ADOPTS WITH AMENDMENTS:

International Residential Code 2009 (IRC 2009)

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Chapter 46 Coastal and Flood Plain Construction Standards

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This section has been amended at the state or city level.
This chapter is a North Carolina addition to the 2009 International Residential Code.

Section R4601 Purpose, Application and Scope

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R4601.1

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The requirements set forth in this section shall apply to all construction located within areas identified by governmental agency (state and federal) as coastal high hazard areas, ocean hazard areas, the regulatory flood plain areas, and all areas designated as 130 mph (57 m/s) wind zone. See Table R301.2(1).

Section R4602 Definitions

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This section has been amended at the state or city level.
BASE FLOOD ELEVATION. The peak water elevation in relation to MSL expected to be reached during a design flood which is established by the North Carolina Building Code Council as a flood having a 1 percent chance of being equaled or exceeded in any given year.

COASTAL HIGH HAZARD AREA. An area subject to coastal flooding and high velocity waters including storm wave wash, as shown by Federal Emergency Management Agency Maps and subject to the approval of the Building Code Council.

FLOOD PLAIN. Land below base flood elevation, which of record has in the past been flooded by storm water-surface runoffs, or tidal influx, and as defined by the Corps of Engineers' maps, the Federal Emergency Management Agency maps or as approved by the Building Code Council.

LOWEST FLOOR. The lowest floor of the lowest enclosed area (including basement). An unfinished or flood-resistant enclosure, usable solely for parking of vehicles, building access or storage in an area other than a basement area is not considered a building's lowest floor: provided
  1. That the walls are substantially impermeable to the passage of water and the structural components have the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy, or
  2. Construction shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing the entry and exit of flood waters.
MSL. Mean Sea Level as defined by National Geodetic Vertical Datum.

OCEAN HAZARD AREA. An area, as identified by the North Carolina Coastal Resources Commission, and subject to approval by the Building Code Council, near the shoreline of the Atlantic Ocean which has been identified as subject to at least one of the following hazards: (A) Historical or predicted future trends of long-term erosion, (B) erosion expected to occur during a coastal storm reaching the base flood elevation, or (C) shoreline fluctuations due to tidal inlets.

Section R4603 Piling Standards

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R4603.1

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All one- and two-family dwellings in areas identified as coastal high hazard areas or ocean hazard areas shall be constructed on a pile foundation of wood or concrete.

R4603.2 Concrete Piles

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Concrete piles may be used if made and installed in accordance with the North Carolina Building Code, Chapter 18.

R4603.3 Size of Wood Piles

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Round timber piles shall not be less than 8 inches (203 mm) in diameter at building level and have a minimum tip diameter of 6 inches (152 mm). Square timber piles shall not be less than 8 inches square (0.005 m2), nominal. Piles supporting uncovered stairs, uncovered walkways and uncovered decks shall be 6 inches x 6 inches (153 mm x 153 mm) minimum, or if round, have a minimum tip diameter of 6 inches (153 mm). Piles supporting uncovered stairs, uncovered walkways and uncovered decks less than 5 feet (1524 mm) above grade may be 4 inches x 4 inches (102 mm x 102 mm) minimum.

R4603.4 Required Depth of Piles

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This section has been amended at the state or city level.
Pile tip shall extend to a depth of not less than 8 feet (2438 mm) below the natural grade or finished grade of the lot, whichever is lower. All pilings within the Ocean Hazard Area shall have a tip penetration of at least 5 feet (1524 mm) below mean sea level or 16 feet (4877 mm) below average original grade, whichever is least. Structures within Ocean Hazard Areas which are placed upon the site behind a line 60 times the annual erosion rate away from the most seaward line of stable natural vegetation are exempt from this additional tip penetration requirement.

R4603.5 Spacing of Wood Piles

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The maximum center-to-center spacing of wood piles shall not be more than 8 feet (2438 mm) on center under load-bearing sills, beams, or girders. However, for dwellings having more than two stories above piles or where the piling spacing exceeds 8 feet (2438 mm) on center, the pile foundation shall be designed by a professional engineer or architect. Pile spacing in the nonload-bearing direction may be 12 feet (305 mm).

R4603.6 Tieing and Bracing of Wood Piles

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If sills, beams or girders are attached to the piling, a minimum of two 5/8-inch (16 mm) galvanized steel bolts per beam member shall be through bolted at each piling connection. Piling shall not be notched so that the cross-section is reduced below 50 percent. Sills, beams or girders may be attached using 3/16 x 4 x 18-inch (5 x 102 x R467 mm) hot dip galvanized straps, one each side, bolted with two 1/2-inch (12.7mm) galvanized through bolts [see Figure R4603.6(a)]. Bracing of pile foundations is required where the clear height from ground to sill, beam or girder exceeds 10 feet (3048 mm) or the dwelling is more than one story above piles. A line of X-bracing is defined as a row of piles with X-bracing provided in at least two bays. A line of X-bracing shall be provided at all exterior pile lines. Where the perimeter lines of X-bracing exceed 40 feet (12192 mm), an additional line of X-bracing shall be provided near the center of the building [see Figure R4603.6(b)]. X-bracing shall be with 2 x 10s through bolted with two 3/4-inch (19.1 mm) bolts at each end. The building inspector may accept alternate bracing designs if they bear the seal of a professional engineer or architect.

FIGURE R4603.6(a)

FIGURE R4603.6(b)
ELEVATIONS (SHOWING POSSIBLE ARRANGEMENT OF X-BRACING IN LINE) (G AND H SIMILAR)

R4603.7

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The minimum net retention of preservatives shall be in accordance with AWPA U1.

