Air barrier material and location
I have several questions involving wall systems. I live in Michigan, Sanilac county (zone 6). 7133 HDD, 477 CDD. We are about 1.75 miles inland west of Lake Huron.
I am looking to build a ~1400 Square foot ranch with a 2+ car attached garage.
I have looked at many different construction systems and I keep coming back to stick built. There are many different ways to build a stick built wall. I think i would prefer a 12” to 16” double stud wall with dense pack cellulose. Sheeted in Structural fiberboard covered in 15# building felt and a ¾” rain screen with Fiber Cement siding. I would also like to place the air barrier next to the cellulose and behind a service cavity then cover with ⅝ drywall preferable type X.
I know this wall will not pass the 60/40 exterior / interior insulation recommendation. My understanding is that that is a problem in the winter when moisture laden air and some vapor diffusion condensate on the cold sheeting. With a proper air barrier very little moisture will reach the cold sheeting. And due to the permeability of the sheeting any condensation that does occur will be allowed to dry without causing damage. I want a wall that dries to both sides. If I understand correctly the outer sheeting should be 5 times more permeable than the inner air / vapor barrier in a predominantly heating climate (Zone 6)
Sorry for the wall of text. I have a question regarding the material to use for the air/vapor barrier and how to create a service cavity.
How should the service cavity be made? The simplest way i can think is to place the air barrier on the outer surface of the interior stud wall. This would allow the open vertical cavities to be used. Drilling paths for cable would be necessary and future modifications would be more difficult. Conduit could be added to reduce future modifications costs.
I also like the idea of placing the air barrier on the inner surface of the interior stud wall and then using horizontal strapping. This would make it easier to run utilities and future changes. This would also allow me to use a thinner material for the air barrier because it will be sandwiched between horizontal strapping and the vertical studs behind it. My question would be what method who be preferred?
The second question would be what material would make a good affordable air barrier. Currently i’m thinking plywood since it is more vapor open than OSB and contains less resins so it is likely to off gas less. I am also very interested in Masonite. Masonite is just wood with no binders and can come in assorted thicknesses. I would really like to use it due to it being more natural with no added resins. I haven’t found any information on others using Masonite as an air barrier and am not aware of the perm rating for it. I am also aware of smart vapor barriers but I would prefer to use something more rigid and durable.
I would greatly appreciate any input on the best way to make an effective service cavity with a durable mostly not toxic air barrier. I would really like to know more about using Masonite.
Posted Oct 26, 2012 1:54 PM ET
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