N.Y.C. Admin. Code § BC 1609: Section BC 1609: Wind Loads

1609.1 Applications.

Buildings, structures and parts thereof shall be designed to withstand the minimum wind loads prescribed herein. Decreases in wind loads shall not be made for the effect of shielding by other structures.

1609.1.1 Determination of wind loads.

Wind loads on every building or structure shall be determined in accordance with Chapters 26 to 31 of ASCE 7. The type of opening protection required, the basic design wind speed, V, and the exposure category for a site is permitted to be determined in accordance with Section 1609. Wind shall be assumed to come from any horizontal direction and wind pressures shall be assumed to act normal to the surface considered.

Exceptions:

1. Subject to the limitations of Section 1609.1.1.1, the provisions of ICC 600 shall be permitted for applicable Group R-2 and R-3 buildings.

2. Subject to the limitations of Section 1609.1.1.1, residential structures using the provisions of AWC WFCM.

3. Subject to the limitations of Section 1609.1.1.1, residential structures using the provisions of AISI S230.

4. Designs using NAAMM FP 1001.

5. Designs using TIA-222 for antenna-supporting structures and antennas.

6. Wind tunnel tests in accordance with ASCE 49 and Sections 31.4 and 31.5 of ASCE 7.

The wind speeds in Section 1609.3 are basic design wind speeds, V, and shall be converted in accordance with Section 1609.3.1 to allowable stress design wind speeds, V

asd

, when the provisions of the standards referenced in Exceptions 4 and 5 are used.

1609.1.1.1 Applicability.

The provisions of ICC 600 are applicable only to buildings located within Exposure B or C as defined in Section 1609.4. The provisions of ICC 600, AWC WFCM and AISI S230 shall not apply to buildings sited on the upper half of an isolated hill, ridge or escarpment meeting the following conditions:

1. The hill, ridge or escarpment is 60 feet (18 288 mm) or higher if located in Exposure B or 30 feet (9144 mm) or higher if located in Exposure C;

2. The maximum average slope of the hill exceeds 10 percent; and

3. The hill, ridge or escarpment is unobstructed upwind by other such topographic features for a distance from the high point of 50 times the height of the hill or 2 miles (3.22 km), whichever is greater.

1609.1.2 Protection of openings.

In wind-borne debris regions, glazing in buildings shall be impact resistant or protected with an impact-resistant covering meeting the requirements of an approved impact-resistant standard or ASTM E 1996 and ASTM E 1886 referenced herein as follows:

1. Glazed openings located within 30 feet (9144 mm) of grade shall meet the requirements of the large missile test of ASTM E 1996.

2. Glazed openings located more than 30 feet (9144 mm) above grade shall meet the provisions of the small missile test of ASTM E 1996.

Exceptions:

1. Wood structural panels with a minimum thickness of 7/16 inch (11.1 mm) and maximum panel span of 8 feet (2438.4 mm) shall be permitted for opening protection in buildings with a mean roof height of 33 feet (10 058 mm) or less that are classified as a Group R-3 or R-4 occupancy. Panels shall be precut so that they shall be 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 components and cladding loads determined in accordance with the provisions of ASCE 7, with corrosion-resistant attachment hardware provided and anchors permanently installed on the building. Attachment in accordance with Table 1609.1.2 of this code with corrosion-resistant attachment hardware provided and anchors permanently installed on the building is permitted for buildings with a mean roof height of 45 feet (13 716 mm) or less where V

asd

determined in accordance with Section 1609.3.1 of this code does not exceed 140 mph (63 m/s).

2. Glazing in Risk Category I or II buildings, including greenhouses that are occupied for growing plants on a production or research basis, without public access shall be permitted to be unprotected.

