From prismoidal at gmail.com Fri Feb 14 13:25:51 2020 From: prismoidal at gmail.com (Clarke Olsen) Date: Fri, 14 Feb 2020 14:25:51 -0500 Subject: [Greenbuilding] wall construction Message-ID: <1F05B0DC-0043-4099-AF6B-D3C3994877A4@fairpoint.net> Can I get a group opinion on stud-wall construction which uses 1/2? foam as air/vapor barrier? 2 x 6 @ 24? oc filled with Roxul. 1/2? foil faced foam w/taped joints 2 x 4 @ 24?oc flat 1/2? drywall 4 x 4 shallow boxes w/mud plates, and all wiring in the furred space. Clarke Olsen clarkeolsendesign.com 373 route 203 Spencertown, NY 12165 USA 518-392-4640 colsen at taconic.net -------------- next part -------------- An HTML attachment was scrubbed... URL: From topher at greenfret.com Mon Feb 17 19:59:44 2020 From: topher at greenfret.com (Topher Belknap) Date: Mon, 17 Feb 2020 20:59:44 -0500 Subject: [Greenbuilding] wall construction In-Reply-To: <1F05B0DC-0043-4099-AF6B-D3C3994877A4@fairpoint.net> References: <1F05B0DC-0043-4099-AF6B-D3C3994877A4@fairpoint.net> Message-ID: <5802bdde-cef4-0ed5-9d5a-f86e569f66ba@greenfret.com> Greetings, I would be concerned about the permeability of OSB on the exterior. I propose something more like: Permeable membrane (water barrier) 5.5" Roxul 1/2" Air sealed, vapor barrier sheet board (e.g. Zip) 3.5" Roxul 1/2" Drywall R-33 1" thicker, but plenty of space for electric boxes, etc. No foam, so probably much cheaper. Better drying characteristics. Better insulation (BTW, I get R-24 for your assembly, apples to apples. less if that 6" is actually 5.5) And you aren't trying to tape up 1/2" foam board. Or better yet: Permeable membrane (water barrier) 9.5" Roxul 1/2" Air sealed, vapor barrier sheet board (e.g. Zip) 3.5" Roxul 1/2" Drywall R-47 Getting into Passivhaus territory. I haven't run WUFI simulations on any of these, but I am concerned about your cavity with OSB on one side and foam on the other. Thank you kindly, Topher -- Topher Belknap Green Fret Consulting Kermit didn't know the half of it... http://www.GreenFret.com/ (207) 882-7652 On 2020-02-14 2:25 PM, Clarke Olsen wrote: Topher, Upstate NY, cold winters. If I used the 2x4s as another wall, I would fill it with more Roxul. I was tring to hold down the thickness, figuring thar 1.5? of dead air is as good as 3.5?, and running 2x4s horizontally as furring strips. Running the drywall vertically means no butt joints. Over windows and doors (3?+/-), 2/2? plywood can be substituted for the 1/2? foam to eliminate the header. 1/2? OSB .5 6? roxul 21 1/2? foil faced foam 4 1.5? air 1. 1/2? drywall .5 total R 27 Clarke clarkeolsendesign.com