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  • PartIIIBuilding Planning and Construction

    CHAPTER3
    BUILDING PLANNING  

    SECTIONR301
    DESIGN CRITERIA  

    R301.1 Application.

    Buildings and structures, and parts thereof, shall be constructed to safely support all loads, including dead loads, live loads, roof loads, flood loads, snow loads, wind loads and seismic loads as prescribed by this code. The construction of buildings and structures in accordance with the provisions of this code shall result in a system that provides a complete load path that meets the requirements for the transfer of loads from their point of origin through the load-resisting elements to the foundation. Buildings and structures constructed as prescribed by this code are deemed to comply with the requirements of this section.

    R301.1.1 Alternative provisions.

    As an alternative to the requirements in Section R301.1, the following standards are permitted subject to the limitations of this code and the limitations therein. Where engineered design is used in conjunction with these standards, the design shall comply with the International Building Code.

    R301.1.2 Construction systems.

    The requirements of this code are based on platform and balloon-frame construction for light-frame buildings. The requirements for concrete and masonry buildings are based on a balloon framing system. Other framing systems must have equivalent detailing to ensure force transfer, continuity and compatible deformations.

    R301.1.3 Engineered design.

    Where a building of otherwise conventional construction contains structural elements exceeding the limits of Section R301 or otherwise not conforming to this code, these elements shall be designed in accordance with accepted engineering practice. The extent of such design need only demonstrate compliance of nonconventional elements with other applicable provisions and shall be compatible with the performance of the conventional framed system. Engineered design in accordance with the International Building Code is permitted for buildings and structures, and parts thereof, included in the scope of this code.

    R301.2 Climatic and geographic design criteria.

    Buildings shall be constructed in accordance with the provisions of this code as limited by the provisions of this section. Additional criteria shall be established by the local jurisdiction and set forth in Table R301.2(1).

    TABLE R301.2(1)

    CLIMATIC AND GEOGRAPHIC DESIGN CRITERIA

    GROUNDSNOWLOADWIND DESIGNSEISMICDESIGNCATEGORYfSUBJECT TO DAMAGE FROMWINTERDESIGNTEMPeICE BARRIERUNDERLAYMENTREQUIREDhFLOODHAZARDSgAIRFREEZINGINDEXiMEANANNUALTEMPj
    Speedd(mph)TopographiceffectskSpecial windregionlWind-bornedebris zonemWeatheringaFrost linedepthbTermitec

    For SI: 1 pound per square foot = 0.0479 kPa, 1 mile per hour = 0.447 m/s.

    1. a.Weathering may require a higher strength concrete or grade of masonry than necessary to satisfy the structural requirements of this code. The weathering column shall be filled in with the weathering index, “negligible,” “moderate” or “severe” for concrete as determined from Figure R301.2(3). The grade of masonry units shall be determined from ASTM C 34, C 55, C 62, C 73, C 90, C 129, C 145, C 216 or C 652.

    2. b.The frost line depth may require deeper footings than indicated in Figure R403.1(1). The jurisdiction shall fill in the frost line depth column with the minimum depth of footing below finish grade.

    3. c.The jurisdiction shall fill in this part of the table to indicate the need for protection depending on whether there has been a history of local subterranean termite damage.

    4. d.The jurisdiction shall fill in this part of the table with the wind speed from the basic wind speed map [Figure R301.2(4)A]. Wind exposure category shall be determined on a site-specific basis in accordance with Section R301.2.1.4.

    5. e.The outdoor design dry-bulb temperature shall be selected from the columns of 971/2-percent values for winter from Appendix D of the International Plumbing Code. Deviations from the Appendix D temperatures shall be permitted to reflect local climates or local weather experience as determined by the building official.

    6. f.The jurisdiction shall fill in this part of the table with the seismic design category determined from Section R301.2.2.1.

    7. g.The jurisdiction shall fill in this part of the table with (a) the date of the jurisdiction’s entry into the National Flood Insurance Program (date of adoption of the first code or ordinance for management of flood hazard areas), (b) the date(s) of the Flood Insurance Study and (c) the panel numbers and dates of the currently effective FIRMs and FBFMs or other flood hazard map adopted by the authority having jurisdiction, as amended.

    8. h.In accordance with Sections R905.1.2, R905.4.3.1, R905.5.3.1, R905.6.3.1, R905.7.3.1 and R905.8.3.1, where there has been a history of local damage from the effects of ice damming, the jurisdiction shall fill in this part of the table with “YES.” Otherwise, the jurisdiction shall fill in this part of the table with “NO.”

    9. i.The jurisdiction shall fill in this part of the table with the 100-year return period air freezing index (BF-days) from Figure R403.3(2) or from the 100-year (99 percent) value on the National Climatic Data Center data table “Air Freezing Index-USA Method (Base 32°F).”

    10. j.The jurisdiction shall fill in this part of the table with the mean annual temperature from the National Climatic Data Center data table “Air Freezing Index-USA Method (Base 32°F).”

    11. k.In accordance with Section R301.2.1.5, where there is local historical data documenting structural damage to buildings due to topographic wind speed-up effects, the jurisdiction shall fill in this part of the table with “YES.” Otherwise, the jurisdiction shall indicate “NO” in this part of the table.

    12. l.In accordance with Figure R301.2(4)A, where there is local historical data documenting unusual wind conditions, the jurisdiction shall fill in this part of the table with “YES” and identify any specific requirements. Otherwise, the jurisdiction shall indicate “NO” in this part of the table.

    13. m.In accordance with Section R301.2.1.2.1, the jurisdiction shall indicate the wind-borne debris wind zone(s). Otherwise, the jurisdiction shall indicate “NO” in this part of the table.

