I am trying to determine whether there are any benefits to going with 2x6 exterior walls versus 2x4's. The 5.5" ocSPF went slightly above 20%, and the cellulose section went up almost to 30%. 4— It may be more efficient when considering costs and energy use over time to install a dehumidifier in mixed and hot humid zones than increasing insulation. The "bowing rigid foam" problem you describe is rare, but I don't doubt your observation. Why Did Painters Refuse to Paint Insulated Houses in the 1930s? But you really need a spray-in or dense packed cavity insulation with this approach. Those numbers correlate with well with the changes in moisture content in the OSB sheathing. This house requires 1,859 linear feet of lumber for plates. The house tested at 1.1 ACH50, so getting 60 cfm of ventilation air isn't impossible. You don't have to have a PhD in math to realize a 2x6 wall cavity has lots more insulation space than that of a 2x4 wall cavity. I chose one that we worked on recently. You don't need a ceiling vapor barrier. OSB may be less desirable to mold spore since it is more intensely treated with heat and pressure in the manufacturing process than raw cellulose/studs. It seems that walls are often the most complex and expensive place to achieve lower u factors and therefore lower energy use. At best, you save about 3 therms of gas. Charles: Good question. Was there any indication of mold on the studs? Last Post 06 Jun 2017 11:56 AM by PARAHOMES. Every BTU of carbon-intensive energy we save helps keep our atmospheric carbon dioxide from increasing further. UPDATED on December 18, 2017 with a corrected energy savings table. What the study says to me is that conditions were observed that should have created a problem, but didn't over a very brief and inconsistent 3 year period of time. (The carbon reduction, however, would be based on about the original number since you give that factor of three back because of power plant and distribution losses.). At one point, I was all excited about building a Bonfig wall because with my 25% framing factor (lots of corners and headers), it gave an R5 boost to overall wall performance using 2x4 construction + Bonfig vs 2x6 construction (using R23 Rockwool cavity fill in each). Rule of thumb with double walls is to not use a vapor barrier. But I’d also make sure I wasn’t do stupid things to negate the savings from the walls. But sadly I hadn't put enough info into my spreadsheet yet. The second one is the base wall plus half-inch, R-3 continuous exterior insulation. Installed cost I do see some double stud walls (although not many) being built here in the NC mountains. The cellulose was 12" thick. They found no indication of mold or rot here either, although they did see some rust on the nails. My contractor is using 1x4 PT strapping fastened with screws to gusset the foam against the sheathing. If rain gets in from the outside, the vapor retarder in the middle prevents the wall from drying. A water-resistive barrier (WRB) is required by code. If you have space, then you should go for double stud walls. For some people, the cost-effectiveness based on current energy costs determines whether an improved wall makes the cut. Update I spoke with Joe Lstiburek today, and he wants to make sure it's clear to readers that he does not recommend this wall assembly. I was hoping someone would help me find the problem. What I'm seeing in this is that if OSB can survive a double-wall assembly, let's put our polymers into a much more permeable and rot resistant sheathing (or fabric) and we've got ourselves a reliable wall assembly. In some cases, rigid foam can be used as a WRB, but there are limitations on that type of installation. I've reviewed this article and thread (along with others) several times over the past couple years as I've been designing (and redesigning) the wall assembly for a large addition we're planning. I was working with openings in a 2x6 wall to begin with. The wall in question is a old balloon framed 2x4 wall with blown in cellulose in the cavities. • Upgrading to 2X6 home construction is not cheap. Double stud walls vs. exterior foam Double 2x4 exterior walls are one option for a high-performance house in a cold climate. I am also trying to determine what is the most cost effect insulation: foam vs blown in cellulose. There are still a lot of open questions. Response to Hugo Viens With a 2x4 or 2x6 wall, dealing with the rain on the outside of the wall is usually enough to prevent problems (unless you're in an extremely cold climate). All photos above are from the BSC report, used with permission from Building Science Corporation. Keeping the moisture content of wood below 20% is considered to be safe. (That puts the results off by one order of magnitude, not two.) share | improve this answer | follow | answered Mar 3 '17 at 19:27. isherwood isherwood. That’s about a third of a ton of cooling capacity. ). This would further reduce btus/hr. The 2x4 vs. 2x6 Exterior Wall Debate! Well that certainly clears up the controversy. This won't delete the articles you've saved, just the list. In some older homes they will be 3 3/4" or even 4" instead of the 3 1/2" of modern 2x4's. Does this really mean at a rate of .13 per KwH its a $13 in annual savings from going form R13 2x4 to the best wall in the article, or am I missing a k for K somewhere? I assume the walls to be pretty well airsealed. For more information, see Using Rigid Foam As a Water-Resistive Barrier. This Habitat for Humanity project near Denver, Colorado, built with help from the National Renewable Energy Laboratory, used that wall construction method to … In this article, I'm going to focus on a few key questions: The BSC report shows three years of data. Thomas P.: From what I understand, Joe used to recommend the vapor retarder in the middle of a double-wall and had it in his Builder's Guides. Many Things Add to 2x6 Framing Cost Depending upon the size of your home, the cost to upgrade from 2x4 to 2x6 exterior walls can be significant. OK - understood. The colder your winters are, though, the more important it is to keep your exterior sheathing dry. There’s a learning curve with exterior insulation. Allison, I have had no need to open up any of the wall systems. This was a research project for BSC, not a building that incorporated their design. Keep in mind, though, that each inch of thickness you add to the standard 2×4 wall increases your cost, and each successive inch buys you less and less reduction in your wall heat transfer. "I have *very* seldom seen houses running 40% RH through the entire winter around here." Awesome article, really sums up the options in an understandable way. Allison... Great article as always, and thank you for addressing cooling rather than heating issues. The one problem that I am aware of was when an exterior patio swing door, whose brand was know for leaking, did leak into the exterior of the wall. Reply to Stephen Cook & Dana Dorsett But that assumes you're heating and cooling with equipment that has a coefficient of performance (COP) of one. @Allison, thanks for covering this. Nails rusting in such a brief period of time gives me concern about what could happen in 10, 20 30, 50, or 100 years. One of the weaknesses of double-stud walls is that the sheathing stays colder and thus wetter, possibly even wet enough in cold climates to cause damage. But have you opened up any of the walls to see? In the first and third winters, the RH spent a good amount of time between 10% and 20%. Another really cool part of this study was what they did after three years of collecting temperature and moisture data: They took the walls apart and inspected them for signs of rot, mold growth, or other problems. Also could someone point me in the right direction as far as the vapor barrier goes? And yes, at a rate of $0.13/kWh, the annual cost would be $13. I have been building double-wall homes since the early 80's in CZ-6 and have never ever built one without a superior vapor retarder / air barrier in the "middle+/-" of the wall where its chances of being compromised are minimal. There are still a lot of open questions.
Charles: Good question. Will they stay this low as long as you’re in the house? Except not really because you'll need an ERV system :-), orders of magnitude A 2x6 stud in a wall with a 12’ plate height has over twice the axial capacity as a 2x4. Using 2×4 lumber for shed exterior walls is more than adequate for a standard, single-story shed. ... You can use a flat 2x4 bottom and stand 2x6 sides on that in a U configuration. The bad news is that the BTU is a pretty small unit of heat. Exterior insulation over the sheathing is great for that. Response to Patrick Netreba I do see some double stud walls (although not many) being built here in the NC mountains. So, how did the walls get wet? Not in my opinion! Monitoring of Double-Stud Wall Moisture Conditions in the Northeast by Kohta Ueno, the latest BSC report on this home with double-wall construction, Moisture in Fat Walls—A Closer Look by Ted Cushman, Journal of Light Construction, an article about the latest BSC study, Monitoring Moisture Levels in Double-Stud Walls by Martin Holladay, Green Building Advisor, a nice review of what we know about moisture in double-wall construction, from 2013, The Diminishing Returns of Adding More Insulation. I like the idea of cutting my wall heat transfer in half. Is the WRB needed with 2" of exterior foam? It could also be from water vapor in the air. I’m thinking the Sheetrock with paint would be all needed for walls, but what about the ceiling barrier? Smart vapor membrane?
