[Greenbuilding] Passive solar in hot, humid climate

[Ian Remmler]

Hi,

I'm planning to build a house in the Austin, Texas area, and I
want to incorporate passive solar heating and cooling into the
design.  Common wisdom around here is that a 2 foot overhang on
the south wall is enough to block the sun in the summer.

But this is based on the sun's path around solstice time.  If my
calculations are correct, in late August at a bit after 1:00
(solar time), the sun will hit about half of the south wall at a
45 degree azimuth.  We had 24 100+ days this August.

I've thought about putting an 8 foot deep porch along the entire
south wall.  Yes, this will prevent much direct gain in the
winter, but I'm wondering if it would be worth it to keep cool
in late summer / early fall (and spring sometimes).  I've only
found a couple of references that recommend this approach, but
before air conditioning it was a common feature of the local
architecture.  So does it make sense to block all direct gain
when it's hot at the expense of some winter heating (which is
really only needed for about two months around here)?

Please share your thoughts and experiences.

Thanks,
    - Ian.