Interior Air Barrier
I’m trying to decide which product to use for my interior air barrier. I’m constructing a double stud wall system and intend on placing my interior air barrier on the outside of my inside stud wall. My choices are..
– Certainteed’s Membrain
– Siga Majpell 5
– ProClima Intello +
– ProClima DB+
Has anyone used any of these products and have any advice either way? Certainteed’s Membrain is the least expensive of the options however I’ve heard that given how thin it is that it isn’t very durable and tears easily, I’ve also been told that at high humidity the pours open so much that it may no longer be considered an air barrier. I’ve put my hands on Siga Majpell, I like it, it is a rugged product but has a very low perm rating (<1.0) which concerns me. ProClima Intello+ is another smart vapor barrier which seems more rugged than MemBrain (based on what I’ve read not personal experience) but is much more expensive than MemBrain. Lastly, ProClima’s DB+ seems to be a lower cost option to Intello but again seems like it could lack durability as it is a paper based products. Has anyone had personal experience with any of these products and could help me make my decision? By the way I’m in zone 6A
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Replies
Brian,
I hope that a GBA reader with experience will be able to provide you some advice on selecting one of the membranes you have listed.
In the meantime, I can't help mentioning an obvious fact: gypsum wallboard is a perfectly good air barrier. Since most homes have walls finished with drywall, it probably makes sense to rely on the drywall as your air barrier.
More information here: Airtight Drywall.
Ive considered using my drywall layer as my air barrier but I'm concerned my drywall guy won't get it right, particularly with all the utility penetrations. I like the idea of the air barrier on the outside of my inside wall effectively creating a utility chase within the inside wall.
If getting a good air barrier at this location proves to be too expensive I may revisit using the ADA.
Why not use plywood?
Joe, I considerrd plywood but itthe is much more expensive per square foot than any of the products I mentioned
Brian,
What is the rest of the story? Which of the double stud walls is the primary structural element? What is the exterior finish material? What are you planning for insulation? How will your walls be braced? If you'll be using sheathing to provide required bracing, simply moving it to the outer face of the inner wall adds NO cost!
With any of the materials you propose sealing around the few penetrations of the air barrier is far more problematic than sealing to plywood or OSB.
For my 'dream house' I'll make the inner wall the primary load bearing one and sheath it's exterior side with plywood, insulate with Roxul comfort bats, use fiberboard exterior sheathing, housewrap, drainage gap and exterior finish (thin brick on metal substrates) Frankly the fiberboard is not needed.
I used MemBrain on my double wall house, in Zone 6 (central NH). I didn't find it to be especially fragile. The high permeability of it when the air next to it is very humid does not reduce its value as part of an air barrier system. In my case, it was applied over the insulation mesh after the wall was blown.
Exterior wall electric outlets and switches were in Airfoil boxes, with wide flanges. I trimmed the MemBrain around the flanges to leave most of the flange exposed, then taped the MemBrain to the flanges. I found this worked better and was faster than using acoustical sealant, which I gave up on after the first few boxes; the insulation bulge tended to push the MemBrain off the flanges, but this was not the case with the tape.
At the tops and bottoms of all exterior walls, at the intersections of interior partitions with exterior walls, and at the tops of all interior wall partitions on the upper level I had the framers hang foot-wide sheets of poly. This let me install the MemBrain room by room and tape it to the strips of poly, for a continuous air barrier all around. I didn't have any problem with the sheetrock crew screwing it up, that I know of. The first blower door result gave me 0.65 ACH50, acceptable by any realistic measure. I wasn't aware of the competing products at the time, so I can't say whether I would have use one instead of MemBrain.
How are you planning on blowing the walls if the Membrain is already in place?
I'm not blowing the walls, I'm insulating with Roxul. Its more DIY friendly.
Do you have a cellulose installer? Have you compared the cost of buying the Roxul vs. having them do the blown in? Roxul ain't cheap.
Brian,
On another of your posts here, I learned that you are planning to use 24" OC framing for your double walls. On that same post you mentioned that you had no good solution to insulating between the walls. FWIW I'm planning a similar double wall & plan on using Roxul comfort bats. My solution to insulating between the walls is use Roxul comfort bats intended for steel studs on 24" centers for that middle layer. The mid wall layer will end up being continuous behind the studs with seams at one edge of each stud. This limits the choice of spaces between walls to 2 1/2", 3 1/2"or 6" with a single layer between walls. As I mentioned in my previous responses I will use plywood on the outer face of the inner (load bearing) wall as my primary air barrier. This will require that I erect the outer wall without sheathing and add exterior sheathing etc after insulation is installed. I'm also now considering using a double wall WOOD basement. The outer basement wall would be 2x8 16" OC sheathed with 3/4" PT plywood and not load bearing but it will support the outer wall above it and the exterior cladding. While the inner wall would be 2x6 24" OC sheathed with 1/2" PT plywood (detailed as the primary air barrier). The inner basement wall will carry the floor and roof loads. I'll make the top plate of the inner basement wall sit 3" below the top plate of the outer to use the floor framing to brace the tops of the basement walls without need for metal structural ties The lumber used in the basement would be graded for foundation use. Using Roxul comfort bats for 2x8 gives about r27 which can be easily upgraded by adding more Roxul in the inner wall.
Oy gevalt - I repeat, have you guys compared the price of hiring out dense pack cellulose vs. Roxul?
Jerry thanks for the background on your design but I think we got off on a tangent.
Dan, yes I have priced DPC. Hiring ssomeone to DP was nearly double the cost if puting in Roxul myself. If I was brave enough to rent a machine and DP myself the price gap obviously closes.
Dan,
What led me to Roxul was the simple fact that I couldn't find a contractor that actually had done DPC in a double wall. Once I considered Roxul it became apparent it yields a 16% higher thermal resistance in any wall cavity. Yes the material cost is roughly double what a contractor pays for cellulose if one buys Roxul from Lowes. (If one prices cellulose at Lowes it is less than 10% more for Roxul.)