Six Myths About Attic Ventilation

Here are six of the most common misconceptions about attic ventilation. Read on to find out what you need to know about attics, soffit vents, passive vs. active ventilation, and what you really need to do to have a well-vented attic space that stays cool and dry.
 

1. If I have roof vents, I have good attic ventilation.

If only it were that simple! We believe that the most effective ventilation uses a ridge vent and soffit venting for the attic. However, this doesn’t mean that if you don’t use a ridge vent your ventilation is kaput.
 
Honestly, any type of “holes” in the top of the attic will work.
 
A good goal with attic ventilation is to have a balanced amount of air coming in to the attic as you have of air leaving the attic; it is also ok if you have a little more air coming in than you do going out (ie. lots of soffit venting). Soffit venting is your main source of intake for an attic. These vents allow cool, dry air to enter the attic at its lowest point and as air travels up and out the higher points (ridge, turbine, gables) so that the airflow removes warm, moist air from inside the attic.
 
However, if your soffit vents are dirty or clogged then you will have little to no airflow through the attic.
 

2. More ventilation is always better.

More is not always better. The thought process goes something like this: “If I add an electric/solar attic fan to my roof, I can help pull out more hot air from the attic and it will be cooler.”
 
WRONG! Choose one type of exhaust vent and go with it because mixing exhaust vents is a bad thing. Air always travels the path of least resistance. When you mix exhaust vents on a roofline, the strongest vent will dominate the air pull and those other exhaust vents will turn in to INTAKE vents. This short-circuits the whole concept of air coming in the bottom and out the top.
 
For example: If you put an electric fan right next to a ridge vent or other passive vent, air can easily come in the ridge vent instead of the soffits. This defeats the whole purpose of having low/high vents.
 
While having plenty of intake (soffit) venting is good, having too much exhaust can actually hinder your goal of cooling the attic air temperature.
 

3. The best way to get air moving in an attic is by using powered vents.

A simple passive system (uses no energy) will work just as well (for free) as a powered (active) system and in almost all instances has the benefit of being silent. We generally don’t promote the use of any sort of powered fans because they’re typically very costly, and the solar ones only work on sunny days.
 
What most people don’t realize is that it’s usually pretty breezy at the top of the roof. You may not notice the breeze lower down on the ground between houses or fences but that doesn’t mean air isn’t moving. With a little breeze two wind turbines can easily pull out as much air as an electric fan can.
 
If you choose to go with the fans, just be sure you also add plenty of intake to FEED those fans air (via soffits). If you don’t, the low pressure in the attic will suck air from the house. This happens all the time with power ventilation & sometimes it will actually make the comfort/efficiency worse.
 
This is because without an intake source, the air in your attic is depressurized and although it can be hard to predict where the “makeup” air will come from, it’s likely going to come from inside your home. The net result is that your home feels warmer faster, so your air conditioner has work harder than ever just to try to keep things comfortable (ie. huge energy waster!).
 
If you have ever had an electric attic fan motor burn out it’s probably because of the high static pressure put on the fan by lack of (or dirty and clogged) soffit (intake) vents.

This is a standard static roof vent used in a passive ventilation system.
Ridge vents are common vents used at the peak of the roofline.
This wind turbine (also called a whirly bird) moves when you have good intake at the soffits.

4. Roof vents suck out warm air from my house in winter.

It’s easy to think this when it’s ripping cold outside and the attic feels “warm.” However, it’s not likely your vents are to blame. The best way to determine if the attic has significant leaks from the inside of the home is to measure the air temperature at night, after the sun has gone down. If your attic is well insulated, the actual temperature of the air inside your attic should be very close to the ambient (outside) temperature.
 
Since most homes are leaky, it shouldn’t be too surprising that some warm air is escaping the attic insulation.
 
In fact, ventilating attic spaces in winter months is actually just as important as venting them in summer! Why? Because in the winter you constantly have water vapor from the inside of the home drifting upward to the attic space. If this vapor doesn’t dry quickly or get exhausted to the exterior atmosphere, you can have big problems. When vapor condenses inside an attic space, water can drip from the underside of the roof and, if the temperature gets low enough, frost (or even ice!) can form inside the attic and ultimately lead to wood rot and mold growth.
 
The best way to combat this is to SEAL your attic floor (under the insulation) in any areas of obvious leakage. Then, make sure your attic floor has the recommended level of insulation for your area. Finally, if you’re trying to reduce heat loss from the home into the attic, you need to consider adding a radiant barrier over your insulation on the attic floor to help the home from radiating heat into the attic space. Our SuperPerf™ radiant barrier is an excellent choice, especially in cold climates where moisture is a significant concern.
 
Learn more about installing radiant barrier foil on top of attic insulation here.
 

5. I can see light from the soffit vents, so they must be open and working. (Or I see the vent covers on the eaves outside under the roof, so I know I have soffit venting.)

Even if you can see soffit vent covers on the outside of the house, this does not mean there is cool air going into the attic. More often that not, soffits are blocked in the inside of the attic by insulation or framing and sometimes a vent cover is installed on the outside of the house, but the soffit behind it isn’t even cut out, or not cut out all the way, to fit the vent.
 
Just because you can see light from the soffit area when you’re inside the attic, doesn’t mean the soffit is clean and unobstructed.
 
The best way is to get up under the soffit vent with a flashlight and see if it’s clean and the hole is cut big enough. If it’s dirty, that is a good sign that air was/is moving through it. Now you just need to clean it to get it functioning properly again. Use a brush to clean the screen and then use a leaf blower and put the nozzle up to the soffit vent to blow off any insulation or other stuff on top of the screen inside the attic. Don’t remove the soffit vents unless you plan on cutting larger holes and installing new vents.
 
If the vent is clean then it may be blocked on the top with insulation or other stuff. Use a leaf blower and blow from the bottom to clear off the top. For more info on how to clean your soffit vents, check out my video on fixing the number one problem in attic ventilation (hint: clean your soffits!).
 
Baffle vents are intended to keep the soffit vent clear and promote air flow, but if they’ve been installed incorrectly, they can be part of the problem too!
 

6. If I have good enough ventilation, I don’t need radiant barrier in my attic.

You would need TENS of THOUSANDS of cubic feet of air per minute passing through the attic to get the temperature to drop. So while it is *possible* to lower attic air temperature with ventilation alone, this will have little to no effect on how hot your house is getting.
 
This would be like blowing a giant fan on your sunny driveway and expecting it not to be hot.
 
If you install a radiant barrier, it will drop the SURFACE temperatures inside the attic compared to the air temperature in the attic. This is really what drives heat flow – the top SURFACE temperature of the insulation. It can easily be 120º or more even if the AIR temperature is only 100º. So no matter how close the attic air temperature is to the outside air temp, you still need to reduce the radiant heat gain into the attic if you want to cool off your home. Learn more about air temperature vs surface temperature in attics here.