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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:
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| AV-4 |
52 |
Sq Feet of Floor |
| AV-6 |
100 |
" |
| AV-8 |
200 |
" |
| AV-10 |
327 |
" |
| AV-12 |
450 |
" |
| AV-14 |
600 |
" |
| AV-16 |
837 |
" |
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| AV-18 |
1050 |
Sq Feet of Floor |
| AV-20 |
1308 |
" |
| AV-24 |
1883 |
" |
| AV-30 |
2941 |
" |
| AV-36 |
4237 |
" |
| AV-42 |
5766 |
" |
| AV-48 |
7533 |
" |
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| 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
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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.
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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
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28 |
= 10 vents req. |
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AV8
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50 |
= 6 vents req. |
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AV12
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113 |
= 3 vents req. |
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AV14
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144 |
= 2 vents req. |
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AV18
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215 |
= 1 vent req. |
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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
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| 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
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| STEP SEVEN |
To obtain the square area, multiply the height (step 6) by half the width (step 3) |
324
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| STEP EIGHT |
To obtain the cubic feet of the attic, multiply the square area (step 7) by the length (step 2) |
63,504
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| 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
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| 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
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AV-8 |
AV-12 |
AV-14 |
AV-18 |
AV-24 |
| 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 |
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| 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
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