    TABLE R301.2(2)

    COMPONENT AND CLADDING LOADS FOR A BUILDING WITH A MEAN ROOF HEIGHT OF 30 FEET LOCATED IN EXPOSURE B (ASD) (psf)a, b, c, d, e

    ZONEEFFECTIVEWIND AREA(feet2)ULTIMATE DESIGN WIND SPEED, VULT (mph)
    110115120130140150160170180
    Roof 0 to 7 degrees11010.0-13.010.0-14.010.0-15.010.0-18.010.0-21.09.9-24.011.2-27.012.6-31.014.2-35.0
    12010.0-12.010.0-13.010.0-15.010.0-17.010.0-20.09.2-23.010.6-26.011.9-30.013.3-34.1
    15010.0-12.010.0-13.010.0-14.010.0-17.010.0-19.08.5-22.010.0-26.010.8-29.012.2-32.9
    110010.0-11.010.0-13.010.0-14.010.0-16.010.0-19.07.8-22.010.0-25.010.0-28.011.3-32.0
    21010.0-21.010.0-23.010.0-26.010.0-30.010.0-35.09.9-40.011.2-46.012.6-52.014.2-58.7
    22010.0-19.010.0-21.010.0-23.010.0-27.010.0-31.09.2-36.010.6-41.011.9-46.013.3-52.4
    25010.0-16.010.0-18.010.0-19.010.0-23.010.0-26.08.5-30.010.0-34.010.8-39.012.2-44.1
    210010.0-14.010.0-15.010.0-16.010.0-19.010.0-22.07.8-26.010.0-30.010.0-33.011.3-37.9
    31010.0-33.010.0-36.010.0-39.010.0-46.010.0-53.09.9-61.011.2-69.012.6-78.014.2-88.3
    32010.0-27.010.0-29.010.0-32.010.0-38.010.0-44.09.2-50.010.6-57.011.9-65.013.3-73.1
    35010.0-19.010.0-21.010.0-23.010.0-27.010.0-32.08.5-36.010.0-41.010.8-47.012.2-53.1
    310010.0-14.010.0-15.010.0-16.010.0-19.010.0-22.07.8-26.010.0-30.010.0-33.011.3-37.9
    Roof > 7 to 27 degrees11010.0-11.010.0-13.010.0-14.010.5-16.012.2-19.014.0-22.015.9-25.017.9-28.020.2-32.0
    12010.0-11.010.0-12.010.0-13.010.0-16.011.1-18.012.8-21.014.5-24.016.4-27.018.4-31.1
    15010.0-11.010.0-12.010.0-13.010.0-15.010.0-18.011.1-20.012.7-23.014.3-26.016.0-29.9
    110010.0-10.010.0-11.010.0-12.010.0-15.010.0-17.09.9-20.011.2-22.012.6-25.014.2-29.0
    21010.0-20.010.0-22.010.0-24.010.5-29.012.2-33.014.0-38.015.9-44.017.9-49.020.2-55.8
    22010.0-19.010.0-20.010.0-22.010.0-26.011.1-31.012.8-35.014.5-40.016.4-45.018.4-51.2
    25010.0-16.010.0-18.010.0-20.010.0-23.010.0-27.011.1-31.012.7-35.014.3-40.016.0-45.4
    210010.0-15.010.0-16.010.0-18.010.0-21.010.0-24.09.9-28.011.2-32.012.6-36.014.2-40.9
    31010.0-30.010.0-33.010.0-36.010.5-43.012.2-49.014.0-57.015.9-65.017.9-73.020.2-82.4
    32010.0-28.010.0-31.010.0-34.010.0-40.011.1-46.012.8-53.014.5-60.016.4-68.018.4-77.0
    35010.0-26.010.0-28.010.0-31.010.0-36.010.0-42.011.1-48.012.7-55.014.3-62.016.0-69.9
    310010.0-24.010.0-26.010.0-28.010.0-33.010.0-39.09.9-44.011.2-51.012.6-57.014.2-64.6
    Roof > 27 to 45 degrees11011.9-13.013.1-14.014.2-15.016.7-18.019.4-21.022.2-24.025.3-27.028.5-31.032.0-35.0
    12011.6-12.012.7-13.013.8-14.016.2-17.018.8-20.021.6-23.024.6-26.027.7-29.031.1-33.2
    15011.2-11.012.2-12.013.3-13.015.6-16.018.1-18.020.8-21.023.6-24.026.7-27.029.9-30.8
    110010.9-10.011.9-11.012.9-12.015.1-15.017.6-17.020.2-20.022.9-22.025.9-25.029.0-29.0
    21011.9-15.013.1-16.014.2-18.016.7-21.019.4-24.022.2-28.025.3-32.028.5-36.032.0-40.9
    22011.6-14.012.7-16.013.8-17.016.2-20.018.8-23.021.6-27.024.6-30.027.7-34.031.1-39.1
    25011.2-13.012.2-15.013.3-16.015.6-19.018.1-22.020.8-25.023.6-29.026.7-32.029.9-36.8
    210010.9-13.011.9-14.012.9-15.015.1-18.017.6-21.020.2-24.022.9-27.025.9-31.029.0-35.0
    31011.9-15.013.1-16.014.2-18.016.7-21.019.4-24.022.2-28.025.3-32.028.5-36.032.0-40.9
    32011.6-14.012.7-16.013.8-17.016.2-20.018.8-23.021.6-27.024.6-30.027.7-34.031.1-39.1
    35011.2-13.012.2-15.013.3-16.015.6-19.018.1-22.020.8-25.023.6-29.026.7-32.029.9-36.8
    310010.9-13.011.9-14.012.9-15.015.1-18.017.6-21.020.2-24.022.9-27.025.9-31.029.0-35.0
    Wall41013.1-14.014.3-15.015.5-16.018.2-19.021.2-22.024.3-26.027.7-30.031.2-33.035.0-37.9
    42012.5-13.013.6-14.014.8-16.017.4-19.020.2-22.023.2-25.026.4-28.029.7-32.033.4-36.4
    45011.7-12.012.8-14.013.9-15.016.3-17.019.0-20.021.7-23.024.7-27.027.9-30.031.3-34.3
    410011.1-12.012.1-13.013.2-14.015.5-17.018.0-19.020.6-22.023.5-25.026.5-29.029.832.7
    450010.0-10.010.6-11.011.6-12.013.6-15.015.8-17.018.1-20.020.6-22.023.2-25.026.1-29.0
    51013.1-17.014.3-19.015.5-20.018.2-24.021.2-28.024.3-32.027.7-37.031.2-41.035.0-46.8
    52012.5-16.013.6-17.014.8-19.017.4-22.020.2-26.023.2-30.026.4-34.029.7-39.033.4-43.7
    55011.7-14.012.8-16.013.9-17.016.3-20.019.0-23.021.7-27.024.7-31.027.9-35.031.3-39.5
    510011.1-13.012.1-14.013.2-16.015.5-19.018.0-22.020.6-25.023.5-28.026.5-32.029.8-36.4
    550010.0-10.010.6-11.011.6-12.013.6-15.015.8-17.018.1-20.020.6-22.023.2-25.026.1-29.0

    For SI: 1 foot = 304.8 mm, 1 square foot = 0.0929 m2, 1 mile per hour = 0.447 m/s, 1 pound per square foot = 0.0479 kPa.

