Things You'll Need
Drill and screws
Enclosed but uninsulated sitting areas are known as three-season porches, but if you live in a northern state, cold weather can reduce that to two or even one-and-a-half seasons. Adding insulation batting to the walls and floor of your three-season porch can extend its usefulness during cold weather. Choose a batting width that is equal to the space between your wall studs to make installation easy.
Remove any interior paneling, exposing the cavities between the wall studs and rafters. The windows take up most of the wall space on most three-season porches, but insulating as much of the walls as you can will go a long way toward providing comfortable temperatures.
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Caulk around window and doorframes, as well as any point where wires or pipes penetrate the wall, roof or floor of the porch.
Slide a piece of insulation batting into the space between two wall studs, the faced side pointing toward you. Push the batting in until it makes contact with the exterior wall, then pull outward until the batting is flush with the edge of the studs. Cut any strips of batting that are too long, rather than folding them over. Reinstall the interior walls, covering the insulation.
Push an insulation batt up between the rafters, faced side down. Hold it in place with one hand while stapling the insulation flanges to the rafters with the other. Avoid compressing the batting, as this will reduce its insulating capacity. Do the same with the remaining rafters until the entire ceiling is insulated. Reinstall the ceiling paneling.
Crawl under your porch and install strips of batting between the floor joists the same way, this time with the facing side upward. The friction between the sides of the batting and the studs will hold the insulation in place. Screw sheets of plywood to the underside of the joists to keep the insulation clean and protect it from wildlife.
Choose insulation of an R-value appropriate for your area's climate for best results. Use an online R-value calculator to easily determine what quality of insulation to buy (see Resources for link).
Replace any single-paned windows with double or triple-pane ones instead, if so desired, to help the insulated porch retain even more heat.