New answers tagged load-bearing
A floor made out of 2x4s would need all the help it can get. Leave it alone or sister it properly, preferably: fix it using sisters. Consult span tables for what to use; I'd guess 2x8s or larger. This isn't really a task for the inexperienced, unless you're willing to ask about 50 more questions and buy a bunch of stuff you're probably never going to use ...
Pre-demolition, this could have been a "double floor" or "double framed floor". If you look up the wikipedia article on floor joists(I would link directly, but I don't have enough rep), it gives you a bit more context. The intention being one set is for the ceiling, and the other is for the floor above. Alternatively, with century homes in particular, you ...
I wouldn't trust a random individual on the internet to correctly identify bearing walls. There are general guidelines for identifying bearing walls, but many exceptions to the rules. Get a competent person in your kitchen to look at the structure. From there, you can figure out the engineering.
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