Most umbrella policies won't take effect until a certain claim amount has been reached, such as $500,000. For that reason, most insurance companies require you to carry that amount of coverage on your underlying policies. For example, you'd need to have a liability limit of $500,000 on your auto insurance in order to purchase an umbrella policy. This ensures you don't have a coverage gap between the limit of your auto policy (or other underlying policy) and the start of your umbrella policy coverage.