Livable space must have heating and cooling, be fully enclosed, have appropriate electrical outlets, proper windows/doors to the exterior, insulation, etc. Basically, it's all of the same requirements your living room has.
Most AZ Rooms are enclosed patios, but unless the room is heated/cooled and finished out to be liveable like a living or family room, it cannot be included as property GLA. It is simply called an AZ Room in the appraisal report grid and is given value as such, but not included in the overall GLA.
GREAT QUESTION : Living space sq ft. under the HVAC system Many sellers and listing agents include a room NOT UNDER HVAC for sq. ft. usually causes many problems for a purchaser submitting an offer on the property. That space is discounted by the appraiser http://www.lynn911.comhttp://www.homes-for-sale-dallas.com