I think I have a foil bubble “insulation” nightmare in the making?
Casey Dragon| Posted inGeneral Questionson
From inside to outside of my wall- sheetrock, foil bubble, studs, foil bubble, plywood, typar, cedar shingles. I am watching my husband (under the direction of my uncle who has worked in construction for 40 years) build my house and I am really concerned that this is not good. We live in Maine, so it gets pretty cold. Also, I was told by another carpenter that this could possibly rot the frame? Am I panicking over nothing or is this going to be a disaster?
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Replies
Casey,
Is there any insulation between the studs? If there is, what type of insulation is it?
If there is no insulation between the studs, this wall assembly does not meet minimum code requirements.
Thank you, Martin. There is no insulation between the studs.
Casey,
The foil-faced bubble pack has a very low R-value. Since the foil faces an air space, you'll get some benefit from the foil (although not from the bubbles). The R-value of this wall assembly is probably about R-3 or R-4 -- in other words, close to worthless, and definitely illegal.
If anyone ever tries to insulate the empty stud cavities in the future with cellulose insulation, the exterior foil layer will contribute to moisture accumulation in the wall cavity, leading to mold and rot.
I hope it is early enough in the construction process to stop this plan in its tracks.
With the two low-E surfaces facing one another across a vertically oriented empty cavity, and the ~R2 per layer of bubbles it might have a center-cavity performance as high as R8, but still well shy of code-minimums. It would in fact perform slightly better if the bubble pack were woven between the studs so that it only contacted the wallboard or sheathing at the sides, and had air gaps between bubble pack and adjacent layers on both sides(not that I'm recommending anyone build that way), due to the doubling of the number of air films, and low emissivity across a relevant air gap in both directions.
In a Maine climate any air leaks into the cavity from the interior will likely end up forming condensation/frost on the cavity side of the exterior bubble pack, which increases it's emissivity, cutting into it's dry-state performance. Then when it warms up in spring it will puddle at the bottom and potentially rot the bottom plate & stud ends, since it can't dry through the bubble pack and only through random minor air leaks. Intentionally creating air leaks to the exterior would mitigate that potential, but only by significantly reducing the overall thermal performance.
If the shingles are already up the best option is to pop the wallboard out- open the whole thing up and cut the bubble pack away from the plywood sheathing. From there you have a number of options- how deep are the studs, and what is your ZIP code (for zeroing in on your climate zone)?
Radiant barriers are the best option if you're in a vacuum, with no convective heat (or moisture) transfer, and sometimes a good option in ultra-arctic conditions where there is zero potential for fiber insulation to dry. But for those of us who live on the earth's surface in locations other than at 3000' in the Antarctic plateau it's not really a solution. To get reasonable performance requires multiple air-tight layers with air spaces between successive layers, which makes for awkward & complex (read "easy to screw up") construction methods.