Free calculator · about two minutes
Does your roof breathe?
Every roof needs air coming in low and going out high, in balance. Many roofs get the exhaust and skip the intake. Put in what is on your house and see the math.
Count what you can see from the yard, or ask the contractor who looked in the attic. Nothing you enter leaves this page.
The house
House not a simple box, or more than one attic?
Finding the floor area. Split the house into rectangles, the way it looks from above. Multiply length by width for each one, then add them together. Measure the outside walls; that is close enough for this check.
More than one attic. Some roofs have attic spaces walled off from each other, like an attached garage, an addition, or a bonus room with its own roof. Air cannot move between them, so each one needs its own intake and exhaust. Run this check once for each attic, using only its floor area and only the vents on that part of the roof.
Adding separate attics together can hide one that has no airflow at all. When it is not clear whether the spaces connect, a look in the attic settles it.
What is up there now
Now vs needed
Three ways this can go
As it is
of the intake it needs
Exhaust only
if only exhaust is added
Balanced
100%
intake and exhaust both met
About this check
This is a basic attic ventilation check. It gives an approximate picture of intake and exhaust from the numbers entered and typical vent ratings. It is not an inspection, a design, or professional advice, and it cannot see the attic, the vents, or the insulation. The right ventilation is confirmed on site by a qualified roofing professional before any work is done. Informify360 is not responsible for decisions made or work done based on this check.
Net free area per vent uses typical manufacturer figures (ridge 18 sq in/ft, box 50, turbine 100, gable 55, continuous soffit 9 sq in/ft, rectangular soffit 56). Check the label on the product being installed.
Take it to the table
Ask any bidder these 6
- 1
What are you doing for intake, not just exhaust?
- 2
How many square inches of net free area does this roof need, and how many will it have when you are done?
- 3
Are you keeping or removing the gable vents? (Mixing gable vents with roof vents can short-circuit both.)
- 4
Are you using one kind of exhaust, or mixing ridge vent with box vents?
- 5
Are the soffits actually open behind the vent, or painted and insulated shut?
- 6
Will you put the ventilation numbers in writing on the estimate?
If a bid does not answer these, ask the bidder to put the answers in writing before you compare price.
Why ventilation matters, in plain language