Tstuds: insulated studs
jackofalltrades777
| Posted in Energy Efficiency and Durability on
Interesting new product. Claim is R-20 and 4x stronger than a 2×6 stud.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
https://www.greenbuildingadvisor.com/question/anyone-seen-or-used-tstuds-thermally-broken-studs-yet
How does the math work on the R-20 value?
Compared to other options with equivalent total wall R value, do they even come close to making economic sense?
R20 in a 2x4 space means R20 in about 3.5”. 3.5” of just polyiso would be about R22, so I question the claim of R20 in the same physical space as a 2x4 while still maintaining the structural abilities of a 2x4.
Bill
The R-20 Tstud is a substitute for a 2x6, not a 2x4. It is 5.5" not 3.5" deep, installed in a wall (as a stud, plate or header). There is an R-30 Tstud that is a substitute for a 2x8 stud. So it is comparable to the insulation in the cavity of a wood stud wall.
Tstuds are a sandwich of two 2x3's (on the flat), with a foam core between the 2x3's, with a wood "dowel" truss structure (inside the foam section) holding the 2x3's in alignment. So Tstuds are 2.5" x 5.5" (or 2.5" x 7.25") in cross-section. The dimension of the Tstud is 2.5" wide, wider than the typical 1.5" stud width. So Tstuds are fatter than regular studs placed in a wall, but the same depth of wall as a typical stud. Since Tstuds are comparable in R-value to the insulation in a stud wall, it doesn't matter from an energy standpoint if they are fatter than regular studs (except batt insulation might be tougher to install in slightly smaller cavity width, 21.5" not 22.5" wide).
Tstuds are more expensive than traditional studs. They claim $1,000 to $1,500 more for a 2,500 SQFT home (although energy efficiency rebates may help reduce the net cost). From my own calculations, it may not be the best place for the most cost-effective energy improvements, except perhaps for Passive House (when major insulation upgrades are necessary and less cost effective by that point).
Their R-value claims seemed a bit of a stretch, but foam can be up to R-7 per inch so the R-value claim seems accurate to me. There would be some thermal bridging through the wood truss members, but 2.5" (or 4.25") of R-7 foam plus 3" of R-1.25 wood yields R-21 for "2x6" Tstuds (or R-33 for "2x8" Tstuds), before the thermal bridging of truss members are taken into account.
For all you fans of adding foam board strips on the inside of a wall to extend the depth of the wall and reduce thermal bridging, this seems the ideal solution. Less labor, faster construction, reasonable cost after energy rebate incentives, and the thermal break occurs in the middle of the wall for somewhat better thermal performance.
I think doing something like this to standard 2x6 or 2x8 stud would work much better:
https://images.adsttc.com/media/images/5cef/319f/284d/d1db/dd00/001f/slideshow/P05_IBA_Timber_Prototype_House_%C2%AEPhoto_Hans_Drexler.jpg?1559179652
No foam needed, no dowels, standard width.
With careful design of the slots (the full length ones they use would weaken it too much) the strength of the stud can be maintained. Toe naling would still be an issue, maybe leave the center section more intact.
For standard construction, you don't need an R21 stud, even an R12 would be a big improvement.
Akos,
Since the stresses on a stud are higher at the top and bottom ends of the stud, it would be possible to carve out some of the wood stud material except at the ends (the last 14-16" or so). That could be filled by blown-in insulation during wall insulation work, or by some attached insulation if using batt insulation. Would reduce weight and increase some insulation value. Doing the structural design, testing and certification to pass inspections would take significant work, though. For builders and designers, seems easier to use typical studs or Tstuds. Unless you want to design, manufacture and market Akostuds!
I checked the R value that they claim, and it matched perfectly except for one facet that I overlooked. I did not account for the wood dowels as they pass through the "web" space. I just treated that volume as foam. So to be accurate, that dowel wood in the foam space would have to be accounted for.
I have some different ideas about specialized double studs, but I am not concerned with bringing the stud volume up the same total R-value as the adjacent wall cavity insulation. Thermal bridging is not just an on or off characteristic as seems to be believed when people talk about eliminating a thermal bridge with a thermal break.
I feel that if there is some degree of loss due to thermal bridging, I can just increase the overall wall insulation thickness to compensate.