Thanks for doing this research and providing the findings. Scott builds superinsulated homes in Massachusetts (climate zone 5A) using double-wall construction. The double wall has a drawback of taking too much space which is an issue. Do You Manage Salespeople by Results or... SRS Distribution Acquires JB Wholesale... Review: ‘Nail Your Numbers: A Path to Skilled Construction Estimating and Bidding', 2021 Gold Nugget Awards Call for Entries Is Now Open, Couple Builds Stunning Miniature Home During Quarantine, Samsung Offers Flexible Style and Operation Settings in Its 4-Door Bespoke Refrigerator, NAHB Identifies Top Trends and Design Features for 2021, Kohler Co.’s New Tone Collection Offers Unique Dual Finish Aesthetics, A Deck Builder's Guide to 'Google My Business', JLC Rolls Out Deck and Railing Skills Workbook, Why Good Reviews are Key to a Contractor’s Success, Webinar: What You Need to Know About Decking. Metal stud walls perform better than wood stud walls. With a basement, the double-stud wall sits on the floor framing, so both walls usually can be framed with 2x4s. Thanks for sharing, I have been trying to follow this issue very closely. Installed Insulation R-value: The thickness of double stud walls varies; however, walls with overall insulation thickness of 9 1 / 2 ” appear to be most common. Most homes, he said, run at about 20-30% RH through the winter, and he considers 40-50% RH to be "crazy-dangerous levels in a New England/Zone 5 type of climate.". First, damp spray cellulose can take too long to dry in a thick wall. spacing, for small sheds and garages with a building widths less than 16 feet. Were they relying on the latex paint as a vapor retarder? double 2x4 wall vs 2x6 wall. "Joe has said for years that building assemblies are more robust than we give them credit for. I'm just thinking that this kind of wall assembly allows moisture to move sideways much more readily than an ordinary stud wall. On a 25-point scale, the 2x6 wall scored 20 and the double 2x4 only 15. 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. Most builders address this by adding plywood gussets. 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? But have you opened up any of the walls to see? Staggered or double stud walls are higher rated than single stud walls. Charles: Good question. Jul 27, 2020 - If you don't like ranting and blabbering, just move on. There are still a lot of open questions. 
 
Charles: Good question. And it takes up so much square footage. BSC principal Joseph Lstiburek is right that a 2x6 wall with 2 inches of foam on the outside will have a lower condensation potential, but foam isn't always acceptable. The graph below shows the interior relative humidity (RH) in the basement and in the north and south rooms where the test walls were located. Because the space between the inner and outer walls creates a thermal break that reduces heat loss through the framing members, the actual R-value will be closer to the nominal than in a standard 2x4 wall. 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. The Framing The wall consists of an inner load-bearing wall and an outer exterior finishing wall. That didn't make tons of sense to me if the majority of the moisture was coming in from vapor diffusion from the interior. In the report's conclusion, he wrote, "Based on the monitored data, calculations, and analysis, all three walls should have been at high risk of failure; the analytic tools used indicate that these walls should have failed. It is an interesting development to see a similar result in walls without a rainscreen gap or even houswrap. But the lowly 2x4 is by no means down for the count. The photo below shows the sensors in one of the walls. members, it can be also achieved through a usage of two sets of wall framing, either via two 2x4 studs, a set of 2x4 and 2x3 studs, or a set of 2x6 and 2x4 studs. 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. When bearing wall heights do not exceed 10 ft. 2 x 4 framing is generally code compliant. Description. The photo below shows thick insulation in the cavities of a home with double-wall construction. It could be rain getting through bad window flashing or a roof leak. I was concidering using them on all the walls except one that will have a larger double, or slide doorway where I'd use 2x4 for added strength. Copyright © 2020 Hanley Wood Media, Inc. All rights reserved. In this article, I'm going to focus on a few key questions: The BSC report shows three years of data. "We like to minimize the use of rigid foam," says company president John Abrams. Going to thicker walls, though, especially double-wall construction with cavities that are 12" thick, makes vapor diffusion of … But complicating factors can quickly erode benefits. Note the deep feel of this window, which is. 2x4 Bracket - rize.alexander-truslit-schule.de ... 2x4 Bracket I have also never had a problem. Did they seal the electrical boxes? As an affiliate, I may collect a share of sales or other compensation from the links on this page. Let Us Put You In Your Element. TABLE 2. Clearly, though, the second winter showed the most potential for moisture problems. Is it not true that mold needs moisture, temperature and food to grow? That makes dense pack cellulose behind netting a better choice here. 