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The Why and How of Proper Roof Ventilation

Updated: Dec 9, 2019



There are many theories behind the importance of roof ventilation.  


Some argue that roof ventilation is only essential in warmer climates.  Some would also

say that as long as you have a few vents in the gables of your house, then you are

properly vented.


Due to these and many more mixed approaches to roof venting, it may become easy to

ignore the importance of proper roof ventilation; including its design, construction, and

implementation.


What happens if you ignore proper roof ventilation?

Sadly, ignoring proper roof ventilation can become a costly mistake to the homeowner’s

structure.  It can cause mold, ice dams, and higher heating and cooling bills.


Improper ventilation can also damage a contractor’s reputation.  If a homeowner

encounters issues with their roof or attic, they will usually blame these issues on the

roofing contractor, and callbacks always reduce a contractor’s profits.


So how can we address these issues with roof ventilation?


This article begins by taking a look at why roof ventilation is so important, and the issues

caused when proper ventilation is ignored.  We will then look at proper ventilation in

both unconditioned and conditioned attics.

Are you ready to learn about proper roof ventilation?  Let’s get started!


The importance of proper roof ventilation



Before we go too far, let’s talk about the “why?” of roof ventilation.


Improper ventilation can cause significant issues to both the customer and the contractor.  The customer may have a damaged roof or attic, while the contractor has a damaged reputation.


Let’s look at how improper roof ventilation can cause issues in each climate type:


Cold Climates



In a cold climate, the primary goal is to keep your roof cold to prevent ice dams.  

We have all seen the damage ice dams can do to a roof and the leaking it can cause.  


Proper ventilation helps keep the roof from getting too warm by removing warm air that rises from the conditioned living space below.

If this warm air is not removed, it warms the roof which can begin melting the snow and start the subsequent thaw/freeze cycle.


Proper roof venting also removes humidity that moves from the conditioned living space to the attic.  This removal helps prevent mold and other moisture issues.


Warm Climates



In a warm climate, ventilation is critical to removing warm air from the attic.  This heated air is often the result of a hot solar-heated roof.

It also helps keep moisture out of the attic, mainly if you live in an area with thunderstorms, heavy precipitation, and wind.  Hopefully, your roof doesn’t let moisture in, but a small leak can quickly cause damage where proper ventilation can help minimize the damage.


Roof ventilation in warm climates also has a financial advantage.  Keeping warm air out of the attic will result in less strain on the home’s cooling system.  The result is lower cooling costs, and more money stays in the homeowner’s pocket.


Mixed Climates

In a mixed climate, which covers much of the USA, proper ventilation provides the benefits of both cold and warm climates depending on the season.  

In the winter time, you don’t have to worry about ice dams on the roof.  Also, in the summertime, you can enjoy lower cooling bills with a moisture-free attic, no matter what the weather brings.


Proper roof ventilation applies to every climate and should not be ignored.  Join us next addition for proper ventilation techniques when working with an unconditioned attic!


5 key principles in venting an unconditioned attic


Now that we know proper ventilation is essential, the next step is gaining the knowledge and skills to ventilate roofs properly.

Let’s start by looking at the steps in proper ventilation of an unconditioned attic.


1.       Completely seal the attic floor

This is the core principle of proper roof ventilation.  Having excessive punctures in the ceiling allows warm air into the unconditioned attic and significantly decreases ventilation efficiency.

Why are extra ceiling punctures a concern?

Excess punctures are sometimes called “Swiss cheese” ceilings.  Every time a hole is made in the ceiling, you have the potential for warm air and humidity to enter the attic.  If you neglect insulating these punctures, you will quickly lose ventilation efficiency.

If you have recessed lighting or ductwork in the attic, take extra care to make sure everything is properly sealed and insulated.  And if possible, keep all ductwork in the insulation, not above where heat is guaranteed to escape into the attic.


2.       Maximize insulation above the top plate



The insulation above the top plate should be equal to or greater than the wall’s thermal resistance.  Find the R-value of the wall, and make sure the top plate insulation is equal to or greater.


