Updated: Mar 31
Residential attic ventilation across the United States has minimum code requirements. 1/300 rule in the US, 1/150 (Double) for international standards. Here, we'll dig into why ventilation is important what bad ventilation can do to your home.
Each day spent inside attics, we continue to learn more and more about how absolutely critical ventilation is for a successful long lasting roofing system. The importance of attic ventilation for your home’s roof cannot go overlooked. Many aspects of your home rely on good attic ventilation. The safety and security of your family relies on the attic ventilation in combination with your roofing system, to allow free Flowing air year round to circulate healthy air. Poor attic ventilation from poor attention to detail during the roof installation can cost homeowners thousands and potentially risk their family’s health overtime.
So, why is attic ventilation so important?
Properly functioning attic ventilation system is made up of a balanced system of intake and exhaust vents
1-Intake ventilation (at the soffits or with shingle over aka smart vents)
2-Ridge Vent or various systems of box exhaust vents (depending on your region)
During Summer, warm air rises and exits the roof through exhaust vents creating a negative pressure pulling in cooler air from the soffits. The attic insulation is in place to prevent hot air from affecting the living space below, keeping it cool. In Winter, air Flows through the attic space helped by wind to circulate moist dense air on the inside through the exhaust to prevent condensation from accumulating the surfaces in the attic which can result in organic growth and warped decking (plywood). Good ventilation in the Winter is meant to dry out moisture that rises into the attic from living activities such as cooking, showering, and even breathing.
To answer why the ventilation between your living area and the roof is so important, we should remember how vital air is for most biological organism to thrive. Click here to learn more about indoor air quality with the United States EPA. Organic growth can thrive is places with poor air Flow leading to serious air quality concerns which should be addressed as soon as possible via abatement. As building materials have become increasingly efficient, without addressing attic ventilation, the air quality can inversely go down. Better envelopes keep the home more weather proof. Synthetic siding underlayments and double or even triple pain windows all sound good for energy efficiency but can release chemicals into the home over time. Better drywall and plaster, extra thick blow-in insulation in your attic are all designed for better weather protection, but can reduce the amount of air moving through the home.
Older homes have it even worse where remodeling and upgraded material are installed without consideration for upgrades to attic ventilation. If the air cannot properly enter the attic space, shingle life can be drastically reduced. Another drawback of the intakes being addressed would be the increased energy costs of the attic overheating and radiating down into the living area of the home. These excessive temperatures, (not being driven out because of inadequate intake ventilation) will slowly compromise the structure integrity of the truss beams over decades which support the roof via a process called sapping. Sapping is where sap, the blood of the wood that makes up the beam, is slowly drawn out of the wood fibers through decades of overheating attic temperatures. This will accelerate the aging of your roof's shingles over time. Where this can cost the home owner is specifically when upgrading to solar where the solar companies will have to reinforce the beams to support the additional weight. It is very rare that a truss will break completely but we've seen in happen in homes with poorly designed ventilation in combination with tile roofing materials.
What can happen when attic ventilation in the roof functions improperly?
-Organic Growth Occurs
-Excessive heat in the living space below
-Premature Granule Loss
-Premature shingle fiberglass is showing
-Ridge cap cracking
Two key components to your attic’s ventilation success is the intake and exhaust. Intake is typically located towards the bottom of the roof line because hot air rises. Exhaust is typically located near the ridge of the roof to expel the hot air that can reach over 160+ degrees in the Summer. Intake is to always balance the amount of exhaust at a manufacturer preferred 50/50 ratio. At Flow Roofing, we take the time to do the calculations to make sure you’re home meets or exceeds the code for residential roofs. Many early homes pre 1980’s didn’t take attic ventilation into consideration as seriously and as a result, attics burned through roofs much faster. Click Here for an early history of attic ventilation. The soffits on these homes sometimes had no ventilation at all! With the roofs inability to replace the hot air with cooler circulated air, asphalt roofing systems would be lucky to last 20 years on these homes. Acceptable by the manufacturers, but frowned upon in the industry, is adding a layer. These homes would be passed down by a homeowner with an acceptable 2 layers, and the new homeowner would continue adding additional one or even a 4th layer before manufacturers started taking notice and voiding warranties. Once you add to the second layer, something called an R-Value (Isolation Factor) increases, further heating the attic, adding to Summer cooling costs as well as reducing the shingle life of the new layer and increasing the number of fastener penetrations. The solutions to little or no soffit intake, or even blocked soffit intakes can vary in cost depending on the remedies taken.