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. I don't like exhaust-only ventilation, but a lot of builders go that route because it's less expensive. The studs are laid out on two-foot centers, with the outer wall bearing the entire structural load. Well that certainly clears up the controversy. It reduces the amount of heat a home loses in winter or gains in summer. 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. Dane Lytle. Since modern two-by-fours are not 4 inches, the true depth of the wall cavity is 3 1/2 inches. I do see some double stud walls (although not many) being built here in the NC mountains. When I asked Kohta Ueno, the author of the BSC report, about this, he said low relative humidities are typical in New England. is an easily assembled, premium quality commercial/residential kit for installing a pocket door into a  
 
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). The set of graphs below shows the moisture content (MC) in the three wall sections (12" ocSPF, 12" cellulose, & 5.5" ocSPF) as well as the outdoor temperature. Staggered or double stud walls are higher rated than single stud walls. 46 - 47. Here we bust some of the unfortunate myths and misunderstandings surrounding this type of wall construction. This also reduces waste. Were they relying on the latex paint as a vapor retarder? 2x6 wall construction and 2x4 walls with exterior rigid ... if a double top plate is installed 2X6 WALLS - NUMBER OF STORIES. Keeping the moisture content of wood below 20% is considered to be safe. What time of year was this house constructed and how much time transpired between framing and insulating? plywood bucks that line each window and door opening—and the 2×12 top plate are the only thermal bridges in the wall framing. Metal stud walls perform better than wood stud walls. They work so well that they’ve become the standard in most modern homes built today. 4. Here at Medeek Design we typically only specify 2 x 4 studs @ 16" o.c. The house tested at 1.1 ACH50, so getting 60 cfm of ventilation air isn't impossible. When you do it by making the walls thicker, you also change the ability of an assembly to deal with moisture because the sheathing stays colder in winter, an issue that painters discovered back in the early days of insulating homes when walls stayed wet and paint peeled off. But once you add second-story walls, you need to reduce the spacing or use 2x6s. Dense-packed cellulose insulation - the History In 2005, Metric Homes of Carp, Ontario de… Great builders add 2.5 inches of closed-cell foam to the headers over windows and doors to help cut down on energy bills. In Martin Holladay's 2013 article on this double-wall construction, Ueno is quoted as saying, "I don’t think it’s an issue. BSC has been working with home builder Carter Scott of Transformations, Inc. on this Building America research project. i am not so convinced on this type of construction. R-values for double walls of varying thicknesses. With this system, you build a house out of 2x4's, fibrous insulation, SOLITEX MENTO Plus weather resistive barrier outboard, INTELLO Plus smart vapor retarder inboard, and not much else. You can get there by building thicker walls and putting more insulation in the cavities, or you can put insulation on the outside of the structure, as in the Perfect Wall. 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. Building Science Corporation (BSC) in Westford, Mass., did a comparison between standard 2x4 single-wall construction and two of the most familiar high-performance alternatives: double 2x4 walls with OSB Sheathing, and 2x6 Advanced Framing with extruded polystyrene foam sheathing (XPS). When they looked at the price of materials and labor, Paul and Tim found that an R-40 2×6 wall insulated with closed-cell spray foam in the cavities and 2 in. And it takes up so much square footage. Some builders get as good performance from 2x4s as from competing systems–and for less cost–by doubling up the frame. The moisture content of the OSB sheathing went above 20% for all three wall types. CS. It may be more of a benefit in colder climates than where I live but my experience is that ceiling insulation is much more important than wall insulation in sunny, warm climates. 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.) I'd like to see how the moisture level at the sheathing compares to a wall with interior side air sealing and vapor control. or 24 in. Insulation is rated in two ways, R-value and U-value. But 2x6 framing, which is a little more than 1.5 times wider, is a common upgrade and is required by some local building codes. Insulation is good. We see this on the north side of sealed attics as well. Not in my opinion! Third, keeping labor costs down will require the framers to be more efficient. Wood Wall framing with 2x4 and 2x6 studs: ... Larsen Trusses in a Double-Stud Wall system: The typical design involves a standard code "tried & tested" traditional stick-framed wall with 2x6s and batt insulation in the cavities, covered with sheathing, then I-joists (TGIs) attached to the exterior of the sheathing to allow for seamless insulation with no thermal bridging. To view different wall assemblies, click on each point below that may apply to your project. 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. 
