Why Do Roofs Have Vents
And are they Important?
The Importance of Proper Roof Ventilation
What happens when a house can’t breathe?
If you have ever opened a refrigerator that’s been unplugged, you already know it’s going to smell bad before you even touch the door. Even if it’s empty and has been cleaned, the sealed air and moisture creates a petri dish that’s perfect for microbes to multiply and thrive. This pressure cooker effect is similar to what happens in your attic when there’s not enough circulation.
Why is roof ventilation important?
Seattle is located in what’s known as an oceanic climate, which means winters are milder (in other words wet) and summers are usually cool and dry. It also means this type of climate is ideal for moss, mold, and algae. This is partly why the Emerald City is renowned for its natural beauty. However, it also causes some issues if your roof, and the space below it, is lacking proper ventilation.
In this article, we will talk about the need for proper ventilation for your house. We will show you how to determine the amount of air flow your house needs, as well as different types of ventilation systems to keep air circulating to keep your home (and your family) from living with mold and mildew.
If you feel like you already know WHY ventilation is important, you can always SKIP AHEAD to the different types of vents and our recommendations.
What is roof ventilation?
Think of roof ventilation as a buildings’ lung’s. It needs to inhale cool fresh air and exhale hot stale air. Circulating air within an attic or a roof needs properly installed vents for the health of your home and you. Ventilating your roof keeps temperature and humidity indoors regulated. These factors, if unbalanced, can cause all sorts of damage to a building and its inhabitants.
What problems occur with poor roof ventilation?
Without proper ventilation a whole series of problems can occur. Some will happen in a relatively short period of time, while other’s will develop over time. Let’s look at some of these and even the things to look out for if you suspect your house might need improved ventilation in the space below the roof.
Unregulated Temperature
Ice Dams:
On those colder winter days and nights, warm air naturally travels upwards to the top of a building – in the attic and roof. Allowing this balmy air to accumulate could lead to one of the worst of issues: ice dams. This occurs when a cycle of snow and ice is melted from the heat under the roof (from that trapped warm air), which then refreezes from the cold winter air outside. Over the course of a few days this builds up and the ice grows higher from the edge of your roof, working its way under the waterproofing meant to shed that water. The result can be anything from a leak to water logged structural parts of the roofing system.
Sauna Effect:
Sauna Effect:
In the warmer months that warm air trapped in the top of your home radiates throughout the rooms. This essentially turns your roof and attic into a sauna that is hot enough you could bake a cake up there! (We don’t recommend this.)
The past few summers have been some of the hottest ever in the Seattle / Tacoma area and residents have found comfort in their air conditioned houses (if you’re lucky enough to have AC). However, if your attic space is well ventilated, it creates a barrier of moderate air which can reduce how hard your AC unit has to work.
Humidity:
Humidity usually goes hand-in-hand with inner coastal areas like Tacoma, Puyallup, Auburn, and the greater Seattle area. High humidity can propagate incredible colonies of mold. We’ve covered the damage to our home and the health of our family that mold can cause in our previous post “10 Tips For Springtime Roof Maintenance“.
Properly ventilating the roof and attic mitigates the humidity indoors, and in turn prevents water damage such as wood rot, and discourages mold from breeding so we and our loved ones aren’t breathing its harmful spores.
Shorter Roof Lifespan
Shorter Roof Lifespan
This is probably the biggest danger of a poorly ventilated roofing system. Deterioration of roofing materials happens much faster with the presence of humidity and heat unable to escape the roof and attic through proper ventilation. Water leaks and wood rot can and will occur, eventually diminishing the strength of the materials and structure.
Your roof is designed to protect you from falling rain and snow. The layers of waterproofing have been engineered to keep moisture from entering the spaces below. When moisture is also trapped beneath them, it eats away at that protection from the inside-out. Unfortunately, this often goes unnoticed for a long time as residents don’t often venture into the spaces below their roof to look for problems when there’s no obvious signs of anything being wrong.
Poor ventilation caused a water leak in my roof?
It’s surprising for homeowners to learn something like a leaky roof was caused by lack of proper ventilation.
As we covered above, if mold is eating away at your roof from the inside, it is logical that a water leak could be related to poor ventilation of the roof and attic. Because our winters are notable for a slow steady drizzle and lack of sunshine, your roof doesn’t get a chance to fully dry out for weeks or months. With proper ventilation, it can at least stay dry on the inside.
