Library temperature and relative humidity

The Folger Shakespeare Library aims to provide the best possible climate for preserving the collection balanced with the needs of people doing desk-work (minimum 68°F in permanent work areas) and with the need for sustainability (a tiny improvement for the collection is not worth destroying the ozone layer).

Climate Liaison: Adrienne Bell, Book Conservator,, x332 (contact Adrienne if it is too hot, too cold, etc. in Central Library, the Exhibition Hall, the Founders' Room, or anywhere else collection material is stored. All requests get routed through the Climate Liaison: Adrienne is trained to read the inner workings of the air handlers in the online system so that the facilities manager is not contacted when a unit is already running at 100% or when it is known a part is on order.)


Research conducted since the 1980s has shown that a cooler, drier environment can exponentially slow the natural chemical decay of library and museum collections. It is not that a little cooler is a little better, and a little cooler than that is a little more better—it is that a little cooler is a lot better, and a little cooler than that is much better. At the same time, research shows that maintaining a “flatline” temperature and humidity, with almost no fluctuation, consumes huge amounts of energy in a climate like ours without a corresponding benefit to the collection.

In other words, it makes sense for the collection and for the environment if the temperature and humidity set points are adjusted twice a year to take seasonal change into account: warmer and and more humid in the summer, when the incoming air is much warmer and more humid; cooler and drier in the winter, with the incoming air is much cooler and dryer. In spring and fall, the outside climate is naturally about right, and essentially only requires energy to pull it into the building and filter out pollutants. At the same time, it is not necessary for the temperature and humidity to hold exactly these two summer and winter points. Short-term fluctuation, as long as it doesn’t reach extremes, is okay for most materials. Collection material that could be permanently damaged by fluctuations will be protected by additional housing (e.g., like 16th-century lute is buffered by being in a lined wooden case inside a closed cabinet).

Currently, the Reading Rooms are often too hot in the summer, particularly the New Reading Room. This is because the only way to keep the humidity from rising so high that paintings will be damaged (and mold could grow) is by providing supplemental re-heat. After the second phase of Reading Room air handler unit upgrades, we will no longer have to do this.