Ed_Orum Posted August 31, 2020 Share Posted August 31, 2020 I have a building that requires continuous (exterior) insulation. The manufacturer states the wall assembly should be (from inside to outside) for either 2x4 or 2x6 wall studs: Gypsum wallboard Vapor Barrier Cavity Insulation Structural Sheathing Vapor Barrier (tyveck) Continuous Insulation (Comfortboard 80) 1x4 Vertical Furring Strips 2x3 Horizontal Furring Strips (Client Specified) Siding I do not see any options for furring strips in the Define Wall Type box. How do I show the vertical and horizontal furring strips in the wall type? Thanks, Lane Link to comment Share on other sites More sharing options...
rlackore Posted August 31, 2020 Share Posted August 31, 2020 I suggest adding the thickness of the furring strips to the thickness of the siding - IOW, use a single wall layer to account for both materials. This is my strategy for rain screens and air spaces. However, this method won't provide an accurate Section or an accurate Material List. FWIW, I don't include the CI as a separate wall layer either - everything to the exterior of the sheathing I roll into a single layer, then I use details, sections, text, and the exterior elevations to communicate the wall construction. But this is a personal choice - everyone has different needs and preferences. Link to comment Share on other sites More sharing options...
BrownTiger Posted August 31, 2020 Share Posted August 31, 2020 Just define your Siding wall type. As others stated I would not use double the furring stripps, not sure if I would have two vapor barriers: one on inside and one on outside, because the cavity moisture will have no place to go. In engineering school they tell you avoid, avoid avoid. [unless you find a one way vapor open barrier, and even than...] Suggested wall: Gypsum wallboard Cavity Insulation Structural Sheathing Vapor Barrier (tyveck) Continuous Insulation (Comfortboard 80) 2x3 Horizontal Furring Strips (Client Specified) Siding Here is example Link to comment Share on other sites More sharing options...
Gawdzira Posted August 31, 2020 Share Posted August 31, 2020 IF you do use an interior vapor barrier. Look at Intello as a solution since it is vapor open. https://foursevenfive.com/products/air-sealing-system/?_bc_fsnf=1&Application=Interior Link to comment Share on other sites More sharing options...
Alaskan_Son Posted August 31, 2020 Share Posted August 31, 2020 7 hours ago, Ed_Orum said: 1x4 Vertical Furring Strips 2x3 Horizontal Furring Strips (Client Specified) I could be wrong, but based on my professional experience, these 2 layers are almost certainly either/or and not both. That being said, you can accomplish what you're after by using a wall type like the one I have defined in the attached plan and then editing the framing in your wall detail. Inspect the wall definition and wall detail in the attached plan to get a better idea. The key things are that you need to properly define some materials, and you need to edit the framing manually. Continuous Insulation Wall Type.plan 1 Link to comment Share on other sites More sharing options...
rlackore Posted August 31, 2020 Share Posted August 31, 2020 I'm going to throw in my two cents on the vapor barrier issue. Depending on the climate zone, local codes may require an interior vapor barrier - the old standby was sheet polyethylene, which is still used and is a true vapor barrier (0.1 perm or less). Nowadays it's preferable to use a vapor semi-impermeable vapor retarder (1.0 perm or less, and greater than 0.1 perm) instead of a vapor barrier. As Alan mentioned, the Pro Clima Intello Plus, imported by 475, is a good product, but it can be difficult to source in some parts of the country. I recommend the Certainteed Membrain, which is also an "intelligent" vapor retarder. Tyvek, and similar "housewraps", are generally vapor permeable (10 perms or greater), and are intended to act as an air and weather barrier, not as a vapor retarder (or vapor barrier). Link to comment Share on other sites More sharing options...
Gawdzira Posted August 31, 2020 Share Posted August 31, 2020 If the interior vapor barrier is a code item, generally a painted drywall surface becomes that vapor barrier. Link to comment Share on other sites More sharing options...
Alaskan_Son Posted August 31, 2020 Share Posted August 31, 2020 1 hour ago, Gawdzira said: IF you do use an interior vapor barrier. Look at Intello as a solution since it is vapor open. https://foursevenfive.com/products/air-sealing-system/?_bc_fsnf=1&Application=Interior 20 minutes ago, Gawdzira said: If the interior vapor barrier is a code item, generally a painted drywall surface becomes that vapor barrier. These are both very dangerous pieces of advice for some of the colder northern climate zones. 1 1 Link to comment Share on other sites More sharing options...
Gawdzira Posted August 31, 2020 Share Posted August 31, 2020 35 minutes ago, Alaskan_Son said: These are both very dangerous pieces of advice for some of the colder northern climate zones. Good to know. I am fortunate to have all my work currently within a few miles of my house (where the only snow is flocking at the tree lot in December). Link to comment Share on other sites More sharing options...
parkwest Posted August 31, 2020 Share Posted August 31, 2020 This is typical... didn't see any details showing 2 vapor barriers... Link to comment Share on other sites More sharing options...
