I am trying to figure out what I need in order to improve the ventilation
of the attic space in the house I have recently purchased. It is about 50
years old, and not surprisingly, it is not vented very well.

While researching this some I have come across the rule thumb that there
ought to be 1 sq. ft. of ventilation for every 150 sq. ft. of attic space.
What I am not certain of is if that rule of thumb includes both exhuast
(such as ridge vents) and intake (such as soffit vents). It seems clear to
me, also, that the ratio of exhaust to intake must make some difference.

Can anyone is this group give me a little more detail in the general
guidelines for properly ventilating an attic.

TIA

James