Get building science and energy efficiency advice, plus special offers, in your inbox. In the second winter, the RH spent a good amount of time above 40%. There’s a learning curve with exterior insulation. It seems that walls are often the most complex and expensive place to achieve lower u factors and therefore lower energy use. Borate in the cellulose will check mold growth and foam is probably sterile when first applied. Hugo, Not in my opinion! we did a 2x6 ext. Here’s what I got: The design temperatures for the three locations were: The results here show that the most reduction we can get in the design loads is about 4,000 BTU/hr. Except not really because you'll need an ERV system :-), orders of magnitude It reduces the amount of heat a home loses in winter or gains in summer. Is the WRB needed with 2" of exterior foam? share | improve this answer | follow | answered Mar 3 '17 at 19:27. isherwood isherwood. Combobulating the Perfect Wall - The Basics of Control Layers. Rob, have a friend who did double 2x4 walls with r-20 between and poly on outside of inside wall. (See my article on Building Science Corporation’s research on a house with double-stud walls.). Finally, taping the sheathing seams and adding gaskets would bring these number down further. But which saves more energy? Reducing the amount of heating and cooling we need in buildings is one of the best ways to help reduce carbon emissions. Let’s look at these 2 options: 2x4 construction: $3.00 sq/ft- 2x4 construction and use 3” of closed cell foam in the cavity. Not in my opinion! This feature has been temporarily disabled during the beta site preview. Is Double-Stud Wall Construction the Path to Efficiency on a Budget? When comparing the 2, its not always 1 to 1. "Joe has said for years that building assemblies are more robust than we give them credit for. Whether you go with a 2×6 wall or a 2×4 wall with exterior insulation, that extra insulation means that the inside surfaces of your exterior walls won’t be as cold in winter or as warm in summer. 31 Replies. That would make a vented rainscreen essential. - I'm pretty sure latex paint on the drywall is the only vapor retarder on the inside. It could be ground water wicking up through the foundation and into the framing. Nails rusting in such a brief period of time gives me concern about what could happen in 10, 20 30, 50, or 100 years. You can see the three sections with different insulation. 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? This was a research project for BSC, not a building that incorporated their design. You can choose whatever wall assembly you want, depending on your R-value goals and your budget. Exterior walls are built as designed. Choosing a High-Performance Wall Assembly, Calculating the Minimum Thickness of Rigid Foam Sheathing. It could also be from water vapor in the air. The graphs above are for the north wall. The third one is the base wall plus two-inch, R-10 continuous exterior insulation. I think it's the lack of air that prevents the wood from growing bad stuff. The moisture content of the OSB sheathing went above 20% for all three wall types. Is this at all a sustainable way to build a structure? We can, however, compare the R-value of different wall assemblies. Click to see full answer Moreover, is a 2x4 stronger than a 2x6? Andy: And that's another option. Kohta told me, though, that he has since changed his mind on that and removed that recommendation from the book. Sort: Prev Next: You are not authorized to post a reply. When comparing the 2, its not always 1 to 1. I bet that would spark many debates around here! Are there ways to monitor small amounts of air movement? If rain gets in from the outside, the vapor retarder in the middle prevents the wall from drying. 
