N.Y.C. Admin. Code § BC 2405: Section BC 2405: Sloped Glazing and Skylights

2405.1 Scope.

This section applies to the installation of glass and other transparent, translucent or opaque glazing material installed at a slope more than 15 degrees (0.26 rad) from the vertical plane, including glazing materials in skylights, roofs and sloped walls.

2405.2 Allowable glazing materials and limitations.

Sloped glazing shall be any of the following materials, subject to the listed limitations.

1. For monolithic glazing systems, the glazing material of the single lite or layer shall be laminated glass with a minimum 30-mil (0.76 mm) polyvinyl butyral (or equivalent) interlayer, wired glass, light-transmitting plastic materials meeting the requirements of Section 2607.

2. For multiple-layer glazing systems, the exterior layer shall be fully tempered glass and the bottom layer shall consist of any of the glazing materials specified in Item 1 above.

Annealed glass is permitted to be used as specified in Exceptions 2 and 3 of Section 2405.3.

Heat-strengthened glass or fully tempered monolithic glass is permitted to be used with screens, as specified in Section 2405.3.

For additional requirements for plastic skylights, see Section 2610. Glass-block construction shall conform to the requirements of Section 2110.1.

2405.3 Screening.

Where used in monolithic glazing systems, heat-strengthened and fully tempered glass shall have screens installed below the glazing material. The screens and their fastenings shall: (i) be capable of supporting twice the weight of the glazing; (ii) be firmly and substantially fastened to the framing members and (iii) be installed within 4 inches (102 mm) of the glass. The screens shall be constructed of a noncombustible material not thinner than No. 12 B&S gage (0.0808 inch) with mesh not larger than 1 inch by 1 inch (25 mm by 25 mm). In a corrosive atmosphere, structurally equivalent noncorrosive screen materials shall be used. Heat-strengthened glass, fully tempered glass and wired glass, when used in multiple-layer glazing systems as the bottom glass layer over the walking surface, shall be equipped with screening that conforms to the requirements for monolithic glazing systems.

Exception: In monolithic and multiple-layer sloped glazing systems, the following applies:

1. Fully tempered glass installed without protective screens where glazed between intervening floors at a slope of 30 degrees (0.52 rad) or less from the vertical plane shall have the highest point of the glass 10 feet (3048 mm) or less above the walking surface.

2. Screens are not required below any glazing material, including annealed glass, where the walking surface below the glazing material is permanently protected from the risk of falling glass or the area below the glazing material is not a walking surface.

3. Any glazing material, including annealed glass, is permitted to be installed without screens in the sloped glazing systems of commercial or detached noncombustible greenhouses used exclusively for growing plants and not open to the public, provided that the height of the greenhouse at the ridge does not exceed 30 feet (9144 mm) above grade.

4. Screens shall not be required in individual dwelling units in Occupancy Groups R-2 and R-3 where fully tempered glass is used as single glazing or as both panes in an insulating glass unit, and the following conditions are met:

4.1. Each pane of the glass is 16 square feet (1.5 m

2

) or less in area.

4.2. The highest point of the glass is 12 feet (3658 mm) or less above any walking surface.

4.3. The glass thickness is 3/16 inch (4.8 mm) or less.

5. Screens shall not be required for laminated glass with a 15-mil (0.38 mm) polyvinyl butyral (or equivalent) interlayer used in individual dwelling units in Occupancy Groups R-2 and R-3 within the following limits:

5.1. Each pane of glass is 16 square feet (1.5 m

2

) or less in area.

5.2. The highest point of the glass is 12 feet (3658 mm) or less above a walking surface.

2405.4 Framing.

In Type I and II construction, sloped glazing and skylight frames shall be constructed of noncombustible materials. In structures where acid fumes deleterious to metal are incidental to the use of the buildings, approved pressure-treated wood or other approved noncorrosive materials are permitted to be used for sash and frames. Framing supporting sloped glazing and skylights shall be designed to resist the tributary roof loads in Chapter 16. Skylights set at an angle of less than 45 degrees (0.79 rad) from the horizontal plane shall be mounted not less than 4 inches (102 mm) above the plane of the roof on a curb constructed as required for the frame. Skylights shall not be installed in the plane of the roof where the roof pitch is less than 45 degrees (0.79 rad) from the horizontal.

Exception: Installation of a skylight without a curb shall be permitted on roofs with a minimum slope of 14 degrees (three units vertical in 12 units horizontal) in Group R-3 occupancies. All unit skylights installed in a roof with a pitch flatter than 14 degrees (0.24 rad) shall be mounted not less than 4 inches (102 mm) above the plane of the roof on a curb constructed as required for the frame unless otherwise specified in the manufacturer's instructions.

2405.5 Unit skylights and tubular daylighting devices.

Unit skylights and tubular daylighting devices shall be tested and labeled as complying with AAMA/WDMA/CSA 101/I.S.2/A440. The label shall state the name of the manufacturer, the approved agency, the product designation and the performance grade rating as specified in AAMA/WDMA/CSA 101/I.S.2/A440. Where the product manufacturer has chosen to have the performance grade of the skylight rated separately for positive and negative design pressure, then the label shall state both performance grade ratings as specified in AAMA/WDMA/CSA 101/I.S.2/A440 and the skylight shall comply with Section 2405.5.2. Where the skylight is not rated separately for positive and negative pressure, then the performance grade rating shown on the label shall be the performance grade rating determined in accordance with AAMA/WDMA/CSA 101/I.S.2/A440 for both positive and negative design pressure and the skylight shall conform to Section 2405.5.1.

2405.5.1 Skylights rated for the same performance grade for both positive and negative design pressure.

The design of skylights shall be based on Equation 24-13.

F

g

 £ PG

(Equation 24-13)

where:

F

g

= Maximum load on the skylight determined from Equations 24-2 through 24-4 in Section 2404.2.

PG

= Performance grade rating of the skylight

2405.5.2 Skylights rated for separate performance grades for positive and negative design pressure.

The design of skylights rated for performance grade for both positive and negative design pressures shall be based on Equations 24-14 and 24-15.

F

gi

 £ PG

Pos

(Equation 24-14)

F

go

£ PG

Neg

(Equation 24-15)

where:

PG

Pos

= Performance grade rating of the skylight under positive design pressure;

PG

Neg

= Performance grade rating of the skylight under negative design pressure; and

F

gi

and F

go

are determined in accordance with the following:

For 0.6W

o

 ³ D,

where:

W

o

= Outward wind force, psf (kN/m

2

) due to basic design wind speed, V, as calculated in Section 1609.

D

= The dead weight of the glazing, psf (kN/m

2

) as determined in Section 2404.2 for glass, or by the weight of the plastic, psf (kN/m

2

) for plastic glazing.

F

gi

= Maximum load on the skylight determined from Equations 24-3 and 24-4 in Section 2404.2.

F

go

= Maximum load on the skylight determined from Equation 24-2.

For 0.6W

o

< D,

where:

W

o

= The outward wind force, psf (kN/m

2

) due to basic design wind speed, V, as calculated in Section 1609.

D

= The dead weight of the glazing, psf (kN/m

2

) as determined in Section 2404.2 for glass, or by the weight of the plastic for plastic glazing.

F

gi

= Maximum load on the skylight determined from Equations 24-2 through 24-4 in Section 2404.2.

F

go

= 0.