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Attic Ventilation Basics

The concept of attic ventilation is pretty simple, if it's explained correctly. My goal here is to explain how attic ventilation works. And if I do this right, you'll also learn how the ventilation of your attic affects a roof structure, roof covering, and the comfort of those living in the house. A few simple rules of thumb can prolong the life of your shingles, roof sheathing, and prevent disastrous moisture and mold problems in the attic. Misconceptions about the air flow in your attic can lead to thousands of dollars in damage and repair costs.
A Different Animal

   First, think of your attic and roof as a separate entity from your home. Your home is a heated (conditioned) area that is designed to keep air IN. We insulate, moisture-proof and throw up every barrier to heat and cold that we can muster. The exchange of air is discouraged in everything we do in the construction process...taping of fiberglass insulation seams, installation of Tyvek wrap, plastic moisture barriers on the floor of crawl spaces, etc. 
   Your attic area is just the opposite, in many ways. Your living space effectively ENDS at the top of your upstairs ceiling. Beyond that, the structure is not living space, but strictly utilitarian. There is a "buffer" area that we call the attic between the living space and the roof structure. If your home doesn't have an open area that can be called an attic, then it likely has a cathedral ceiling or a finished attic that is used for living space. Above the attic, we have a structure that is designed to keep moisture out: the roof. If you think of your attic and roof in these terms, you're miles ahead of most people's thinking.
   Many of people make the mistake of TREATING their attic as if it were living space. By that I mean, they think it should be as air-tight as their living room. Not so. Attics should be designed to breathe, and breathe deeply.
Air Flow is Key 

   As a former Home Inspector, I've seen the bewildered look in my clients' eyes as I explain that their attic is smothering. No air movement, no fresh air, and nothing to cool the roof surface to outdoor temperature. I can look at the roof surface of a home and tell you whether there is mold in the attic, without setting foot up there. Clues like cracked or curled shingles, absence of ventilated soffit, gable vents or ridge vents adds up to no air flow, and big problems.
   In a perfect world, the insulation above your living space (ceiling / floor of attic) keeps heat in. Of course, in warmer weather, you would hope that it would keep the COOL air in. Either way, beyond that point, you should let the outdoor temperature take over. Your attic should be at or below the outdoor temperature.
   To accomplish this, your attic needs a lot of air exchange. Perforated soffit is designed to allow air to flow in, and upward. In case you're not familiar with the term, soffit is the material on the underside of the eaves (overhang) of your roof. After entering the soffit, air needs to flow upward and exit through gable vents or ridge vents, cooling the roof structure and roof covering to outdoor temperature. Again, terminology....gable vents are vents that are installed on the "ends" of the roof rise, and ridge vents are installed at the peak of the roof.

What happens WITHOUT enough air flow?

   Well, a lot of bad things. First, the roof surface will heat up in warm weather. This can cause asphalt and fiberglass shingles to crack and curl. Shingles can deteriorate in as little as 2 years without proper attic ventilation.
   If air isn't allowed to escape the attic, the moisture that it contains will eventually condense onto attic surfaces as the air temperature drops in the evening. Moisture and warmth are the perfect recipe for mold, and mold is the most opportunistic organism there is. Mold spores can lie dormant for many years, waiting for moisture. All it takes is one instance of poor ventilation, and you'll be growing a Chia Pet in your attic.

Solar Fans and other Thermostatically Controlled Ventilation

   The main point I'm trying to make is that a properly insulated attic should be very near the outside temperature at any given time. You need to think of your attic as a living, BREATHING organism. It is the buffer zone between the harsh outdoor conditions and (ideally) your comfortable living space.
   There are times when, no matter how well you've ventilated your attic space, it needs a little help with moving the fresh air IN and the moist, warm air OUT. 
That's where a ventilation fan comes into play. The electricity use is minimal (if ANY, with a solar attic fan) and you'll always be assured that your attic is well ventilated and functioning the way it should.

   There are many options available when it comes to attic fans....from simple to high tech. You can opt for a switch-operated fan, which you can turn on and off manually, or from any number of thermostatically-controlled units that basically take care of themselves. All are efficient at their purpose: moving air through the attic area in order to allow your "buffer zone" to function properly.

   I've always chosen the type that is easier and more convenient...the automatic ones. Call me lazy, call me technology-dependent, call me anything you want. But damned if I'm going to hang around the house all day monitoring the attic temperature and switching a fan on and off. So in my humble opinion, a thermostatically-controlled unit is the way to go.

   A gable-mounted fan is a good choice for attic ventilation, since the fan can usually be installed in an existing opening in the gable wall. Many homes already have some sort of gable vent, since this type of attic ventilation has been the industry standard for many years. For ease of installation, this is the best option. You won't be paying your contractor a king's ransom to install the attic fan, and it's rather efficient. 
   I love them. Within an hour of having an attic fan installed, I noticed a huge difference in the ambient temperature in the house. After the installation, my electric bill actually DROPPED....I think it was because my air conditioning wasn't working as hard to maintain the setting in the house. Attic fans....the thermostatically controlled type... can be set to kick on when the attic temperature reaches a certain point, pushing the hot air out and drawing in fresh air from outdoors. Worth the money, for sure.

