You could use a smaller version, with wider beam width and lower gain, but trying to receive already weak and/or multipath signals from inside an attic that will further weaken and reflect/refract them is going to be tough I would think. But here's the web page, with links to the specs. These aren't the only ones out there either, of course.
http://www.antennacraft.net/Antennas/AntennasHBU.html