Most seeds will remain viable in storage for several years if they’re kept under optimal conditions—namely, low humidity and low temperatures (ideally 42°F or less).
A simple way to think about it is: The sum of the temperature (in Fahrenheit) and the percent relative humidity should equal less than 100.
Now, that’s not the best-case scenario, but it’s the best real-life scenario. If you keep your seeds at 55°F with 35 percent relative humidity (which is feasible for a basement), you’re right at the upper end of what’s considered “optimal conditions.”
Places you generally want to avoid for seed storage are laundry rooms, bathrooms, attics, rooms that get plenty of sun, and uninsulated garages or outbuildings.
Remember: The worst conditions for stored seeds are places with high moisture and high temperatures.