    1. a.The effective wind area shall be equal to the span length multiplied by an effective width. This width shall be permitted to be not less than one-third the span length. For cladding fasteners, the effective wind area shall not be greater than the area that is tributary to an individual fastener.

    2. b.For effective areas between those given, the load shall be interpolated or the load associated with the lower effective area shall be used.

    3. c.Table values shall be adjusted for height and exposure by multiplying by the adjustment coefficient in Table R301.2(3).

    4. d.See Figure R301.2(7) for location of zones.

    5. e.Plus and minus signs signify pressures acting toward and away from the building surfaces.

    TABLE R301.2(3)

    HEIGHT AND EXPOSURE ADJUSTMENT COEFFICIENTS FOR TABLE R301.2(2)

    MEAN ROOF HEIGHTEXPOSURE
    BCD
    151.001.211.47
    201.001.291.55
    251.001.351.61
    301.001.401.66
    351.051.451.70
    401.091.491.74
    451.121.531.78
    501.161.561.81
    551.191.591.84
    601.221.621.87

    For SI: °C = [(°F)-32]/1.8.

    FIGURE R301.2(1)

    ISOLINES OF THE 971/2-PERCENT WINTER (DECEMBER, JANUARY AND FEBRUARY) DESIGN TEMPERATURES (°F)

    FIGURE R301.2(2)

    SEISMIC DESIGN CATEGORIES—SITE CLASS D

    1. a.Alaska and Hawaii are classified as severe and negligible, respectively.

    2. b.Lines defining areas are approximate only. Local conditions may be more or less severe than indicated by region classification. A severe classification is where weather conditions result in significant snowfall combined with extended periods during which there is little or no natural thawing causing deicing salts to be used extensively.

    FIGURE R301.2(3)

    WEATHERING PROBABILITY MAP FOR CONCRETEa, b

    Notes:

    1. 1.Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10m) above ground for Exposure C category.

    2. 2.Linear interpolation between contours is permitted.

    3. 3.Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area.

    4. 4.Mountainous terrain, gorges, ocean promontories, and special wind region shall be exmined for unusual wind conditions.

    5. 5.Wind speeds correspond to approximately a 7% probability of exceedance in 50 years (Annual Exceedance Probability = 0.00143, MRI = 700 Years).

    FIGURE R301.2(4)A

    ULTIMATE DESIGN WIND SPEEDS

    Notes:

    1. 1.Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10m) above ground for Exposure C category.

    2. 2.Linear interpolation between contours is permitted.

    3. 3.Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area.

    4. 4.Mountainous terrain, gorges, ocean promontories, and special wind region shall be exmined for unusual wind conditions.

    5. 5.Wind speeds correspond to approximately a 7% probability of exceedance in 50 years (Annual Exceedance Probability = 0.00143, MRI = 700 Years).

    FIGURE R301.2(4)B

    REGIONS WHERE WIND DESIGN IS REQUIRED

    For SI: 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa, 1 mile = 1.61 km.

    1. a.In CS areas, site-specific Case Studies are required to establish ground snow loads. Extreme local variations in ground snow loads in these areas preclude mapping at this scale.

    2. b.Numbers in parentheses represent the upper elevation limits in feet for the ground snow load values presented below. Site-specific case studies are required to establish ground snow loads at elevations not covered.

    For SI: 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa, 1 mile = 1.61 km.

    1. a.In CS areas, site-specific Case Studies are required to establish ground snow loads. Extreme local variations in ground snow loads in theses areas preclude mapping at this scale.

    2. b.Numbers in parentheses represent the upper elevation limits in feet for the ground snow load values presented below. Site-specific case studies are required to establish ground snow loads at elevations not covered.

    FIGURE R301.2(5)

    GROUND SNOW LOADS, Pg, FOR THE UNITED STATES (lb/ft2)

    Note: Lines defining areas are approximate only. Local conditions may be more or less severe than indicated by the region classification.

    FIGURE R301.2(6)

    TERMITE INFESTATION PROBABILITY MAP

    For SI: 1 foot = 304.8 mm, 1 degree = 0.0175 rad.

    Note: a = 4 feet in all cases.

    FIGURE R301.2(7)

    COMPONENT AND CLADDING PRESSURE ZONES

    R301.2.1 Wind design criteria.

    Buildings and portions thereof shall be constructed in accordance with the wind provisions of this code using the ultimate design wind speed in Table R301.2(1) as determined from Figure R301.2(4)A. The structural provisions of this code for wind loads are not permitted where wind design is required as specified in Section R301.2.1.1. Where different construction methods and structural materials are used for various portions of a building, the applicable requirements of this section for each portion shall apply. Where not otherwise specified, the wind loads listed in Table R301.2(2) adjusted for height and exposure using Table R301.2(3) shall be used to determine design load performance requirements for wall coverings, curtain walls, roof coverings, exterior windows, skylights, garage doors and exterior doors. Asphalt shingles shall be designed for wind speeds in accordance with Section R905.2.4. A continuous load path shall be provided to transmit the applicable uplift forces in Section R802.11.1 from the roof assembly to the foundation.

    R301.2.1.1 Wind limitations and wind design required.

    The wind provisions of this code shall not apply to the design of buildings where wind design is required in accordance with Figure R301.2(4)B.

    Exceptions:

    1. 1.For concrete construction, the wind provisions of this code shall apply in accordance with the limitations of Sections R404 and R608.

    2. 2.For structural insulated panels, the wind provisions of this code shall apply in accordance with the limitations of Section R610.

    3. 3.For cold-formed steel light-frame construction, the wind provisions of this code shall apply in accordance with the limitations of Sections R505, R603 and R804.

    In regions where wind design is required in accordance with Figure R301.2(4)B, the design of buildings for wind loads shall be in accordance with one or more of the following methods:

    The elements of design not addressed by the methods in Items 1 through 5 shall be in accordance with the provisions of this code.

