saw the blog at Houston Texans with several nice updates, twitters, so on
http://blog.houstontexans.com/
added this to mentioned 18 UDFA
"The Texans had 52 players under contract heading into today, along with eight draft picks and two tendered veterans, Arian Foster and Mike Brisiel. That leaves them room for 28 players to add to the roster, including UDFAs."
So, that could imply 10 experienced FA to add yet which might be some of their own FA most likely.
added another UDFA not mentioned above
Zane Parr, Virginia , LB/DE Height / Weight:6-6 / 275
combination of size, speed and agility , came out as a junior