Planning a Screened Porch or Outdoor Room Expansion

Porch, deck or covered patio

Any outdoor addition is a trade between shelter, bug control and cost. A deck is the cheapest to frame and gives open sky, but no shade or rain cover. Leaves and grime collect on it, and wood decks need regular cleaning and refinishing.

A covered patio puts a roof overhead and leaves the sides open. It blocks midday sun and most rain, so furniture stays cleaner. Wind-blown rain and insects still get in. Patios usually sit at ground level on a concrete slab or pavers, which suits a slab-on-grade ranch with its floor only a step above the yard.

A screened porch adds walls of insect screen to a roofed structure. It needs a proper roof connection, footings and framing, so it costs more and takes longer than either alternative. In return, it is a room you can use from spring well into fall, with a breeze and without bites.

Roof tie-ins

The roof connection is where porch projects succeed or leak. A poorly planned tie-in brings rot, staining on the interior wall and a sagging edge. There are two common approaches.

A shed roof slopes away from the house in a single plane. It is the simplest to frame and flash, and it attaches below the existing eaves. On a ranch with low eaves, though, there may not be enough height at the house wall to give the shed roof a workable slope and still leave decent headroom at the outer edge. Measure this before falling in love with a drawing.

A gable roof runs out from the house with a ridge of its own. It allows a taller, vaulted ceiling inside the porch, which helps with light and air. Tying it into the main roof means cutting back shingles, framing valleys and weaving step flashing and valley flashing under the existing roofing so water is shed past the joint.

Loads have to go somewhere. At the house side, the porch roof bears on a ledger or beam fastened to the house framing, or on the existing wall. At the outer edge, posts carry a beam down to footings. Footings must go below the local frost depth where frost applies, and ledger fasteners, flashing and spacing follow the local code and the engineer or plans examiner.

Permits, setbacks and zoning

A roofed addition to a house needs a building permit in nearly every jurisdiction. The plans examiner checks footing sizes, beam spans, rafter sizing and connections, and inspectors look at footings and framing before they are covered.

Zoning sets the outer limits. Setback rules fix the minimum distance from the porch to the front, side and rear lot lines, and many towns limit how much of a lot can be covered by structures and paving. A porch that fits the yard can still fail the setback by a couple of feet, so check the survey and the zoning code before paying for drawings. Some subdivisions also have deed restrictions or an HOA review.

Lights, outlets and ceiling fans need an electrical permit and a licensed electrician. Exterior outlets need weather-resistant, GFCI-protected receptacles with in-use covers.

Materials for heat and humidity

Humidity, summer sun and rain are hard on wood and paint. Choosing materials that resist rot and movement keeps the porch from becoming a maintenance project.

Pressure-treated southern pine is the usual choice for posts, beams and joists. It resists rot and insects, but it arrives wet and shrinks as it dries, which can twist and check boards. Use treated lumber rated for ground contact anywhere near the soil, and fasteners rated for treated wood.

Capped composite decking resists rot, fading and stains and needs no stain. Cellular PVC trim works well for post wraps, fascia and screen stops, since it does not absorb water and holds paint well.

Screen comes in several grades. Standard fiberglass screen is inexpensive and easy to install but tears under claws and in high wind. Heavier vinyl-coated polyester pet screen stands up to dogs and cats. Aluminum screen holds its tension over wide panels but dents. Spline-and-frame systems make torn panels easy to replace.

Air, light and the bugs below

Screens stop mosquitoes, but a still porch on a humid evening is still uncomfortable. Ceiling fans move the air, and since mosquitoes are weak fliers, a steady breeze discourages the few that get in. Use fans listed for the location: damp-rated under a solid roof, wet-rated where rain can reach.

Gapped decking lets insects in from below. One fix is to staple screen across the tops of the joists before laying the deck boards; another is a tight tongue-and-groove porch floor laid with a slight slope so rain blowing through the screen drains off.

Adding a fireplace

An outdoor fireplace stretches the porch season into cold weather. A masonry fireplace is extremely heavy and needs its own foundation, separate from the porch framing. Prefabricated fireboxes are lighter and are installed according to their listing, with the clearances and chimney parts the maker specifies.

Clearances to combustibles are set by code and by the unit's instructions. Framing, posts and the porch ceiling must stay outside them, and a non-combustible hearth extension of stone, tile or concrete is required in front of the opening. The chimney has to rise far enough above the porch roof, and above nearby parts of the house roof, to draw properly. A spark arrestor cap keeps embers off the roof and out of the trees. Gas fireplaces need a licensed gas fitter and a permit.

Frequently asked questions

Do I need a permit for a screened porch?

Almost always. A roofed structure attached to the house is a building project, and the building department reviews footings, framing and the roof connection. Zoning rules also control how close the porch can come to property lines and how much of the lot can be covered.

What is the difference between damp-rated and wet-rated ceiling fans?

Damp-rated fans are listed for covered outdoor spaces where humidity and condensation occur but rain does not hit the fan directly. Wet-rated fans are built for places where rain or spray can reach them. A screened porch with a deep roof usually takes damp-rated fans; anything exposed needs wet-rated.

Can a screened porch floor keep out mosquitoes?

Not on its own if it is gapped decking. Insects come up through the gaps from underneath. Stretching screen across the joists before the decking goes down, or using a tight tongue-and-groove porch floor, closes that route.

How does a new porch roof attach to an existing house?

The porch roof framing is carried on a ledger or beam fastened to the house framing, or tied into the existing roof. Flashing laps under the siding or shingles above the connection so water is shed over it rather than behind it.