    Where ASCE 7 or the International Building Code is used for the design of the building, the wind speed map and exposure category requirements as specified in ASCE 7 and the International Building Code shall be used.

    R301.2.1.1.1 Sunrooms.

    Sunrooms shall comply with AAMA/NPEA/NSA 2100. For the purpose of applying the criteria of AAMA/NPEA/NSA 2100 based on the intended use, sunrooms shall be identified as one of the following categories by the permit applicant, design professional or the property owner or owner’s agent in the construction documents. Component and cladding pressures shall be used for the design of elements that do not qualify as main windforce-resisting systems. Main windforce-resisting system pressures shall be used for the design of elements assigned to provide support and stability for the overall sunroom.

    • Category I: A thermally isolated sunroom with walls that are open or enclosed with insect screening or 0.5 mm (20 mil) maximum thickness plastic film. The space is nonhabitable and unconditioned.

    • Category II: A thermally isolated sunroom with enclosed walls. The openings are enclosed with translucent or transparent plastic or glass. The space is nonhabitable and unconditioned.

    • Category III: A thermally isolated sunroom with enclosed walls. The openings are enclosed with translucent or transparent plastic or glass. The sunroom fenestration complies with additional requirements for air infiltration resistance and water penetration resistance. The space is nonhabitable and unconditioned.

    • Category IV: A thermally isolated sunroom with enclosed walls. The sunroom is designed to be heated or cooled by a separate temperature control or system and is thermally isolated from the primary structure. The sunroom fenestration complies with additional requirements for water penetration resistance, air infiltration resistance and thermal performance. The space is nonhabitable and conditioned.

    • Category V: A sunroom with enclosed walls. The sunroom is designed to be heated or cooled and is open to the main structure. The sunroom fenestration complies with additional requirements for water penetration resistance, air infiltration resistance and thermal performance. The space is habitable and conditioned.

    R301.2.1.2 Protection of openings.

    Exterior glazing in buildings located in windborne debris regions shall be protected from windborne debris. Glazed opening protection for windborne debris shall meet the requirements of the Large Missile Test of ASTM E 1996 and ASTM E 1886 as modified in Section 301.2.1.2.1. Garage door glazed opening protection for windborne debris shall meet the requirements of an approved impact-resisting standard or ANSI/DASMA 115.

    Exception: Wood structural panels with a thickness of not less than 7/16 inch (11 mm) and a span of not more than 8 feet (2438 mm) shall be permitted for opening protection. Panels shall be precut and attached to the framing surrounding the opening containing the product with the glazed opening. Panels shall be predrilled as required for the anchorage method and shall be secured with the attachment hardware provided. Attachments shall be designed to resist the component and cladding loads determined in accordance with either Table R301.2(2) or ASCE 7, with the permanent corrosion-resistant attachment hardware provided and anchors permanently installed on the building. Attachment in accordance with Table R301.2.1.2 is permitted for buildings with a mean roof height of 45 feet (13, 728 mm) or less where the ultimate design wind speed, Vult, is 180 mph (290 kph) or less.

    TABLE R301.2.1.2

    WINDBORNE DEBRIS PROTECTION FASTENING SCHEDULE FOR WOOD STRUCTURAL PANELSa, b, c, d

    FASTENER TYPEFASTENER SPACING (inches)a, b
    Panelspan ≤4 feet4 feet <panel span ≤ 6 feet6 feet <panel span ≤ 8 feet
    No. 8 wood screw basedanchor with 2-inch embedmentlength16108
    No. 10 wood screw basedanchor with 2-inch embedmentlength16129
    1/4-inch lag screw based anchorwith 2-inch embedment length161616

    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound = 4.448 N, 1 mile per hour = 0.447 m/s.

    1. a.This table is based on 180 mph ultimate design wind speeds, Vult, and a 33-foot mean roof height.

    2. b.Fasteners shall be installed at opposing ends of the wood structural panel. Fasteners shall be located not less than 1 inch from the edge of the panel.

    3. c.Anchors shall penetrate through the exterior wall covering with an embedment length of not less than 2 inches into the building frame. Fasteners shall be located not less than 21/2 inches from the edge of concrete block or concrete.

    4. d.Panels attached to masonry or masonry/stucco shall be attached using vibration-resistant anchors having an ultimate withdrawal capacity of not less than 1,500 pounds.

    R301.2.1.2.1 Application of ASTM E 1996.

    The text of Section 2.2 of ASTM E 1996 shall be substituted as follows:

    • 2.2 ASCE Standard:

      ASCE 7-10 American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures

      The text of Section 6.2.2 of ASTM E 1996 shall be substituted as follows:

    • 6.2.2 Unless otherwise specified, select the wind zone based on the ultimate design wind speed, Vult, as follows:

    • 6.2.2.1 Wind Zone 1–130 mph ≤ ultimate design wind speed, Vult < 140 mph.

    • 6.2.2.2 Wind Zone 2–140 mph ≤ ultimate design wind speed, Vult < 150 mph at greater than 1 mile (1.6 km) from the coastline. The coastline shall be measured from the mean high water mark.

    • 6.2.2.3 Wind Zone 3–150 mph (58 m/s) ≤ ultimate design wind speed, Vult ≤ 170 mph (76 m/s), or 140 mph (54 m/s) ≤ ultimate design wind speed, Vult ≤ 170 mph (76 m/s) and within 1 mile (1.6 km) of the coastline. The coastline shall be measured from the mean high water mark.

    • 6.2.2.4 Wind Zone 4–ultimate design wind speed, Vult > 170 mph (76 m/s).

    R301.2.1.3 Wind speed conversion.

    Where referenced documents are based on nominal design wind speeds and do not provide the means for conversion between ultimate design wind speeds and nominal design wind speeds, the ultimate design wind speeds, Vult, of Figure R301.2(4)A shall be converted to nominal design wind speeds, Vasd, using Table R301.2.1.3.

    TABLE R301.2.1.3

    WIND SPEED CONVERSIONSa

    Vult110115120130140150160170180190200
    Vasd858993101108116124132139147155

    For SI: 1 mile per hour = 0.447 m/s.

    1. a.Linear interpolation is permitted.

