Hay in the Hay Loft?
When a structural engineer wants to know what the space will be used for, they are typically trying to figure out what live loads should be applied to structure. Depending on the usage of an area the loading will vary.
For example, if the space is going to be used as a storage area the live load is going to be higher than if the space was used as a residential living space. Typically, the higher the volume of people the higher the loading is going to be, like corridors, classrooms, and other assembly areas. Another area that higher loading is used is in storage areas. Structural engineers have no idea what could be placed in this space, it could be anything from your collection of teddy bears and pillows to antique cast-iron tools. Because of this range the engineers tends to lean towards a more cautious number.
There are general rule of thumbs that are used to come up with the live load but when this question is asked the engineer is looking for anything specific that might add weight to the structure or need design consideration. Two good examples of this is first a hot tub. The floor under a hot tub needs to be designed so there isn’t excessive deflection under the weight of the water. The second example is a spiral stair case. The spiral stair case is great for a compact space but structurally the stairs put a large point load on the floor under the center pole. This point load needs to be transferred through the framing system.
So this question is again asked for accuracy in the design of the structure. Also, don’t give the engineer a hard time if they ask if hay is going to be stored in the hay loft. You would be amazed how many people call the space a hay loft but don’t plan on ever putting any hay there.