Many open-air porches can be converted to three-season rooms. How easily this can be done depends a great deal on how ornate the porch is. It’s relatively simple to install window and screen units and a door on a porch that has rectilinear posts and simple railings. Adding windows and a door to a porch that has tapered or heavily molded columns, elaborate brackets, and complex or curved railings requires more thought, more construction skills and usually incurs more cost.
Door, window, and screen units are often much the saem for simple and complicated installations alike. The extra cost and installation expertise comes from figuring out how to fill in between rectangular door, window, and screen unit, and the existing curved porch columns and railings.
Converting a porch to a sunroom is a bit more difficult and expensive. Insulated windows and doors are costlier than those with single-pane glass. Insulating an existing porch floor and roof isn’t necessarily expensive or difficult, but it may not be very effective either. Nevertheless, charming sunrooms have been made from porches.
Before you consider how to convert an existing porch, make sure it is structurally sound. It will require good footings and foundations; no rotting or deteriorating posts, joists, floor boards, or roof members; and no leaning or tilting. If it’s going to cost a lot of money to fix the structure before you convert the space, you should probably tear off the existing porch and build from scratch.
Converting a Deck
A deck is often an ideal site for a three-season room or sunroom addition. Decks are usually located where sun, shade, and wind conditions on your property are optimal. They are usually adjacent to a room in the house that is desirable for connection to a three-season porch or sunroom. They likely already have a door or sliding door suitable for access to the new room, and they can provide, at the least, a ready-made floor or subfloor.
Before you convert a deck, thefootings will need to be inspected to see if they are large enough to carry the additional load of walls and roof. A contractor or codes department can help with these calculations. If the footings are insufficient, you may be able to enlarge them with additional concrete, or it may require temporary supports, while tearing out existing footings and re-pouring the foundation.
Because most patios are just a slab of concrete on the ground, you’ll need to add footings to support the room’s structure. The most cost-effective way to do this is to trench footings around the outside of the slab and erect the walls on those footings, with the slab “floating” inside the footings. If the patio is larger than the room you want to add, you can cut through the concrete and pour footings for the walls. This process can cost more than demolishing the patio and building from scratch, so do a thourough evaluation before undertaking it.
Photo below shows an enclosure constructed on top of an existing composite deck.