 
. Roofing to withstand high wind and siding for two reasons. Such was the case with South Mountain Co. (SMC), a West Tisbury, Mass., design/build company that strives to reduce its homes' environmental impact. High Performance Walls || CZ 3-5 12 Framing Details for Cladding Systems That Do Not Require Additional Framing for Trim FILLER or CONTINUOUS SHEATHING Make sure the edges of the two plates are flush. on center; be sure that the interior finish materials and the siding are compatible with the stud spacing. Notice that the two spray foam sections stay below 20% moisture content for all but a few months in the second winter. They found no damage here and no evidence of mold or rot. Borate in the cellulose will check mold growth and foam is probably sterile when first applied. No more. I'd like to see how the moisture level at the sheathing compares to a wall with interior side air sealing and vapor control. A big appeal is that 2x4 platform framing is familiar to every carpenter and is easily taught to an unskilled crew. on center. With the amount of windows in houses nowaways, double 2x4 walls seem kind of a waste of time. There are two main types of lumber. It was not addressed for several years and rot was the result, however, I doubt that the lack of a vapor retarder would have helped it to dry to the inside and may well have caused more damage. 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. Charles: As with a vapor retarder in the middle, putting closed cell foam on the sheathing also prevents drying to the inside. Allison: I will challenge Joe's "change of mind". A basic wall frame includes: the soleplate, the top plate, the studs, and in the case of walls that exceed 10 feet in length, fire blocking is required between the studs. 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. Was there any indication of mold on the studs? Read until the end of this post if you would like to know the advantages and disadvantages of each type. When the drywallers leave, the opening is finished. All photos above are from the BSC report, used with permission from Building Science Corporation. Studs can be either 16 in. double (2x4) wall with 240 mm R: SI-6.0 m: 2 °K/W insulation has whole-wall R-value of R: SI-5.3 m: 2 °K/W (Straube and Smegal, 2009). The sheathing next to the cellulose insulation goes above 20% in all three winters, at least in some places. Use fiberboard or gypsum sheathing, which are more vapor open, and they might not get as wet. The gap also muffles sound transmission, a real plus if the home is sited on a busy road. Is this at all a sustainable way to build a structure? The photos below show the disassembly. Minimum code requirements for insulation, moisture, and air leakage are based on a typical 2x4 or 2x6 (16” or 24” on center) single stud wall. First of all, double stud walls are relatively affordable. With construction codes demanding higher insulation levels, the market share for this old standby has taken it on the chin from alternatives such as 2x6s with foam sheathing, structural insulated panels, and insulated concrete forms. The 5.5" ocSPF went slightly above 20%, and the cellulose section went up almost to 30%. With half the wood use, a single top plate seems like the smarter (and greener) option. Normally one 2x4 is used to form the soleplate, and in the case of load bearing walls, two 2x4's are stacked to form the top plate. I do see some double stud walls (although not many) being built here in the NC mountains. This was a research project for BSC, not a building that incorporated their design. Doing so can even save time and money on trim work. They found no indication of mold or rot here either, although they did see some rust on the nails. Andy: And that's another option. If the Advanced Framing double stud wall used 2 sill plates, then the USA New Wall will actually use slightly less lumber. The Cost to Build a House: 2x4 versus 2x6 Walls. Walls will be less drafty improving the overall comfort level of the living space. "Splitting the plate lets [a builder] change the depth of the wall on the fly, depending on how much interior space and R-value he needs," Higginbotham says. There is a big difference in compressive strength, resistance to buckling, and lateral deflection between a 9' 2x4 wall and a 9' 2x6 wall. Gary: Yes, they do. The 1500 Series Pocket Door Frame for 48 in. The good news is that by mid-summer, the moisture content was back down to about 10%. gap between them, connected by 5-in.-wide, 1⁄2-in.-thick plywood gussets fastened 32 in. Only the builders will know the reason as to why the house manages energy so well. CS. These gussets—1⁄2-in. How to Achieve R-21 in a 2x4 Wall. Insulation for 2x4 Walls In most wall applications, you will use R-13 or R-15 kraft-faced fiberglass insulation rolls for these two-by-four stud walls. Any info on how the interior side of the wall was treated regarding vapor? For instance, SMC's crews install wood sills on all the windows before hanging the drywall, then use drywall returns on the sides and top of the opening. There may be structural issues. The result: Airtight shells that have yet to experience condensation problems. The decision to use the double-stud wall method for the ProHOME came down to a matter of cost. NOTE: Comments are moderated. 1. The typical solution is to angle the sides of window openings 45 degrees into the room. And did the moisture cause problems? For one thing, joining intersecting walls is easy: overlap and nail off. It is an interesting development to see a similar result in walls without a rainscreen gap or even houswrap. By code, 2x3's may be used for this purpose if the wall is no taller than 10 feet and the studs are spaced every 16 inches. If I were building a house for myself here in the mild climate of Georgia and were choosing from the wall assemblies above, I’d go with the 2×4 wall with 2 inches of continuous exterior insulation. Double Walls, Truss Walls, I-joist Walls. 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. Are there ways to monitor small amounts of air movement? Builders considering this system should keep in mind some details. 