How To Write A Diminished Value Claim Letter . Document the amount of your lost value by ordering your diminished value report. The below writing guide and tips should help you draft this formal letter to perfection. Sample Demand Letter To Insurance Company For Property Damage from mamiihondenk.org This letter is in response to my inability to collect diminished value damages. Value, the damages include compensation for: Diminished value refers to how much the car had been worth before the collision and the value after all repairs have been completed for the automobile.