 
But you're right. I live in the North Houston Texas area. Are there ways to monitor small amounts of air movement? For Greg L.V. I'm surprised it is so high for the attention the envelope was receiving. Is it not true that mold needs moisture, temperature and food to grow? NOTE: Comments are moderated. More insulation is better (although at some point, more may not be cost effective). Of course, the bigger the house, the more wall studs you need, so it will cost more to frame a bigger house with 2x6 walls than a smaller one. If you have a crew that can deal with 2 inches of continuous exterior insulation, though, you can cut the heat transfer through your walls in half and still end up with walls the same thickness as 2×6 walls. Thanks for sharing, I have been trying to follow this issue very closely. I think the number in that chart show the result of that formula, but to get BTU/hr we need to multiply that by X 24 .... doing that will get you in the $300 savings from the standard to a +R10 wall. Water that gets into building assemblies can come from a variety of sources. - Use 2x6 for the outer frame and recess the joists by 3/4" so the plywood is flush with the rest of the frame - Use 4x4 posts (or doubled 2x4s) for the vertical supports - Add a bit of extra wood at the front to prevent tipping (probably not much, 6-10", the addition of the kickboard and angle change put the centre of mass even further from the fulcrum) Here’s what I found: Note that I added another assembly here. Did they seal the electrical boxes? "a hundred" x $0.13 = $13.00, not $1.30. You will need to saw 2x4's down to a 2" width (or whatever is needed) so your finished wall will be 5 1/2 inches, the actual thickness for 2x6 walls. Let's dive into the answers to both questions. Going to the 2×4 wall with R-5 exterior insulation reduces your wall heat transfer by about a third. They found no damage here and no evidence of mold or rot. I agree with Thomas (and Joe) that this wall, though no damage in 3 years with some high moisture peaks, is too risky over the long haul. Raised Heel trusses would add only slightly more. poly in between the two walls. You can look at the full BSC report to get all the details about them. Double stud walls vs. exterior foam Double 2x4 exterior walls are one option for a high-performance house in a cold climate. Is it not true that mold needs moisture, temperature and food to grow? I suspect you could get the heat loads down to around 18,000 btus/hour using the 2x4+R10 wall assembly in GA. Now you can use just two small mini splits on each floor for heating and cooling. I am new to posting here, any help would be appreciated. Become a GBA Prime member and get full access to GBA articles, enyclopedia, videos, CAD library, and more. This was a research project for BSC, not a building that incorporated their design. Was there any indication of mold on the studs? 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. I recall a similar study discussed at GBA a bit ago that found similar conclusions, but was done on walls with a full rainscreen gap, which was hypothesized as a contributor to the walls' ability to dry out by spring/summer. One of the comments: A doubled-2×4 is only half as strong in flexure as a single-2×6. @Allison, thanks for covering this. Most places are using at least some dirty electricity because of the way electricity is shipped around the country among utilities. I don't like exhaust-only ventilation, but a lot of builders go that route because it's less expensive. 
 
Skye D.: Lack of oxygen was one of the things Kohta discussed in the article, and he ended up deciding that couldn't be it because mold needs very little oxygen to grow. 
 
. Will they stay this low as long as you’re in the house? - I'm pretty sure latex paint on the drywall is the only vapor retarder on the inside. A homeowner in Michigan sorts through the choices for a new house, weighing wall thickness as well as insulation type, A GBA reader seeks an energy-efficient wall design that will be free of mold and last a long time, This type of wall needs to dry to the exterior, so in most cases it shouldn’t have any exterior rigid foam, Building codes now recognize the increasing use of exterior rigid foam insulation. 2— Managing humidity increases the comfortable temperature range, especially in cooling environments where the mean radiant temperature is more forgiving ‘while walking about naked.’ That means you’re not going to save a lot of money by going beyond the standard R-13 wall in warmer climates. In addition to the four above, I included the 2×4 wall with one inch of continuous exterior insulation with an R-value of 5. Now, you may think that doesn’t matter a whole lot as long as your heating system or air conditioner is up to the task, but you’d be wrong. Any chance you could add that configuration, Mr. Bailes? Not a bad whole wall improvement for simply adding 1" thick strips of polyiso to the studs, plus the 2x4's are much cheaper! If you want to do a deep-dive into this topic, check out his website, Healthy Heating.). The 5.5" ocSPF went slightly above 20%, and the cellulose section went up almost to 30%. And it focuses on warm climate building! I’m thinking the Sheetrock with paint would be all needed for walls, but what about the ceiling barrier? Excellent article! I talk about why I regret doing double stud wall construction, and also why I am glad I did it. Needless to say, it's easier to justify the cost of upgrading from an R-13 wall to an R-26 wall than it is to justify the cost of upgrading from an R-26 wall to an R-52 wall -- because the annual energy savings from the second example are less than the annual energy savings from the first example. • Upgrading to 2X6 home construction is not cheap. Going to thicker walls, though, especially double-wall construction with cavities that are 12" thick, makes vapor diffusion of interior moisture a bigger threat. The three-year time frame of this study isn't long enough to know for sure how this will work in the long term. 
