This is a very common problem with Trulia and Zillow. They only take into account the current market value of the home based on recent sales in the area and the average sales price for that zip code. There is no consideration for upgrades or additions or even features. It is a flawed system. If you'd like a free Comparative Market Analysis to find out the actual market value of your home, I'd be glad to help. Call anytime.
Jeff Metcalf, REALTOR(R)
Watson Realty Corp.