Alaskan_Son Posted August 31, 2020 Share Posted August 31, 2020 18 minutes ago, parkwest said: This is typical... didn't see any details showing 2 vapor barriers... In your example, presumably, the taped/edge sealed rigid insulation IS the building wrap. I think vapor barrier was a poor choice of words to describe the Tyvek building wrap/air barrier mentioned in the OP. Anyway, most rigid insulation works as a building wrap on its own (and even a vapor barrier if it's properly sealed at the edges). I think ComfortBoard is mineral wool, which doesn't have any such properties. Link to comment Share on other sites More sharing options...
rlackore Posted August 31, 2020 Share Posted August 31, 2020 1 hour ago, Alaskan_Son said: These are both very dangerous pieces of advice for some of the colder northern climate zones. Perhaps in Alaska where you encounter subarctic and arctic conditions, but in my opinion, an "intelligent" vapor retarder is suitable as the interior vapor control layer in cold climates. Latex paint is also a possibility, but because it's always vapor permeable (i.e. not hygroscopic - its permeability doesn't adjust to the indoor relative humidity), you have to make sure you've got a good air barrier and can limit air movement into the wall at penetrations, etc. So, what's the basis of your opinion? Link to comment Share on other sites More sharing options...
rlackore Posted August 31, 2020 Share Posted August 31, 2020 9 minutes ago, Alaskan_Son said: I think vapor barrier was a poor choice of words to describe the Tyvek building wrap/air barrier mentioned in the OP. Agreed. 9 minutes ago, Alaskan_Son said: Anyway, most rigid insulation works as ... a vapor barrier if it's properly sealed at the edges. In my experience this is true only if it's foil-faced, otherwise, most unfaced products are considered a Class I vapor retarder (vapor semi-impermeable, 0.1 to 1.0 perms) at thicknesses of greater than 1 inch, and a Class II vapor retarder (vapor semi-permeable, 1.0 perm to 10.0 perms) at thicknesses of one inch or less. Link to comment Share on other sites More sharing options...
GeneDavis Posted August 31, 2020 Share Posted August 31, 2020 A guy in my area built a "net zero" house, conventional 2x6 framing with smart-framing details, the continuous insulation being two layers of 2" rigid foam that went atop taped Huber ZipWall sheathing. The insulation went down continuously to the footings. To effect a vapor barrier, the outer layer of 4x8 foam sheets were gapped 3/8" and sprayfoam went into the joints, then the joints all got taped. The siding was vertical board and batten, really nice western red cedar 1x12 boards and 5/4 x 2 battens. The sub-purlins for attaching the siding was 5/4x2 atop strips of the product shown in the picture, which allows water to get through and down. It has a trussed roof with 28 inch heel height and the attic has 24 inches of cellulose on the floor. Link to comment Share on other sites More sharing options...
Alaskan_Son Posted August 31, 2020 Share Posted August 31, 2020 1 hour ago, rlackore said: So, what's the basis of your opinion? Just 20 years of firsthand experience in the industry, many hours in the classroom studying building science, many more hours studying and researching building science on my own, and several certifications in the same. Around here, our vapor barrier actually needs to have a perm rating of 0.06 or less. At best, a good latex paint is roughly 20 times that permeable and at worst its closer to 200 times...and that's assuming it's been applied properly and that it maintains that value indefinitely (which of course it won't). 1 Link to comment Share on other sites More sharing options...
Alaskan_Son Posted August 31, 2020 Share Posted August 31, 2020 1 hour ago, rlackore said: In my experience this is true only if it's foil-faced, otherwise, most unfaced products are considered a Class I vapor retarder (vapor semi-impermeable, 0.1 to 1.0 perms) at thicknesses of greater than 1 inch, and a Class II vapor retarder (vapor semi-permeable, 1.0 perm to 10.0 perms) at thicknesses of one inch or less. I wasn't getting that precise. It obviously depends on the type of foam and type of facing. I was just speaking very generally and pointing out that a building wrap may not be necessary if the foam itself suffices. The product mentioned in the OP almost certainly does NOT. Around here on the other hand, we commonly use an EPS product that has both a plastic facing and a foil facing. It's actually too impermeable in many applications. Link to comment Share on other sites More sharing options...
jmsisco Posted September 1, 2020 Share Posted September 1, 2020 Attached are some good Articles from Building Science regarding Air Barriers, Drainage Planes, Vapor Barriers, and the Perfect Wall BSD-104_Understanding Air Barriers.pdf BSD-105_Understanding_Drainage_Planes.pdf BSD-106_Understanding Vapor Barriers_2013.pdf bsi-001_perfect_wall_2010rev2_0.pdf 2 1 Link to comment Share on other sites More sharing options...
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