Garage Attic gets a Thick Winter Coat.

The last big change inside the garage was when I added the attic baffles.  That was in august.  Little has changed since.  That changed today!  With interior framing on the house underway, I really wanted to make some headway with attic insulation in the garage so I could continue some framing details in parallel with the framers.   The insulation needed to be installed before adding the interior OSB to the underside of the trusses and tying the internal air barrier to the external one.

I mentioned in a previous post that my garage will be a workshop.  I want it to be fairly energy efficient so I opted to add 3" of exterior foam on the outside of the building to prevent thermal bridging.  I also want it to be as air tight as possible...which is probably not that possible with a leaky garage door but we'll see.  A typical wall section is composed of  3" EPS, OSB, 2x6 stud wall, then drywall.  The exterior OSB joins were caulked with acoustical sealant and further sealed with 3M 8067 tape.  The air sealing details in the plans were fairly easy to follow but some thought had to go into transitioning the air barrier from the exterior to the interior.  The air barrier upstairs is composed of OSB attached to the underside of the trusses.  So at the second floor level upstairs, the air barrier transitions from the OSB on the exterior of the 2x6 wall to the interior underside of the OSB attached to the trusses.    Once the gable ends were framed and sheathed, a strip of 15 mil vapor barrier was draped from inside to outside all the way along the top of the gable walls and on the second floor deck to the outside OSB.  At this point, trusses were added and the construction continued.  At the outside, the vapor barrier was lifted and a bead of acoustical sealant ran along its length sticking it to the exterior OSB.  the vapor barrier was also taped to the osb using 3m 8067.  Photo 1-1 through 1-3 illustrates the vapor barrier hanging out over the gable top plate and after taping to the exterior OSB (Photo 1-3).  The same detail exisited at the 2nd floor deck.

I had two choices for insulation.  Blown in cellulose or blown in fibreglass.  Although evidence suggests that cellulose has been shown to provide better R-value under cold conditions, it is more prone to settling unless dense packed.  Given that the ceiling will be closed in with OSB, evaluating settling after the fact will not be that easy.  Based on this, it made sense to choose longterm performance without settling so I chose fibreglass.

I contracted Bill Gifford (Home Shield Insulation, to complete this part of the project.  I met Bill at the Canadian Home Builders Association (Newfoundland and Labrador Division) Home Show.  Bill and I had been conversing about the project for months so the day finally arrived for him to be onsite (Photo 2-1).    The product they are using is Owens Corning ProPink.  It comes packages as a fibreglass ingot.  Its compact and hard.  Its almost hard to believe that it blows out as a fine fibrous clumps...but it does!  For vaulted applications like this one, a breathable retainer fabric is stapled to the bottom of the trusses (Photo 2-3, 2-4).  Bill staples the fabric to the bottom of the trusses with a pneumatic stapler about every 1".  He attached one course.  He told me that sometimes people put the fabric everywhere and then blow it in through holes in the fabric.  He said that the problem is that you can't really see where it is going when you are applying the insulation to a deep truss space like the one in my garage attic.  Instead he stands and blows the cavity full from above, always inspecting to make sure that the insulation filled the bottom of the cavity without voids (2-6, 2-7, 2-8).  Then he works his way up the whole cavity.  Bill's father mans the hopper at ground level (Photo 2-10).  He feeds the machine as it needs insulation....this is one hungry machine!

A few hours later the guys had finished filling most of the truss bays (Photo 2-10) and were up to the flat part of the ceiling.  Based on the depth of the trusses, the R value is about 60.  They will be back next week to complete the job.  In the meantime we are going to attach OSB under the trusses where the insulating has been completed.  We're one step closer to a finished attic in the garage!

Photo 1-1 Blue vapor barrier can be seen at the top of the gable wall between the top wall plate and the truss.

Photo 1-2. Blue vapor barrier can be seen at the top of the garage gable wall between the top wall plate and the truss.

Photo 1-3 Blue vapor barrier tape sealed to the OSB air barrier.

Photo 2-1 Home Shield Insulation on site 

Photo 2-2 Blown in attic insulation.  It comes packaged as a hard block in a plastic bag.

Photo 2-3 ProPink fabric installed under the trusses.

Photo 2-4 ProPink fabric installed under the trusses. Notice the blue vapour barrier.  It will be tape sealed to the bottom of the OSB.

Photo 2-5 Bills father loading the hopper with insulation.

Photo 2-6 Blowing fibreglass into the bottom of the truss space

Photo 2-7 Filling the truss cavity/

Photo 2-8  Evenly filling the bottom cavity of the truss

Photo 2-9 Stuffing insulation into a hungry machine!

Photo 2-10  Almost complete!


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