Impact window and door replacement on the North Carolina coast

Debris protection

Required for glass east of the Intracoastal Waterway, from the South Carolina line to Beaufort Inlet (Section R202). The protection passes a large-missile impact test, or is a precut wood panel built to the code (Section R301.2.1.2).

Town rules

A town can set its own debris region, as Holden Beach does in its flood chapter.

Design wind speed

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

Pressure rating

Every window and door, on every house. Garage doors too, with one flood-zone exception. It grows with the wind speed and the roof height (Section R609.2; Tables R4502(a) and R4502(b)).

Building permit

None for windows or doors replaced on a single-family house, for $40,000 or less and done to code (General Statute 160D-1110).

Energy code

A U-factor of 0.35 or lower for a whole new window, in climate zone 3, which takes in all three counties (Table N1102.1.2).

The debris rule follows the Intracoastal Waterway. East of it, from the South Carolina line to Beaufort Inlet, the state code draws a windborne debris region. On this coast, that means the barrier islands, such as Oak Island, Wrightsville Beach and Topsail Beach. There, glass in windows, doors and garage doors has to be protected from flying debris. Mainland towns such as Southport, Leland and Wilmington sit outside it.

A town can also write a line of its own. Holden Beach's flood chapter defines its own debris region, by distance from the coast and by wind speed. For a lot near any line, we confirm which rule applies before anything is ordered.

The pressure rule applies everywhere.

Every window and door has to be designed for the wind loads at your house. So does a garage door, with one flood-zone exception. Wind pushes on the wall it faces and pulls on the others. So each unit is rated both ways, pushed in and pulled out. The rating it needs grows with the design wind speed and the height of the roof. On a tall house at 150 mph, a window has to hold nearly twice the pressure it would on a low house at 130.

Where a window sits on the wall matters too. Wind pulls hardest near the corners of a house. So the code lets a window or door more than 4 feet from a corner carry a lower rating. That reduction does not apply to garage doors. Why a coastal house needs its own standard shows how wind works on a house.

On the mainland, the choice is yours.

Outside the debris region and any town rule, impact protection is your call. The pressure rating still applies. Some owners choose impact glass anyway. Where tall pines stand close to the house, as in St. James, a storm can turn their limbs into flying debris. Impact glass also protects the house when nobody is there to close it up.

The permit follows the cost and the structure.

North Carolina law exempts replacing windows or doors on a single-family house from a building permit. The job has to cost $40,000 or less and meet the building code. A job over $40,000 needs a permit. So does work on a load-bearing part of the house, at any cost. Widening an opening means a new header over it, so we treat that as permitted work.

A historic district reviews windows too.

In Southport's local historic district, exterior work needs a certificate of appropriateness, whether or not it needs a building permit. The review covers the type and style of windows and doors. In Wilmington's local districts, the commission's secretary can grant the certificate for a short list of items that meet the city's design standards. Storm windows, storm doors, shutters and garage doors are on it. Older houses covers the historic districts in more detail.

An opening has two jobs in a storm. It keeps the wind out, and it sheds the rain. Once wind gets in through a failed opening, it pushes out on the walls and the roof. Rain driven past the frame runs down to the framing below, unless the flashing sends it back out.

How each opening goes in

• The old unit comes out, and we check the framing and sill it sat on
• A sill pan goes under the new unit, sloped or sealed to send water out
• The unit is set, shimmed and anchored to its maker's instructions
• Side and head flashing lap over the pan, each piece over the one below
• The water barrier above laps over the head flashing
• The gap between frame and framing is sealed for air from inside
• Trim and siding go back over the flashing

Where the maker's instructions give no flashing detail, the code calls for a pan at the sill. The pan is sealed or sloped so water drains to the outside of the wall, with flashing at the head and sides as well. How a coastal wall drains explains why the order of the flashing decides whether an opening drains or traps water.

What the old window uncovers

Taking out an old unit shows the framing around it. Water that got past the old window runs down to the sill, so we look hardest there. Rotted framing is repaired before the new unit goes in. Damage that only shows once the old unit is out is carried as an allowance in the price. When the siding around the windows is failing too, the job becomes a wall job, covered on our exterior envelope page.

Sealed for air, too

The gap between the new frame and the wall framing gets sealed from inside. It is one of the joints the energy code has sealed in a new house, and we seal it the same way. Airtightness covers the other joints a tight house depends on.

Doors carry ratings of their own.

Glass doors follow the same debris rule as windows. A sliding door carries the same kind of lab label a window does. A swinging entry door is tested and labeled to a door standard, or tested another approved way. Solid or glass, every outside door needs a pressure rating. Glass in a door counts as a hazardous location, so in most cases it has to be safety glass. The same goes for low glass beside a stair or its bottom landing.

Garage doors are rated for wind too.

A garage door is a big opening. If it gives way in a storm, wind rushes in and pushes out on the walls and roof. The code has garage doors tested for wind pressure, and each has to pass a standard written for garage doors (ANSI/DASMA 108). The pressure it must hold comes from the code's own garage door table. Like a window's, it grows with the wind speed and the height of the roof. A ground-level garage door under a house on pilings in a flood zone can be exempt, under conditions the code sets.

Where the debris rule applies, glass in a garage door has to be protected too. It meets an approved impact standard, such as ANSI/DASMA 115, which strikes the door with a missile and then cycles the wind pressure. The code's debris rule for garage doors speaks to their glass. On a door with no glass, you can still choose one tested for impact.

The choice comes down to how you live with storm season. Impact glass is always in place, so the house is covered while you are away. Shutters and panels ask someone to close them before each storm. Panels also need a dry place to keep them in between. Whichever you choose, each opening still carries its pressure rating.

A screened porch can stay open.

Where protection is required, a covered porch closed in with screen needs no impact protection of its own. Neither does one closed with removable vinyl or acrylic panels. The protection moves to the wall between the porch and the house, at every opening in it. Removable panels carry a decal saying they come down when wind tops 75 mph.

Read the label before you buy.

A product shows what it does on its label. The design pressure says how much wind load the unit holds, pushed in and pulled out. The impact rating says it passed the missile test. Impact units carry a label naming the maker, the ratings and the inspection agency. We check both ratings against your house, opening by opening.

The glass meets the energy code too.

A whole new window also meets North Carolina's energy code. In climate zone 3, which takes in all three counties, its U-factor has to be 0.35 or lower. The U-factor measures how fast heat passes through, so lower is better. A job that replaces fewer than half the windows may match the ones already there, like or better.

Frames and hardware face salt air as well as wind. Coastal durability covers how we choose materials for this coast.

What we record for each opening

• Its size, and which wall it sits in
• The roof height, and how far it sits from a corner
• Whether the debris rule or a town rule applies
• Any glass near a door, a stair or its bottom landing
• Whether the framing and sill around it are sound
• Any historic district review, and the permit path

What you decide

• Impact glass, or tested shutters or panels
• The frame, the glass and the style
• Which windows, doors and garage doors join the job
• Whether new siding joins the job too

Each choice goes into your private online workspace, with the reason behind it. When the job grows past the openings, how we assess a house explains the wider record we start from.

In a flood zone, the windows count.

In a mapped flood zone, a window package counts toward the 50 percent flood rule. It adds to everything else done to the house inside your town's time window. New windows, a new roof and a kitchen in the same year can reach the line on an older cottage. So we check all the work inside your town's time window against its rule first. The town-by-town table lists each rule.

Smaller jobs are welcome.

This is often a smaller job: one slider, a garage door or a few windows. We take those on too. One opening gets the same rating check, flashing and record as twenty.