FWIW, the FCC is on your side:
http://www.fcc.gov/guides/over-air-r...n-devices-rule
http://www.fcc.gov/guides/installing...tellite-dishes
Mounting outside, clear of obstructions almost always provides superior reception results.
While the 4221 will do very well receiving UHF signals, there are also VHF signals that are available. (KUHT, KTRK, KHOU & KDHU)
One approach would be to use the 4221 or similar antenna from another vendor. (The Antennas Direct DB2e and DB4e come to mind.) Plus, an Antennacraft Y5713. This would be a good option if you wanted to shift the aim of the UHF antenna to include the main group of signals at 136° and the few others at 89° (aim about half way between the two groups). The Y5713 would point at 136° and be combined into the same coax with a UVSJ.
A simpler approach that is also quite likely to accomplish the same result would be an Antennacraft HBU-33 aimed between 136° and 89°.
I want to echo signals unlimited's caution re. foil backed insulation. If present, the attic will be a poor location for an antenna.