Fixing vaulted ceiling insulation mess
Hello!
We’re exploring ways to improve the subpar insulation job for the vaulted ceilings of our three-year-old home. Our current setup is under-insulated, has mold issues, and differs from the options shown in these links:
We’re in Climate Zone 3B
Two options we are considering:
1. From the top:
a) remove the solar panels, asphalt shingles, radiant sheathing and polyiso insulation (foil-faced)
b) add fiberglass batts, sheathing, rigid foam, outer sheathing, asphalt shingles and solar panels
2. From the bottom:
a) move family out of the house
b) remove the shiplap MDF, drywall and existing polyiso and batt insulation
c) add closed cell spray foam
d) add new drywall and shiplap MDF and move back in
The second option is only possible if we can use the existing roof sheathing, which is Eclipse OSB radiant barrier (perforated), facing down. I don’t know if there is a way to remove the radiant barrier or if there’s a solution that involves leaving it.
Both options require removing the current polyiso insulation, and I’m really worried about how much will escape the trash bin during demolition.
The images explain our situation a little better and explain why we are willing to do something so extreme. Any ideas on a different approach are welcome!
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Replies
I think most of your issues would be solved by a code sized diffusion vent at the ridge of the cathedral ceiling:
https://buildingscience.com/documents/guides-and-manuals/gm-2101-guide-building-conditioned-unvented-attics-and-unconditioned
This would save you having to demo everything. This also adds a path for moisture to be vented with any section with rigid underneath so those can stay as well.
Thanks Akos,
I'm concerned that ridge ventilation may struggle with my thin, cluttered ceilings. The attached picture provides more detail.
Those ridges look to be decent size, a diffusion vent there should work at least for all the sections with fluffy between the rafters.
I know those are not deep rafters and it is not a lot of insulation but you are also in pretty mild climate. Not much energy is to be saved there by adding more insulation.
If you want to improve your energy efficiency, work on sealing up the roof properly. This would mean pulling the soffits and air sealing all the blocking between the rafters.
Unfortunately the section with cut and cobble polysio will have to come out, there is no way of saving that. You can re-insulate with batts and similar diffusion vent afterwards.
For the flat roof with the deck on top, if there is mod issues there, pretty much your only option is spray foam bellow. You don't need much about 1" is good enough for condensation control in your climate. You could insulate on top as well with rigid insulation above the deck but that would mean pulling up the mud base.
Thanks again! I've organized your approach into a table below to confirm my understanding. Depending on the level of support we receive from our GC and his subs, we may have to go this route. I wish I had paid closer attention to this during construction instead of relying so much on the city inspector.
Yup, that is a good summary for the cathedral section. I believe you only need R5 exterior rigid for condensation control, no issue with going with more.
For the vented roof, do you actually have issues there? I most climates cut and cobble in a vented attic works as long as the ceiling does not have a vapor barrier.
Note that you can also converter the vented attic into an unvented attic with a diffusion vent at the ridge the similar as the rest. You can leave the insulation on the floor but you would have to seal up the soffit area.
Our vented attic is mostly OK, but it still has two issues:
1) Approximately 50% of the attic has foil-coated polyiso installed above the drywall and below the OSB in the flat-floor sections.
2) ventilation is only coming from six ridge vent holes, 1/3750 of the attic area - I think we missed the 1/150 target. We would be in better off but the dormer vent installers just missed the attic space. However, compared to everything else, this should be an easy fix.