The Importance of Proper Attic & Roof Ventilation

From the Desk of:
Jeff Remas, President
REMAS Inspections, Inc.
www. Painspector.com
877-223-4462

Just about everyone has an attic. Whether you use it for storage, finished space or never even look up there, you need to be aware of potential problems that can happen due to poor attic ventilation. Poor ventilation is not just a problem with attics. It affects cathedral ceilings the same way except you have no access into your cathedral ceiling so problems are normally severe by the time there are signs inside.

Why do we need our attic and cathedral ceilings to be well ventilated?

There are actually two main reasons this is important: Temperature & humidity control. Without temperature and humidity control an attic is likely to cause moisture- and heat-related problems.

Temperature & humidity control go together and need to be controlled during warmer months to keep attics cool by using ventilation to prevent hot, moist air from warping the roof sheathing. It also stops shingles from deteriorating prematurely due to excessive heat & moisture build up. Cooler air in the attic makes a home much easier to cool, which can result in lower energy costs.

During the cooler months, temperature & moisture control through ventilation is needed to keep attics dry. It stops water from backing up under shingles, damaging insulation, and rotting the framing. It also helps prevent ice dams from forming. Ice dams pose a special problem because they prevent melted water from running off the roof. Ice dams usually cause leaks inside your home, resulting in framing and drywall damage along with the potential to harbor mold. 

Typical attic airflow----------->

The real cause of ice damming

In our northern climate, especially Northeastern Pennsylvania and the Poconos, the potential for ice damming is great and an all too common occurrence. There is one common misconception about the cause of ice dams. Recently while at a training seminar the subject of ice dams came up and a contractor said the cause was rain gutters. This could not be farther from the truth. The real cause is a combination of poor attic ventilation, and inadequate insulation.

An attic must be very close to the outside temperature to prevent ice dams from forming. Yes, we want a very cold attic in the winter time, the colder the better. This is why a well insulated attic with a good vapor barrier and minimal air leakage is needed. When hot air escapes from inside the home is heats the framing and decking of the attic if there is not adequate ventilation to let the heat escape. This causes the snow to melt on the roof. You will notice this during winter months when you look at older homes and they lose the snow off of their roof sooner than well insulated, new homes. As snow on a roof above the attic melts, it slowly drips down to the lower edge of the roof line. The lower edge of the roof is called the eve or soffit. This area is on the outside of the home and where they hang over there is no heat therefore this portion of the roof is much colder. It is as this point the dripping, melting snow stops because it is now freezing. Any roof whether it has gutters or not has the potential for ice dam growth. If you do not maintain your gutters the ice can build up and create more of a problem for you making the ice dam larger. But again, gutters are not the cause of ice dams, they can, however, make them worse. 

<-----------------How ice dams occur 

Other problems that start in the attic

Ice dams are not the only problem in the winter time. The moist air that escapes gets trapped in an inadequately vented attic and becomes frost on the bottom of the roof decking. This will cause heaving of the roof, cracking of the shingles and as it melts it drips off of the nails creating dark spots on your insulation. The biggest problem is the fact that this moisture penetrates the wood decking causing it to rot, warp and promote wood eating fungus and mold growth. As the winter season gives way to warmer temperatures, the potential for mold growth intensifies. Mold in the attic soon becomes mold inside the home and the walls.

Moisture and humidity

There are a few sources that feed moisture into attics. Those sources are: a wet crawlspace, a wet basement, bathroom vents, vent less gas appliances such as propane logs or wall heaters and finally stove vents that discharge into the attic.

• Wet basements and crawlspaces generate a lot of moisture vapor that transmits right up into the attic.
• All bathroom vents should be through the roof or side wall, never terminate inside a soffit. A soffit acts an in inlet and will bring that moisture right back in, causing mold.---------->
• Vents for cooking appliances should terminate outside.
• If you have a recirculation vent that is on an exterior wall, I would recommend that you vent it to the exterior.
• A good insulation vapor barrier will help ease the amount of water that transmits into the attic. A family of 4 generates an average of 2-4 gallons of water vapor per day!

Achieving adequate ventilation

Optimal attic ventilation is done by having at least 1 square foot of ventilation for every 150 square feet of attic space by using a combination of vented soffit and a ridge vent. The soffit vents need to be kept open by the use of baffles in the attic between rafters that keep the insulation from blocking the opening; this is the number one ventilation problem found in attics.

If you have a hip roof with minimal horizontal ridge then a power vent is the next best option. Many new construction roof lines are complicated creating poor attic ventilation, so discuss your options with your architect and builder.

There are many products out there to ventilate your attic. Always do your homework and research prior to making that decision. As far as ridge vents are concerned, those with an outside baffle that keep rain and wind out are far better than simple, inexpensive rolled ridge vent. I personally recommend ShingleVent®II manufactured by Air Vent. The comparison data on this product appears to be unmatched by any competitor. I recently inspected a house that was nearing one million dollars with granite counter tops and other high end amenities. The roof ventilation was poor and they used the cheapest rolled ridge vent out there. This was a complete mismatch in my opinion.   

<------------Ridge vent sample

Different methods of terminating bathroom vent------------------------->

The attic & roof need to peacefully coexist

If you are planning on replacing your roof, make sure that the roofing contractor who comes out to gives you and estimate also inspects the attic. This is the mark of a true professional. Ask them if they want to take a look in your attic. If they say “no” then you can eliminate them as a potential contractor.

It is advisable to tear off any existing layers and place down an “ice & water” barrier under the bottom edge of the roof. A second layer of shingles is acceptable in most cases, but not advisable. It can cause weight issues on your roof during snow periods and makes a good installation harder. Three layers are not acceptable and against the building code.

Preventative maintenance pays off

I would recommend that everyone take the time to inspect his/her attic just a little bit closer and if you have any questions, call a professional. Adequate attic insulation and ventilation are a very important part of maintaining your home. It helps with energy efficiency, air quality of the interior, shingle longevity and the structural stability of your roof. A little preventative maintenance can only benefit you and your home in the long term. Don’t wait until it is too late.

Comments

[David Kurtz]

Thank you for posting information on attic ventilation. It is of great importance that homeowners be made aware of this.

DCI Products has been stressing this for years and now thanks to the Green initiative, homeowners are starting to pay attention to messages like yours and ours.

If you have any questions regarding ventilating attic space, please do not hesitate to call or pass along our phone number and email.

DCI Products : 800-622-4455
email: davidkurtz@dciproducts.com