diff --git a/facho/facho.py b/facho/facho.py
index 712bb7b..6ab9b19 100644
--- a/facho/facho.py
+++ b/facho/facho.py
@@ -131,16 +131,8 @@ class FachoXML:
         self.builder.append(elem, new_elem)
         
     def add_extension(self, extension):
-        root_tag = self.builder.get_tag(self.root)
+        extension.build(self)
 
-        # construir las extensiones o adicionar en caso de indicar
-        xpath, elements = extension.build(self)
-        if isinstance(elements, str):
-            elem = self.set_element('/'+ root_tag + xpath, elements)
-        else:
-            for new_element in elements:
-                elem = self.find_or_create_element('/' + root_tag + xpath)
-                self.builder.append(elem, new_element)
     
     def fragment(self, xpath, append=False, append_not_exists=False):
         nodes = xpath.split('/')
diff --git a/facho/fe/fe.py b/facho/fe/fe.py
index b6e1531..744371b 100644
--- a/facho/fe/fe.py
+++ b/facho/fe/fe.py
@@ -63,7 +63,6 @@ class DianXMLExtensionCUFE(FachoXMLExtension):
         fachoxml.set_element('/fe:Invoice/cbc:UUID', cufe, schemeName='CUFE-SHA384')
         fachoxml.set_element('/fe:Invoice/cbc:ProfileID', 'DIAN 2.1')
         fachoxml.set_element('/fe:Invoice/cbc:ProfileExecutionID', self._tipo_ambiente())
-        return '', []
         
     def issue_time(self, datetime_):
         return datetime_.strftime('%H:%M:%S%z')
@@ -133,7 +132,7 @@ class DianXMLExtensionSoftwareProvider(FachoXMLExtension):
                                       **SCHEME_AGENCY_ATTRS)
         software_provider.set_element('/sts:SoftwareProvider/sts:SoftwareID', self.id_software,
                                       **SCHEME_AGENCY_ATTRS)
-        return '', []
+
 
     
 class DianXMLExtensionSoftwareSecurityCode(FachoXMLExtension):
@@ -240,7 +239,6 @@ class DianXMLExtensionSigner(FachoXMLExtension):
         extcontent = ublextension.find_or_create_element('/ext:UBLExtension:/ext:ExtensionContent')
         fachoxml.append_element(extcontent, signature)
         
-        return '', []
         
 
 class DianXMLExtensionAuthorizationProvider(FachoXMLExtension):
@@ -253,7 +251,7 @@ class DianXMLExtensionAuthorizationProvider(FachoXMLExtension):
         attrs = {'schemeID': '4', 'schemeName': '31'}
         attrs.update(SCHEME_AGENCY_ATTRS)
         fexml.set_attributes(dian_path, **attrs)
-        return '', []
+
     
 
 class DianXMLExtensionInvoiceAuthorization(FachoXMLExtension):
@@ -284,7 +282,7 @@ class DianXMLExtensionInvoiceAuthorization(FachoXMLExtension):
                                     self.from_)
         invoice_control.set_element('/sts:InvoiceControl/sts:AuthorizedInvoices/sts:To',
                                     self.to)
-        return '', []
+
 
         
 class DianZIP: