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rStud insulated 2×6 studs

Milan Jurich | Posted in Green Products and Materials on

Although not as effective in eliminating bridging, the rStud 2×6 looks interesting in lieu of external rigid foam over OSB sheathing based on local area construction practices.  Have any technical reports been published as of yet that anyone is aware of regarding results with the product?  Curious as to its strength & performance when compared to traditional 2×6’s.  Interesting option to consider with Zip exterior sheathing and good air sealing followed by a blown in insulation such as Manville Spider. Not sure of its cost effectiveness as compared to 2×6 construction with 2″ of exterior XPS in zone 5. Haven’t seen much other than some press news a while back. Thanks.

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  1. GBA Editor
    Martin Holladay | | #1

    Milan,
    It all comes down to cost, doesn't it? A thermally broken stud makes sense -- but only if you are building a thin wall with a single row of studs.

    If you are building a double-stud wall (or if you are using exterior rigid foam), you don't need to invest in expensive thermally broken studs, because your wall assembly already addresses thermal bridging.

    So that raises the question: who builds with plain old 2x4s or 2x6s anymore? Perhaps builders in Florida. But the problem with a 2x4 or 2x6 wall is you can't get much R-value in them. So if you want your wall R-value to be more than R-20, you need a different approach.

  2. Milan Jurich | | #2

    Martin,
    In this on-line community, there appears to be few to none building new single wall homes with 2x4 or 2x6 studs ... fundamentally double wall or exterior rigid foam to address the thermal break issues which I'm seeing make the most sense. Yet, the thought that only Florida is building this way is surprising, as the vast majority of new high end custom built homes in Central OH (zone 5) are built just that way ... 2x4 or 2x6 with blown cellulose or fiberglass insulation at best covered in OSB, tyvek or a rolled on liquid barrier exterior to the sheathing and clad directly with fiber cement siding with no furriing space. This means essentially that the minimum is being done to achieve a weaker energy code ... other than an individual's desire to improve upon that code because it makes more sense. When one speaks with the framers of these custom homes or the builders in the field, there is little to no familiarity with a double stud wall or the application of exterior rigid foam. In fact, I only know of one that's adding 2" of EPS subslab insulation, 2" of EPS exterior to OSB for walls, and raised heel trusses to target R60 in the attic space. If one wishes to establish a reasonable comparative cost to build a home with double walls or exterior rigid foam ... then even with clearly defined specs and wall detailing, there's still a lack of practical application of that level of detailing in the trades ... in central OH and most likely in Florida. There needs to be more builders in our area with the knowledge and experience of a M. Chandler , yourself and others on the GBA staff. Thanks for listening to a frustration.

  3. GBA Editor
    Martin Holladay | | #3

    Milan,
    You make an excellent point, and my reference to Florida was glib (and inaccurate).

    However, if those builders in Ohio want to build a better wall, the question still remains: for the limited improvement in wall R-value, do rStuds make sense? Or is it possible that other methods of improving a wall's R-value are cheaper?

  4. Milan Jurich | | #4

    Martin,
    Agree with you. At this point, it's really a "if they want to build a better wall", as the code simply doesn't require it. I'm certain that will change for the better in the future, but it's anybody's guess in terms of timing. With the current state of non-high performance walls being constructed here, which method do you think would be more easily understood and applied by the trades with little to no current practical experience? Exterior rigid foam as described in your various articles?

  5. GBA Editor
    Martin Holladay | | #5

    Milan,
    I guess most framers say they find it easier to learn and implement double-stud walls than foam-sheathed walls. The details are more intuitive -- it's just framing.

  6. Milan Jurich | | #6

    Thanks Martin ... a couple of follow-ups, Is there a good link to the "best cost competitive way to construct a double framed wall"? Similar to the articles you've prepared outlining the details of rigid foam application? A definitive guide of sorts from Fine Homebuilding or GBA? Sounds like it might be the best solution in our area at present. Other follow-up's ... Is sheathing a double stud wall with rigid foam on the exterior necessary in a zone 5 if dense packed cellulose is the insulating agent? If not, then just applying a wrinkled wrap to aid water drainage followed by fiber cement cladding or Zip sheathing/standard wrap with a vented zone (furring for example as opposed to a mesh or woven product) to achieve better drying potential and provide for a smooth, non wavy surface with the cladding?

  7. GBA Editor
    Martin Holladay | | #7
  8. Aj Builder, Upstate NY Zone 6a | | #8

    New construction costs way more than the price of a foreclosure purchase of which there are millions of such now. So... to price a new home at a sellable price... today... is insanity. For the masses... it is always about price and bling. Wait... even for the million dollar green LEED projects... same thing... price and bling... just that the bling also entails lots of "green" bling.

    Superinsulated homes... there are a few of us that love them... but about as common as running into a red fox.

  9. Gordon Taylor | | #9

    Same in Seattle. Who builds with plain old stud walls anymore? Only just about everybody. I'm not a builder; I'm a bus driver, and I get around a lot. In the last five years, thanks to this site among others, I've become sensitized to high-performance building, and I notice it when I see it. Just up the street from me a Swedish-auto repair shop went up using SIPs. That was exciting to see, but it was the only thing to see. Everything else is stick building at its most boring.