Rooftop Gardens:
Growth of moss and algae is another common roofing problem that is accelerated by a lack of roof ventilation. Rooftop Gardens and “living roofs” are pretty cool, when they’re intentional and maintained, but it’s not something you want to cultivate by accident. We have explored in more detail about the effects of algae in our previous post: 10 Tips for Springtime Roof Maintenance, and one point to consider how damaging their effects are: is that it consumes the limestone filler in the roof shingles. Essentially, over time this process degrades the durability of the shingles, and can eventually cause a water leak.
Do It For Your Health!
Ensuring proper roof ventilation for your home will minimize these structural problems a great deal, but the possible issues aren’t limited to your house alone.
Mold and mildew thrive in environments that are humid. With the wet rainy nature of the Pacific Northwest, compounded with hot stale air trapped in the roof and attic, it won’t take long for the fungi to colonize further and move into the main part of your home (you may notice signs in the ceilings and walls).
Those living in the home can also show symptoms of impaired respiratory health, sometimes before you even find signs of mold and mildew.
If you’ve ever had an issue with mold in the past or you’re a homeowner with loved ones who may have allergies and asthma, we would strongly recommend being proactive by installing an air quality monitoring system. Each room can have its own detector, and the real-time collected data on your home’s indoor air quality can alert you to any irregular levels of humidity, temperature or presence of mold.
New Roof Ruined By Poor Ventilation:
A Case Study From Our Files...
Recently our Anytime Roofing team was called to a home in Lake Tapps experiencing problems with mold growth in their roof’s insulation. During the roof inspection, our team noticed at once the lack of ventilation was likely exacerbating the mold. This isn’t the worst we’ve seen, but it was definitely a problem!
In this case the hot air was intended to escape through a ridge vent, which is a type of vent we will cover in the next section. The problem is the opening for this ridge vent was well below the recommended minimum of 3 inches. This left far too little space for trapped warm and moist air to escape. To make matters worse, the insulation had been stacked high all the way to the edges where their soffit vents were, essentially choking off the intake of fresh air.
The current owners of this home had purchased the home just a few years prior and had no idea of the problem until they noticed an unusual level of mold inside their house. While they had wisely chosen to have the house professionally inspected before they closed on the property, the inspector somehow missed this in their report.
The Remedy:
Click Photos To Enlarge Or Pause
Once it was determined that a majority of the plywood sheathing and roof joists had mold growing in them, and some areas of rot were discovered, there was nothing to do but cut it all out. We started by removing their shingles which was truly unfortunate because the roof had another estimated 15-20 years of lifespan left on it.
The next step was to remove a majority of the plywood that had been impregnated with mold spores. This gave our crews a chance to better identify the structural problems which we addressed next. We treated some areas of dry-rot and then beefed-up the support by sistering additional rafters to the trusses and vertical framing for added support.
Most of the insulation had to be replaced and we increased the intake of fresh air by adding baffles to prevent soffit vents from becoming blocked off again. Once this was complete we started covering the exposed attic again ensuring an appropriate gap was left at the ridge to allow hot air to escape through the ridge vent.
Additionally, a separate issue of pooling water on a section of flat roof was remedied by increasing the slope to enhance proper drainage. Once complete the flat roof section was covered in torch down roofing and the pitched roof received Malarkey Vista shingles in the color Storm Gray. We also went back to replace some sections of facia boards and gutters after the roofing portion of the job was complete.
Which ventilation system is best for my roof?
Now that you’re aware of the potential problems and how it benefits your home to have a proper ventilation system in place. Below we will get into some of the different ventilation systems, both mechanical and passive. We will also cover how to determine the number of recommended roof vents for a given area.
There are a several combinations of ventilation systems we could recommend to suit your roof. While some of these options can be equally effective, only a professional roofer can best advise you based on your home’s specific situation. In some cases though, you may be able to make a choice based on the aesthetic the different vents give your home’s overall curb appeal.
Generally speaking, ridge vents and soffit vents work well together. The ridge vents (located at roof peaks) ‘exhale’ warm air while soffit vents (found underneath roof eaves) ‘inhale’ outside air. In attic walls, gable vents can be installed to draw air both in and out. Wind-powered turbine vents are also effective, as they spin to draw out stale air from the attic and roof.
Ridge Vents
Along a roof’s peak is where a ridge vent would be installed. Being placed on the highest part of the house makes it a very effective system. There’s nowhere else for this hot air to get trapped as it meets the small openings of the ridge vent to naturally escape to the outside.