R4603.8 Piling May Be Placed by Auger, Jetting or Drop Hammer

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Piling shall receive a final set by drop hammer or other approved methods, acceptable to the building inspector to ensure compaction of material at end bearing.

Section R4604 Elevation Standards

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R4604.1

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The lowest structural member, excluding pilings and bracing supporting the lowest habitable floor in the coastal high hazard area and ocean hazard area, shall be elevated above the base flood elevation.

R4604.2

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The elevation of the first habitable floor of all structures in the regulatory flood plain except in the coastal high hazard areas shall be above the base flood elevation.

Exception: This requirement does not apply to the addition, renovation or reconstruction to any building which was constructed prior to the initial Flood Insurance Study for that area if the addition, renovation or reconstruction does not exceed 50 percent of the present market value of the structure.

R4604.3

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Where walls are constructed below flood elevation in coastal high hazard area and ocean hazard area, they shall be constructed in a manner to eliminate wave forces on the piling.

Section R4605 Construction Materials and Methods Standards

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R4605.1

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The requirements of Sections R4605.2 through R4605.9 are applicable in the coastal high-hazard area, the ocean hazard area, and all areas defined as 130 mph (57 m/s) wind zone.

R4605.2

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Every rafter or roof truss shall be anchored to the bearing wall as required by Section 4408. At the ridges, rafters shall have a minimum 1 x 6 or 2 x 4 collar or wind beam. Every third rafter not to exceed 4 feet (1219 mm) on center shall be anchored vertically with minimum 1 x 6 or 2 x 4 from its midpoint to ceiling joists below.

R4605.3 Wood Frame Wall Construction

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Maximum stud spacing shall be 16 inches o.c. (406 mm) for 2 x 4s and 24 inches (610 mm) for 2 x 6s. See Section 4405 for wall construction requirements. See Section 4408 for uplift anchorage requirements. Wood structural panel sheathing, including endwall sheathing, shall extend 12 inches (305 mm) beyond construction joints and shall overlap girders their full depth. Panels may be installed with face grain either parallel or perpendicular to stud.

For SI: 1 inch = 25.4 mm.
FIGURE R4605.3(a)
TWO-STORY WALL SECTION (TYPICAL)

FIGURE R4605.3(b)

R4605.4

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Equal or better methods of tying structures together and to foundations designed for a specific building by a registered design professional shall be accepted by the building inspector.

R4605.5

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In the coastal hazard area and the ocean hazard area, all metal connectors and fasteners outside of conditioned spaces shall be hot-dip galvanized steel after fabrication and meet ASTM A 153. Exposed metal connectors, such as tie-down straps on porches, decks, and areas under the structure, shall be a minimum 3/16-inch (5 mm) thick, and shall be hot-dip galvanized after fabrication and meet ASTM A 123 or ASTM A 153. Stainless steel light-gage metal connectors shall be permitted in exposed or partially exposed locations. Metal connectors of approved equivalent corrosion-resistant material may be accepted. See Table R4605.5.

TABLE R4605.5a
CORROSION RESISTANCE
(Applies only to Structure(s) Located in Coastal High-Hazard Areas and Ocean Hazard Areas)
OPEN (exterior, porches, under house) EXPOSURE LEVEL VENTED/ENCLOSED (attic, floor trusses, enclosed crawl spaces and stud cavity) CONDITIONED (heated/cooled living areas)
Nails, staples, screws Hot-dip galvanized Hot-dip galvanized -
Nuts, bolts, washers, tie rods Hot-dip galvanized Hot-dip galvanized -
Steel connection plates & straps
(3/16" minimum thickness)
Hot-dip galvanized after fabrication Hot-dip galvanized -
Sheet metal connectors, wind anchors, joists hangers, steel joists and beams Stainless steel or hot-dipped galvanized after fabrication Hot-dip galvanized after plate fabrication or triple galvanizedb Hot-dip galvanized or triple galvanizedb
Truss plates Stainless steel or hot-dipped galvanized after fabrication Hot-dip galvanized after fabrication, stainless steel, triple galvanizedb or in accordance with TPI-1 of the Truss Plate Institute within 6'-0" of a gable louver, ridge or soffit vent. Otherwise Standard galvanizedb. Standard galvanizedb
  1. Applies only to structures located in Coastal High-Hazard Area and Ocean High Hazard Area.
  2. Triple galvanizing — G185, standard galvanizing — G60 both per ASTM A 653/A 653M.

R4605.6 Building Anchorage

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This section has been amended at the state or city level.
  1. For masonry buildings, the roof structure, including rafters and joists, shall be anchored to the wall in accordance with Section R606.9.2.1. All mortar used for masonry walls shall be Type M or S.
  2. For masonry or wood frame buildings, all sills, beams or girders which resist uplift (including interior sills, beams, girders, and joists where the perimeter is unenclosed) shall be anchored to the footing in accordance with Section 4404. Footing dowel bars shall have an 8-inch (203 mm) hook.
  3. Where wood partitions and masonry walls join, the stud abutting the masonry shall be double and bolted to the masonry with three 1/2-inch (13 mm) galvanized bolts.
  4. Steel and wooden columns and posts, including porch columns, shall be anchored with metal ties and bolts to their foundations and to the members that they support.

R4605.8 Insulation

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Insulation installed in floors in buildings elevated on pilings shall be held in place with plywood with exterior glue or other material approved by the building inspector.

R4605.9 Accessory Structures

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Detached accessory structures and out buildings shall be bolted to their foundation or otherwise constructed so as to prevent overturning during high winds.
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