







1994 UNIFORM BUILDING CODE
1505.3 Ventilation. Where determined necessary by the building official due to atmospheric or climatic conditions, enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain and snow. The net free ventilating area shall not be less than 1/150 of the area of the space ventilated.
Venting by Square Footage of the Building
Exceptions:
1. The area may be 1/300 of the area of the space ventilated provided 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the space to be ventilated at least three feet above eave or cornice vents with the balance of the required ventilation provided by eave or cornice vents.
2. The area may be 1/300 of the area of the space ventilated provided a vapor retarder having a transmission rate not exceeding 1 perm is installed on the warm side of the attic insulation.
Application: One vent for exhaust per:





AV4 
52 
Sq Feet of Floor 
AV6 
100 
" 
AV8 
200 
" 
AV10 
327 
" 
AV12 
450 
" 
AV14 
600 
" 
AV16 
837 
" 

AV18 
1050 
Sq Feet of Floor 
AV20 
1308 
" 
AV24 
1883 
" 
AV30 
2941 
" 
AV36 
4237 
" 
AV42 
5766 
" 
AV48 
7533 
" 






TO DETERMINE THE VENTING REQUIREMENTS
The following formula makes it easy to calculate exactly how many of each type of vent you will need for a given application
.
STEP 1: Calculate your attic size in sq. ft.
STEP 2: 1/300 Rule: Step 1 x .24 = Total sq. inches of ventilation requirement for exhaust.
STEP 3: Step 2 ÷ Free area of vent chosen from data sheet = number of vents required.



Home is: 30' W x 40' L
= 1,200 sq. ft.
x .24 = 288 Total sq. inches of ventilation required for exhaust
288 ÷ the sq. inch opening size of ventilator
288 ÷ 28 sq. inch opening of the AV6 = 10.28
Rounds to 10
2. 1,200 x 2.4 = 288 sq. ft. in req.
3. 288 ÷ 
AV6

28 
= 10 vents req. 

AV8

50 
= 6 vents req. 

AV12

113 
= 3 vents req. 

AV14

144 
= 2 vents req. 

AV18

215 
= 1 vent req. 






TO DETERMINE THE SIZE AND QUANTITY OF POWERED VENTILATORS REQUIRED BASED UPON THE CUBIC FEET OF AN ATTIC OR BUILDING AND THE AMOUNT OF AIR CHANGES DESIRED


STEP ONE 
Measure the width of the building 
72 
STEP TWO 
Measure the length of the building 
196 
STEP THREE 
Divide the width of the building (step 1) in half 
36 
STEP FOUR 
Obtain the pitch of the roof 
3 by 12 
STEP FIVE 
Calculate the height per foot in feet. Divide 3" by 12" 
0.25 
STEP SIX 
Multiply half the width of the building (step 3) by height per foot (step 5) to obtain the height of the attic 
9

STEP SEVEN 
To obtain the square area, multiply the height (step 6) by half the width (step 3) 
324

STEP EIGHT 
To obtain the cubic feet of the attic, multiply the square area (step 7) by the length (step 2) 
63,504

STEP NINE 
Determine the amount of air changes desired per hour 
4 
STEP TEN 
To obtain the cubic feet per hour air exhausted, multiply by the number of air changes wanted per hour (step 9) by the cubic feet of the attic (step 8) 
254,016

STEP ELEVEN 
To calculate CFM, divide cubic feet per hour (step 10) by 60 
4,233.6 
STEP TWELVE 
Compare (step 11) with Aura Fan Ventilator to determine which unit or units will provide the CFM required

AV8 
AV12 
AV14 
AV18 
AV24 
CFM 
200 
700 
1,000 
2,200 
4,000 
CFM Needed 
4,233.6 
4,233.6 
4,233.6 
4,233.6 
4,233.6 
Units Needed 
21.2 
6.0 
4.2 
1.9 
1.1 
Rounded 
21 
6 
4 
2 
1 


STEP THIRTEEN 
Calculate the free air space in inches required for fresh air inlet according to UBC (step 1 x step 2 x .48) 
6,774