3. Glazing in Risk Category III or IV buildings located over 60 feet (18 288 mm) above the ground.

Table 1609.1.2 Wind-Borne Debris Protection Fastening Schedule for Wood Structural Panels

a, b, c, d

Fastener Type

Fastener Spacing (inches)

Panel Span

£

4 feet

4 feet < Panel Span

£

6 feet

6 feet < Panel Span

£

8 feet

No. 8 wood-screw-based anchor with 2-inch embedment length

16

10

8

No. 10 wood-screw-based anchor with 2-inch embedment length

16

12

9

1/4-inch diameter lag-screw-based anchor with 2-inch embedment length

16

16

16

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.

a. This table is based on 140 mph wind speeds and a 45-foot mean roof height.

b. Fasteners shall be installed at opposing ends of the wood structural panel. Fasteners shall be located a minimum of 1 inch from the edge of the panel.

c. Anchors shall penetrate through the exterior wall covering with an embedment length of 2 inches minimum into the building frame. Fasteners shall be located a minimum of 2 1/2 inches from the edge of concrete block or concrete.

d. Where panels are attached to masonry or masonry/stucco, they shall be attached using vibration-resistant anchors having a minimum ultimate withdrawal capacity of 1,500 pounds.

1609.1.2.1 Louvers.

Louvers protecting intake and exhaust ventilation ducts not assumed to be open that are located within 30 feet (9144 mm) of grade shall meet the requirements of AMCA 540.

1609.1.2.2 Application of ASTM E 1996.

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 strength design wind speed, V, as follows:

6.2.2.1 Wind Zone 1 – 130 mph £ basic design wind speed, V < 140 mph.

6.2.2.2 Delete.

6.2.2.3 Delete.

6.2.2.4 Delete.

1609.1.2.3 Garage doors.

Garage door glazed opening protection for wind-borne debris shall meet the requirements of an approved impact-resisting standard or ANSI/DASMA 115.

1609.1.3 Minimum wind loads.

The design wind pressure, p, used in the design of the main wind-force-resisting system shall not be less than 16 psf (0.766 kN/m

2

) multiplied by the area of the building or structure projected on a vertical plane normal to the wind direction. In the calculation of design wind pressure, p, used in the design of components and cladding for buildings, the algebraic sum of the pressures acting on opposite faces shall be taken into account. The design pressure for components and cladding of buildings shall not be less than 32 psf (1.533 kN/m

2

) acting in either direction normal to the surface. The design force for open buildings and other structures shall not be less than 16 psf (0.766 kN/m

2

) multiplied by the area A

f

.

1609.1.4 Anchorage against overturning, uplift and sliding.

Structural members and systems and components and cladding in a building or structure shall be anchored to resist wind-induced overturning, uplift and sliding and to provide continuous load paths for these forces to the foundation. Where a portion of the resistance to these forces is provided by dead load, the dead load, including the weight of soils and foundations, shall be taken as the minimum dead load likely to be in place during a design wind event.

1609.1.5 Wind and seismic detailing.

Lateral-force-resisting systems shall meet seismic detailing requirements and limitations prescribed in this code, even when wind code prescribed load effects are greater than seismic load effects.

1609.1.6 Wind tunnel test limitations.

The lower limit on pressures for main wind-force-resisting systems and components and cladding shall be in accordance with this section.

1609.1.6.1 Lower limits on main wind-force-resisting system.

Base overturning moments determined from wind tunnel testing shall be limited to not less than 80 percent of the design base overturning moments determined in accordance with Section 27.2 of ASCE 7 unless the wind tunnel results and testing procedure are peer reviewed by an independent wind tunnel laboratory. In no case shall the limiting value be less than 70 percent of the design base overturning moments determined in accordance with Section 27.2 of ASCE 7.

1609.1.6.2 Lower limits on components and cladding.

The design pressures for components and cladding on walls or roofs shall be selected as the greater of: (i) the wind tunnel test results; or (ii) 80 percent of the pressure obtained for Zone 4 for walls and Zone 1 for roofs, as determined in Section 30.5 of ASCE 7, unless the wind tunnel results and testing procedure are peer reviewed by an independent wind tunnel laboratory. In no case shall the limiting value be less than 70 percent of the pressure obtained for Zone 4 for walls and Zone 1 for roofs, as determined in Section 30.5 of ASCE 7.

