diff --git a/BuildingSync.xsd b/BuildingSync.xsd
index 4ce137ea..e702ef62 100644
--- a/BuildingSync.xsd
+++ b/BuildingSync.xsd
@@ -1109,28 +1109,16 @@
                                   </xs:simpleContent>
                                 </xs:complexType>
                               </xs:element>
-                              <xs:element name="WallID" minOccurs="0">
-                                <xs:annotation>
-                                  <xs:documentation>ID number of the wall type associated with this side of the section.</xs:documentation>
-                                </xs:annotation>
-                                <xs:complexType>
-                                  <xs:sequence>
-                                    <xs:element name="WallArea" minOccurs="0">
-                                      <xs:annotation>
-                                        <xs:documentation>Exposed, above-grade, opaque wall area of this type. (ft2)</xs:documentation>
-                                      </xs:annotation>
-                                      <xs:complexType>
-                                        <xs:simpleContent>
-                                          <xs:extension base="xs:decimal">
-                                            <xs:attribute ref="auc:Source"/>
-                                          </xs:extension>
-                                        </xs:simpleContent>
-                                      </xs:complexType>
-                                    </xs:element>
-                                  </xs:sequence>
-                                  <xs:attribute name="IDref" type="xs:IDREF" use="required"/>
-                                </xs:complexType>
-                              </xs:element>
+                              <xs:choice>
+                                <xs:element ref="auc:WallID" minOccurs="0"/>
+                                <xs:element name="WallIDs">
+                                  <xs:complexType>
+                                    <xs:sequence>
+                                      <xs:element ref="auc:WallID" minOccurs="0" maxOccurs="unbounded"/>
+                                    </xs:sequence>
+                                  </xs:complexType>
+                                </xs:element>
+                              </xs:choice>
                               <xs:element name="WindowID" minOccurs="0">
                                 <xs:annotation>
                                   <xs:documentation>ID number of the window type associated with this side of the section.</xs:documentation>
@@ -17520,4 +17508,26 @@
       <xs:enumeration value="High"/>
     </xs:restriction>
   </xs:simpleType>
+  <xs:element name="WallID">
+    <xs:annotation>
+      <xs:documentation>ID number of the wall type associated with this side of the section.</xs:documentation>
+    </xs:annotation>
+    <xs:complexType>
+      <xs:sequence>
+        <xs:element name="WallArea" minOccurs="0">
+          <xs:annotation>
+            <xs:documentation>Exposed, above-grade, opaque wall area of this type. (ft2)</xs:documentation>
+          </xs:annotation>
+          <xs:complexType>
+            <xs:simpleContent>
+              <xs:extension base="xs:decimal">
+                <xs:attribute ref="auc:Source"/>
+              </xs:extension>
+            </xs:simpleContent>
+          </xs:complexType>
+        </xs:element>
+      </xs:sequence>
+      <xs:attribute name="IDref" type="xs:IDREF" use="required"/>
+    </xs:complexType>
+  </xs:element>
 </xs:schema>
diff --git a/proposals/2020/Allow Multiple Walls for Side.md b/proposals/2020/Allow Multiple Walls for Side.md
new file mode 100644
index 00000000..e1b121af
--- /dev/null
+++ b/proposals/2020/Allow Multiple Walls for Side.md	
@@ -0,0 +1,13 @@
+# Allow Multiple Walls for Side
+
+## Overview
+
+This proposal is to modify the `auc:Side` to allow an unbounded number of `auc:Wall` IDs to be referenced
+
+## Justification
+
+Currently you can only reference one wall ID for each `auc:Side`. This is an issue if a side of a building is composed of more than one wall type.
+
+## Implementation
+
+This proposal suggests the schema creates a choice between a single `auc:WallID` (how things currently are), or `auc:WallIDs` which contains an unbounded number of wall IDs. This is non-breaking and the former choice could be dropped in the next major release.