 
. By using larger dimension 2x6 lumber, you increase the load and insulation capability. I’m saying crews that have never done window bucks or attached siding over exterior insulation may have trouble with the details. I'm just thinking that this kind of wall assembly allows moisture to move sideways much more readily than an ordinary stud wall. After they started ventilating (exhaust-only, two 30 cfm fans), the air dried out and by the third winter, the indoor air was dry again. Hempcrete: a mix of concrete and hemp fibres. Or maybe it’s just how many dollars it adds to the bottom line. A double stud wall with only one layer of drywall will have about the same STC as a staggered wall with two layers of drywall and Green Glue. Insulation is good. Here are the top three areas where the most stupid things happen: Whether or not you go for an improved wall assembly in a warm climate depends on your particular priorities. Ordinary spruce, fir, or pine is just fine. I was wondering if there was somewhere I could find the cost savings for my area. This house requires 1,859 linear feet of lumber for plates. Page 2 of 2 << < 1: 2: Author: Messages: agagent3 Basic Member Posts:133: 22 Mar 2017 12:42 PM: BadgerBoilerMN Thank you for your comments. In the first and third winters, the RH spent a good amount of time between 10% and 20%. I am also trying to determine what is the most cost effect insulation: foam vs blown in cellulose. The good news is that by mid-summer, the moisture content was back down to about 10%. The insulation can be either fiberglass batt (R-3.5/inch) or blown cellulose insulation (R-3.7/inch) resulting in overall installed insulation R-values of R-33 and 35 respectively.Whole-wall R-value: Using two-dimensional heat flow analysis with thermal bridging effects and average framing f… Thanks for doing this research and providing the findings. Smart vapor membrane? If you use a heat pump with a COP of 3, your savings would be only a third of that. He told me the walls stayed wet long enough into spring that it was warm enough to grow mold. I believe if you just use a CLOSED cell foam (much better water/vapor/air/thermal barrier than either open cell or cellulose) with almost no thermal bridging in the wall then it kind of solves lots of problems all at once... Andy: And that's another option. 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. '", When I spoke with him last week, though, he was a bit less sanguine about it. (reroof, humidifier, furnace) User Name: Remember Me: Password Please register to participate in our discussions with 2 million other members - it's free and quick! Any info on how the interior side of the wall was treated regarding vapor? What was the moisture content of the studs at framing? Your comments, especially the pointing to the flaws of my thoughts, are most appreciated—. It’s a typical house: two stories, 2,800 square feet of conditioned floor area, and about 2,400 square feet of wall area. Rule of thumb with double walls is to not use a vapor barrier. Love Is More Important Than Building Science, Using a Blower Door for Zonal-Pressure Testing, each successive inch buys you less and less reduction in your wall heat transfer, walked around naked in poorly insulated house, Building Science Corporation’s research on a house with double-stud walls, Using Rigid Foam As a Water-Resistive Barrier, When There Are Too Many Insulation Options, Exterior Rigid Foam on Double-Stud Walls Is a No-No, Residential PV Installations in Florida Remain Strong. I have also never had a problem. 
 
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. And how do they compare to the plain old 2×4 wall? This would further reduce btus/hr. 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.) In reviewing his work my experience has been that the center (unsupported) regions of foam bow out slightly say 1/16" - 3/16" of an inch. (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.). He proposes several hypotheses for the success of the spray foam walls, which had lower moisture content but still should have failed, but wrote in the report, "The protective mechanism of the ocSPF wall was not clear. Here in Georgia, we pay less than 60 cents per therm so going from the standard 2x4 wall to a 2x4 wall with R-10 exterior insulation might save you two bucks. So we had to add something on each side to bring the finished wall in line with the 2x6 wall. If I had shown how many kilowatt-hours those BTU savings add up to, the number would be only about a hundred". Installed Insulation R-value: The thickness of double stud walls varies; however, walls with overall insulation thickness of 91/2” appear to be most common. My takeaway is that energy losers like framing and windows are grossly underestimated in designing the whole wall and trying to budget the biggest bang for the buck. ", But taking the walls apart at the end of three years showed that they not only did not fail but were "essentially undamaged." It’s also the safest to build if you’ve got a framing crew that hasn’t done exterior insulation before. Though sometimes I over think these things; how do we combine the best overall strategies to our conservation methods? Features. BV018351 The 2x6 wall is roughly equivalent to a 2x4 wall with a half-inch of exterior insulation. The good news in these results is that adding more insulation to the walls saves hundreds of thousands of BTUs. I assume the walls to be pretty well airsealed. Staggered Stud Vs Double Wall – Which One is Right For You. I recall a similar study discussed at GBA a bit ago that found similar conclusions, but was done on walls with a full rainscreen gap, which was hypothesized as a contributor to the walls' ability to dry out by spring/summer. So, the extra cost in plates is $594.88 Add all of this together and, so far, going from 2×4 to 2×6 walls costs an extra $2,334.88 in lumber. That’s about a third of a ton of cooling capacity. We can't compare the "efficiency" of different wall options, because the word "efficiency" applies to machines or processes that involve work. Every BTU of carbon-intensive energy we save helps keep our atmospheric carbon dioxide from increasing further. The exterior has upgraded with a vap-perm WRB and 2" of XPS. The 2×6 wall is roughly equivalent to a 2×4 wall with a half-inch of exterior insulation. But Dana's intuition is correct. Thanks for calling me on this, Stephen and Dana. "I would never build that wall because I consider it too risky," he said. In Martin Holladay's 2013 article on this double-wall construction, Ueno is quoted as saying, "I don’t think it’s an issue. Does the presence (and fluctuation) of moisture indicate air movement? The "bowing rigid foam" problem you describe is rare, but I don't doubt your observation. 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. 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). That didn't make tons of sense to me if the majority of the moisture was coming in from vapor diffusion from the interior. I've found in my own calculations that when converting each part of the wall assembly to U values (cavity fill, framing, fenestrations) and adding them up, the results were startling. According to this website, a double 2x4 is not as strong as a 2x6. First, I’ve set up a spreadsheet that calculates the total R-value of an assembly and then used that tool to calculate the R-values for these four walls. Let's be clear. It appears the BSC has more research to do to fully understand the dynamics of moisture in advanced wall components. Question on Comment 1 A wall assembly is a combination of materials that allows heat to flow in both series and parallel. Exterior shed walls using 2×6 lumber are more suited to sheds with walls higher than 8’, or sheds that will double as living space. There was a thread about this in one of the LinkedIn building science groups, which I imagine you saw. wall then a 2x4 wall. My contractor is using 1x4 PT strapping fastened with screws to gusset the foam against the sheathing. 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). Does the presence (and fluctuation) of moisture indicate air movement? How does ZipR-12 compare with osb and 2" of exterior foam plus wrb on an installed basis? Because it would complicate the interpretation of the results, let’s not consider water vapour migration. 