Table 5-2 – 506.7
TABLE 5-2 Reduction of Duct Clearance with Specified Forms of Protection
Clearance reduction applied to and covering all combustile surfaces with the distance specified as required clearance with no protection in 506.7.2
Minimum Allowable Reduction in Clearance (%)
Form of Protection
As Wall Protector
As Ceiling Protector
3-1/2 in. (90 mm) thick masonry wall without ventilated airspace 1/2 in. (13 mm) thick noncombustile insulation board over 1 in.
mm) glass fiber or mineral wool batts without ventilated airspace
in. (0.61 mm) (No. 24 gauge) sheet metal over 1 in. (25.4 mm) glass
fiber or mineral wool batts reinforced with wire, or equivalent, on rear face with at least a 1 in. (25.4 mm) air gap 3-1/2 in (90 mm) thick masonry wall with at least a 1 in (25.4 mm) air gap 0.024 in. (0.61 mm) (No. 24 gauge) sheet metal with at least a 1 in. (25.4 mm) air gap 1/2 in. (13 mm) thick noncombustible insulation board with at least a 1 in.
mm) air gap
in. (0.61mm) (No. 24 gauge) sheet metal with ventilated airspace over
in. (0.61 mm) (No. 24 gauge) sheet metal with at least a 1 in. (25.4 mm)
air gap 1 in. (25.4 mm) glass fiber or mineral wool batts sandwiched between two sheets 0.024 in. (0.61 mm) (No. 24 gauge) sheet metal with at least a 1 in. (25.4 mm) air gap
Extent of protection required to reduce clearances from ducts.
be permitted to be reduced to six (6) inches (15 cm) from combustible materials and 1/2 inch (13 mm) from combustible construction.
Exception No. 2: When the combustible material and construction is protected by the use of materials or products listed for protection purposes or in accordance with Table 5-2.
506.7.1.1 Spacers and ties for protection materials shall be of noncombustible material a n d s h a l l n o t b e u s e d d i r e c t l y b e h i n d t h e d u c t . 5 0 6 . 7 . 1 . 2 W i t h a l l c l e a r a n c e r e d u c t i o n systems using a ventilated airspace, air
r e d u c t i o n s y s t e m s u s i n g a v e n t i l a t e d s p a board) shall have a minimum density of eight (8) lb./ft.3 (3.6 kq/m3) and have a c e . 5 0 6 . 7 . 1 . 3 M i n e r a l w o o l b a t t s ( b l a n k e t circulation shall be provided as described in Table 5-2. There shall be at least one (1) inch (2.5 cm) between the wall protector and combustible walls and ceilings for clearance, o r m i n i m u m m e l t i n g p o i n t o f 1 , 5 0 0 ˚ F ( 8 1 6 ˚ C ) . 5 0 6 . 7 . 1 . 4 I n s u l a t i o n b o a r d u s e d a s a p a r t o f a clearance-reduction system shall have a thermal conductivity of 1 Btu in./ft.2 hr˚F (0.14 W/m2 hr˚C) or less. Insulation board shall be formed of noncombustible material.