N.Y.C. Admin. Code § MC 308: Section MC 308: Clearance Reduction

308.1 Scope.

This section shall govern the reduction in required clearances to gypsum board, combustible materials and combustible assemblies for chimneys, vents, kitchen exhaust equipment, mechanical appliances, and mechanical devices and equipment.

308.2 Listed appliances and equipment.

The reduction of the required clearances to combustibles for listed and labeled appliances and equipment shall be in accordance with the requirements of this section, except that such clearances shall not be reduced where reduction is specifically prohibited by the terms of the appliance or equipment listing.

308.3 Protective assembly construction and installation.

Reduced clearance protective assemblies, including structural and support elements, shall be constructed of noncombustible materials. Spacers utilized to maintain an airspace between the protective assembly and the protected material or assembly shall be noncombustible. Where a space between the protective assembly and protected combustible material or assembly is specified, the same space shall be provided around the edges of the protective assembly and the spacers shall be placed so as to allow air circulation by convection in such space. Protective assemblies shall not be placed less than 1 inch (25.4 mm) from the mechanical appliances, devices or equipment, regardless of the allowable reduced clearance.

308.4 Allowable reduction.

The reduction of required clearances to combustible assemblies or combustible materials shall be based on the utilization of a reduced clearance protective assembly in accordance with Section 308.4.1 or 308.4.2.

308.4.1 Labeled assemblies.

The allowable clearance reduction shall be based on a reduced clearance protective assembly that has been tested and bears the label of an approved agency.

308.4.2 Reduction table.

The allowable clearance reduction shall be based on one of the methods specified in Table 308.4.2. Where required clearances are not listed in Table 308.4.2, the reduced clearances shall be determined by linear interpolation between the distances listed in the table. Reduced clearances shall not be derived by extrapolation below the range of the table.

Table 308.4.2 Clearance Reduction Methods

b

Type of Protective Assembly

a

Reduced Clearance With Protection (inches)

a

Horizontal combustible assemblies located above the heat source

Horizontal combustible assemblies located beneath the heat source and all vertical combustible assemblies

Required clearance to combustibles without protection (inches)

a

Required clearance to combustible without protection (inches)

a

36

18

9

6

36

18

9

6

Galvanized sheet metal, minimum nominal thickness of .0296 inch (No. 22 Gage), mounted on 1-inch glass fiber or mineral wool batt reinforced with wire on the back, 1 inch off the combustible assembly

18

9

5

3

12

6

3

3

Two layers of galvanized sheet metal, minimum nominal thickness of 0.024 inch (No. 24 Gage), having a 1-inch airspace between layers, spaced 1 inch off the combustible assembly

18

9

5

3

12

6

3

3

Two layers of galvanized sheet metal,minimum nominal thickness of 0.024 inch (No. 24 Gage), having 1 inch of fiberglass insulation between layers, spaced 1 inch off the combustible assembly

18

9

5

3

12

6

3

3

0.5-inch inorganic insulating board, over 1 inch of fiberglass or mineral wool batt, against the combustible assembly

24

12

6

4

18

9

5

3

3 1/2-inch brick wall, spaced 1 inch off the combustible wall

—

—

—

—

12

6

6

6

3 1/2-inch brick wall, against the combustible wall

—

—

—

—

24

12

6

5

For SI: 1 inch = 25.4 mm, °C = ((°F)-32)/1.8, 1 pound per cubic foot = 16.02 kg/m

3

, 1.0 Btu

·

in/(ft

2

·

h

·

°F) = 0.144 W/m

2

·

K.

a. Mineral wool and glass fiber batts (blanket or board) shall have a minimum density of 8 pounds per cubic foot and a minimum melting point of 1,500°F. Insulation material utilized as part of a clearance reduction system shall have a thermal conductivity of 1.0 Btu

·

in./(ft

2

·

h

·

°F) or less. Insulation board shall be formed of noncombustible material.

b. For limitations on clearance reduction for solid fuel-burning appliances, masonry chimneys, connector pass-throughs, masonry fireplaces and kitchen ducts, see Sections 308.4.2.1 through 308.4.2.5.

308.4.2.1 Solid fuel-burning appliances.

The clearance reduction methods specified in Table 308.4.2 shall not be utilized to reduce the clearance required for solid fuel-burning appliances that are labeled for installation with clearances of 12 inches (304.8 mm) or less. Where appliances are labeled for installation with clearances of greater than 12 inches (304.8 mm), the clearance reduction methods of Table 308.4.2 shall not reduce the clearance to less than 12 inches (304.8 mm).

308.4.2.2 Masonry chimneys.

The clearance reduction methods specified in Table 308.4.2 shall not be utilized to reduce the clearances required for masonry chimneys as specified in the New York City Building Code and Chapter 8 of this code.

308.4.2.3 Chimney connector pass-throughs.

The clearance reduction methods specified in Table 308.4.2 shall not be utilized to reduce the clearances required for chimney connector pass-throughs as specified in Section 803.10.4.

308.4.2.4 Masonry fireplaces.

The clearance reduction methods specified in Table 308.4.2 shall not be utilized to reduce the clearances required for masonry fireplaces as specified in the New York City Building Code and Chapter 8 of this code.

308.4.2.5 Kitchen exhaust ducts.

The clearance reduction methods specified in Table 308.4.2 shall not be utilized to reduce the minimum clearances required by Section 506.3.11 for kitchen exhaust ducts enclosed in a shaft.