Your house insurance policy is not an investment policy to be drawn upon when a situation like this arises, it is for specific perils that are named on the policy, such as fire, lightning, explosion, storm damage etc., gradual deteroritation is not covered I regret to say and your Insurer will turn the claim down and will most probably log the details, for reference in the event of any future claims. I know this is not what you want to hear, but with falling premiums, Insurers are very alert to this.