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Attic insulation project

jmcnamara | Posted in General Questions on
This email touches on a few topics covered often on the podcast and in the magazine.
After having an independent energy-audit done, I undertook some of the easier recommended improvements.  And in May we’re having the following work done:  1. the old insulation/debris removed, 2. the K&T rewired, & 3. air-sealing (blower-door directed) & then 4. the blown-in cellulose. 
(There’ll be 14-day window between the attic clean-out day & the new insulation. During that interval, the attic’s remaining K&T gets disconnected & removed.)
The plan had seemed straight-forward. I picked this company due to its emphasis on building science’s best practices, but now I realize I’ve still got questions & concerns:
First : the insulation project manager believes the soffit vents may be non-functioning i.e. not connected into the attic, just “for show”. He said that he sees it all the time. His proposal is to install 2 intake vents lower down on the back south-facing side of the roof to provide source air if the soffits are, in fact, non-functional (the ridge vent is functional & there are opposing gable vents too.)
And second: there are 2 voids or channels running down on a diagonal from the attic (on the east & west sides; east = left side in the attached image) around a ‘squeeze closet’* then into the porch ceiling. Those closets & walls get mighty cold in winter. The insulator’s plan is to blow cellulose down the void/channel enough to cover the top of the closets. I wonder how effective this will be. I’m thinking that I should open the porch ceiling & attack it from below with foam board (cut-n-cobble) and a caulk gun.
[*Squeeze closets are 14″ deep & extend apprx 3′ to one side & 1′ to the other.]
[Note: In the image provided: 
the yellow represents the floor of the attic & the connection from attic down under the roof and then into the porch ceiling;
the pink area is where an insulation sandwich of XPS & fiberglass batts was installed between the porch ceiling and the floor of the master bedroom (no subfloor); the pink question mark is the zone I worry isn’t well insulated; 
and the green box is one of the two squeeze closets on either side of the bedroom.]
I would appreciate any thoughts. Am I over-thinking things here?

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  1. Expert Member
    Akos | | #1

    With this type of work, the most important thing to get right is air sealing. Since lot of the spaces are awkward, the best is either spray foam or dense pack.

    For your squeeze closet area, this will block the roof vent channel, which in most cases is not a problem as long as the attic space above it is vented. Your installer can get a semi dense pack with a standard cellulose machine with a reducer to 1.5" hose. Slow but you only have to do a small area.

    Typically the floor overhangs above a porch are only 2x6. No matter what you put in there, it won't be a lot of R value, it will be better but it will still be cold. To properly fix problem, you need to pull the porch ceiling and insulate with a thick sheet of continuous rigid insulation under the joists.

  2. walta100 | | #2

    There are few times when I recommend spray foam and a conditioned attic but retrofitting a story and a half building is when the risk and high cost of spray foam is worth it in my mind.

    Without the spray foam the warm air between the ceiling and the upstairs floor will find an exit thru the knee wall and out attic vents. In theory the contractor could fit XPS tightly enough to stop the air flow but getting to the leaks puts the workers in tight miserable locations and it turns out that money alone is people enough to make people do perfect work in those conditions.

    Be sure your bid includes a before the work begins blower door number and an after the work is completed blower door number.


  3. jmcnamara | | #3

    Walter - but I don’t have knee walls. Does that change your analysis?

    Akos - I will email the project manager about the tighter hose, that sounds promising.
    As for the porch, I’m thinking, since I’m putting a new ceiling ( just painted osb now), to open & assess the ‘sandwich’ when the weather improves. At that time, I will update this thread with photos of that situation.

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