I use to think that since it is within the house, and that molds are natural occurrences then it should be covered by the policy- wrong. Sewage backup or repair is an additional policy in itself and this is one of the limits of a homeowner insurance policy. If you feel like you haven’t checked your sewage system for years then try to have it assessed or purchase the policy. Molds on the other hand, form only in humid areas and so they’re not usually within the term coverage. If the location of your property is in a humid vicinity then consider buying a mold insurance- it should be much cheaper than having it removed every year.