I am a great fan of large roof overhangs.
They protect the house walls,
keep rainwater away from the foundations,
eliminate the need for
gutters, and allow you to keep casement
windows and sliding doors open
during summer rainstorms. Large
overhangs are also a key design
element in those useful and handsome
styles that stem from the
Craftsman tradition.
However, large overhangs present
critical structural problems, which are
made more complicated when the
roof is insulated rather than the attic
floor. I usually insulate my houses at
the roof plane because this creates
useful insulated space throughout the
upper level, avoids unsatisfactory
(and often incomplete) insulation
conditions at kneewalls, and allows
me to create cathedral ceilings.
Structure versus fresh air. The
problem stems