SECTION M-1103.0 REDUCED CLEARANCES

M-1103.1 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 M-1103.2 or M-1103.3.[33]

M-1103.2 Labeled assemblies: The allowable clearance reduction shall be based on an approved reduced clearance protective assembly that has been tested and bears the label of an approved agency.

M-1103.3 Reduction table: The allowable clearance reduction shall be based on one of the methods specified in Table M-1103.3. Where required clearances are not listed in Table M-1103.3, 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 M-1103.3
Type of protective assembly a,b	Reduced clearance with protection (inches)a,b
	Horizontal combustible assemblies				Horizontal combustible assemblies, combustible assemblies located beneath the heat
	Required clearance to combustibles without protection (inches)a,b				Required clearance to combustibles without protection (inches)a,b
	36	18	9	6	36	18	9	6
Galvanized sheet metal, minimum nominal thickness of 0.024 inch (No. 24 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
Galvanized sheet metal, minimum nominal thickness of 0.024 inch (No. 24 Gage), spaced 1 inch off the combustible assembly	18	9	5	3	12	6	3	2
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
½-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 ½-inch brick wall, spaced 1 inch off the combustible wall	--	--	--	--	12	6	6	6
3 ½-inch brick wall, against combustible wall	--	--	--	--	24	12	6	5
Note a. Mineral wood batts (blanket or board) shall have a minimum density of 8 pounds per cubic foot and have a minimum melting point of 1,500 degrees F. Insulation material utilized as part of a clearance reduction system shall have a thermal conductivity of 1.0 (Btu  in. ) sq. ft.  hr.  degrees F.) or less. Insulation board shall be of noncombustible material. Note b. 1 inch = 25.4 mm; Degrees C. = [(degrees)-32]/1.8; 1 pound per cubic foot = 16.02 kg/m3.

M-1103.3.1 Solid fuel-burning appliances: The clearance reduction methods specified in Table M-1103.3 shall not be utilized to reduce the clearance required for solid fuel-burning appliances that are labeled for installation with clearance of 12 inches or less. Where appliances are labeled for installation with clearances of greater than 12 inches, the clearance reduction methods of Table M-1103.3 shall not reduce the clearance to less than 12 inches.

M-1103.3.2 Masonry chimneys: The clearance reduction methods specified in Table M-1103.3 shall not be utilized to reduce the clearances required for masonry chimneys as specified in Sections M-1207.4 and M-1208.4.

M-1103.3.3 Chimney connector pass-throughs: The clearance reduction methods specified in Table M-1103.3 shall not be utilized to reduce the clearances required for chimney connector pass-throughs as specified in Sections M-1216.3.4.1.

M-1103.3.4 Masonry fireplaces: The clearance reduction methods specified in Table M-1103.3 shall not be utilized to reduce the clearances required for masonry fireplaces as specified in Section M-1404.4.

M-1103.3.5 Kitchen exhaust ducts: The clearance reduction methods specified in Table M-1103.3 shall not be utilized to reduce the clearances required by Section M-506.4 for kitchen exhaust ducts enclosed in a shaft.