Ever wonder what those funny little squares are on top of your roof? Or maybe your roof doesn’t have any, but your neighbor - who just replaced his roof and didn’t have any before the replacement – now has them all along the ridge of his house. What gives? And why do some properties have those louver-type windows in the attic?
The answer is simple: attic ventilation.
Why is this important? The obvious reason is to reduce hot air from building-up in the attic, but there’s so much more to it than that. An improperly vented attic can cause shingle and structure deterioration, ice dams in the winter, excessive energy consumption, and in extreme cases, can cause moisture build-up – which in turn can be the source of mold.
So, how do you avoid all of this? The solution is simple: install and maintain adequate attic ventilation.
Attic Ventilation Requirements
Per the International Building Code, 2012 Edition, adequate attic ventilation requires “enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof framing to have cross-ventilation for each separate space. The net free vent area (NFVA) shall not be less than 1:150 of the area of the space being vented. Blocking and bridging must be arranged so they do not interfere with air movement; air space no less than 1 inch must be provided between any insulation or obstruction and the roof sheathing. Ventilation openings must be protected to prevent rain or snow infiltration.” To put that in layman’s terms, for every 150 sq ft of attic space, there must be at least 1 square foot of NFVA. Further, the ventilation must be balanced between the soffits or eaves and the upper portion of the roof.
There are many different types of roof vents available, each with their own set of idiosyncrasies and ideal applications. Why a specific type of roof vent was installed in place of another one is rarely a simple case of aesthetic preference, but rather, is based on the type of property, the area where the vent will be installed and the amount of negative space around the vent. Aesthetics comes in a distant fourth in that equation.
Now, do some simple math with us: if your attic is roughly 20’ x 30’, you have approximately 600 sq ft of attic space. This would require a minimum of 4 NFVA. This should be comprised of a combination of exhaust vents along the ridge of the roof (maybe a ridge vent or roof louvers) and intake vents along the base of the roof (soffit or eave vents) in order to be compliant with IBC 2012.
Are Your Exhaust Fans Up to Code?
Additionally, if you have any exhaust fans installed in your home, it's wise to have them checked to ensure they are properly vented. We can’t tell you how many times we encounter a bathroom exhaust fan that is venting INTO the attic, or a range hood that is improperly vented. Each of these issues may seem small on their own, but when combined with the elements and cooling temps in the fall and winter or rising temps in the summer, these can create major areas of concern. A quick trip into the attic by a Licensed, Professional Roofing Contractor can quickly spot this.
So, take a look at your roof. What do you see? If you see aging and cracked shingles and your roof is less than 10 years old, or if you’ve noticed that you keep your thermostat set at 72 in the winter but your house always seems cold, it’s possible that an improperly vented attic could be the culprit. Your local Licensed, Professional Roofing Contractor can easily tell if you have the signs of a problem.
Ventilation people….don’t install a roof without it.
Or, for a little more “light reading”, you can take a peek at the AirVent, Inc. booklet, “Principles of Attic Ventilation”.