    R301.2.1.4 Exposure category.

    For each wind direction considered, an exposure category that adequately reflects the characteristics of ground surface irregularities shall be determined for the site at which the building or structure is to be constructed. For a site located in the transition zone between categories, the category resulting in the largest wind forces shall apply. Account shall be taken of variations in ground surface roughness that arise from natural topography and vegetation as well as from constructed features. For a site where multiple detached one- and two-family dwellings, townhouses or other structures are to be constructed as part of a subdivision or master-planned community, or are otherwise designated as a developed area by the authority having jurisdiction, the exposure category for an individual structure shall be based upon the site conditions that will exist at the time when all adjacent structures on the site have been constructed, provided that their construction is expected to begin within one year of the start of construction for the structure for which the exposure category is determined. For any given wind direction, the exposure in which a specific building or other structure is sited shall be assessed as being one of the following categories:

    1. 1.Exposure B. Urban and suburban areas, wooded areas or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger. Exposure B shall be assumed unless the site meets the definition of another type exposure.

    2. 2.Exposure C. Open terrain with scattered obstructions, including surface undulations or other irregularities, having heights generally less than 30 feet (9144 mm) extending more than 1,500 feet (457 m) from the building site in any quadrant. This exposure shall also apply to any building located within Exposure B type terrain where the building is directly adjacent to open areas of Exposure C type terrain in any quadrant for a distance of more than 600 feet (183 m). This category includes flat, open country and grasslands.

    3. 3.Exposure D. Flat, unobstructed areas exposed to wind flowing over open water, smooth mud flats, salt flats and unbroken ice for a distance of not less than 5,000 feet (1524 m). This exposure shall apply only to those buildings and other structures exposed to the wind coming from over the unob structed area. Exposure D extends downwind from the edge of the unobstructed area a distance of 600 feet (183 m) or 20 times the height of the building or structure, whichever is greater.

    R301.2.1.5 Topographic wind effects.

    In areas designated in Table R301.2(1) as having local historical data documenting structural damage to buildings caused by wind speed-up at isolated hills, ridges and escarpments that are abrupt changes from the general topography of the area, topographic wind effects shall be considered in the design of the building in accordance with Section R301.2.1.5.1 or in accordance with the provisions of ASCE 7. See Figure R301.2.1.5.1(1) for topographic features for wind speed-up effect.

    In these designated areas, topographic wind effects shall apply only to buildings sited on the top half of an isolated hill, ridge or escarpment where all of the following conditions exist:

    1. 1.The average slope of the top half of the hill, ridge or escarpment is 10 percent or greater.

    2. 2.The hill, ridge or escarpment is 60 feet (18 288 mm) or greater in height for Exposure B, 30 feet (9144 mm) or greater in height for Exposure C, and 15 feet (4572 mm) or greater in height for Exposure D.

    3. 3.The hill, ridge or escarpment is isolated or unobstructed by other topographic features of similar height in the upwind direction for a distance measured from its high point of 100 times its height or 2 miles (3.2 km), whichever is less. See Figure R301.2.1.5.1(3) for upwind obstruction.

    4. 4.The hill, ridge or escarpment protrudes by a factor of two or more above the height of other upwind topographic features located in any quadrant within a radius of 2 miles (3.2 km) measured from its high point.

    R301.2.1.5.1 Simplified topographic wind speedup method.

    As an alternative to the ASCE 7 topographic wind provisions, the provisions of Section R301.2.1.5.1 shall be permitted to be used to design for wind speed-up effects, where required by Section R301.2.1.5.

    Structures located on the top half of isolated hills, ridges or escarpments meeting the conditions of Section R301.2.1.5 shall be designed for an increased basic wind speed as determined by Table R301.2.1.5.1. On the high side of an escarpment, the increased basic wind speed shall extend horizontally downwind from the edge of the escarpment 1.5 times the horizontal length of the upwind slope (1.5L) or 6 times the height of the escarpment (6H), whichever is greater. See Figure R301.2.1.5.1(2) for where wind speed increase is applied.

    TABLE R301.2.1.5.1

    ULTIMATE DESIGN WIND SPEED MODIFICATION FOR TOPOGRAPHIC WIND EFFECTa, b

    ULTIMATE DESIGNWIND SPEED FROMFIGURE R301.2(4)A(mph)AVERAGE SLOPE OF THE TOP HALF OF HILL, RIDGE OR ESCARPMENT (percent)
    0.100.1250.150.1750.200.230.25
    Required ultimate design wind speed-up, modified for topographic wind speed-up (mph)
    110132137142147152158162
    115138143148154159165169
    120144149155160166172176
    130156162168174179N/AN/A
    140168174181N/AN/AN/AN/A
    150180N/AN/AN/AN/AN/AN/A

    For SI: 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm.

    1. a.Table applies to a feature height of 500 feet or less and dwellings sited a distance equal or greater than half the feature height.

    2. b.Where the ultimate design wind speed as modified by Table R301.2.1.5.1 equals or exceeds 140 miles per hour, the building shall be considered as “wind design required” in accordance with Section R301.2.1.1.

    Note: H/2 determines the measurement point for Lh. L is twice Lh.

    FIGURE R301.2.1.5.1(1)

    TOPOGRAPHIC FEATURES FOR WIND SPEED-UP EFFECT

    FIGURE R301.2.1.5.1(2)

    ILLUSTRATION OF WHERE ON A TOPOGRAPHIC FEATURE, WIND SPEED INCREASE IS APPLIED

    FIGURE R301.2.1.5.1(3)

    UPWIND OBSTRUCTION

    R301.2.2 Seismic provisions.

    The seismic provisions of this code shall apply as follows:

    1. 1.Townhouses in Seismic Design Categories C, D0, D1 and D2.

    2. 2.Detached one- and two-family dwellings in Seismic Design Categories, D0, D1 and D2.

    R301.2.2.1 Determination of seismic design category.

    Buildings shall be assigned a seismic design category in accordance with Figure R301.2(2).

    R301.2.2.1.1 Alternate determination of seismic design category.

