Baffled by Baffles...


Attic ventilation is important.  The attic is hot in the summer,  and cold in the winter.  When humidity is high, the materials in the attic absorb moisture.  When the air is dry, it looses moisture.  Moisture from within the house can also enter the attic if there are bad air sealing details.  In the winter, good ventilation also decreases the occurence of ice damming.  These are just some of the reasons that attics should be ventilated.

Ventilation can be achieved in many ways.  Most attics ventilate in a passive manner.  Nature takes care of the ventilation as long as you provide a pathway for air to exchange.  Typically this involves the installation of some kind of soffit venting under the eave, a pathway to the attic space, and vents on the roof.

My plans specified Accuvent baffles for the attic of the house and garage.  I had never seen these offered by any of the building suppliers.  In fact, I had only ever seen the two types of baffles:  Truevent (TrueFoam Newfoundland Styro, http://truefoam.com/insulation-products/truevent) or Raft-R-Mate (Owens Corning, https://www.owenscorning.com/roofing/products/raft-r-mate).  These have their advantages and disadvantages.  The main disadvantage for my build was the height of the truss heel required to get 26" of cellulose insulation in the attic.The Truevent requires some sort of blocking at the eave in order to keep insulation from spilling into the soffit space.  Raft-R-Mate has a corrugated section that allows for the shape of a heeled truss but its small and my feeling was, with 26" of insulation, they may not stand up to the weight of the insulation pushing outwards on the baffle above the existing blocking from the foam wall exterior.   I figured additional blocking may have to be added to get them sealed up enough to prevent insulation from spilling into the soffit.  With this in mind I was set on finding a semi-local source for Accuvent.

After some searching I found Charlie Stacey.  Charlie owns and operates Total Insulation and Coatings; A local business which provides many insulation solutions.  One of them was Accuvent! I was happy to find this product locally.  Accuvent comes in several varieties.  The one stocked locally is the original Accuvent (Photo 1-1) .  Photo 2-2 shows how the baffle would normally be installed.  The front lip of the baffle is typically stapled to the top wall plate.  Since the truss heel is high (ie 18"), I had to get creative.  I moved the stapling lip to the outside of the top wall plate, folded it in the opposite direction and stapled it in place.  Although Accuvent is probably strong enough to hold back the weight of insulation, in this application it wasn't necessary because foam from the exterior wall extends up beyond the soffit space and acts as a retainer for the insulation (Photo 1-4 ie to the right of the installed baffle you can see the exterior foam extending up the heel of the truss.).  One Accuvent wasn't quite long enough.  My solution was to cut an Accuvent in half and install it above (Photos1-5, 1-6).  To get the most length out of the cut baffle, I aligned the indented reinforcement bars on the cut baffle with the one already installed and then stapled the baffle in place (Photo 1-6).   The final height at the end of the baffle will be about 16" above the level of the cellulose. This should be enough to prevent wind washing which leads to a decrease in the effectiveness of the attic insulation.

The attic of the garage uses chord trusses (Photo 1-7) so there needed to be some sort of ventilation extending from the soffit to the ridge vent.  I also used Accuvent for this application.  The Accuvent specially designed for cathedral ceilings probably would have worked better for this but I think the Accuvents will work out fine.   I installed these up the length of the roof deck between the trusses and terminated it at the top of the ridge girder (Photo 1-8).  As in the attic for the house, the exterior foam sheathing extends up the side of the builing into the soffit space.  It provided a blocking to support the back of the accuvent.  Since there was no way to secure the end of the accuvent (ie  the end is hanging in front of foam Photo 1-9)  I pulled the end tight and then secured it to the foam using some scrap 3M 8067 that I had left over from some previous taping (Photo 1-10).  I was surprised.  Nothing sticks to EPS foam...But 3M 8067actually works really well.   Once the insulation is in place, there will be nowhere for the baffle to go.  It will be wedged securely between the exterior foam and the insulation.  If the tape fails its no big deal.


Photo 1-1.  Original Accuvent
Photo 1-2 Typical installation


Photo 1-3.  My installation work around to account for the depth of the 2x8 wall and the 18" heel on the truss.



Photo 1-4.  Accuvent installed.


Photo 1-5.  Extend Accuvents by cutting in half.


Photo 1-6 Accuvent installation complete.


Photo 1-7.  Accuvents installed in the garage attic.


Photo 1-8 Accuvents terminating at the ridge girder.


Photo 1-9 End of baffle hanging in front of the soffit foam blocking


Photo

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