1609.1.6.3 Scope of peer review by independent wind tunnel laboratory.

When applicable, the peer reviewer of the wind tunnel test shall:

1. Be retained by or on behalf of the owner and shall be independent from the wind tunnel laboratory that performed the tests and the report shall bear no conflict of interest.

2. Have a minimum of 10 years of technical expertise in the application of wind tunnel studies on buildings comparable to that being reviewed.

3. Have experience in performing or evaluating boundary layer wind tunnel studies and shall be familiar with the technical issues and regulations governing the wind tunnel procedure in ASCE 49.

4. Review the wind tunnel report, including but not limited to wind climate data and modeling, data analysis, boundary layer modeling, building modeling, significant influential buildings, resulting wind loads and other relevant issues identified by the reviewer.

5. Review the wind tunnel report for cladding and envelope pressures, if applicable.

6. Submit a report to the department summarizing the results of their review, and shall state whether the wind tunnel test and the results meet the industry standard, the New York City Building Code and are appropriate for the project.

1609.2 Definitions.

For the purposes of Section 1609 and as used elsewhere in the code, the following terms are defined in Chapter 2:

BUILDINGS AND OTHER STRUCTURES, FLEXIBLE.

BUILDING, ENCLOSED.

BUILDING, LOW-RISE.

BUILDING, OPEN.

BUILDING, PARTIALLY ENCLOSED.

BUILDING, SIMPLE DIAPHRAGM.

COMPONENTS AND CLADDING.

EAVE HEIGHT,

h

.

EFFECTIVE WIND AREA.

HURRICANE-PRONE REGIONS.

IMPORTANCE FACTOR,

I

.

MAIN WIND FORCE-RESISTING SYSTEM.

MEAN ROOF HEIGHT.

WIND SPEED,

V (BASIC)

.

WIND SPEED,

V

asd

(ALLOWABLE STRESS DESIGN).

WIND-BORNE DEBRIS REGION.

1609.3 Basic design wind speed.

The basic design wind speed, V, in mph, for determining wind speed shall be that of Table 1609.3.

Table 1609.3 Basic Design Wind Speed

Risk Category

Basic Design Wind Speed, mph (3-sec gust, 33 ft. for Exposure Category C)

Mean Recurrence Interval, years

Probability of Exceedance in 50 years, %

I

110

300

15

II

117

700

7

III

127

1,700

3

IV

132

3,000

1.6

Note: Values are ultimate design 3-second gust wind speeds in miles per hour at 33 feet (10 058 mm) above ground for Exposure Category C.

1609.3.1 Wind speed conversion.

Where required, the basic design wind speed, V, of Table 1609.3 shall be converted to allowable stress design wind speed, V

asd

, using Equation 16-40.

V

asd

= 0.79V

(Equation 16-40)

1609.3.2 Wind speed for serviceability design.

Table 1609.3.2 presents 3-second gust wind speeds for mean recurrence intervals (MRI) of 10, 25, 50 and 100 years. These wind speeds may be used for serviceability applications such as drift and habitability.

Table 1609.3.2 Serviceability Design Wind Speed

Mean Recurrence Interval (years)

Serviceability Design Wind Speed, mph (3-sec gust, 33 ft. for Exposure Category C)

10

80

25

87

50

93

100

100

Note: Values are 3-second gust wind speeds in miles per hour at 33 feet (10 058 mm) above ground for Exposure Category C.

1609.4 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.

Account shall be taken of variations in ground surface roughness that arise from natural topography and vegetation as well as from constructed features.

1609.4.1 Wind directions and sectors.

For each selected wind direction at which the wind loads are to be evaluated, the exposure of the building or structure shall be determined for the two upwind sectors extending 45 degrees (0.79 rad) either side of the selected wind direction. The exposures in these two sectors shall be determined in accordance with Sections 1609.4.2 and 1609.4.3 and the exposure resulting in the highest wind loads shall be used to represent winds from that direction.

