Mildly Infuriating

I don't know if I'm supposed to upvote you because I like your comment or downvote you for being right.

unless you don’t consider steel frame buildings and pole sheds, but why wouldn’t you?

You do not, in fact, count those buildings towards your houses square footage. Doing so would open yourself up to all sorts of liability.

Covered, enclosed porches can only be included if heated and using the same system as the rest of the house. Garages, pool houses, guest houses, or any rooms that require you to leave the finished area of the main house to gain access are not counted in the square footage of a house. source

The only common situations in which the exact size of a home may be legally important would be:

1. For tax appraisal purposes
2. For qualifying for a certain mortgage or home equity loan
3. If a buyer has already bought, or at least has signed a contract on a home, and now claims that fraud was committed because the home is not as large as advertised. source

For further considerations of those that are interested (ANSI Draft, figure 1, page 6, outside source as the real ansi website is just atrocious to navigate and I'm not gonna dox myself by loading up local code.)

As shown, the upper-level plan has an open foyer and a protruding window that does not extend to the floor; neither area contributes to the square footage of the upper level. The calculated finished square footage of the entry level does not include the protruding fireplace, covered patio, garage, or unfinished laundry. The finished area of the basement is counted toward the below- grade finished square footage in its entirety, including the area under the stairs that descend from the entry level. The area of the unfinished utility room is calculated by using the method prescribed in the standard but is not included in the below-grade finished square footage.

All that aside, you're slapping a 25'x52' shed onto your 1/4 acre property? That's almost 20% of your land use not including lot encroachment setback, drainage, and basic driveway/building infrastructure. It's your property so definitely do as you wish, but to think this is a common practice or a desirable thing outside of niche hobbyists or being used for work related activities/storage is nonsense. Neighborhood flooding, no natural green spaces for habitats, it all sounds like a horrible dystopia on your mini-compound.

Excellent point. The initial intent of my squabble wasn't trying to deny that counter-examples exist, just that when comparing 100 houses to 100 apartments, that there seemed to be losses in living space for the apartment (law of averages and whatnot).

I had made another comment on that /c/FuckCars thread that calculated that if all of the homes had 1-car garages (which is not uncommon for a lot of dense low-density suburbs), then the homes would be 1740 SqFt with the garage / 1500 SqFt Livable, and the apartments would be 1009 SqFt livable. So a 33% loss of livable space in the image with what I would consider a reasonable assumption.