- Visually unobtrusive with its low profile
- Continuous venting along entire roof line
- Maintenance free and low cost
- Requires no energy to perform
- Passive system less effective without breeze
- Challenging to inspect on roofs with steep pitch
Gable vents
Gable vents are installed in the walls of houses with a gable end. Some can be as large as a window and come in many styles that can be visually appealing. These larger units with louvers also let some natural light into the attic, but need to keep animals out with some type of barrier. They can vent stale air out of the roof and attic quite well.
Depending on the number of these vents and their placement, they can be effective for intake, exhaust, and circulating large amounts of air. A gable end vent can be improved even more with the aid of an attic fan to assist the air flow.
- Easy installation with minimal maintenance
- Capable of moving large volumes of air
- Low risk of leaking when properly installed
- Less effective if only source of ventilation
- Increased chance of animal infestation
Eave and soffit vents
These air venting systems collect fresh air from the outside to enter the roof and attic space. Ideally they work in conjunction with a secondary vent allowing the warm air to be pushed out through the exhaust point, such as a ridge vent. This creates a well circulated space.
Eaves that are not enclosed will typically have holes cut in the blocking where the rafters hang over the wall. These holes then have some galvanized wire mesh that prevents animals entering the space under the roof. This type of vent is typically called “Bird Blocking” (So creative, right?)
Soffits that are enclosed have a more finished look but they still need to allow airflow to enter. Here you can use either a continuous track vent, or 2-6” inserts. In these cases you will still want to install Bird Blocks because animals can enter the enclosed soffit, but you don’t want them getting into the roof space. When using soffit vents, air baffles should be used to prevent insulation from blocking the airflow.
- Balances humidity and temperature when used with other vents
- Prevents small animals from entering the roof and attic
- Openings are rather small so more of these vents are needed
- Passive system less effective without breeze
- Can easily become blocked by insulation or bee/bird nests
Turbine Vents
A turbine is ideal for sections of a roof that get a good crosswind because this air venting system is wind-powered. It rotates to draw out the hot air inside a roof and attic, but can be combined with an electric motor to assist its effectiveness. Because they have moving parts, we recommend inspecting them when doing your yearly roof inspections to ensure they’re spinning freely.
Some of these traditional vents can look like a “Chef Hat” and for that reason their distinct shape is considered by some as visual clutter if seen from the street side of the home. By the same token, other people love this traditional look. The Turbine vent has been around for a long time and you will see variations of them on old barns, commercial buildings, and homes alike.
- Energy-efficient mechanical system
- Capable of moving more air than a passive vent
- Presents an “Old-School” look often found on barns
- Not as effective in without wind to spin the turbine
- Visually obtrusive for those that want a clean look
- Moving parts need inspection and maintenance
Power Vents
As you could probably guess by the name, power vents use an electric fan to force warm air out, or draw fresh air into the attic and roof space.
The electric fan can move a constant volume of air even on windless days, reducing the amount of trapped hot moist air. This can cool the top of the house quite effectively, but it requires electricity and can generate noise which will increase overtime without some maintenance.
Most models have a thermostat that causes the fan to turn on automatically when it senses the temperature exceeds a balanced threshold. Some also include a humidistat to function similarly if there’s a high level of humidity in the space.
Modern power vents can come with a small solar cell to power the fan. This option not only saves on the home’s electric bill, but means installation doesn’t require an electrician to install wiring to the vent’s location. The upside is when the sun is out and the air is heating up, the solar panel is usually getting ample light to power the fan. The downside is that the solar panel will lose efficiency over time and need to be replaced. As light fades in the evening and hot air remains trapped, this vent becomes more of a passive vent than a powered one.
- Energy-efficient mechanical system
- Capable of moving more air than a passive vent
- Presents an “Old-School” look often found on barns
- Not as effective in without wind to turn the turbine
- Visually obtrusive for those that want a clean look
- Moving parts need inspection and maintenance
Flat Roof Ventilation
Most of the vents we covered here apply well with a pitched roof because this is the most common type of roof. Flat roofs, and to some degree the roofs above vaulted ceilings have slightly different ventilation needs. A flat roof has a much smaller air pocket, but can suffer from the same fate if inadequate air flow persists over several seasons.