    The seismic design categories and corresponding short-period design spectral response accelerations, SDS shown in Figure R301.2(2) are based on soil Site Class D, as defined in Section 1613.3.2 of the International Building Code. If soil conditions are other than Site Class D, the short-period design spectral response accelerations, SDS, for a site can be determined in accordance with Section 1613.3 of the International Building Code. The value of SDS determined in accordance with Section 1613.3 of the International Building Code is permitted to be used to set the seismic design category in accordance with Table R301.2.2.1.1, and to interpolate between values in Tables R602.10.3(3), R603.9.2(1) and other seismic design requirements of this code.

    TABLE R301.2.2.1.1

    SEISMIC DESIGN CATEGORY DETERMINATION

    CALCULATED SDSSEISMIC DESIGN CATEGORY
    SDS ≤ 0.17gA
    0.17g < SDS ≤ 0.33gB
    0.33g < SDS ≤ 0.50gC
    0.50g < SDS ≤ 0.67gD0
    0.67g < SDS ≤ 0.83gD1
    0.83g < SDS < 1.25gD2
    1.25g < SDSE

    R301.2.2.1.2 Alternative determination of Seismic Design Category E.

    Buildings located in Seismic Design Category E in accordance with Figure R301.2(2) are permitted to be reclassified as being in Seismic Design Category D2 provided that one of the following is done:

    1. 1.A more detailed evaluation of the seismic design category is made in accordance with the provisions and maps of the International Building Code. Buildings located in Seismic Design Category E in accordance with Table R301.2.2.1.1, but located in Seismic Design Category D in accordance with the International Building Code, shall be permitted to be designed using the Seismic Design Category D2 requirements of this code.

    2. 2.Buildings located in Seismic Design Category E that conform to the following additional restrictions are permitted to be constructed in accordance with the provisions for Seismic Design Category D2 of this code:

      1. 2.1.All exterior shear wall lines or braced wall panels are in one plane vertically from the foundation to the uppermost story.

      2. 2.2.Floors shall not cantilever past the exterior walls.

      3. 2.3.The building is within the requirements of Section R301.2.2.2.5 for being considered as regular.

    R301.2.2.2 Seismic Design Category C.

    Structures assigned to Seismic Design Category C shall conform to the requirements of this section.

    R301.2.2.2.1 Weights of materials.

    Average dead loads shall not exceed 15 pounds per square foot (720 Pa) for the combined roof and ceiling assemblies (on a horizontal projection) or 10 pounds per square foot (480 Pa) for floor assemblies, except as further limited by Section R301.2.2. Dead loads for walls above grade shall not exceed:

    1. 1.Fifteen pounds per square foot (720 Pa) for exterior light-frame wood walls.

    2. 2.Fourteen pounds per square foot (670 Pa) for exterior light-frame cold-formed steel walls.

    3. 3.Ten pounds per square foot (480 Pa) for interior light-frame wood walls.

    4. 4.Five pounds per square foot (240 Pa) for interior light-frame cold-formed steel walls.

    5. 5.Eighty pounds per square foot (3830 Pa) for 8-inch-thick (203 mm) masonry walls.

    6. 6.Eighty-five pounds per square foot (4070 Pa) for 6-inch-thick (152 mm) concrete walls.

    7. 7.Ten pounds per square foot (480 Pa) for SIP walls.

    Exceptions:

    1. 1.Roof and ceiling dead loads not exceeding 25 pounds per square foot (1190 Pa) shall be permitted provided that the wall bracing amounts in Section R602.10.3 are increased in accordance with Table R602.10.3(4).

    2. 2.Light-frame walls with stone or masonry veneer shall be permitted in accordance with the provisions of Sections R702.1 and R703.

    3. 3.Fireplaces and chimneys shall be permitted in accordance with Chapter 10.

    R301.2.2.2.2 Stone and masonry veneer.

    Anchored stone and masonry veneer shall comply with the requirements of Sections R702.1 and R703.

    R301.2.2.2.3 Masonry construction.

    Masonry construction shall comply with the requirements of Section R606.12.

    R301.2.2.2.4 Concrete construction.

    Detached one- and two-family dwellings with exterior above-grade concrete walls shall comply with the requirements of Section R608, PCA 100 or shall be designed in accordance with ACI 318. Townhouses with above-grade exterior concrete walls shall comply with the requirements of PCA 100 or shall be designed in accordance with ACI 318.

    R301.2.2.2.5 Irregular buildings.

    The seismic provisions of this code shall not be used for irregular structures located in Seismic Design Categories C, D0, D1 and D2. Irregular portions of structures shall be designed in accordance with accepted engineering practice to the extent the irregular features affect the performance of the remaining structural system. Where the forces associated with the irregularity are resisted by a structural system designed in accordance with accepted engineering practice, design of the remainder of the building shall be permitted using the provisions of this code. A building or portion of a building shall be considered to be irregular where one or more of the following conditions occur:

    1. 1.Where exterior shear wall lines or braced wall panels are not in one plane vertically from the foundation to the uppermost story in which they are required.

      Exception: For wood light-frame construction, floors with cantilevers or setbacks not exceeding four times the nominal depth of the wood floor joists are permitted to support braced wall panels that are out of plane with braced wall panels below provided that:

      1. 1.Floor joists are nominal 2 inches by 10 inches (51 mm by 254 mm) or larger and spaced not more than 16 inches (406 mm) on center.

      2. 2.The ratio of the back span to the cantilever is not less than 2 to 1.

      3. 3.Floor joists at ends of braced wall panels are doubled.

      4. 4.For wood-frame construction, a continuous rim joist is connected to ends of cantilever joists. When spliced, the rim joists shall be spliced using a galvanized metal tie not less than 0.058 inch (1.5 mm) (16 gage) and 11/2 inches (38 mm) wide fastened with six 16d nails on each side of the splice or a block of the same size as the rim joist of sufficient length to fit securely between the joist space at which the splice occurs fastened with eight 16d nails on each side of the splice; and

      5. 5.Gravity loads carried at the end of cantilevered joists are limited to uniform wall and roof loads and the reactions from headers having a span of 8 feet (2438 mm) or less.

    2. 2.Where a section of floor or roof is not laterally supported by shear walls or braced wall lines on all edges.

      Exception: Portions of floors that do not support shear walls or braced wall panels above, or roofs, shall be permitted to extend not more than 6 feet (1829 mm) beyond a shear wall or braced wall line.