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. Even Habitat for Humanity chose it for a Wheatridge, Colo., home because of its "volunteer-friendly construction techniques.". 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. 2x4 boards are cheap and easy to work with, but they're usually meant for construction projects. If you are running "exhaust-only" fans for a super tight home - where is the replacement air coming from? Wall Assembly. The general idea behind these walls systems is to built a much thicker wall to allow for much higher insulation values but still using the standard thin wall (2x4… Charles: As with a vapor retarder in the middle, putting closed cell foam on the sheathing also prevents drying to the inside. More insulation is better (although at some point, more may not be cost effective). 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'll write another article about his thoughts and what he does recommend. This is constructed by having a 2×4 stud-wall, then a gap, and then a second stud-wall, either 2×4 or 2×3. The results were surprising because the moisture content of the sheathing had gone so high in the second winter. Excellent article! Staggered Stud Wall Construction . Because 2x6 lumber comprisess more wood, it is more expensive. on center) and sandwiched between top and bottom plates. "I would never build that wall because I consider it too risky," he said. Is r19 good for walls? 2x6 walls are bigger than 2x4 walls. This is logical, and makes sense, but will not be nearly as important as the insulation factor in the walls and windows. 2x4 stud, 5/8" gyp (2 layers total), Batt insulation. In some older homes they will be 3 3/4" or even 4" instead of the 3 1/2" of modern 2x4's. This was a research project for BSC, not a building that incorporated their design. "You can't do that with 2x6s and foam.". 2x4 vs 2x6 Framing Video. The general idea behind these walls systems is to built a much thicker wall to allow for much higher insulation values but still using the standard thin wall (2x4), or smaller lumber. Does the presence (and fluctuation) of moisture indicate air movement? The data from the south wall show the same basic pattern, but the moisture contents are all lower. Single or Double Top Plate—Diminishing Returns?  
 
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.) The advantages of the double stud-wall, beyond the obvious extra insulation, is that there are few, if any, thermal bridges. Thomas P.: If you've been doing it your way for decades and haven't had a problem, that says a lot. Use R-19 or R-21 kraft-faced fiberglass insulation for two-by-six (2x6) walls.This combination ensures that the insulation is neither too loose nor too tightly packed within the walls.Two-by-four (2x4) stud walls with true 4-inch depth.One may also ask, how much insulation do I need for a 2x6 wall? Minimum code requirements for insulation, moisture, and air leakage are based on a typical 2x4 or 2x6 (16” or 24” on center) single stud wall. This is one of the reasons people go for staggered stud walls. The three-year time frame of this study isn't long enough to know for sure how this will work in the long term. 
 
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. Some use them on each stud, some on every other stud. It could also be from water vapor in the air. Modern conventional home building normally makes use of 2x4 lumber (top line above, second from left) in constructing exterior walls. Going to the 2x4 wall with R-5 exterior insulation reduces your wall heat transfer by about a third. They're harder to lift and the headers on exterior walls require more work. ProSales is the authoritative and independent multi-media source of news, information, and expertise for pro-oriented building supply dealers and distributors in the U.S. How to Build Using Double-Wall 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. If rain gets in from the outside, the vapor retarder in the middle prevents the wall from drying. Author. The walls are then filled with insulation. I assume the walls to be pretty well airsealed. Publisher Name. Any info on how the interior side of the wall was treated regarding vapor? 2x4 studs, 5/8" gyp (2 layers total), Batt insulation. In this "Energy Smart Details" article, architect Rachel Wagner describes how to build double-stud walls and how to insulate them most effectively to achieve high R … The comparison looked at thermal control, durability, buildability, cost, and material use. Measure your existing two by fours. It could be ground water wicking up through the foundation and into the framing. Going to the 2x4 wall with R-5 exterior insulation reduces your wall heat transfer by about a third. x 80 in. ", In a Journal of Light Construction article on this study, Ueno told author Ted Cushman that Joe Lstiburek appears to be right. For instance, some builders save time by having the supplier pre-cut all lumber to the exact lengths needed. the home convects like crazy. Kohta told me, though, that he has since changed his mind on that and removed that recommendation from the book. That would make a vented rainscreen essential. What was the moisture content of the studs at framing? or 24 in. As Mark Bomberg says, 'We measure the moisture content of wood during the winter but it rots during the summer. (R-value refers to the insulation’s resistance to heat flow. Elements Design Build L.L.C. This is a solid demonstration of that fact.". One reason for the low number: BSC believes the double 2x4 is at risk for moisture-related durability issues. Check the wall for plumb with a carpenter's level, then nail the bottom plate to the floor. 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. © 2021, Energy Vanguard | 533 West Howard Avenue, Suite E, Decatur, GA 30030, Monitoring of Double-Stud Wall Moisture Conditions in the Northeast, How to Spot Deceptive Heating Efficiency Claims, Combustion Safety 101: Three Types of Problems, How to Make a High-MERV DIY Portable Air Cleaner, How to Make a Good High-MERV Filter Even Better, 10 Consequences of Keeping Your Home Really Cold in Summer.