Using ZIP System for a REMOTE designed house
The REMOTE system uses the “perfect wall” concept (Insulation outside the sheathing), but uses a rather conventional vented attic. The unconventional aspect of the attic is that it is incredibly sealed.
We are designing a REMOTE Passive House for central Ohio, and I would like your opinion concerning how to make that sealed ceiling.
One could use the Grace Ice and water shield on a plywood ceiling. I have concerns about that because I will have to design in areas of dropped ceilings to allow for utilities, and I believe that the Grace product will become detached over time.
Another possibility might be taped ZIP System. The much lighter weight of the tape might help keep it in place as it hangs on the underside. On a similar note, a liquid applied flashing to the entire underside of the plywood would eliminate all tapes. Both these ideas have one significant flaw – these are vapour permeable. REMOTE wants a vapour retarder, but then they use 6 ml Polyethylene, a barrier (like I used in my former residence in Edmonton AB) in their manual.
I plan to put 16″ wide strips of sealed and taped plywood on all the cap plates before the trusses are installed. I will follow up with bigger sheets to fill in the field afterward.
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Take a peak at how the attic works in this article: https://www.greenbuildingadvisor.com/blogs/dept/green-building-curmudgeon/topping-out
Particularly the photos at the end. Might have some good ideas for what you're trying to achieve.
Thank you Brendan. After jumping to the link, I remembered seeing that article. That is fine if you are stick building your roof. I am too far down the raised heal truss path now. A big advantage of the said article, is that you have some built in runs for utilities, though.
Steve,
Taped drywall is an excellent air barrier. It sounds like you are using Andrew Webster's approach for creating an air seal at the junction where the ceiling meets the exterior walls (described in this Fine Homebuilding article: A Practical Air-Sealing Sequence, and shown in the detail reproduced below).
If you use common sense for penetrations -- which is to say, have as few ceiling penetrations as possible -- there is no reason to choose an exotic material for your ceiling air barrier. Drywall is cheap and effective.
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our method is to install a permeable membrane, (Majpell, a SIGA product, available through High Performance Building Supply in Portland, Me) on the bottom cord of the trusses and tape the joints. Then we strap the ceiling 16" OC which gives us a place to install LED "recessed style" lights and run wiring within the envelope. As with ZIP sheathing, you will need to tape any penetrations through the membrane.
Bob; that sounds cool, but I am going to have 2' of cellulose sitting on that ceiling. It has to be able to support that.
You can sheath with 7/16 OSB and tape seams if you want to.