Back in the days of coal fires and no central heating. A coal delivery man came with horse and cart they had a rope and pulley system to hoist up the heavy hessian bags so the ground floor would have a man securing bags to a rope and a wooden door that opended on the first or second floor would have a servant or coalmans apprentice on the upper level to pull up the bags this is where they’re stored so it was done for convenience less labour. Ice was also delivered on pallets and sacks of grain if there wasn’t a purpose made coal store/ice/grain store. Here’s an example this is my neighbour.

“The Manor House” Victorian, C early 1880’s

Now an Architects Firm ironically built by a prominent Architect in the town built two historic buildings across the road and many others locally.

Round the back is a car park and a purpose built store

So it looks like a backwards L shape where there’s windows this is now a small kitchen but originally the whole part would have been stores for coal ice grain etc and may or may not have connected to the main house the above example is still connected (many people block off access) an extension if ya willnote the wooden door for access and a now blocked off upper level. Not every house had the example above some had that seemingly random door in the house but generally if you had servants and could afford to have a house built like this then it definitely would have had a separate outhouse. I think this is what you’re talking about it sounds like it to me though i don’t know what it’s proper name is if it had one it’s the stores or coal store/house outhouse silo many different names.

“Mews Houses” Bruton Place, Mayfair, London. External door on second floor level, this is building 3 of 3 identical buildings next to each other, they were horses stables originally I believe because they’re a typical design of such a structure in this country and they are identical to the building below which is known to have historically been a horses stables aka “mews”

“Mews House” Mayfair, London.

In this above example the winch still remains above the door on the second floor level, using a rope and pulley system this is what sacks were hauled up into the building with. All these buildings in this post originally had this winch for this purpose and these last two pictures would have had horse feed sacks loaded into and stored.