One of the things homeowners almost never ask us during a roofing estimate is about attic ventilation.
They’ll ask about shingles.
They’ll ask about colors.
They’ll ask about warranties and price.
Very few people ask:
“Is my attic actually getting enough ventilation?”
It’s something we look at on our roofing projects because installing a ridge vent doesn’t automatically mean the attic is properly ventilated.
You need air coming in, too.
A ridge vent is only half of the system
Think about attic ventilation as having two sides.
You have intake, normally located down at the eaves through vented soffit.
Then you have exhaust, which may be provided by a ridge vent or another type of attic vent. The system needs both.
One problem we see regularly is a house with a good amount of exhaust ventilation but very little intake.
We’ll look at the soffit and sometimes find several solid pieces between every vented section.
Depending on the soffit product and the amount of ventilation the attic requires, that may not provide anywhere near enough intake.
We actually calculate the ventilation
We don’t just look at the house and say, “That seems like enough vents.”
For the roofs we evaluate, we gather information including the attic/roof size, roof pitch, shape of the roof, eave length, ridge length, soffit configuration and the NFA of the ventilation products being used.
NFA stands for Net Free Area. Basically, it tells us how much actual open area a ventilation product provides for air movement.
When applicable, we use the 1/300 rule to determine the ventilation requirements and then evaluate how much intake and exhaust the roof needs.
Here’s a simplified example.
Suppose an attic contains 1,800 square feet.
Using a 1/300 calculation:
1,800 ÷ 300 = 6 square feet of ventilation
There are 144 square inches in a square foot:
6 × 144 = 864 square inches of total NFA
Ideally, that ventilation is appropriately distributed between intake and exhaust.
That means simply saying, “There’s a ridge vent up there” doesn’t answer the question. We need to know how much airflow the entire system can actually provide.
What happens when there isn’t enough intake?
Heat is one concern.
Moisture is another.
A poorly functioning attic ventilation system can contribute to excessive heat and moisture
accumulation in the attic. Under the right conditions, that can contribute to condensation, mold and deterioration of the roof deck.
We’ve seen some pretty extreme examples.
One house we inspected had a hip roof with essentially no intake ventilation at all.
There were no usable eave intake vents and no gable intake. The roof had three box vents
providing exhaust, but there wasn’t an adequate source of replacement air entering down low.
There was also substantial mold in the attic.
For that roof, we installed a Lomanco Deck-Air intake system along with ridge ventilation to create an intake-and-exhaust system that could actually move air through the attic.
What if the house doesn’t have soffits?
That’s another problem we encounter.
You can’t add vented soffit to a house that doesn’t have an appropriate soffit/eave configuration and pretend the problem is solved.
In situations where traditional soffit intake isn’t available, one option we use is a deck-mounted intake ventilation system, such as Lomanco Deck-Air.
It allows us to introduce intake air near the lower portion of the roof without relying on conventional soffit vents.
The appropriate solution depends on the roof. That’s why we calculate ventilation instead of automatically installing the same setup on every house.
Sometimes the ventilation system isn’t the problem
This is where attic moisture can get interesting.
We had one home in Auburn, Michigan with a significant amount of attic mold.
The source wasn’t simply inadequate soffit or ridge ventilation.
The home’s bathroom exhaust was terminating inside the attic.
Every time somebody used the bathroom exhaust fan, warm, moisture-laden air was being dumped directly into the attic.
There was enough mold damage that the roof decking ultimately had to be replaced. We corrected the bathroom exhaust so it vented through the roof rather than into the attic.
We’ve encountered another variation of the same problem.
On a different house, the attic appeared to have adequate intake and exhaust ventilation, yet there was still some mold.
The bathroom exhaust terminated through the soffit.
Our concern was that moisture being discharged at the soffit could be drawn back toward the attic through nearby intake ventilation.
When we replaced the roof, we moved the bathroom exhaust termination through the roof and replaced the affected decking.
That’s why diagnosing attic moisture isn’t always as simple as adding another vent.
More ventilation isn’t automatically better
This is another misconception. The objective isn’t to put as many vents on the roof as possible. The goal is to create an appropriately designed intake-and-exhaust system for that particular attic.
The shape of the house matters. A simple gable roof may have plenty of ridge available for exhaust. A complicated hip roof can have much less usable ridge relative to the attic area.
Soffit configuration matters.
Roof size matters.
The ventilation product’s NFA matters.
Even the way existing ventilation systems interact with one another can matter.
That’s why we evaluate ventilation as a system rather than counting the number of vents visible from outside.
We learned firsthand how much attic heat can matter
There’s actually a personal reason I’m particular about ventilation. When the central air conditioning at my own house went out, the upstairs wouldn’t drop below about 80 degrees.
We installed a 40-watt Remington solar attic fan. Within about a week, even without the central AC running, the upstairs didn’t go above about 72 degrees under the conditions we were experiencing at the time.
That’s obviously one house and shouldn’t be taken as a promise that installing an attic fan will drop every home’s temperature by eight degrees.
But experiencing the difference firsthand reinforced something we already see on customers’ homes: what’s happening in the attic can have a noticeable effect on the house below it.
We look at ventilation when we’re replacing your roof
Midland Roofers doesn’t look at a roof as just shingles. When we’re evaluating a roofing project, we also look at the components that allow that roof and attic to function properly.
That includes intake ventilation, exhaust ventilation, soffit, roof decking, underlayment, flashing and other parts of the roofing system.
Midland Roofers is the exterior division of Chad Moody Building & Remodeling, and we primarily serve homeowners and businesses throughout Midland, Bay City, Saginaw and the surrounding Mid-Michigan area.
If you’re replacing your roof—or you’re dealing with excessive attic heat, moisture or mold—it’s worth determining whether the existing ventilation system is actually appropriate for the attic.
Contact Midland Roofers to schedule an inspection or roofing estimate.