Sunrooms and three-season rooms

We start from the assessment. It puts the house on record before a price, along with any porch or deck you want to close in. You keep the drawings, and your private online workspace holds each choice with its reason.

Two kinds of room

Some rooms fall in between. A three-season room can take fixed glass, and then that glass carries the wind ratings a sunroom's does. Leave a room open to the house, and it becomes living space under the full energy code. Then it is built the way a room addition is.

An open or screened porch is on our porches page, and an open deck is on our deck page.

What you decide

• Three seasons with panels, or a sunroom heated and cooled all year
• A new room on a new footing, or a porch or deck you have now, closed in
• Which side of the house it goes on, and which way the glass faces
• Overhangs and shades, and panels or windows that open
• The door between the room and the house
• The floor, a ceiling fan, lights and outlets

How a sunroom goes together

What we find under an old porch or deck is priced as an allowance.

An old porch, deck or slab can hide rot or damage, and so can the house wall where the doorway goes. Damage that only shows once the work opens it up is carried as an allowance in the price.

Code in force

2018 North Carolina Residential Code. A sunroom is a one-story room on the house, with glass over more than 40 percent of its outside walls and roof (Section R202). New work meets the rules for a new structure (Section R102.7.1).

Design wind speed

Brunswick and New Hanover: 140 mph west of US 17 and 150 mph east of it. Pender: 130 mph, apart from Topsail Township at 140 west of the Intracoastal Waterway and 150 east (Table R301.2(4)).

Debris region

East of the Intracoastal Waterway, from the South Carolina line to Beaufort Inlet. Here, that means the barrier islands (Section R202). Fixed glass there is protected from flying debris (Section R301.2.1.2).

Building permit

Always for a new sunroom: its new walls and roof are load-bearing work, outside the $40,000 permit exemption. Closing in a porch needs one too when it adds load-bearing framing, wiring, or heating and cooling (General Statute 160D-1110).

Using the room

Once the inspector issues a certificate of compliance after the final inspection (General Statute 160D-1116).

Closing in a porch or deck you have

Many sunrooms begin as a screened porch or an open deck. Glass or panels turn it into a room, and a room asks more of its frame. Walls and glass add weight, and they catch wind the open porch let through. So the first question is what holds it up.

The code's deck rules cover decks and roofed porches that are open or screened, and a room of glass falls outside them. Whether your old deck, posts or slab can carry the room is an engineer's call, made first. A porch on posts may need new footings under its new walls. On a raised house on pilings, the sunroom must be engineered and permitted.

Look at the windows that open onto the porch today. If one is a bedroom's way out in a fire, the code wants that opening to lead to a yard or the street. Close in the porch, and the new room stands in the way. How that bedroom gets out then becomes part of the design.

In a mapped flood zone, space closed in below the flood height may hold only parking, access or storage. So a sunroom sits at or above that height, and its cost counts toward your town's 50 percent rule.

Close in a porch, and zoning counts it as a room.

Zoning often treats an open deck or porch more gently than a room. Closing one in can run into a setback or a coverage cap it used to clear. Here is how three towns count it.

On the oceanfront, glass adds floor area.

On the oceanfront, the state's setback grows with the house's total floor area. A roofed porch stays out of that total while it is open or screened. Closed in with glass or vinyl, it counts, and the added floor area has to meet the setback.

Along a sound, a tidal creek or many canals, the state's 30-foot buffer from the water applies to a sunroom as to any addition. A few exceptions exist. Our page on room additions covers those waterfront rules.

A historic district reviews it first.

In Southport's local historic district, a certificate of appropriateness from the Historic Preservation Commission comes before the building permit for exterior work. In Wilmington's locally designated historic districts, exterior changes need approval first.

A house built before 1978

A house built before 1978 falls under North Carolina's lead-safe renovation rules. On an older house, an NC-accredited inspector tests materials that may hold asbestos before demolition, such as joint compound or old flooring and its glue. Older houses covers what else a house's age can change.

Removable panels keep it a porch.

