Just found this info from the Wessex Sound and Film Archive. I try to keep my films in ideal conditions, but with the hot summers that we occasionally get, temperature will rise above 60f, unless you are lucky enough to have a basement to store these things in.
It is advisable to store film and sound recordings in their proper containers in dark, cold and (not too) dry conditions, which are as constant as possible year round. They should be stored away from pipes, heaters and radiators, sinks, windows, electrical appliances and concrete floors. Lofts, basements, garages, sheds, bathrooms, kitchens, utility rooms and conservatories are not suitable. Excessive temperatures, humidity and dirt can destroy films and sound recordings, as can fire, flood and contamination from insects and rodents.
Reasonable temperatures for long term storage lie in the range 10-16°C (50-60°F) within a low relative humidity of 50-55%; over 65% allows mould growth to occur and may trigger other problems like 'vinegar syndrome' . Official recommendations for archival storage are more stringent and depend upon the type and format of material concerned: most colour films will eventually fade unless kept below 2°C, for example.