What kind of loss will I have if I install this antenna on our 2nd
story roof, but below the ridge line? We live in a neighborhood where
no one has an antenna and wife is worried about the ascetics of it.

When the antenna is pointing towards transmitter towers for which it
has a clear field of view (that is, not towards the house's ridgeline)
it ought to work well. The presence of the ridgeline "behind" the
antenna ought to have only a minor effect, because the antenna is
equipped with a reflector that will make it quite insensitive to
signals arriving from behind.

On the other hand, if you rotate it so that it's trying to "see
through" the ridge line of the house, to a transmitter tower located
on the opposite side of the building, it could perform rather
poorly. Just how poorly will depend on the actual construction of the
roof. If there's a significant amount of metal involved (if e.g. the
inside of the roof is insulated with batts of fiberglass that have a
foil vapor barrier) you'd have to expect a lot of signal attenuation,
and you might or might not get an acceptable signal. In this
situation, you might actually get a more usable signal by rotating the
antenna so that it points _away_ from the transmitter, and towards a
nearby building or other structure which reflects some of the signal
from the transmitter.

The key thing to remember is that UHF signals travel almost entirely
by "line of sight", and to a lesser extent by line-of-sight with one
or more reflections. You can't count on much of the signal either
getting through, or diffracting around solid obstacles between your
antenna and the transmitter.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!