THE ARMPIT OF THE HOUSE
Armpits, in general, have an undeservedly bad reputation. When was the last time you saw an armpit in a cologne commercial? Yes, they are smelly, hairy and unglamorous, but they perform an important, if frequently overlooked, function. The profundity of sweat excreted there helps to cool and aerate the body. When someone sits back in a chair with their hands folded behind their head and their elbows extended at obtuse angles, one can see the armpits at work. In hot weather, there will be a patch of moisture or even a stain where the arms meet the torso of the body.
If a house were a human body then the soffit would be the armpit. The soffit occupies a similar location with respect to the structure. It is the area on the underside of what is commonly referred to as the overhang. The overhang serves two purposes: 1) it protects the siding from excessive weather; and 2) it creates a place for the soffit.
Though the soffit and armpit perform similar functions, the soffit does not produce sweat. Through a screened opening, it allows air into the attic. The air cycles to the vents to carry heat and moisture out of the house. This is important because moisture in the attic will cause rot in sheathing and rafters.