Hope this helps.
On the website www.handyman.com they have an articlethat may be of help.
On the home page there is a column on the left side. Clickon "project library". This takes you to a list ofprojects.
In the first column under "Improvements" click on the projecttitled "Improve Attic Ventilation".
Hopefully this is exactly the info you are looking for.
© 2016 Renovate Your World LLC