I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear about your situation.
Oregon law requires all landlord to maintain rental premises in a fit and habitable condition. Ore. Rev. Stat., Section 90.320. The absence of a back fence would not be enough to cancel the lease on its own, but you do have a right to live in a property that has working toilets and no mold. The statute specifically requires that plumbing fixtures be maintained in good working order. The statute also requires that electrical lighting be maintained in good working order, so lights shouldn't fall from the ceiling and need to be replaced if they do.
When a landlord violates that obligation related to an essential service, the tenant has a right to serve the landlord with a written notice given the landlord 7 days to fix the problem, or the lease will terminate in 30 days. Ore. Rev. Stat., Section 90.360. Working toilets and plumbing are an essential service. The light fixture is not - and probably is not enough on its own to justify terminating the lease (unless you have exposed wires hanging down or something). The notice is extremely important, because if you do not serve the landlord with written notice that you plan to move due to violation of the law, then you'll be found to have broken the lease and could be required to pay rent until a new tenant is found. If the landlord makes the repairs within 7 days, then the lease will remain in effect.
Also, if the toilet presents a recurring problem within 6 months after you give that notice, then you can give 14 days written notice and vacate. You just need to have all of the necessary documentation to protect yourself if the landlord tries to sue.
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