are allowed as thematic surface boundaries of the space elements defined in the CityObjectGroup module:
+
+[[cityobjectgroup-boundaries-table]]
+.CityObjectGroup space elements and their allowed thematic surface boundaries
+[cols="2,6",options="headers"]
+|===
+^|*Space element* ^|*Allowed space boundaries*
+  |_grp:CityObjectGroup_  a|  * _core:ClosureSurface_
+                        * _gen:GenericThematicSurface_
+                        * possible surface elements from ADEs
+|===
diff --git a/CityGML/requirements/cityobjectgroup/REQ_CityObjectGroup_Boundaries.adoc b/CityGML/requirements/cityobjectgroup/REQ_CityObjectGroup_Boundaries.adoc
new file mode 100644
index 0000000..497e3a4
--- /dev/null
+++ b/CityGML/requirements/cityobjectgroup/REQ_CityObjectGroup_Boundaries.adoc
@@ -0,0 +1,6 @@
+[[req_cityobjectgroup_boundaries]]
+[width="100%",cols="2,6"]
+|===
+^|*Requirement  {counter:req-id}* |*/req/cityobjectgroup/boundaries*
+2+|<<cityobjectgroup-boundaries-table>> lists the surfaces that are allowed as thematic surface boundaries of the space elements defined in the CityObjectGroup module. If a space element is bounded by thematic surface boundaries using the property _core:boundary_ (type: _core:AbstractSpaceBoundaryPropertyType_), the property SHALL contain exactly one surface element from <<cityobjectgroup-boundaries-table>> that is supported for the specific space element. If no surface element is supported, the space element SHALL NOT be bounded by thematic surface boundaries.
+|===