Convert decks to screen rooms by examining the existing posts and foundation, adding more support if necessary, choosing a roof, closing floor spaces and adding screening. Do this work yourself if you have advanced skills, or consult with a professional.
Check with your local building code authorities to verify the type of foundation that is necessary to add a screened porch with a roof. Add more posts and foundation piers if necessary, or pour a solid concrete foundation. Add more or larger joists and beams, as the porch is much heavier than the deck with the addition of the roof. Remove the railings if you are building a floor-to-ceiling screened porch.
If there are spaces between the existing deck floorboards, attach mesh screen or landscape paper to the underside of the floor to keep bugs out. Alternatively, replace the existing deck with tongue-in-groove or other types of flooring with no spaces in between the boards. For the roof, choose a design that matches the house, and use the same building materials as the main roof. Rearrange the gutters and spouts as needed to ensure proper water runoff. Choose and install screening that best suits the new porch, such as pre-made panels, fiberglass, bronze or monel.