3.       Have the soffit vented continuously

The location of the soffit vent is important.  Ideally, you want the vent as far away from the building as possible.

The main reason for this is that the sun hitting the side of the building causes a larger concentration of warm solar-heated air along the structure.  As this warm air rises, it creates a buildup of warmer air under the soffit.


If the vent is too close to the building, this warm air becomes the primary source of ventilating air.  Large amounts of this warm, humid air quickly hurt ventilation efficiency.


4.       Have adequate airspace

Adequate airspace between the roof sheathing and top of the insulation is critical since this space regulates how much air can enter the attic.  The main argument arises in discussing how big it should be.


Most building codes call for a minimum of 1” to be adequate airspace.  However, many builders with ventilation experience agree that this is too small.  In colder climates, the recommended airflow is closer to 2”.


Why is this increased space important?

The argument for this larger space is simple, especially if ice dam prevention is the primary goal.  The cause of ice dams is warm air in the attic which warms the roof and causes the freeze/thaw cycle.  Therefore, if more air can cycle through the attic properly, it will keep the warm air to a minimum.


5.       Slightly pressurize the attic

This is another issue where some builders differ from the code.  Most building codes will recommend having equal intake and exhaust for proper ventilation.

However, if you can configure the ventilation where the eaves have slightly more pressure than the ridge, this pressurizes the attic and moves the attic air through more quickly and efficiently.


To get proper attic pressurization, an ideal ratio of ventilation between the eaves and ridge is 60/40.


Key principles in venting a conditioned attic



How is proper ventilation achieved if you have conditioned living space in your attic?  Houses that have attic dormers, particularly Cape Cod homes, are good examples of having a conditioned attic.


A common question, particularly when the attic is conditioned, is if ventilation is vital if you have a well-insulated roof deck and roof assembly.

After all, if there is a well-established insulation layer in the roof deck, then all the heat should stay inside and all the cold outside, right?

While this is correct in many areas, it is incorrect in high snow areas.


The R-value impact of snow



If you live in an area of high snow (50-60 psf or higher), you should have your roof vented even if your attic is properly conditioned.


The reason is simple:  Snow has an R-value around R-1 per inch of snow.  

If you receive significant snow and your conditioned attic is not vented, the snow can act as a thermal blanket and begin an ice dam cycle on your roof.


The other danger with an ice dam on an unvented roof is that you have a higher potential for snow and ice overhangs.  Not only are these overhangs potentially dangerous if they fall, but they can also create heat buildups similar to a roof or soffit overhang.  


The result can be a buildup of warm air directly under the snow/ice overhang which results in more thawing, freezing, and larger ice dams.


Let’s look at a few principles for proper ventilation in conditioned attics.


Properly venting the roof deck

Similar to proper ventilation in an attic, there are code requirements to be aware of when venting a conditioned attic.


The code requires the roof deck above the conditioned space to be open and free from insulation from the eaves to the ridge.  It requires the venting area to be a minimum of 1 inch.


However, many agree that the roof deck will vent more properly with a 1-2” clearance.

One of the concerns with venting the roof deck is properly insulating around the rafters and making sure there are no leaks.  While this may cause extra labor during installation, it is worth the time to avoid future issues caused by improper insulation.


When venting the roof deck, make sure you install a secure ridge vent that allows ventilation without compromising the roof’s safety, particularly if you live in a high-wind area.


The concern is that wind can drive rain, precipitation, or even burning embers into the roof soffit and cause water damage or a fire.  Installing a secure ridge vent will provide proper ventilation without allowing these to enter the roof deck.



Conclusion

Proper roof ventilation is often neglected as being an essential part of a structure’s design and construction.  Sadly, this approach often results in ice dams, moisture in attics, and other avoidable roof issues.


Focusing on proper roof ventilation, particularly when coupled with a secure ridge vent, provides sustainable construction and peace of mind for both the contractor and homeowner.


If you are a contractor looking for a standing seam metal ridge roof vent that will making your roofing business more efficient and productive, then contact SnapZ today for a quote!

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