First, you should enter your location into www.tvfool.com
(both "Click Here" to see predictions and "Start Here" to see an individual station colorized coverage map and post the RESULTS URL (webaddress at top of browser) so we can see it.
If you are in the "flatlands" of Irvine, there is lots of signal strength, whereas if you are behind a hill there is less. You'll lose 13 dB +/- 7 dB of signal strength in a "typical" attic...and perhaps higher if foil backed insulation and /or trees are also blocking the signal. Despite all that, you'll probably have sufficient signal strength and should use a Preamp to drive multiple TVs. Since there are several strong FM stations 7-11 miles away, to avoid harmonic and intermodulation interference from FM stations, you should ONLY amplify UHF, so I would recommend Winegard AP-4700 which simply passes through the VHF signals:
You will also need a VHF Antenna to receive Ch7, 9 & 11, such as Antennacraft Y-5-7-13. A UHF/VHF Combiner (e.g. UVSJ) can combine the signals from the two antennas either prior to the Preamp....or if you want to save 0.5 dB Noise Figure, use it AFTER the Preamp, being sure to use a UVSJ type device which has DCPASS on the UHF port: R-S or A-D, but NOT Pico-Macom or Holland.
Attic locations can be tricky, so try several different locations and heights to find the "sweet spots"....
PS: My son sucessfully uses CM4228 8-Bay UHF and 10-Element Hi-VHF Band Yagi in his attic---70 miles
from Mt Wilson North of French Valley Airport (North of Temecula).Edited by holl_ands - 3/27/13 at 2:50pm