Just doing the underside of the roof isn't the complete way of doing this.
Originally Posted by JOHNBUSHE
All exterior surfaces of the attic --- underside of the roof ---- gable walls ---- etc. --- need to be covered.
This creates a semi-conditioned space by raising the inside temperature during the winter and lowering the inside temps. during the summer.
When this happens there isn't a necessity to require the attic to breath per Se.
By raising the temperature and closing off the venting you are maintaining a pressurized space with a more constant temperature lessening vapour drive from the interior into the attic and condensing ---- though it still is important to seal any penetrations from the interior into the attic.
"" an ounce of perception -- a pound of obscure "