Where do they store two yrs worth of food? That’s a lot of storage space.
Most people shoot for a years supply, but more never hurts. But you are right it’s a lot of space.
Many homes in Utah county have cold storage rooms as part of the basements. Even if the person does not plan on using it, the builders recommend it for resale value.
I personally store my wheat outside in containers on the south(least sun) side of my house. All the rest of my storage is in my basement in a cold storage room. The worst place is a garage/shed that gets full sun, but still better than not having it.
Before my current house I stored it under the bed and in the closet. Just look at the things under your bed or in your closet and say would I rather have that space taken up by food storage, or would I rather have that thing. You would be surprised how much food you can fit in places.
Having a 3900 sq ft house helps. When my house was half that size, the storage was divided between the garage and parts of the bedroom closets. The 55 gallon drums of water were stored outside. Now that I live in a place that gets as cold as -21 F, I'll have to find a better solution for the water storage. The basement remains at a steady +64 F all year long.