Vitruvius on the Properly Situated Villa Library

Marcus Vitruvius Pollio (80-15 BCE) was a Roman architect and military engineer that lived during the fall of the Roman Republic and the beginning of the imperial era. He is best known for his work "On Architecture" which influenced many great writers and thinkers over the centuries. Vitruvius dedicated Book 6 of this work to the topic of planning a Roman Villa. In one section he discussed the importance of orienting certain rooms towards the sunlight.

"I shall now describe how the different sorts of buildings are placed as regards their aspects. Winter triclinia and baths are to face the winter west, because the afternoon light is wanted in them; and not less so because the setting sun casts its rays upon them, and but its heat warms the aspect towards the evening hours. Bed chambers and libraries should be towards the east, for their purposes require the morning light: in libraries the books are in this aspect preserved from decay; those that are towards the south and west are injured by the worm and by the damp, which the moist winds generate and nourish, and spreading the damp, make the books mouldy." (De Arch., 6.4.1)

It is notable that Vitruvius includes a "library" with all the rooms that make up an ideal Roman Villa. 
The other interesting facet are the effects that solar heat, moisture, and airflow have upon the proper storage and preservation of the books. He indicates that libraries that face away from the morning sun (to the south and west) are in danger of becoming worm eaten and moldy, and decayed with moisture.
Though this is a passing statement by Vitruvius, I gather that it reflects an observed (and perhaps calculated) reality of the preservation and decay of books. Even when stored within a personal library (thus the owner would have vested interest its maintenance and preservation) books could still be subjected to decay and damage. This is not unlike the comments made by Galen that some of books he encountered in the Roman libraries were often in an almost unusable state due to decay and moisture (Peri Alupias 19)
These factors affected the longevity and useful life of books, even when stored within a personal library.
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Vitruvius, De Architectura. (Joseph Gwilt, translator. London: Priestley and Weale, 1826).