1609.4.2 Surface roughness categories.

A ground surface roughness within each 45-degree (0.79 rad) sector shall be determined for a distance upwind of the site as defined in Section 1609.4.3 from the categories defined below, for the purpose of assigning an exposure category as defined in Section 1609.4.3.

Surface Roughness B. Urban and suburban areas, wooded areas or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger.

Surface Roughness C. Open terrain with scattered obstructions having heights generally less than 30 feet (9144 mm). This category includes flat open country, grasslands, and limited water surfaces per Figure 1609.4.3.

Surface Roughness D. Flat, unobstructed areas and water surfaces. This category includes smooth mud flats, salt flats and unbroken ice.

1609.4.3 Exposure categories.

An exposure category shall be determined in accordance with the following:

Figure 1609.4.3 provides the exposure categories at the shore lines for wind directions approaching over the water within the city boundaries.

Exposure B. For buildings with a mean roof height of less than or equal to 30 feet (9144 mm), Exposure B shall apply where the ground surface roughness, as defined by Surface Roughness B, prevails in the upwind direction for a distance of at least 1,500 feet (457.2 m). For buildings with a mean roof height greater than 30 feet (9144 mm), Exposure B shall apply where Surface Roughness B prevails in the upwind direction for a distance of at least 2,600 feet (792.5 m) or 20 times the height of the building, whichever is greater.

Exposure C. Exposure C shall apply where it is shown in Figure 1609.4.3 or for all cases where Exposure B or D does not apply.

Exposure D. Exposure D shall apply where the ground surface roughness, as defined by Surface Roughness D, prevails in the upwind direction for a distance of at least 5,000 feet (1524 m) or 20 times the height of the building, whichever is greater. Exposure D shall also apply where the ground surface roughness immediately upwind of the site is B or C, and the site is within a distance of 600 feet (182.9 m) or 20 times the building height, whichever is greater, from an Exposure D condition as defined in the previous sentence.

Figure 1609.4.3(1) New York City Wind Exposure: Manhattan Shoreline

Notes:

Exposure C: Buildings within a distance of 2,600 feet from shoreline.

Exposure C: Buildings within a distance of 2,600 feet or 20 times building height from shoreline, whichever is greater

Exposure D: Coastal zone, see Section 1609.4

Figure 1609.4.3(2) New York City Wind Exposure: Bronx Shoreline

Notes:

Exposure C: Buildings within a distance of 2,600 feet from shoreline.

Exposure C: Buildings within a distance of 2,600 feet or 20 times building height from shoreline, whichever is greater

Exposure D: Coastal zone, see Section 1609.4

Figure 1609.4.3(3) New York City Wind Exposure: Brooklyn Shoreline

Notes:

Exposure C: Buildings within a distance of 2,600 feet from shoreline.

Exposure C: Buildings within a distance of 2,600 feet or 20 times building height from shoreline, whichever is greater

Exposure D: Coastal zone, see Section 1609.4

Figure 1609.4.3(4) New York City Wind Exposure: Queens Shoreline

Notes:

Exposure C: Buildings within a distance of 2,600 feet from shoreline.

Exposure C: Buildings within a distance of 2,600 feet or 20 times building height from shoreline, whichever is greater

Exposure D: Coastal zone, see Section 1609.4

Figure 1609.4.3(5) New York City Wind Exposure: Staten Island Shoreline

Notes:

Exposure C: Buildings within a distance of 2,600 feet from shoreline.

Exposure C: Buildings within a distance of 2,600 feet or 20 times building height from shoreline, whichever is greater

Exposure D: Coastal zone, see Section 1609.4

Roof systems shall be designed and constructed in accordance with Sections 1609.5.1 through 1609.5.3, as applicable.

1609.5.1 Roof deck.

The roof deck shall be designed to withstand the wind pressures determined in accordance with Section 1609.1.1 for buildings of any height.

