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Unvented attic space in 1930s Cape Cod

ajriddle | Posted in General Questions on

My wife and I are in the process of doing a kitchen remodel in our 1939 Cape Cod (1.5 story) in zone 4A.   There are a lot of wonky complications due to previous owner remodels and also just a Cape Cod with dormers. 

There was ductwork in the unvented attic space above the kitchen supplying an upstairs bedroom and the first floor kitchen and dining room that we discovered in poor condition so we removed the old ductwork in this small unvented attic space (roughly 5’x9′ on a corner of the roof where two different angles meet).   

Now we are trying to figure how to insulate the attic space and after reading about a hundred posts and dozens of articles I feel very unsure about what to do because of our complications and budget.

Complication #1:  It is an unvented attic with no overhang at all for adding ventilation.

#2:  It shares some sort of thin fiberboard wall with the utility room for furnace and water heater after previous owners converted the garage to a conditioned living space except for the back utility area.

#3:  Roof is only about 10 years old in good condition from previous owners but is asphalt shingles on top of wood shingles over skip sheathing (perpendicular 1×4 slats with about 6 inch gaps between them with shingles nailed into them).   Roof is constructed with 2×4 rafters

A new roof is completely out of our budget, especially as we plan to only be living in this house for about 3 to 5 more years.

The ductwork and semi-conditioned utility room makes me think spray foaming the interior of the roof deck is the only option, but I’ve seen it mentioned here that you can’t spray foam with skip sheathing which leaves me just clueless as what to do.   

Before I opened up the attic space (because of kitchen renovation) there was some kind of very old (about 1/2 inch thick) paper wrapped insulation nailed to the knee walls and someone had put down about 1/2 inch thick unfaced fiberglass in a few places above the old ceiling.

Are there any options here for someone on a tight budget?  I’m know that pretty much any option will not get me anywhere near code level of r-38 but what can I do to at least something while I have this attic space open.

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  1. gozags | | #1

    You plan to live there for a short time - is the insulation upgrade for comfort, energy usage?

    Is the roof framing strictly cathedral ? /\ or are there collar ties or other structural members and you have a flat ceiling on portions of the second floor? /-\

  2. ajriddle | | #2

    Yes, they are all cathedral ceilings except for the gabled T-shaped attic space where the roof ridge is (about the top 3ft of roof) and and doesn't have airflow to the unvented spaces on the sides of the knee walls in cathedral ceilings.

    The cathedral knee walls are all lath & plaster but the ceiling of the space below this attic space will be sheetrock when done with kitchen remodel.

    I've added pictures, the fiberglass insulation you see I just put there yesterday before doing research as a replacement for the about 1/2 inch thick double-sided paper insulation that basically was just something like sawdust inside. There is kraft facing on the fiberglass facing the interior of the living space, but I can easily remove the fiberglass. Keep in mind there is duct work for 3 rooms in this attic space and no way to re-route them.

    Looking at is there any reason to not seal this attic space off and install batt insulation above the 1st floor ceiling and on knee walls? It appears in this article doing this to an unvented devil's triangle is an option.

  3. gozags | | #3

    Airs-sealing the new work is key from what I understand. Insulating the ceiling and kneewalls is what I have in my Cape and I think that is the preferred way (without a foam over roof replacement) for this type of build. However, the one issue you have is the duct work in that space, which isn't ideal. I am not sure what the prescription there is, other than insulating the ducts themselves, if you have access. Minimally, duct mastic on the seams and penetrations in the metal duct work, to lessen any leaking.

    It's a small space, it looks like - if the duct work was lower the below ceiling and not tracking along the roof rafters I wonder if you could just get a bag of blow-in insulation from a big box and hand cover that whole area, covering the ducts if possible? Not sure how messy that is.

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