Que tal não usar mod_rewrite e usar a instrução de redirecionamento.
#Virtual Host for IA sub web
<VirtualHost *:80>
ServerName www.ia.domain.com
ServerAlias <other domain names they want to associate with this directory; ex: ia.domain.com>
Redirect permanent / http://www.domain.com/ia_new_web_location/
</VirtualHost>