Also excluded from Covered Causes of Loss forms, but generally not insurable, are loss by wear and tear, gradual deterioration, rust, corrosion, latent defect, insect or animal damage, etc. The question is still open as to what, if any, effect the “concurrent causation” exclusionary language has on losses in these categories when damage due to any of these produces other not-excluded damage. Previously, only the excluded damage, i.e., the rust damage requiring repair, would not be covered—but resulting damage to other property would be covered. In considering what coverage to purchase, comparison of exclusions from form to form is most important.
Most insurers insist on a mandatory deductible clause applying per occurrence to all or most of the insured causes of loss. A $100 or $500 minimum deductible is common, but higher optional deductibles at progressively reduced premiums are generally also available. In deciding what level of deductible to choose, several factors should be considered: