Smart Vapor Retarder
arnoldk
| Posted in General Questions on
Hi,
I am looking for anyone to share their knowledge or experience using one of the below smart vapor retarder in their wall assembly. I am trying to pick within option would be best in terms cost and durability.
Pro Clima – Intello
Pro Clima – DB+
Pro Clima – DB+
CertainTeed – MemBrain
Thank you,
Arnold
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What is your proposed wall assembly and insulation method?
The wall assembly I will be using for my build is the following and it will be around an R-60.
Siding (Lap siding)
Rainscreen
WRB
Exterior insulation (1.25" Comfortboard)
2x6 with batt insulation
0.5" Fiberboard structural sheathing (Air Barrier)
3.5" space with batt insulation
2x4 with batt insulation
Vapor retarder
Drywall
Arnold
Intello is very rugged and has a wide range permeance range between dry and wet, 0.1 to 13 perms.
DB+ is also rugged, is paper-based, with a range of 0.8 perms dry to 8 perms wet. It is the most expensive of your options.
Membrain is less rugged--you can't dense-pack blown insulation against it--and it is the most vapor-open of the options, ±1 perm dry and 35 perms wet. It is the least expensive of your options.
https://foursevenfive.com/intello-plus/
https://foursevenfive.com/db/
https://www.certainteed.com/resources/30-28-159_MemBrainTechnicalBrochure_July_2019.pdf
Hi Michael,
do you have any experience using any of these products? I was leaning towards Membrain because of cost but wondering if Intello may be worth the extra cost for being more rugged.
Thank you,
Arnold
Arnold, I have installed a lot of Intello and find it durable and easy to work with.
I have not installed DB+ but trust the relevant information at foursevenfive.com. I think the primary reason for using it is if you are trying to minimize petroleum-based products in your house.
I have not installed Membrain but have been mentally cataloguing opinions from those who have. Some say it tears if you look at it sideways but most say it's reasonably tough, just not suitable for dense-packing.
Almost 9 months late to this conversation, Michael, but would spacing 16" OC horizontal 1x3 furring strips (or even 8", if need be) be sufficient to give MemBrain enough strength to hold back a cellulose dense pack? Having already purchased the MemBrain, I really hope so.
I used MemBrain on my house. Cellulose was dense-packed (late 2010) behind netting, and the MemBrain was applied over the result. Electrical boxes on exterior walls were Airfoil, which have a flange around them. The MemBrain was applied over these, and a knife used to cut the MemBrain about halfway across the width of the flanges. Strips of tape secured the MemBrain to the flanges to maintain the air barrier. I first tried acoustic sealant between film and flanges, but after a doing a few I saw that wasn't working well. Outward pressure of the cellulose tended to lift the MemBrain off the sealant, so I switched to the tape. The tape was one designed for taping overlap joints of sheets of polyethylene and similar materials. I used that also to seal the edges of the MemBrain to strips of poly run perhaps 6" out from under the wall framing and foot-wide strips hung over the tops of the wall framing. MemBrain sheets on the ceiling were sealed to that joint. Hanging strips of poly over the walls early on let the MemBrain be installed room by room later. Doing it as part of framing would have subjected that thin film to inevitable physical damage. Doing it right before sheetrocking minimized exposure time.
I've used Intello, and I note that installing dense pack cellulose is easier with netting than with Intello, so this two-layer approach could help ease that process, especially if you aren't 100% confident in the skills of your dense pack crew.
I've used MemBrain and had no problems with it, aside from the fun of unfolding it off the roll in some relatively small rooms, but that's not a unique issue with this particular product. I put it up with a bead of urethane caulk and a pneumatic staple gun -- one that shoots the "regular" stapels, not the narrow crown type. I had no problems with it tearing, it seemed pretty tough to me. I also found the 3M flashing tape I used to seal seams and boxes to it stuck very well.
I was installing over mineral wool batts, so there wasn't any real pressure on the MemBrain aside from it's own weight.
Bill
Are these "smart" vapor retarder worth the substantial cost difference when compared to standard 6 mil poly in ac zone 6 climate (Ottawa, Canada)?
Thank you,
Arnold
If vapor drive is virtually always from interior to exterior, poly is fine. If vapor drive is from exterior to interior at some points of the year, typically when you turn on an air conditioner, poly is bad. As the climate crisis continues, those of us in zone 6 who use little or no air conditioning now will almost certainly use it more in the future. So I would say that yes, variable permeance membranes are worth the extra cost because they will help ensure a safe, long-lasting building envelope.
Thanks for that Michael. I guess I just have to close my eye and make the purchase. Just like ripping off a band aid, short term pain for long term gains.
I am pretty certain the building inspector in Ottawa will want to see some type of vapor barrier membrane and won't accept latex pain.
Arnold
VPMs are especially important with highly insulated walls, because moisture that does get into the assembly has less heat energy available to push it through to the exterior than it would in a code-minimum assembly. I know of many projects with thick walls that perform well without a VPM but a few that don't; I'd rather spend a bit more to sleep well at night than get involved in mold or lawsuits.
You might want to check the VPM's performance numbers with your inspector or the building code; some places have specific rules that essentially require nothing but a full vapor barrier.
I'm using Membrain currently. I find it quite durable and easy to work with. I did accidentally drop a ladder on it at one point, which punched a hole, but it's easy to tape up with Tuck Tape.
Membrain is 10x the cost of 6 mil poly. Whether that's worth it totally depends on your wall assembly. If you're in a situation where you can design the wall to dry properly with 6 mil poly then by all means use the poly and save yourself the bucks.
In my case I'm doing a retrofit and think I may wrap the home in foam in the future. In that case if I used poly as my air barrier I'd create a moisture sandwich with the foam. The price premium was worth it to leave open the possibility of doing exterior foam in the future.