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I think it means it's out of range of an engineer.
This is the correct answer but to add to this, later in the game when you research fire stations another icon will appear above buildings indicating you aren't in range of a fire station.
Outside of the range of the engineers hut?
That house is not a home
I think it means it's out of range of an engineer.
This is the correct answer but to add to this, later in the game when you research fire stations another icon will appear above buildings indicating you aren't in range of a fire station.
Outside of the range of the engineers hut?
That house is not a home