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Attic Ventilation

"An overlooked area of your home"

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.  Think about this, you just moved into your brand new home and the first year you have a mild winter.  The second year is a little different.  The winter is much harsher, and more importantly, the one year warranty on your home has expired.  You start to notice some moisture staining inside your home where the exterior walls meet the ceilings.  Upon further investigation you see that you have significant ice damming.  During spring you go up into your attic and notice the moisture level is higher and you have a black growth on the bottom of the roof plywood.  Not what you expected for a new home is it?  Unfortunately, this happens all the time.  After you pay for contractors to tear out the damaged drywall inside the home, clean the mold and improve ventilation, you feel violated and let down.  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?  Great question and I will answer it for you right now.  There are actually two main reasons: Temperature and humidity control.  Without temperature and humidity control, an attic is likely to cause moisture and heat related problems. 

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, it 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.

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.
            There are a few sources that feed moisture into attics.  Those sources include: 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 sidewall; never terminate inside a soffit.  A soffit acts an in inlet and will bring that moisture right back in.  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.

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.

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 and water” barrier under the bottom edge of the roof.  A second layer 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. 
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.  Waiting can cost you thousands of dollars in damage.

Jeff Remas, Inspector
REMAS Inspections, Inc.
www. Painspector.com
877-223-4462