  10. Milan Jurich | | #10

    Martin,
    Thanks for the links ... much appreciated!  Will investigate the double wall details.

    AJ,
    On a side note while talking about who's building with single 2x6 wall construction ... I believe you posted a link in the past to this type of construction by a Minneapolis builder which caught my attention:

    http://www.minnesotagreenhomebuilder.com/docs/Amaris%20Wall%20Section.pdf

    Are there any showstoppers with this that you see that might trip up local framers ... maybe the appropriate pitch between the 2x6's to attach the Dow SIS properly and provide for a furred out nailing surface for cladding such as fiber cement siding as the SIS is not a nailbase?  At first glance, it appears to offer a nice level of performance without sacrificing interior space as a double wall would, with all things being equal from an exterior sizing viewpoint, with the caveat that R-26 is the best you can achieve with closed cell spray foam (CCSF) in a single 2x6 studded wall as shown in the attachment.  Is the strength from SIS coupled with closed cell spray equal to or better than if using OSB and blown cellulose/or fiberglass.  Also, can proper drainage planes (window detailing, etc.) be set-up without an additional exterior housewrap ... just relying on a tape such as Weathermate?  Not looking to change the subject greatly, but it sort of went along with the comment re: who's building high performance with a single wall of 2x6 studs with r-values greater than 20.

  11. GBA Editor
    Martin Holladay | | #11

    Milan,
    I don't see any downsides to the wall assembly you linked to -- except that it uses a lot of spray foam, a product that some green builders are trying to avoid because of the global warming potential of the blowing agents.

  12. TJ Elder | | #12

    Not meaning to pile onto Martin over this comment, but "who builds with plain old 2x4s or 2x6s anymore?" It's pretty unusual even among LEED projects in this region (pacific NW) to have more insulation than you can stuff between 2x6 framing. Code minimum for walls is currently R-21, which you can meet with higher density fiberglass batts in a 2x6 frame. People think high-performance walls means spray foam instead of batts, or in some cases foam sheathing (i.e. 1/2" foam). I'm always slightly amazed at how many LEED points people can rack up without taking the wild and crazy step of increasing R-values to beyond code minimum.

  13. GBA Editor
    Martin Holladay | | #13

    T.J.,
    Yeah, I'm not going to live this one down. Typing too fast today -- before my brain is engaged.

  14. John Zito | | #14

    I've been stalking a high end (2 m+) new construction in my area (zone 5) : 2 x 6 walls with spray (not sure if cc or oc) and batt fill (no exterior foam), same in the basement and not sure about the attic (keep in mind, I'm stalking in drive by mode). Yesterday as I crept by, a well driller and HVAC contractor were walking around the property, so I'll assume GSHP. Fortunately , it will be, as the sign says, "another LEED certified project".

  15. Jerry Liebler | | #15

    I found a bit of information on these on the WWW. The 2x6 will structurally replace a select structural grade 2x6 when used as a stud. the 12 foot length sells for $10.65 + shipping. Let's assume we are insulating with Roxul and building a 10 foot wall 16" OC so 4 foot of all will need 4 pieces (one for the plates) Conventional wood studs with a 20% framing fraction gives about r16 while the r studs would be r22 so for $42.6 we have added 240 r sq ft. but normal 2x6 cost about $0.40/ft & we;d need 42' or $16.80 so we got 240 r sq ft of insulation for about $ 25.80 or about $0.11/r sq ft Which is above the cost of Roxul bats (about $0.06/rsq ft) but well under the cost of EPS (about $ 0.12/rsqft) and much under polyiso at about $0.14/ r sq ft. So it'll cost more for enough foam to get the same wall r! But, interestingly, if I revisit my assumptions and instead use 24"OC the cost for the added r is right at the Roxul level.
    So if you can add cellulose or Roxul they probably don't make economic sense but if they reduce or better yet eliminate foam they definitely do make sense. Or if you are trying to get a thinner wall they may even make sense in double walls as the 2x6 adds the same r as 1 1/2" of Roxul bats.

  16. Jerry Liebler | | #16

    I found a bit of information on these on the WWW. The 2x6 will structurally replace a select structural grade 2x6 when used as a stud. the 12 foot length sells for $10.65 + shipping. Let's assume we are insulating with Roxul and building a 10 foot wall 16" OC so 4 foot of all will need 4 pieces (one for the plates) Conventional wood studs with a 20% framing fraction gives about r16 while the r studs would be r22 so for $42.6 we have added 240 r sq ft. but normal 2x6 cost about $0.40/ft & we;d need 42' or $16.80 so we got 240 r sq ft of insulation for about $ 25.80 or about $0.11/r sq ft Which is above the cost of Roxul bats (about $0.06/rsq ft) but well under the cost of EPS (about $ 0.12/rsqft) and much under polyiso at about $0.14/ r sq ft. So it'll cost more for enough foam to get the same wall r! But, interestingly, if I revisit my assumptions and instead use 24"OC the cost for the added r is right at the Roxul level.
    So if you can add cellulose or Roxul they probably don't make economic sense but if they reduce or better yet eliminate foam they definitely do make sense. Or if you are trying to get a thinner wall they may even make sense in double walls as the 2x6 adds the same r as 1 1/2" of Roxul bats.

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