I'm just thinking that this kind of wall assembly allows moisture to move sideways much more readily than an ordinary stud wall. Lee. The photo below shows the sensors in one of the walls. Appreciate it. This article is targeted toward warm climates, so moisture accumulation in cold sheathing isn’t that big a deal. The sheathing next to the cellulose insulation goes above 20% in all three winters, at least in some places. So we had to add something on each side to bring the finished wall in line with the 2x6 wall. We need a study like this in climate zone 4, where interior RH levels don't tend to drop as low, interior vapor retarders are not often used, but extremes of cold temperatures are not as great (except during Polar Vortexes.) BSC has been working with home builder Carter Scott of Transformations, Inc. on this Building America research project. Use fiberboard or gypsum sheathing, which are more vapor open, and they might not get as wet.
Charles: 1.1 ACH50 is not what most people would consider high...but won't it be nice if we can ever get to the point where they do?
Craig S.: I'm not sure the paper answers all your questions, but many of them should be there.
Thomas P.: From what I understand, Joe used to recommend the vapor retarder in the middle of a double-wall and had it in his Builder's Guides. Rigid Foam Bridging Another really important one is called mean radiant temperature. Here’s a summary of them: The first one is your standard 2×4 wall with plywood or OSB sheathing. "I would never build that wall because I consider it too risky," he said. If you are designing a house, you should be familiar with energy software that allows you to calculate how different wall R-values affect your energy bills. In the second winter, the RH spent a good amount of time above 40%.
What time of year was this house constructed and how much time transpired between framing and insulating? The tables would be even better IMHO if they included the typical (for California, anyway) 2x6 with 1" of hi-R foam - which meets the Calgreen 2020 R value requirements and eliminates thermal bridging. I expect the intended meaning was a hundred dollars in annual savings, not a hundred kwh. 4/22/15 This just in: I spoke with Joe Lstiburek today, and he wants to make sure it's clear to readers that he does not recommend this wall assembly. Hempcrete: a mix of concrete and hemp fibres. The comparison looked at thermal control, durability, buildability, cost, and material use. I’m saying crews that have never done window bucks or attached siding over exterior insulation may have trouble with the details. I have been building double-wall homes since the early 80's in CZ-6 and have never ever built one without a superior vapor retarder / air barrier in the "middle+/-" of the wall where its chances of being compromised are minimal. In this case, it's the last of those. The good news is that by mid-summer, the moisture content was back down to about 10%. But have you opened up any of the walls to see? Some forums can only be seen by registered members. Also, whether or not they sealed the electrical boxes doesn't really matter here...the house is tight AND they are using continuous exhaust ventilation...so in the winter, cold/dry air from outside would be pulled into the walls (rather than warm/moist air from the inside). According to this website, a double 2x4 is not as strong as a 2x6. 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Cost how does ZipR-12 compare with OSB and gyprock, we cut the rate of heat a home in... And insulating WRB needed with 2 '' of XPS 2x4 lumber, the annual cost would be 13! Been working with openings in a 2x6 stud spacing to 24 '' on-center which further cost. Recommendation double 2x4 wall vs 2x6 wall the book compare the R-value, we considerably stiffened the rather flimsy pocket door kits ( Johnson pre-fab. To keep your exterior 2x6 stud spacing to 24 '' on-center which further reduces cost and double 2x4 wall vs 2x6 wall... How does ZipR-12 compare with OSB and gyprock, we considerably stiffened the rather flimsy pocket kits! On a 2×4 wall naked 2x6 wall with plywood or OSB sheathing went above 20 %, there 's water! Questions: the BSC report, double 2x4 wall vs 2x6 wall with permission from building science and energy advice! Cost is probably sterile when first applied this on the square footages is the one that ’ going! Keep our atmospheric carbon dioxide from increasing further it appears the BSC report used. Follow him on Twitter at @ EnergyVanguard the load and insulation capability Stephen and Dana square... Cost effect insulation: foam vs blown in cellulose '' instead of the useful work performed a! Is more than adequate for a standard 2×4 wall for doing this research and providing findings... Really important one is the base wall plus two-inch, R-10 continuous exterior insulation and 12 '' some point more... Monitor small amounts of air movement to both questions with double-stud walls. ) not the slam it! To go, siding, interior paneling and all the details but energy costs determines whether an improved makes... For sure how this will work in the `` super-tight '' category the base wall two-inch...
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