    3. 3.Where the end of a braced wall panel occurs over an opening in the wall below and ends at a horizontal distance greater than 1 foot (305 mm) from the edge of the opening. This provision is applicable to shear walls and braced wall panels offset in plane and to braced wall panels offset out of plane as permitted by the exception to Item 1.

      Exception: For wood light-frame wall construction, one end of a braced wall panel shall be permitted to extend more than 1 foot (305 mm) over an opening not more than 8 feet (2438 mm) in width in the wall below provided that the opening includes a header in accordance with the following:

      1. 1.The building width, loading condition and framing member species limitations of Table R602.7(1) shall apply; and

      2. 2.Not less than one 2 × 12 or two 2 × 10 for an opening not more than 4 feet (1219 mm) wide; or

      3. 3.Not less than two 2 × 12 or three 2 × 10 for an opening not more than 6 feet (1829 mm) in width; or

      4. 4.Not less than three 2 × 12 or four 2 × 10 for an opening not more than 8 feet (2438 mm) in width; and

      5. 5.The entire length of the braced wall panel does not occur over an opening in the wall below.

    4. 4.Where an opening in a floor or roof exceeds the lesser of 12 feet (3658 mm) or 50 percent of the least floor or roof dimension.

    5. 5.Where portions of a floor level are vertically offset.

      Exceptions:

      1. 1.Framing supported directly by continuous foundations at the perimeter of the building.

      2. 2.For wood light-frame construction, floors shall be permitted to be vertically offset when the floor framing is lapped or tied together as required by Section R502.6.1.

    6. 6.Where shear walls and braced wall lines do not occur in two perpendicular directions.

    7. 7.Where stories above grade plane partially or completely braced by wood wall framing in accordance with Section R602 or cold-formed steel wall framing in accordance with Section R603 include masonry or concrete construction. Where this irregularity applies, the entire story shall be designed in accordance with accepted engineering practice.

      Exception: Fireplaces, chimneys and masonry veneer as permitted by this code.

    R301.2.2.3 Seismic Design Categories D0, D1 and D2.

    Structures assigned to Seismic Design Categories D0, D1 and D2 shall conform to the requirements for Seismic Design Category C and the additional requirements of this section.

    R301.2.2.3.1 Height limitations.

    Wood-framed buildings shall be limited to three stories above grade plane or the limits given in Table R602.10.3(3). Cold-formed, steel-framed buildings shall be limited to less than or equal to three stories above grade plane in accordance with AISI S230. Mezzanines as defined in Section R202 that comply with Section R325 shall not be considered as stories. Structural insulated panel buildings shall be limited to two stories above grade plane.

    R301.2.2.3.2 Stone and masonry veneer.

    Anchored stone and masonry veneer shall comply with the requirements of Sections R702.1 and R703.

    R301.2.2.3.3 Masonry construction.

    Masonry construction in Seismic Design Categories D0 and D1 shall comply with the requirements of Section R606.12.1. Masonry construction in Seismic Design Category D2 shall comply with the requirements of Section R606.12.4.

    R301.2.2.3.4 Concrete construction.

    Buildings with exterior above-grade concrete walls shall comply with PCA 100 or shall be designed in accordance with ACI 318.

    R301.2.2.3.5 Cold-formed steel framing in Seismic Design Categories D0, D1 and D2.

    In Seismic Design Categories D0, D1 and D2 in addition to the requirements of this code, cold-formed steel framing shall comply with the requirements of AISI S230.

    R301.2.2.3.6 Masonry chimneys.

    Masonry chimneys shall be reinforced and anchored to the building in accordance with Sections R1003.3 and R1003.4.

    R301.2.2.3.7 Anchorage of water heaters.

    Water heaters shall be anchored against movement and overturning in accordance with Section M1307.2.

    R301.2.2.4 Seismic Design Category E.

    Buildings in Seismic Design Category E shall be designed to resist seismic loads in accordance with the International Building Code, except where the seismic design category is reclassified to a lower seismic design category in accordance with Section R301.2.2.1. Components of buildings not required to be designed to resist seismic loads shall be constructed in accordance with the provisions of this code.

    R301.2.3 Snow loads.

    Wood-framed construction, cold-formed, steel-framed construction and masonry and concrete construction, and structural insulated panel construction in regions with ground snow loads 70 pounds per square foot (3.35 kPa) or less, shall be in accordance with Chapters 5, 6 and 8. Buildings in regions with ground snow loads greater than 70 pounds per square foot (3.35 kPa) shall be designed in accordance with accepted engineering practice.

    R301.2.4 Floodplain construction.

    Buildings and structures constructed in whole or in part in flood hazard areas (including A or V Zones) as established in Table R301.2(1), and substantial improvement and restoration of substantial damage of buildings and structures in flood hazard areas, shall be designed and constructed in accordance with Section R322. Buildings and structures that are located in more than one flood hazard area shall comply with the provisions associated with the most restrictive flood hazard area. Buildings and structures located in whole or in part in identified floodways shall be designed and constructed in accordance with ASCE 24.

    R301.2.4.1 Alternative provisions.

    As an alternative to the requirements in Section R322, ASCE 24 is permitted subject to the limitations of this code and the limitations therein.

    R301.3 Story height.

    The wind and seismic provisions of this code shall apply to buildings with story heights not exceeding the following:

    1. 1.For wood wall framing, the story height shall not exceed 11 feet 7 inches (3531 mm) and the laterally unsupported bearing wall stud height permitted by Table R602.3(5).

    2. 2.For cold-formed steel wall framing, the story height shall be not more than 11 feet 7 inches (3531 mm) and the unsupported bearing wall stud height shall be not more than 10 feet (3048 mm).

    3. 3.For masonry walls, the story height shall be not more than 13 feet 7 inches (4140 mm) and the bearing wall clear height shall be not greater than 12 feet (3658 mm).

      Exception: An additional 8 feet (2438 mm) of bearing wall clear height is permitted for gable end walls.

    4. 4.For insulating concrete form walls, the maximum story height shall not exceed 11 feet 7 inches (3531 mm) and the maximum unsupported wall height per story as permitted by Section R608 tables shall not exceed 10 feet (3048 mm).

    5. 5.For structural insulated panel (SIP) walls, the story height shall be not greater than 11 feet 7 inches (3531 mm) and the bearing wall height per story as permitted by Section R610 tables shall not exceed 10 feet (3048 mm).

