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Cathedral ceiling insulation situation

rossn1 | Posted in General Questions on


I need a little insulation guidance on an existing cathedral ceiling roof assembly, prior to re-roofing.

I have an older home near Denver that was remodeled by the prior owner, unpermitted, about 15 years ago. They created a vaulted ceiling in an area that is a large master suite containing the bedroom, walk-in closet, and bathroom; the bedroom and bathroom are open to each other. There is also a half bath and pantry as part of the cathedral section.

I am replacing the roof, and suspected the prior contractor wasn’t that knowledgeable. So I went to inspect the roofing assembly from two whole house speaker penetrations on the bed and bath sides (both near low points), and here is the composition I found, from the outside-in. They created the cavity by sitering 2×12’s onto the existing 2×4 rafters.

Bathroom Side:
Roof sheathing
1.5″ Air gap
Rough-cut Cardboard baffle
Unfaced R-30? yellow fiberglass insulation
Vapor Barrier

Bedroom Side:
Roof sheathing
1.5″ Air gap
Rough-cut Cardboard baffle
Kraft Faced R-30? pink fiberglass insulation

On the bedroom side there was a radial dark pattern extending a few inches beyond the circular speaker penetration, consistently dark in the center and patchy at the edges. The facer had been cut by the hole saw that was used to cut the drywall, and was slightly recessed due to the speaker pushing it up. The dark spot didn’t appear to be something that could be scraped off (was more integrated into the paper), and I took a small sample of it. No where in the assembly did I observe anything else on framing, cardboard, insulation, or elsewhere that appeared to be mold like… it looked clean to me. Admittedly, I did not look at the back of the drywall, nor at any high points.

To further complicate matters, the reason I checked the bedroom side was due to the fact I found a turtle vent and soffit vent in line with the first spot I checked, and wasn’t sure if they put baffles throughout or just in those locations. The bedroom side bay had no venting. Only 2 bays appear to be vented on each side, and the soffit design has a sloped underside that matches the roof pitch (4/12). I would add that the roof is being replaced under insurance, and I will also have to replace facia and some areas of soffit. There may be some funds from insurance for insulation on top of the decking, since I will be removing 1/2″ and likely going with a less expensive metal roof. I also have an option that covers code upgrade requirements, but that would likely only support code requirements above the sheathing and due to timing, I may not be able to reap code upgrade benefit.

Aside from the low R-Value of the assembly and likely leakiness, what concerns should I have about the current assembly, and if needed, what would be the approach to address this from the outside, cost effectively?

What are the code violations, for around 15 years ago? Current local code requires R54.

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  1. user-2310254 | | #1


    Since you are asking about potential risk, I suggest reading this article:

  2. Expert Member
    Akos | | #2

    Your sealing is reasonable well built. Not the highest efficiency ( roughly R25 to R28 whole assemlby) but not too bad.

    The big issue is the big holes. You have to get rid of those speakers and any canned pot lights. The pot lights can be replaced with the newer flat LED lights are much more air tight.

    The ventilation is also insufficient, if you are re-roofing make sure they put in a ridge vent and makes sure you have proper sized soffit vents in EACH bay. Also check that the vent channel in each bay is clear.

    Re-insulating to code would reduce your loads a bit but it is a lot of work and I doubt it would ever pay in energy savings. Fixing the ceiling air leaks is a lot of easy money saved.

  3. rossn1 | | #3

    I'm not sure opening up every of fiberglass to free air flow will be a good strategy... baffles are only roughly cut. My thought is more along the lines

    I'm not sure why speakers would be an issue. By their design, speakers are air tight, and at most should require some sealing. Understood the can lights are leaky, though they are IC rated, so I would think some caulking around the edge would be sufficient.

    My thoughts are more along the lines of a sealed roof assembly, adding 2 layers of 1.5" staggered polyiso to the roof deck, with a 1" vented layer on-top, and then consider filling the baffles with cellulose.

    Does Dana still watch this Q&A section?

    1. user-2310254 | | #4

      From the article I referenced in my initial response:

      "Recessed can lights should never been installed in insulated rafter bays. Period, full stop, end of story."

      "Make sure the roof assembly is as close to airtight as you can make it. If you are using fluffy insulation, you need two air barriers: one below the insulation, and one above the insulation."

  4. Expert Member
    Peter Engle | | #5

    You can't effectively put rigid insulation on top of the sheathing unless you do something to the 1.5" air gap under the sheathing. Convection in that space will kill most of the added R-value of the topside insulation. Waste of money. I agree with Steve, and the article he cites. Flush-mount airtight LED fixtures are WAY better than IC rated cans. If the speakers are really airtight, they may be OK, but you sill need to caulk them to the ceiling.

    It's hard to tell from your photo what the black stain is. If it is entirely on/in the kraft paper facing, it is likely asphalt used to make the kraft paper a vapor retarder. The bleed-through of the asphalt often look a bit like mold, but it's not. An easy test is to wipe it with bleach. If it's mold, it will wipe off and/or change color. If bleach doesn't touch it, it's probably asphalt. Alternately, if it's suspended in the FG insulation itself, it is probably house dust that's been filtered out of the air as it rises into the rafter cavity around the speaker cutout. That's a sign of how much air is leaking into the roof around the unsealed speaker can. If the sheathing itself is stained directly above the cutout, that's most likely moisture/mold staining caused by condensation of moisture in the airstream leaking around the speaker. Again, the bleach test can help tell if it's mold.

  5. Expert Member
    Akos | | #6

    Depending on what climate zone you fall into in Denver, you need between 40% to 50% of the whole roof R value to be the rigid above the roof deck.

    So if you take your R30 batts, dense pack the 1.5" gap, bringing your fluffy up to ~R36. This means you need R24 to R36 (5" to 6" of polyiso) above the deck. That is a lot of rigid insulation. Doable, but won't be cheap.

    If you do want to improve the R value of the assembly, the easier would be a layer of interior rigid insulation covered with a new layer of drywall or some nice stained T&G. There you can go with a few inches of foam without issues and would increase the assembly R value significantly as it reduces the thermal bridging of the rafters. This is not cheap either, so it is only worth it if you need to cover up some bad drywall or popcorn ceiling.

    Like Peter mentioned, if you see mold or dust above the speaker, it means the speaker enclosure is leaking.

    With a vented cathedral roof, you want to have as solid warm side air barrier as possible. You fix the air leaks, add in the correct venting, your assembly will work just fine.

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