In a three-season room, clear vinyl or acrylic panels close in a roofed porch. The code treats them as a windbreak, so they need no wind or impact rating. The trade-off: the panels come out before the wind passes 75 mph, and a decal on each one says so. The wall between the room and the house then faces the storm, and every window and door in it carries the ratings.

Fixed glass carries a rating.

Each window, door and fixed pane is rated for the push and pull of the wind at your house. The rating it needs rises with the wind speed and the height of the roof (Table R4502(a)).

East of the Intracoastal Waterway, the glass is also protected from flying debris. That means impact-rated glass, or shutters or precut panels the code accepts. On the mainland, that protection is your choice. Impact windows and doors explains the ratings.

A wall of glass is engineered.

All of Brunswick and New Hanover Counties, and Topsail Township in Pender, sit at 140 or 150 mph. There, the code braces every wall with wood panel sheathing. A wall that is mostly glass leaves little room for it. Where sheathing covers less than a quarter of a wall's length, that wall has to be engineered (Section R4506.2).

The roof is tied down in one unbroken chain, from the rafters through the posts and walls to the foundation (Section R4508.1). That chain carries the upward pull of the wind on the roof down to the ground.

Low glass near the floor is safety glass.

Glass in a door is safety glass, apart from small or decorative panes. So is a large pane that reaches low to the floor beside a walking surface, unless a rail at waist height guards it (Section R308.4). In a room of glass, that covers many of the panes.

Salt air calls for galvanized hardware.

East of the Intracoastal Waterway, metal connectors and fasteners outside the heated part of the house are hot-dip galvanized, or an approved equal (Section R4606.1). In a three-season room, that takes in every strap and hanger. Coastal durability covers how salt air shapes the hardware we choose.

Which way it faces

West glass takes the low afternoon sun, in the warmest part of the day. East glass takes the morning sun. South glass takes the summer sun high overhead, where a roof overhang can shade much of it. For warm climates, ENERGY STAR says glass that lets in little of the sun's heat matters on south, east and west walls. So the first question for your room is which way it will face.

Glass that holds back the heat

The number to compare is the solar heat gain coefficient, or SHGC. It measures how much of the sun's heat the glass lets in, and a lower number lets in less. The code caps it for the glass in a cooled sunroom (Section N1102.3.5). Going lower than the cap is your choice, and it is worth weighing on west glass.

Shade and moving air

Shade and air are design choices we make with you. The solid roof keeps the high midday sun off the room. A deeper overhang can shade the sunny side, and shades can cut the glare. In hot climates, ENERGY STAR calls generous shade on south-facing glass especially effective. Panels or windows that open let a breeze through, and a ceiling fan keeps the air moving.

Heated and cooled, behind a door

A sunroom you heat and cool is kept apart from the house by a wall with a door. It runs on its own system, or its own zone. The code calls that thermal isolation. In return, the room's glass and insulation may meet lighter values than the house's (Sections N1102.2.13 and N1102.3.5). A new wall or door between the room and the house still meets the house's full rules.

The system is sized from a load calculation for the room (Section M1401.3). A glass room gains heat fast, and an oversized unit cools the air before it can dry it. HVAC design covers why size matters in a humid house.

In North Carolina, heating and cooling is licensed trade work with its own permit, like plumbing, gas and electrical work. So the HVAC trade sizes the system and installs it under that permit. Our note on planning for moisture explains why an air conditioner has to pull water out of the air too.

Left unheated, it is an outdoor room.

Say a sunroom has no heating or cooling, and a wall and a door keep it apart from the house. Then the code asks for no heat in it (Section R303.10). The State Fire Marshal's office calls such rooms outdoor rooms, used by the season. A three-season room left unheated is one of them.

Open to the house, it is living space.

A room left open to the house heats and cools with it, and it meets the full energy code. The state draws one more line for a room that opens into the house. With glass on less than 40 percent of its walls and roof, it meets the heating and insulation rules of the house. Either way, it is built as a room addition is.