Solar Attic Fans for Attic Ventilation

   What contributes to a stuffy attic more than anything else? The sun. You've probably noticed that as the sun rises and warms the exterior (and the roof) of your home, that it becomes increasingly stuffy and stale without opening windows or turning on the air conditioning unit to move air through the home.

   The sun BAKES the shingles on a home without proper attic ventilation. After the tar in a roofing shingle goes through several thousand cycles of melting and abuse from the elements, it becomes brittle and begins to crack. It only takes a few brittle, cracked roofing shingles to allow rain water inside and create some REAL headaches for a home owner. Decayed roof sheathing, moisture, mold, and those wonderful DRIPS from the ceiling are a stark reminder that you need to think of the health of your attic space and it's protector....the roof.

   I hope you're beginning to see how important the ventilation in your attic really IS.

   Back to the subject at hand. Given that the single-most influence on your roof, (and thereby your attic space), is the sun and it's effects, why not combat those effects by utilizing the sun itself?
   Solar attic fans do just that. As the attic space warms up from the irradiation of the sun, the ventilation port opens wider to allow the solar fan to move more warm, stale air out of the attic area. Most solar attic fans are surface-mounted, meaning that they are installed directly through the roof surface where they are most efficient. The warmer your attic gets, the more air it moves OUT of the attic area to help maintain a comfortable temperature inside the home, prolong the life of your roof covering, and prevent miseries like mold and moisture damage in your attic.
   And if you've been listening closely, you'll realize that a comfortable temperature in your living space is just a SIDE-EFFECT and an added benefit of maintaining the health of your attic area.
   Solar attic fans can be found in several sizes to accommodate the square footage of your home. Most of them have a great warranty and are made by very reputable manufacturers...let's face it - these days, nobody wants to put their name on an inferior product, especially in the blossoming market of solar powered products. 

   I would recommend OVER-sizing rather than cutting corners by installing a solar attic fan that may not move enough air through your attic area. The reason is quite simple: solar attic fans cost (on an average) about $300 for a unit that will ventilate 1400 SF quite well. And a roof replacement? About $11,000, based on a 2500 square foot home.

   Let's see....$600 for 2 solar fans or $11,000 to replace the roof covering? I'm thinking I'd go solar. I haven't personally used a solar attic fan in any of my homes, since the attic ventilation that I had was quite adequate. However, I did a little research on it and the reviews are pretty favorable. One of the recurrent complaints that I read were about home owners who couldn't HEAR the unit running, and were suspicious that it was not working properly, or defective. Solar attic ventilation units are "whisper-quiet", which I suppose is why people question whether they're working. 
   I haven't checked into it, but there may even be rebates or tax incentives for installing solar powered products in your home. Please update me on this if you have any 


Ice Dams

   Another result of poor attic ventilation is ice dams. Of course, this is a problem normally seen in northern climates. Attics with poor ventilation allow the buildup of heat in the attic, usually from heat escaping the living space. The heated attic air warms the roof surface, melting snow on the roof. As the snowmelt runs down the roof, the water is cooled at the eaves where it freezes once again.       After a few days of this, the ice at the eaves forms a barrier, and any further snowmelt collects behind the barrier. Eventually, this  allows water to back up under the shingles, damaging the roof sheathing, attic insulation, and possibly causing a drip into the living space. Starting to see how important attic ventilation can be?


  Preventing a financial attic or roof catastrophe is pretty easy if you follow a few simple rules:

1: Make sure there is air flow from the eaves. This is normally the point where air ENTERS your attic. If the soffit of your home isn't perforated to allow air movement, either replace it with perforated soffit, or install round air vents under the eaves to allow air flow.

2: Make sure the air can exit. Either gable vents or ridge vents should be present, or ideally...both. If you have gable vents, be sure that they're unobstructed. If your home lacks a perforated ridge vent along the peak, install ridge ventilation so that warmed air can escape at the highest point of the attic. This can be done without replacing much of the roof covering in most cases.

3: Check your attic insulation. In frigid areas, experts recommend 12' of fiberglass insulation between the living space and attic, giving you an R-value of 38. Sounds excessive, but it isn't. The more heat you can prevent from escaping into your attic, the healthier your attic and roof will be.

   Be sure that the FLOOR of your attic has uniform coverage: it doesn't help you a bit to have a foot of insulation if an entire batt of insulation has been rolled back, allowing warm air to enter the attic.

   Insulation should never be compressed into a space, but the edges should fit snugly between the ceiling joists. If your home has a cathedral ceiling or a finished attic space, the same rules apply. Air should be "tunneled" from the eaves, behind the insulation that is installed between the roof rafters, and allowed to exit at the peak or at gable vents. Plastic, cardboard, and styrofoam baffles are available at home stores, which can be installed between the roof sheathing and insulation to allow unobstructed air flow from the eaves to the unheated space. 

   Hopefully this article has helped you gain a better understanding of how your attic area is designed to work. Feel free to  email me if you're experiencing an attic issue. Knowledge is contagious...let's spread it.


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