Condensation with SmartBaffle Insulation
I used to build cathedral ceilings with a “hot roof”. After reading many articles on here, I decided to switch to a ventilated cathedral roof system, as outlined in many articles on here. I decided to use “smart baffles” SmartBaffle Insulation baffle with 2 inch air channel (dciproducts.com) for my air channel/insulation stand off barrier. I built the entire ceiling, changed the attic venting to a ridge vent and correct soffit ventilation…lots of work that I wouldn’t do with a “hot roof” and felt good about the end product….until I did a spot check and found LOTS of condensation on the underside of the “smart baffles” at night time. The condensation did disappear by mid-day next day as temperatures increased, but I don’t like the idea of having that much moisture in my roof assembly. Am I overthinking this? Should I not be worried that all the smart baffles are completely covered in condensation droplets on cold nights even though it seems to have evaporated by mid-day the next day?
I’m seriously considering tearing it all out and replacing the “smart baffles” with 1 1/4″ SilveRboard XS perforated insulation board that has an R rating of roughly 5.5 at 25 degrees F. It has a perm rating of about 1.75 at this thickness. The way I see it, this SilveRboard XS graphite foam board should eliminate or minimize condensation and hopefully allow any moisture that does accumulate to escape slowly through the board and up into the air channel?
Building is in San Diego. We probably get 10-15 nights a year where the temp drops below 30. Many winter nights are in the high 30s- mid 40s. Day temps are usually 50s-60s winter and 70s-90s summers.
Building materials from inside to out are as follows
5/8″ T&G shiplap
5/8″ drywall (fire barrier)
23/32 cdx plywood (I know, not necessary but being used as a nailing surface for the T&G and for psuedo beams)
7.25″ Rockwool (R30)
2″ air gap
20 year old roof assembly (plywood, tar paper, shingles).
No plans for an interior side vapor barrier but the ceiling is AIR SEALED very well. Zero air leaks through the ceiling assembly.
The ceiling joists are 2x10s (9.25″ tall) so I am working with limited space.
1. Should I rip out the “smart baffles” and replace with 1.25″ SilveRboard that is R5.5 with a perm rating of 1.75? Or simply allow the smart baffles to accumulate condensation on the interior side on cold nights and hope it doesn’t mold before the next hot day makes it evaporate?
2. I’m limited on space, especially now that I may need such a thick baffle material. If I use the 1.25″ SilveRboard, can I reduce my air gap to 1″? Or should I reduce it to 1.5″ and then just compress the mineralwool an additional 1/2″ to fit in my now smaller insulation area? I’m not fond of attempting to cut 1″ or 1.25″ off the top of all the mineral wool insulation that is already installed. Hoping to simply pull it out, replace baffle, and reinstall same insulation that is already cut to fit.
3. Should I air seal these 1.25″ baffles and rely on the 1.75 perm rating to allow drying? Or leave them unsealed on the sides (ie: “intentionally leaky” where they meet the 2×10 ceiling joists, to ensure that any moisture can quickly escape? Or will the small gaps between the foam board and 2×10 ceiling joists actually cause condensation on its own? I’m not very fond of the 1.5 perm rating of the foam board which may end up more as a moisture barrier over time after getting covered with a layer of dirt/dust over time?
Sorry for the long post and thank you in advance for any knowledge or ideas you may have to share.
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