Why is there a garden in my attic?

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    I have posted in the past about attic ventilation and how there are many ways to achieve good attic ventilation.  Ventilation can consist of passive means that utilize soffit vents, roof vents, gable vents and ridge vents.  Sometimes mechanical means are utilized with the installation of wind driven turbine type vents, and sometimes electrically or solar powered vents are installed.  See these three links to past posts to learn more about roof ventilation:

     When the trades don’t talk to each other, @#$% happens!

    What is Giovanni Venturi doing in my attic?  

    Not all “short-circuits” are electrical!

    For my money, any time passive approaches can be utilized to do the job this should be encouraged as the use of electricity is costly.

     By far the best passive approach is the use of soffit vents in conjunction with ridge vents.  I have done several posts in the past regarding the Venturi effect that is created with the use of ridge vents and how this effect helps this approach be superior to roof vents and gable vents.  I have also posted as to why combinations of systems are a problem.

     At a recent inspection of a 5 year old townhouse, inadequate ventilation of the attic was evidenced by the beginning presence of mold or mold-like/fungal growth on the roof sheathing.  Movement of air through the attic needs to be sufficient to prevent moisture laden air to stagnate where it can condense on the cold roof surface.  Moisture was likely finding its way into this attic through poorly sealed ceiling fans and an attic access hatch that was not weather-stripped.  The ventilation system was not adequate to keep this moisture flushed out of the attic space.  Moisture laden air can also move into the attic from the exterior as well.

     In this first picture one can see the darkening of the roof surface between the trusses where the mold or mold-like fungal growth is beginning to form.

Poor attic ventilation

     The interesting thing about this structure was that provision for a ridge vent was made for installation of a ridge vent but it was never installed.  Note the gap at the ridge in the next picture.  The black area is the roof felt paper covering over the hole that was left for the ridge vent.  At the center bottom of the picture can be seen the lone gable vent that is cut in half by the end wall framing—-further compromising the effectiveness of what was already inadequate.

Ridge Vent not installed

     While most aspects of home construction are not in themselves “rocket science,” the building science aspect of the home comes pretty close.   All of the trades—-all of those putting the pieces together, should have proper interdisciplinary training in Building Science in order to better understand how the building works as a whole.

     In this case all openings into the attic space will need to be properly sealed and/or weather-stripped, the continuous type ridge vent will need to be installed, and the gable vent will need to be removed.

 

 

 

Charles Buell

 

 

 

 

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