Installation Guide

Roof Deck: Use only over a well-seasoned, supported wood deck, tightly constructed with
maximum 6" wide lumber, having adequate nail-holding capacity. Plywood decking as
recommended by The Engineered Wood Association is acceptable.
For ridge vent to function properly, it must be the only exhaust vent for the vented attic
space. Do not use with gable-end louvers,turbines, roof vents, or power vents.
Slope Restrictions: Use only on slopes between 3/12 and 16/12.
STEP 1
Calculations for a Balanced Ventilation System
To achieve a “balanced system” with Cobra
®
4' rigid vents, there must be an air intake
system (i.e., soffits or undereave vents). For proper ventilation, the amount of undereave
ventilation must equal the amount of ventilation at the ridge.
NOTE: Consult local building codes for other ventilation requirements.
NOTE: In no case should the amount of exhaust ventilation exceed the amount of intake ventilation.
To determine the minimum square feet of net free ventilating area (NFVA) needed for a
balanced ventilation system, use the following formula:
Cobra
®
4' rigid vents have 18.0 square inches of NFVA per lineal foot. To determine
how many feet of Cobra
®
4' rigid vent is needed, use the following formula:
1/2 x (Min. sq. ft. of NFVA needed) x 144 / 18.0
=
Min. lineal feet of ridge
vent needed
To determine the amount of undereave vent required,use the following formula:
X
=
NFVA (Sq. in. per. lin. ft.) of the undereave vent or intake vent system selected
1/2 x (Min. sq. ft. of NFVA needed) x 144/X = Min. lineal feet of undereave
vent needed
STEP2
Instruction For Slots
After calculating the total length of Cobra
®
4' rigid vent needed, determine the necessary
slot opening required.
Note: If installing on an existing roof, remove the cap shingles from the ridge.
Roofs without a ridge board: cut a
7
/
8
" opening along the ridge on each side (Figure A).
Roofs with a ridge board: cut a 1
5
/
8
" opening along the ridge on each side (Figure B).
Note: Maximum slot opening is 3
1
/
4
" wide.
Mark off and cut the slot opening, making sure that the ends of the opening stop at least
6" from any end walls and at least 12" from hip and ridge intersections or chimneys.
(Figure C).
Where short ridges (dormers, ridge intersections) are used, mark and cut the slot and
make sure that the end of the opening stops at least 12" from the ridge intersection
(Figure D).
5
/8
”
1
1
/4
”
3
5
/8
”
1
Fig. A
Fig. B
Fig. C
Fig. D
Sq. ft. of attic floor space
Min. Sq. ft. of NFVA needed
300
=
APPLICATION INSTRUCTIONS
SNOWC O UNTR Y
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RIGIDVENT
2
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2
RIGIDVENT
3
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SNOWC O UNTR Y
ADVANCED
Exhaust Vent For Roof Ridge Exhaust Vent For Roof Ridge Exhaust Vent For Roof Ridge Exhaust Vent For Roof Ridge