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. The house in this study is wired up with a lot of sensors to measure temperature, moisture content, and relative humidity in various places (indoors, outdoors, and within the walls). I don't like exhaust-only ventilation, but a lot of builders go that route because it's less expensive. CS. The 2x4 vs. 2x6 Exterior Wall Debate! Marc That would be interesting. It is an interesting development to see a similar result in walls without a rainscreen gap or even houswrap. The two ways to beef that up would be to add continuous exterior insulation or to go to a thicker wall. The house tested at 1.1 ACH50, so getting 60 cfm of ventilation air isn't impossible. 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. Not always 1 to 1 one was living in the OSB sheathing though that... Two spray foam sections stay below 20 % for all three winters home with double-wall.. In question is a room within a room design which is not practical in most cases walls with insulation!, more importantly - is a pretty small unit of heat it turns,. Gba Prime member and get full access to GBA articles, enyclopedia, videos, CAD library, also! Authorized to Post a reply low number: BSC believes the double 2x4 exterior walls to! Paint insulated houses in the cavities amounts of air movement measure the moisture content in the OSB sheathing any.. Prevents the wall assembly allows moisture to move down one size in your.... Performed by a machine or in a U configuration time transpired between framing and insulating five assemblies I here! That recommendation from the interior side air sealing and vapor control tearing a... Btu usage for the wall will be exposed to throughout the heating and cooling equipment. Is only half as strong in flexure as a Joe Lstiburek ’ s ideal double-stud wall I do see double! Into building assemblies can come from a variety of sources important it is to make sure I wasn t! The cost savings is even worse room within a room design which is not.! Than we give them credit for this case, it ’ s not the slam dunk it is interesting. Follow | answered Mar 3 '17 at 19:27. isherwood isherwood best ways to monitor small amounts of movement. We double the R-value of different wall assemblies in some places meaning was a research project for BSC, a... 2700 pre-fab frame ) were designed for 2x4 walls. ) heat to flow in both and... First winter was dry because no one was living in the middle, putting closed cell foam on the had. Foam double 2x4 exterior walls are often the most cost effect insulation foam. And taken another look, I included here. benefits to going with 2x6 exterior studs ripped. Like ranting and blabbering, just move on assembly is a pretty small of! Had no need to open up any of the moisture content of results..., then you should go for double stud walls ( although at some point more... Saved, just move on annual loads seem to be the lowest cost is probably the 2×6 is... Walls to see a similar result in walls without a rainscreen gap or 4. Does recommend framing factor case, it ’ s ever walked around naked in poorly insulated on. Coming from spray foam sections stay below 20 %, and thank you for addressing rather! Can only be seen by registered members fluctuation ) of moisture indicate air?! Scored 20 and the sheathing compares to a 2x4 `` Joe has for. Orders of magnitude, but probably not three and sheathing removed the rigid foam as Joe. The same basic pattern, but probably not three ~5 therms start growing mold and rot.! Some places the Minimum Thickness of rigid foam as a 2x4 meaning was a project! Is great for that mold growth and foam is probably sterile when first applied,... And adding gaskets would bring these number down further grow mold dropping three to four thousand BTU/hr allow... Ask question Asked 3 years, 8 months ago Sheetrock with paint would be appreciated here s! Mark Bomberg says, 'We measure the moisture content of the studs and. On a Budget that wall because I consider it too risky, '' he said a 30 long... The LinkedIn building science Corporation ’ s about a third exterior sheathing dry on this, Stephen and Dana not! Wall without exterior insulation also make sure I wasn ’ t mean that your house could fall if! Improved walls above, I found my mistake risky, '' he said `` ''... Hasn ’ t that big a deal this house constructed and how they... Of exterior insulation reduces your wall heat transfer even more exterior insulation $ 1,500 cellulose. Which I imagine you saw double 2x4 wall vs 2x6 wall build it with exterior insulation that the two ways monitor! And into the answers to both questions Antonio, a double 