red rosin paper as an air barrier?
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Can red rosin paper with taped seems be considered an air barrier?
either for a ceiling or an interior wall. the paper goes on top of faced fiberglass insulation. tongue and groove or shiplap boards are then on top of the taped rosin paper.
Aside from taped drywall– if rosin paper is not an adequate air barrier —what are the alternatives?
thanks,
forrest
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Replies
Forrest, while you probably wouldn't want to try to breathe through a piece of rosin paper, it's not a good air barrier because it's too fragile and gets even more brittle as it ages. Here is a collection of GBA articles to get you started: https://www.greenbuildingadvisor.com/collection/air-barriers-air-sealing
A few common air barriers used on the inside face of a wall:
- Taped drywall
- Smart vapor retarder membranes such as: Certainteed MemBrain, Siga Majrex, Pro Clima Intello Plus. These are class II vapor retarders and are safe to use as an interior air barrier in most circumstances.
- Vapor barrier membranes such as 6-mil poly: this is a class I vapor retarder and you need to be cautious about putting a vapor barrier like this on the interior of your wall in some climate zones, as well as considering how your wall is intended to dry and if you are creating a wall with a double vapor barrier that will inhibit drying.
thanks for your response! maybe a step up would be ram board with their seam tape?
Nope. It is still paper.
What is your objection to the Class II vapor retarders, such as the ones listed above?
I'm also curious what you are trying to accomplish. If it's minimizing use of plastics, this is a paper-based air control membrane: https://foursevenfive.com/db/.
I was aiming for less plastics, and the paper or ram board seemed an inexpensive solution to me. after seeing how robust the ram board is, I really don't see why it wouldn't work. I understand it would want to get brittle with age though. The DB product looks like a good alternative. thank you
A lot of products that seem robust at first won't be over time. Rosin paper after years in service will get so brittle that it will fall apart if you blow on it. It gets very crumbly. Ram board is intended for temporary protection of floors while you're doing work, so it's presumably not designed or tested for long term applications either. I wouldn't trust it for something that is critical to the long term performance of the structure like an air barrier.
If you want to avoid plastic materials, I'd use drywall. If you only need the drywall as an air barrier, and you have a finished wall of T+G boards, you could consider 3/8" or even 1/4" drywall, although the thinner drywall panels often cost the same or even more than the more common 1/2" thickness so you won't necassarily save any money, and the hanging/mudding/taping labor is about the same regardless.
The usual way to do something like this is to use housewrap, such as Tyvek, but that's a plastic material. If you're trying to avoid petroleum products, note that plastic does NOT necassarily mean it was derived from petroleum. Many plastics use natural gas as a feedstock. You can even find "biopolyethylene", which is polyethylene that uses ethanol as a feed stock, and ethanol is typically made from corn. If you use biopolyethylene, you end up with a plastic product for your air barrier that is made from corn. It's the exact same polymer, just a completely different original source for the molecules used in the polymer chains.
Note that if you use polyethylene, you are using a VAPOR barrier too, which may complicate other parts of your wall assembly depending on what you're building. Keep that in mind.
Bill
Ramboard would hold up better than rosin paper, and it is airtight. Where I think it would eventually fail is the tape. Cardboard (such as Ramboard) is acidic and gets brittle with time. I'm not sure how long tape will hold--maybe a few years, possibly a few decades. I haven't seen long-term testing. For such an important element of the building envelope, I would stick with something intended and tested for the purpose.
Drywall is an air barrier, as Bill mentions. In fact its airtightness is what defines an air barrier.