Attic Ventilation - Go With The Flow

By Frank Ross

A roof can fail as a result of numerous causes. Inadequate ventilation, a common one, can be easily remedied or prevented. A thorough inspection of the roof and attic reveals the current state of these components.  Homeowners can then determine what measures, if any, would be necessary to lengthen the life of the roof.

Many homes in the United States were built without adequate ventilation. Homes in our southwest Utah area are no exception.  Just the other day a new home I inspected was found not to have any provision for ventilation at all. 

Proper ventilation is a consideration many homeowners overlook when adding ceiling and attic insulation.  I have found gable end vents blocked off by well-intentioned homeowners “to keep the cold air out.”  Their main concern may be to reduce energy costs and all too often insulation is installed over existing soffit or gable vents reducing or eliminating the movement of air.  Lack of air flow can lead to trouble.

Without the air flow created by good cross ventilation, hot, moist air becomes trapped in the attic. With changes in temperature the moisture condenses and saturates the roof decking - the plywood or other sheet material installed over the trusses that makes up the primary support surface for the roof covering.  Condensation causes the deck to rot, warp, delaminate and deteriorate, a condition which often goes unnoticed until the roof begins to leak or the inspector falls through during an inspection.  Moisture can also saturate the insulation causing it to become matted down and somewhat less effective.  A few times I have found the bathroom exhaust venting into the attic, thus adding moisture to the area.  I have also seen buckets and cans in the attic catching water from roof leaks.

          Another problem results from the trapped hot air.  Elevated temperatures in the attic can cause asphalt shingle roofs to “cook” causing them to crack, curl and warp.  The resulting life expectancy of the roof is reduced dramatically.   Excessive heat also dries out the wood structure and can force air conditioning systems to work overtime.

          A common belief is that a system containing soffit and ridge vents should be employed because it will draw air across the entire underside of the roof deck. Both types of vents are easily blocked either by insulation as mentioned above or snow or debris rendering them useless.  A better system for pitched roofs with open soffits is soffit screens installed every eight feet combined with dormer vents out of sight on the back side of the house.

          If you need to have a leak repaired or add attic vents please hire a professional roofer that will do the job properly. Last summer I “added” an attic vent while at an inspection. I was walking an asphalt shingle roof and in the blink of an eye my left leg went through the roof all the way up to my hip and gave me one doozy of a bruise. The shingles had been “repaired” at one time with silicon seal where they had been leaking but the silicon seal hadn’t completely stopped the leak and continued moisture intrusion rotted that section of the roof. My inspection of the attic interior showed the roof sheathing to be so rotten it was just hanging together by a thread in the area where my leg went through the roof. I included digital photographs of the hole in the roof from both the inside and outside in my report to the buyer.  I also shared the photos with the homeowner.  She had a roofer on site in less than an hour and he confirmed that the roof leak had never been repaired but simply patched.

Generally, ventilation recommendations which are by shingle manufacturers, local building officials and roofing product dealers should be considered and implemented.  Whenever in doubt, seek the advice of a professional.

Frank Ross is a Certified Utah Home Inspector for Pillar to Post Professional Home Inspection and a full member of the National Association of Certified Home Inspectors.  Readers may contact Mr. Ross at (435) 867-6400 or frank.ross@pillartopost.com.  You can learn more about Pillar To Post Professional Home Inspection at www.pillarposthomeinspection.com