Increasing the total NFA (Net Free Area, area where air can flow in freely. Example 2x10 intake = 20NFA) of the intake ventilation can be done by: (Most Expensive)
1-Increasing the total quantity of soffit intake vents while adding baffling between the trusses to eliminate blocked air flow.
(At The Time Of Roof Installation)
2-Installing a smart vent at the edge of the roof line depending on designated cold zone region combined with baffling to prevent blockage.
-May not be possible if not in a cold zone. Exposed eves over even 12 inches can result in needed the next alternative, shingle over smart vent intakes.
(At the Time of New Roof Installation)
-Installing shingle-over smart vents that allows cool air to enter over an obstructions
The 7 signs of inadequate attic ventilation & reasons why
1-Higher Temperatures in living area
-Poor isolation and balanced intake and exhaust ventilation
2-Sapping in the trusses
-Overheating attic temperatures
3-Premature granule loss
-Poor asphalt quality and overheating decking from improper attic cooling
Poor ventilation causes snow to melt and refreezes as it hits the eve causing ice to refreeze back up the roof line and potentially into the home.
-condensation/moisture hitting the roof deck causing the plywood to expand
6-Organic growth problems
-improper air circulation from an unbalanced ventilation system
7- Curling Shingles
-Over heating decking, shingle lifespan is over
Describe how shingles break down overtime
Shingle are made of 4 layers. Asphalt, Fiberglass, then more asphalt then granules. The granules from the top protect the layers below. Poor asphalt quality, a characteristic of under performing shingles that won’t hold onto granules their full warrantied life. When the granules aren't being held by quality asphalt, they roll right down the roof once the single begins to overheat from various failing roof ventilation. Once off, the bare asphalt has no UV protection and accelerated shingle decay continues. Ultimately whats left is the fiberglass mat that hold the bottom and top layers of asphalt together. By the time fiberglass is showing, penetrations may become exposed and begin to leak.
Best solutions to attic ventilation -shingle over intake + ridge exhaust vent
Pros: Prevents hot air from pocketing, balanced intake
Cons: Done at the time of new roof
-mechanical solar fan (warranty concerns depending on the manufacturer)
Pros: Uses no electricity, quiet, additional cooling for the roof
Cons: Expensive, Added, Penetrations, Potential Warranty Issues
-1/150 Balanced Box/Ridge + Shingle Over Intake
Pros: Most affordable
Cons: Done at the time of new roof
-Soffit remodeling + Baffling
Pros: Effective, hidden from view, increased air flow
Cons: Expensive, laborious, doesn’t address balancing the exhaust
What are the solutions?
Best solution to poor attic ventilation is to start with designing the roof around getting the ventilation above acceptable code and, to use high quality shingle products from the beginning. Malarkey is our shingle of choice at Flow roofing because of their increased granule retention, upcycled rubber and plastic to protect against UV damage,
Ridge Vent Or Box Vent Exhaust ?
Box Vents or Turtle vents are a component of your exhaust ventilation. They come in various sizes but come with some potential draw backs. Not only do that lack the proper design to maximize air flow, the placement usually allows hot air to pocket at the ridge of the attic space increasing the decking departure which can cause premature granule loss as discussed above.
Ridge Vents have a slightly higher NFA rating depending on the manufacturer for increased air flow as well as an engineered baffle that maximizes the Bernoulli principle to allow how air to be pulled through the exhaust vent assuming balanced intake. They also clean up the roofs visible penetrations for a better overall aesthetic.
In summary, attic ventilation is more important than the product you choose to install. We'll continue to cover all aspects of roofing ventilation in depth throughout time. Reach out with any questions anytime. Call Flow Roofing anytime at 503-936-2476, or email email@example.com or through our website. Thank you for considering Going With The Flow!