roofer wants to add 2 more roof vents when reroofed. I have 2 already. says it will give more ventilation to attic. house built in 2001. do I really need to have 2 more holes cut in my roof

Exteriors Roofing
2

Hello Deb,

In order to answer this question, a square footage calculation must be made. Please see below:

This calculator offers two methods of NFVA calculation:
1:150 (1 sq. ft. of ventilation for every 150 sq. ft of attic floor space).
1:300 (1 sq. ft. of ventilation for every 300 sq. ft of attic floor space).

The US FHA requires a minimum of 1:300 NFVA. However, for optimal performance, Owens Corning recommends using the 1:150 rule. Additionally, you may be required to meet the 1:150 rule, depending on your local building codes.

Both of these calculations are based on an ideally balanced system (50% intake, 50% exhaust).

Best Regards,
Matthew
Avant-Garde

3

Generally speaking, you need a ratio of 1:300, where for every 300 square feet of ceiling space, you need 1 square foot of attic ventilation

4

This is the answer.
Measure out the space sq, of the flat area. You will need 1 1" vent per 150 so divide the total area by 150.The answer is right there on how mant 1 sq vents are needed.
Only change this calculation up to 300 if its not cold in summer n hot in winter.
Please consider gable vents before cutting any additional holes.