If you’re trying to vent your flat roof the common practice of soffit vents still applies to bring in fresh air, but you have a few options for the exhaust which are less common on pitched roofs. The most popular vents are the Pop Vent, Keepa vent, Breather vent, and Mushroom vent. All of these vents elevate the opening slightly higher than pitched roof vents. This is partly to allow for natural air currents to draw air out of them, but also to prevent standing water to make its way into the roof if drainage problems occur.
Which roof vent should I use?
Now that we’ve covered many of the available vents, you’re probably wondering which is right for you. We recommend a combination of ridge vents and soffit vents for most roofs of low to steep pitches. This combo is a common type of air ventilation system that is ideal for most homes in the Seattle & Tacoma climate and is most effective in areas with good airflow or breeze.
If you live in ‘the valley’ around Auburn, Algona, Sumner, and Puyallup we might recommend adding additional vents or a power assisted ventilation unit as some of these areas don’t get as much cross winds compared to Federal Way and Des Moines near the water, or Black Diamond near the higher elevations.
The balance of moisture and temperature inside each roof and attic will be different. We recommend consulting a professional like Anytime Roofing to determine if your current ventilation is adequate or if improvements can be made.
Obviously if you have a mold situation happening, then it needs to be addressed ASAP. Other times to evaluate your attic’s ventilation would be when getting the roof replaced. It’s much easier and cost effective to make changes at this time as work is already being done so changes can be integrated into the larger job.
For very low pitch and flat roofs, turbine or powered vents (either hard wired or solar powered) would be most effective. Solar-power can provide cooling to the building for those times when there’s no wind.
Of course, as with any of our roofing materials, proper installation and maintenance is imperative for these components effectiveness and longevity in holding up to Seattle’s weather.
Can I install roofing vents myself?
Technically, there’s nothing stopping you. However, ask yourself if you could identify one that is improperly installed and how to install it properly so it vents efficiently for your home. Safety should be the number one priority for any homeowner wanting to undertake a DIY project. Yet, the experience of such a roofing project amongst professional roofing contractors is incomparable. Finally, we would recommend having vents professionally installed because unlike other DIY home projects, if you miss something the problems could stack up before you’re aware that a problem exists.
Well what could go wrong installing vents?
Once you’ve made that opening in your roof for your air ventilation system…well, it needs to be near-perfect for the vent.
Incorrect vent size: Larger roof spaces need more vents, so too few vents won’t circulate enough air inside to balance temperature and humidity. Similarly, if the exhaust vents are too small, it’s not effectively allowing hot air out
Is there such a thing as too much ventilation for my home?
Homeowners may be a little surprised to learn that if these roof vents are made too large, or if there are more venting systems than necessary for the size of the space, it can actually be a hindrance too. Without getting into details, a balance needs to be found.
There’s a general rule: per 300 sq ft of attic space needs one ventilation system. For roofs without a vapor barrier, the general rule is one vent for every 150 sq ft. Placement distance between each vent installation also needs to be calculated for optimum air ventilation depending on the pitch of the roof.
Obstructed vents
Insulation obstructing airflow to the vent will undoubtedly prevent hot air from escaping the roof and attic space. That insulation then becomes one of the first to be damaged by humidity and temperature in the form of mold. While some insulation materials are treated to be mold resistant, nothing is mold proof.
Ineffective placement of vents
If the ventilation systems are too close or far apart, airflow and pressure will be unbalanced throughout the attic. Some sections may get too hot and other sections too cold, so distance between each should be adequate and even for a balance of airflow inside.
Exhaust and intake vents too close together: Placing an exhaust vent (that releases hot air) too close to an intake vent (drawing in fresh air from outside the roof) is quite ineffective. The same hot air that just escaped from an exhaust vent can get immediately drawn in by the intake vent. Or vice versa with fresh air coming in through one and then flowing straight out through the other. Separate the two to optimize their opposite functions by installing them as far apart as possible in the attic space and roof.
In Conclusion
There are a variety of air ventilation systems that could work best for your type of roof. If properly chosen, calculated, and installed these measures will keep your attic dry and prolong the life of your roof, as well as, prevent serious problems in the interior of your home. We highly recommend working with a professional roofing contractor like Anytime Roofing to undertake such an essential component of your roof that keeps your home and family inside safe and comfortable through each of the seasons here in the Pacific Northwest.
The exact type of system best for your situation depends on: building size, roofing materials, location, environment and climate. It’s all well and good to have a few different types of ventilation systems, but then make sure to keep up with the maintenance of them, so they continue to function at their very best.
