There are lots of studies that are thrown around on how much money you can expect from your investment in home improvements. Some of them, frankly, are contradictory.
Don't build a deck addition
While your area may expect an outdoor entertaining area, if your deck is of at least a similar size to other small outdoor spaces, you're likely to see $0 return for this. In fact, decks and patios are shown to have no contributory value in most markets in the RVA area.
Don't add a fireplace
99% of the contracts that I see have the following sentence, "Seller makes no warranty as to the function of the fireplace." In other words, "I didn't use it, in fact I forgot all about it." In the early 1900's a fireplace was a desired feature in a home, today, no one uses it. If I place an object in your home for 5 years, and you never use it, how valuable is it to you?
Don't build a pool
For the most part, a pool is a hole in the ground to throw money in, year after year after year. Part of the market wants a house with a pool, and part of the market will not buy a house with a pool due to the insurance increase, and annual maintenance costs. These are a very low ROI proposition investments.
Don't build a massive addition
Before you build an addition, save yourself a future headache and get an appraisal. If you build an addition that makes your home 50% larger than the entire area you're in, there is a high likely hood that you will see a very low ROI for that addition.
Don't over-improve your property
If homes in your neighborhood have hardwood floors and laminate counters - marble floors, granite counters and imported hardwood shiplap is probably going to be a waste of money. The old rule applies "Don't buy the best house in the neighborhood," to this as well. The highest return on investment will always be for homes that "conform to the market," in other words, that look like everything else.