Fun fact. When you have a piece of a home that was used to make a bigger home, but at one point someone just had that piece of home insured it turns out to be sort of a cluster f**k of a situation when it comes to insurance.
While my situation is not normal; it is also not unheard of (thankfully). There is indeed insurance for the un-insurable. To get it you (in Texas) you have to find an agent that will write a Government insurance plan for the property.
This is of course like Government cheese in the sense that it is indeed cheese, but its not a Kraft single by any means. Government insurance is meant to cover only the most wicked of situations (think, fires, explosions, meteors etc.). Some of the common situations you might encounter as a home owner, like a tree falling on your house is not covered.
When I was told about the insurance, I was skeptical that this would be very affordable as I had already heard rates from $3,500 to $4,000 per year or more for a home costing less than $200k. That was of course before they just outright denied any coverage due to the house build / situation.
Turns out that Government insurance is not that bad. Certainly not as affordable as I could get if this was just classified as a single family home but closer to that $2,500 per year range (which is still more than $1,500 per year than I pay for my suburban home).
You have to be careful though as this insurance does not cover everything a normal policy would and should only be used for the worst of worst calamities. You can purchase some supplemental insurance that helps which I will also investigate but for now if you are in a situation where you are being turned down by multiple companies for insurance and are in Texas, find an agent that can write a government insurance policy. Your 100% guaranteed to be approved.