    Individual walls or wall studs shall be permitted to exceed these limits as permitted by Chapter 6 provisions, provided that story heights are not exceeded. An engineered design shall be provided for the wall or wall framing members where the limits of Chapter 6 are exceeded. Where the story height limits of this section are exceeded, the design of the building, or the noncompliant portions thereof, to resist wind and seismic loads shall be in accordance with the International Building Code.

    R301.4 Dead load.

    The actual weights of materials and construction shall be used for determining dead load with consideration for the dead load of fixed service equipment.

    R301.5 Live load.

    The minimum uniformly distributed live load shall be as provided in Table R301.5.

    TABLE R301.5

    MINIMUM UNIFORMLY DISTRIBUTED LIVE LOADS (in pounds per square foot)

    USELIVE LOAD
    Uninhabitable attics without storageb10
    Uninhabitable attics with limited storageb, g20
    Habitable attics and attics served with fixed stairs30
    Balconies (exterior) and deckse40
    Fire escapes40
    Guards and handrailsd200h
    Guard in-fill componentsf50h
    Passenger vehicle garagesa50a
    Rooms other than sleeping rooms40
    Sleeping rooms30
    Stairs40c

    For SI: 1 pound per square foot = 0.0479 kPa, 1 square inch = 645 mm2, 1 pound = 4.45 N.

    1. a.Elevated garage floors shall be capable of supporting a 2,000-pound load applied over a 20-square-inch area.

    2. b.Uninhabitable attics without storage are those where the clear height between joists and rafters is not more than 42 inches, or where there are not two or more adjacent trusses with web configurations capable of accommodating an assumed rectangle 42 inches in height by 24 inches in width, or greater, within the plane of the trusses. This live load need not be assumed to act concurrently with any other live load requirements.

    3. c.Individual stair treads shall be designed for the uniformly distributed live load or a 300-pound concentrated load acting over an area of 4 square inches, whichever produces the greater stresses.

    4. d.A single concentrated load applied in any direction at any point along the top.

    5. e.See Section R507.1 for decks attached to exterior walls.

    6. f.Guard in-fill components (all those except the handrail), balusters and panel fillers shall be designed to withstand a horizontally applied normal load of 50 pounds on an area equal to 1 square foot. This load need not be assumed to act concurrently with any other live load requirement.

    7. g.Uninhabitable attics with limited storage are those where the clear height between joists and rafters is not greater than 42 inches, or where there are two or more adjacent trusses with web configurations capable of accommodating an assumed rectangle 42 inches in height by 24 inches in width, or greater, within the plane of the trusses.

      The live load need only be applied to those portions of the joists or truss bottom chords where all of the following conditions are met:

      1. 1.The attic area is accessible from an opening not less than 20 inches in width by 30 inches in length that is located where the clear height in the attic is not less than 30 inches.

      2. 2.The slopes of the joists or truss bottom chords are not greater than 2 inches vertical to 12 units horizontal.

      3. 3.Required insulation depth is less than the joist or truss bottom chord member depth.

      The remaining portions of the joists or truss bottom chords shall be designed for a uniformly distributed concurrent live load of not less than 10 pounds per square foot.

    8. h.Glazing used in handrail assemblies and guards shall be designed with a safety factor of 4. The safety factor shall be applied to each of the concentrated loads applied to the top of the rail, and to the load on the in-fill components. These loads shall be determined independent of one another, and loads are assumed not to occur with any other live load.

    R301.6 Roof load.

    The roof shall be designed for the live load indicated in Table R301.6 or the snow load indicated in Table R301.2(1), whichever is greater.

    TABLE R301.6

    MINIMUM ROOF LIVE LOADS IN POUNDS-FORCE PER SQUARE FOOT OF HORIZONTAL PROJECTION

    ROOF SLOPETRIBUTARY LOADED AREA INSQUARE FEET FOR ANYSTRUCTURAL MEMBER
    0 to 200201 to 600Over 600
    Flat or rise less than 4 inches perfoot (1:3)201612
    Rise 4 inches per foot (1:3) toless than 12 inches per foot (1:1)161412
    Rise 12 inches per foot (1:1)and greater121212

    For SI: 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa, 1 inch per foot = 83.3 mm/m.

    R301.7 Deflection.

    The allowable deflection of any structural member under the live load listed in Sections R301.5 and R301.6 or wind loads determined by Section R301.2.1 shall not exceed the values in Table R301.7.

    TABLE R301.7

    ALLOWABLE DEFLECTION OF STRUCTURAL MEMBERSb, c

    STRUCTURAL MEMBERALLOWABLEDEFLECTION
    Rafters having slopes greater than 3:12 withfinished ceiling not attached to raftersL/180
    Interior walls and partitionsH/180
    FloorsL/360
    Ceilings with brittle finishes (including plasterand stucco)L/360
    Ceilings with flexible finishes (including gypsumboard)L/240
    All other structural membersL/240
    Exterior walls—wind loadsa with plaster orstucco finishH/360
    Exterior walls—wind loadsa with other brittlefinishesH/240
    Exterior walls—wind loadsa with flexible finishesH/120d
    Lintels supporting masonry veneer wallseL/600

    Note: L = span length, H = span height.

    1. a.For the purpose of the determining deflection limits herein, the wind load shall be permitted to be taken as 0.7 times the component and cladding (ASD) loads obtained from Table R301.2(2).

    2. bFor cantilever members, L shall be taken as twice the length of the cantilever.

    3. c.For aluminum structural members or panels used in roofs or walls of sunroom additions or patio covers, not supporting edge of glass or sandwich panels, the total load deflection shall not exceed L/60. For continuous aluminum structural members supporting edge of glass, the total load deflection shall not exceed L/175 for each glass lite or L/60 for the entire length of the member, whichever is more stringent. For sandwich panels used in roofs or walls of sunroom additions or patio covers, the total load deflection shall not exceed L/120.

    4. d.Deflection for exterior walls with interior gypsum board finish shall be limited to an allowable deflection of H/180.

    5. e.Refer to Section R703.8.2.

    R301.8 Nominal sizes.

    For the purposes of this code, dimensions of lumber specified shall be deemed to be nominal dimensions unless specifically designated as actual dimensions.