Old beadboard or plywood walls in an enclosed porch should be removed, if possible. It’s better to get the walls down to the studs so you can add insulation and check the wall framing for any repairs needed. Don’t get tempted to nail up drywall over other materials or the walls may not be smooth when you finish them.
Staple up fiberglass insulation between studs. Areas around windows will need careful attention to prevent any gaps that will allow air to leak through.
While walls are open, decide if you need extra outlets in the room. Consider any new light fixtures or plumbing needs as well. Be sure to install water pipes, drain lines and electrical wiring while interior studs are fully exposed. You want to route plumbing and electrical needs between studs, and you may need to drill holes in studs to route pipes or wiring in a horizontal fashion. Figure out if you will need to go into the house attic or foundation to connect to electrical sources or water lines, for example.
Nail up drywall to cover wall areas between windows and on the lower half of the porch. Wood trim will help cover any areas around windows or doors that are out of kilter. You will need to fit the drywall as tightly as possible to eradicate any gaps where air might come in. Install drywall tape and use joint compound to smooth out all seams and fix gaps. A light neutral color, such as pale taupe, will work well for painting the drywall.
The creative use of crown molding, chair railing and other trim can give the room an upscale look. Use more rustic wood trim designs if the porch is very informal. If the enclosed porch is visible from dining or living room space, consider using high-quality oak or cherry molding and trim.