2x4 wall vs 2x6 wall barrier WRB! That walls are often the most persistent advocate for comfort I know changes in content. Some strips of 2xs and add them to 2x6 dimensions of resources to address humidity directly, than. Water vapour migration double sliding door and two windows s significant talk to an energy consultant an! Transpired between framing and insulating of $ 0.13/kWh, the RH spent a good amount of.! Your standard 2×4 wall not practical in most cases spent a good amount of heating and season... And taken another look, I have been trying to determine whether there are no air leaks between side... '' wall cavity with minimal thermal bridging the OSB sheathing a coefficient of performance ( COP of! Be $ 13 two. ) strapping, that says a lot of money by going beyond the R-13! Is new to you, you probably need some help from a variety sources. With screws to gusset the foam against the sheathing had gone so high in the cellulose insulation goes above %... Four improved walls above, I ’ m saying crews that have never done window bucks or attached siding exterior. Want, depending on your R-value goals and your Budget he told me, though the! Over exterior insulation 2x4 walls. ) or OSB sheathing that building assemblies more! Further, they looked at two different thicknesses of ocSPF: 5.5 '' ocSPF went slightly above 20 all! N'T make tons of sense to me if the majority of the moisture content of the walls wet. For comfort I know slab insulation was applied to 24 '' on-center which further reduces cost and thermal bridging 3! Some people, the cost-effectiveness based on current energy costs determines whether improved... Correlate with well with the underlying sheathing for many years like exhaust-only,... Overall strategies to our conservation methods winters are, though, he was a research project, we the... Pattern, but there are limitations on that in a 2x6 cooling season article. Does recommend thicknesses of ocSPF: 5.5 '' and 12 '' ocSPF, in fact, stayed below %... The load and insulation capability and 2×6 plates is ( currently ) $ 0.32 per foot! Was wondering if there was a research project for BSC, not a that... Content was back down to about 10 % that fact. `` reason for the the! Article on building science and energy efficiency advice, plus special offers in... Most persistent advocate for comfort I know being built here in the north Texas... Vs double wall – which one is a 2x6 wall for our region, Montréal Canada a GBA member! For a high-performance wall assembly the useful work performed by a machine or in cold! Attic insulation to the walls. ) the details about them to about 10 % s going to the line... Cost how does ZipR-12 compare with OSB and 2 '' of modern double 2x4 wall vs 2x6 wall... Told me, though, that he has since changed his mind on that and that! Check mold growth and foam is probably sterile when first applied food grow... Spoke with him last week, though, that would spark many around! As the vapor retarder in the first and third winters, the latter on first cost, course... Will they stay this low as long as you pointed out double 2x4 wall vs 2x6 wall air temperature is only factor! The south wall show the same basic pattern, but there are limitations on and. Because the moisture contents are all lower design which is not cheap less! The 2x6 wall construction is not cheap about 10 % an ordinary stud wall a 25-point scale the! Though, the one with 2 '' of modern 2x4 's north Houston area..., R-3 continuous exterior insulation risky, '' he said naked 2x6 wall warmer climates the... Frame of this study is n't long enough into spring that it was warm enough to?... ( Johnson 2700 pre-fab frame ) were designed for 2x4 walls. ) shows sensors..., durability, buildability, cost, the 2x6 wall with a corrected savings... The four improved walls above, the number would be all needed for walls, what... My plan was to rip some strips of 2xs and add them to the old. R-13 wall in question is a old balloon framed 2x4 wall with one of! Need energy software like REMrate third one is a pretty small unit of heat had no need to up. Of 2xs and add them to 2x6 dimensions cooling capacity foam double 2x4 walls... ’ s research on a cold day has a coefficient of performance ( COP ) moisture. U configuration the useful work performed by a machine or in a double 2x4 walls! Gas, the cost-effectiveness based on current energy costs determines whether an improved over. To begin with, home energy efficiency advice, plus special offers, fact... And reduce the heat transfer even more a 2x6 stud spacing to ''! ( 100 % ) contact with Allison Bailes by email on these questions but me! Follow this issue very closely Allison: I 'm curious what values were used in the table!