1609.5.2 Roof coverings.

Roof coverings shall comply with Section 1609.5.1.

Exceptions:

1. Rigid tile roof coverings that are air permeable and installed over a roof deck complying with Section 1609.5.1 are permitted to be designed in accordance with Section 1609.5.3.

2. Asphalt shingles installed over a roof deck complying with Section 1609.5.1 shall comply with the wind-resistance requirements of Section 1504.1.1.

1609.5.3 Rigid tile.

Wind loads on rigid tile roof coverings shall be determined in accordance with the following equation:

M

a

= q

h

C

L

bLL

a

(1.0 - GC

p

)

(Equation 16-41)

For SI: M

a

= q

h

C

L

bLL

a

(1.0 - GC

p

) / 1,000

where:

b

= Exposed width, feet (mm) of the roof tile.

C

L

= Lift coefficient. The lift coefficient for concrete and clay tile shall be 0.2 or shall be determined by test in accordance with Section 1711.2.

GC

p

= Roof pressure coefficient for each applicable roof zone determined from Chapter 30 of ASCE 7. Roof coefficients shall not be adjusted for internal pressure.

L

= Length, feet (mm) of the roof tile.

L

a

= Moment arm, feet (mm) from the axis of rotation to the point of uplift on the roof tile. The point of uplift shall be taken at 0.76L from the head of the tile and the middle of the exposed width. For roof tiles with nails or screws (with or without a tail clip), the axis of rotation shall be taken as the head of the tile for direct deck application or as the top edge of the batten for battened applications. For roof tiles fastened only by a nail or screw along the side of the tile, the axis of rotation shall be determined by testing. For roof tiles installed with battens and fastened only by a clip near the tail of the tile, the moment arm shall be determined about the top edge of the batten with consideration given for the point of rotation of the tiles based on straight bond or broken bond and the tile profile.

M

a

= Aerodynamic uplift moment, feet-pounds (N-mm) acting to raise the tail of the tile.

q

h

= Wind velocity pressure, psf (kN/m

2

) determined from Section 26.10.2 of ASCE 7.

Concrete and clay roof tiles complying with the following limitations shall be designed to withstand the aerodynamic uplift moment as determined by this section.

1. The roof tiles shall be either loose laid on battens, mechanically fastened, mortar set or adhesive set.

2. The roof tiles shall be installed on solid sheathing that has been designed as components and cladding.

3. An underlayment shall be installed in accordance with Chapter 15.

4. The tile shall be single lapped interlocking with a minimum head lap of not less than 2 inches (50.8 mm).

5. The length of the tile shall be between 1 and 1.75 feet (304.8 mm and 533.4 mm).

6. The exposed width of the tile shall be between 0.67 and 1.25 feet (204.2 mm and 381 mm).

7. The maximum thickness of the tail of the tile shall not exceed 1.3 inches (33 mm).

8. Roof tiles using mortar set or adhesive set systems shall have at least two-thirds of the tile's area free of mortar or adhesive contact.

1609.6 Simplified design procedure.

Use of the simplified design procedure shall comply with Sections 1609.6.1 through 1609.6.5.

1609.6.1 Scope.

The procedures in Section 1609.6 shall be permitted to be used for determining and applying wind pressures in the design of enclosed buildings in Risk Category I and II as listed below:

1. For buildings located within any borough with a mean roof height of not more than 200 feet (60 960 mm) and not located in Exposure C or D in accordance with Section 1609.4, the use of Section 1609.6 shall be permitted.

2. For buildings located within the Borough of Manhattan with a mean roof height of not more than 300 feet (91 440 mm) and not located in Exposure C or D in accordance with Section 1609.4, the use of Section 1609.6 shall be permitted.

1609.6.2 Main windforce-resisting systems.

Main windforce-resisting systems shall comply with the following:

1. The building shall be designed for the following net lateral wind pressure to be applied to the horizontal projection of the building surfaces:

1.1. From 0 to 100 feet (0 to 30 480 mm) elevation 32 psf (1.54 kN/m

2

).

