As a leading home improvement contractor in Yorktown, Virginia we work on decks on a weekly basis.  We have tons of experience with building, repairing and maintaining decks.  We have talked with thousands of clients and we get asked several of the same questions each week.  One of the main questions we get asked is if you can convert my deck into a screen porch?  The short answer is no.  The deck foundation is different then what you need for a screen porch that will have a roof structure.  Most decks have footers around the post and that is it, but a screen porch requires a continuous footer (Picture a concrete border around the perimeter of your structure).