I was working on Fillmore, and I got that house-on-fire event that Sir VG got in his run. Kind of annoying, because I wasn't sure what caused it. I tried to find out what my latest attempt and Sir VG's run had in common. I noticed that in both runs, enough enemies were killed before the first construction phase to cause not just a corn field to be constructed, but also a house. So I did a little experiment: I saved state, then waited until the fire event happened. I then waited again, but this time I destroyed the suspicious house with lightning right before the fire event would normally happen. That time, it didn't happen, and it didn't happen even when I waited long enough for another house to be built on the same location. I reloaded the save state, and tried destroying the offending house immediately after it was built instead of just before the fire event would normally occur. No fire event happened, even when another house was built over the same location. So I'm guessing the way to prevent the fire event is to not kill too many enemies before the first construction phase, so that that house doesn't get built.
The location of the special house is in this image
EDIT: Looks like the maximum number of enemies you can kill before the first construction phase and still not get the house is 7.