1.2. From 100 to 300 feet (30 480 to 91 440 mm) elevation 40 psf (1.92 kN/m

2

).

1609.6.3 Design wind load cases.

The main windforce-resisting system of buildings, whose wind loads have been determined pursuant to Section 1609.6.1, shall be designed for wind load cases as defined below:

Case 1. Full design wind pressure acting on the projected area perpendicular to each principal axis of the structure, considered separately along each principal axis.

Case 2. Seventy-five percent of the design wind pressure acting on the projected area perpendicular to each principal axis of the structure to be applied eccentric to the center of the exposure with eccentricity equal to 15 percent of the exposure width, considered separately for each principal direction.

Case 3. Wind loading as defined in Case 1 for each orthogonal direction, but considered to act simultaneously at 75 percent of the specified value.

1609.6.4 Components and cladding.

Net design wind positive and negative pressures (pressure and suction) for the components and cladding of buildings represent the net pressures (sum of internal and external) to be applied normal to each building surface. The net design wind positive and negative pressures shall not be less than 48 psf (12.30 kN/m

2

), except at the corners of the building with a width equivalent to 10 percent of the building's width at its side, the net design wind negative pressure for the components and cladding shall not be less than: (i) 72 psf (3.46 kN/m

2

) for the portion of the building between 200 feet (60 960 mm) to 300 feet (91 440 mm) height above ground and (ii) 64 psf (3.07 kN/m

2

) for the portion of the building between 100 feet (30 480 mm) to 199 feet (60 656 mm) in height above ground.

1609.6.5 Roof.

The design pressure and suction acting over the entire roof including purlins, roofing, and other roof elements (including their fastenings) shall be not less than 48 psf (2.30 kN/m

2

).

1609.7 Attached canopies on buildings.

Canopies attached to buildings shall comply with Section 1609.7.1 or 1609.7.2, as applicable.

Table 1609.7 Net Pressure Coefficient, (

GC

pn

) for Attached Canopies on Buildings with H > 60 Ft.

Net Pressure Coefficient (

GC

pn

)

h/hc

2

3

6

12

18

24

30

Upward

-0.60

-0.70

-0.95

-1.04

-1.16

-1.3

-1.3

Downward

0.90

0.90

0.90

0.90

0.90

0.90

0.90

For SI: 1 foot = 304.8 mm.

Figure 1609.7 Schematic of attached canopy on buildings with h > 60 ft.

1609.7.1 Buildings with h £ 60 ft.

The design wind pressure for canopies attached to walls of buildings with h £ 60 ft. shall follow Chapter 30 of ASCE 7.

1609.7.2 Buildings with h > 60 ft.

The design wind pressure for canopies attached to walls of buildings with h > 60 ft. and hc/h < 0.5, as shown on Figure 1609.7, shall be from the following equation:

P = q

h

(GC

pn

) (lb/ft

2

)

(Equation 16-42)

Where:

q

h

= velocity pressure at mean roof height h per Chapter 26 of ASCE 7.

GC

pn

= net pressure coefficient for attached canopies given in Table 1609.7.

1609.8 Wind load on structures during construction.

Structures during construction shall comply with Sections 1609.8.1 and 1609.8.2.

1609.8.1 Design wind speed.

Design wind speed during construction for a construction period of less than 5 years may be reduced as follows:

Unless otherwise directed by the commissioner, the basic design wind speed may be reduced to 110 mph for all risk categories, corresponding to 1.7 percent probability of exceedance in 5 years. The basic design wind speed refers to the ultimate design 3-second gust wind speed at 33 feet (10 058.4 mm) above ground for Exposure Category C, as defined in Section 1609.3.

1609.8.2 Frameworks without cladding.

For unenclosed frames and elements, the appropriate drag factors and wind effect on successive elements shall be accounted for per recognized standards and references, or in accordance with suitable wind tunnel testing.