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Tstuds - Engineered Lumber

Tstuds - Engineered Lumber

Tstuds - Engineered Lumber

I just ran across these and am curious to see if anyone has seen or used them yet?

It is essentially a truss that uses 2x3's as the cords and wood dowels as the webs (5.5" depth). It is sold both bare as well as with closed cell foam insulation installed in the webbing, resulting in a stud with an R20 insulation value. I am curious to hear peoples thoughts.

RE: Tstuds - Engineered Lumber

Just like any of these new-fangled systems, I think they will be a total pain in the butt to design around. Notice how their literature does not give axial or bending capacities - only stresses.

RE: Tstuds - Engineered Lumber

I agree. With the insulation it implies usage as an exterior wall stud. Without testing and documents giving the rated capacities for axial plus wind, I would not use them.

If none are present, then it is a money issue with the company. You do not have a responsibility to the company to use your liability exposure for their gain. Steer clears of this and other similar situations.

Mike McCann, PE, SE (WA, HI)

RE: Tstuds - Engineered Lumber

Are we really losing a ton of heat through the studs? If you use a 6x wall, then the insulation is what's doing all the work. The stud may lose some heat, but come on, how is this really worth the extra cost?

RE: Tstuds - Engineered Lumber

Another "green" gimmick. The heat losses and gains through the walls are a minor percentage of the total. Even in today's tighter residential construction, air movement (leaks) accounts for most of the energy losses, with glass a close or sometimes distant second, and losses through walls a very distant 3rd. With these fancy studs, the reduction in overall R-value for the wall is about 5% of what is already a minor percentage of the energy losses. The savings would be too minuscule to quantify.

Structural insulated panels (SIPs) are a far superior solution that has been around for several decades, and actually decreases labor, offsetting at least some of the increased cost of the materials.

In many climates, insulated concrete forms offer greater energy efficiency than even the SIPs. In addition to the insulation value which is huge, the thermal mass moderates temperatures between day and night, so in dry northern climates, like where I live, there's a good portion of the year where the inside of the house stays comfortable through the 85 degrees of daytime and through the 40 degree overnight temperatures, without much, if any heating or cooling required.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Tstuds - Engineered Lumber

I don't have direct experience with these, but will admit that I can see some benefit to it. Previous comments about the impact of thermal bridging through studs being minor seem to be at odds with my math. On a typical wood-framed wall with 2x6 studs at 16" centres, the effective R value will compute somewhere around 75% of the R-value of the cavity. That reduction is due to thermal bridging through the studs. If one were to account for framing around doors and windows, the additional headers, jack studs, sill plates, etc. would cause the effective R-value to further decrease.

I just plucked open their Canadian evaluation report, and a quick breeze seems to show good design values. Perhaps I am missing something that led to @XR250's complaint? I don't think I'd be running to these at a full sprint, but they do seem neat.

RE: Tstuds - Engineered Lumber

I am not a residential guy, nor wood, my comment on this is only a layman's opinion.

I think the stud has contributed very little to the 25% lose in R-value. In my old house, when interior panel was taken down, I could feel drift came out from the tiny gap between the insulation and the stud, especially around windows and doors. I believe a majority of the lose was due to this leak, rather than the stud, which had remained close to the room temperature. I don't know if the 25% lose is pointing to the newer construction only, or older house is included as well.

RE: Tstuds - Engineered Lumber

I'm not sure how you get to the 25% reduction in R-value, Craig_H. I just used the numbers in the 'ad' linked in the OP - R-value of 6.8 for a 2x6 stud and R19 for the cavity. Assuming that the system being advertised matches the R19 of the remainder of the wall, the overall R-value of the T studs wall is 19. With the studs making up only 9.4% of the wall (1.5"/16"), the standard stud wall has an average R-value of 17.9, a 6% reduction.

As I said before, what I remember from my heating and cooling systems class in college (granted, that was nearly 20 years ago) is that losses through the walls are a minor contributor to the total energy losses in a typical building. So you have a minor reduction to a minor portion of the energy loss.

The owner would likely be much better served by spending the extra $$ on better windows, extra insulation in the attic and/or crawl space, higher efficiency heating and cooling equipment, or higher quality doors.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Tstuds - Engineered Lumber

If you want a continuous envelope like what the T-studs are trying to provide, it seems easier to use the Zip System insulated sheathing. It negatively impacts the shear strength and stiffness of any exterior shear walls, but it I would think that would be easier to overcome than a 60% reduction in the net area of the stud for compression. There's also Structurally Insulated Panels (which I'm guessing is where these guys got the idea). They have the added benefit of the "kit of parts" type construction, too. All in all this seems like a gimmick. May prove its worth eventually, though.

RE: Tstuds - Engineered Lumber

One issue see is how to get out-of-plane point loads from a sill or header into a king stud. Not much meat there to fasten to. Might have to substitute a real 2x6 in those situations.
Kinda like having to use an LVL for point loads in a I-joist floor system. Probably fine for common studs. I agree with PhamEng about using Zip-R instead - even though i hate the squishy part. I have ended up simply spec'ing normal OSB where I need additional shear capacity.

RE: Tstuds - Engineered Lumber

I got my values from the Canadain Wood Council's wall database: Link. For the arbitrary baseline wall of 2x6 studs 16" on centre, generic finishes, the effective R-value is 15.79. The R-value in the centre of the cavity is 21.39. That means that the effective is 73.8% of the cavity value.

As with anything in our world, there are many ways to skin the cat, and these seem to be one newer option to complement the variety of other options (insulated sheathing, exterior insulation & rainscreen assemblies, double-stud walls, etc). I do like the brainstorming of potential sticky points, such as XR250's point about the amount of wood available to take a fastener.

RE: Tstuds - Engineered Lumber

I appreciate everyone's thoughts and comments.
I personally haven't done much of any wood design as my background is in utility and industrial areas. I did grow up working for a small residential construction company so I have built many houses and post-frame buildings - so it keeps me somewhat interested in the topic. I also tend to watch This Old House where it seems they focus on energy efficiency for new construction and the impression I get is that with new energy efficiency trends, the biggest issue left (other than windows) is the thermal bridging provided by the framing. I agree that these certainly won't replace traditional framing anytime soon, but it did peak my interest when considering the "net zero" high efficiency trend some people are after.

RE: Tstuds - Engineered Lumber

I found some good information on insulated walls in this article. It includes some example numbers for typical residential construction.

Quote (Linked article)

The example wall section at right consists of two different cross sections: (A) where there are no 2x4 studs: it's sheetrock-insulation-plywood-siding, and (B) the section where there are studs: it's sheetrock-2x4-insulation-2x4-plywood-siding. In this example, the 2x4s are 24" apart, that means every 24" section of wall consists of 22.5" of assembly A and 1.5" of assembly B.

The R value for section A is: .6 (sheetrock@ R1 per inch) + 33.3 (cellulose@ R3.7 per inch) + .5 (plywood@ R1 per inch) + .5 (siding+air barrier: estimate )=R34.9.

The R value for section B is: .6 (sheetrock@ R1 per inch ) +3.5(2x4)+7.4(cellulose) + 3.5(2x4) + .5 (plywood) + .5 (siding) = R16.

To get the R value of the complete wall, we add up the U values of each section multiplied by what percentage of the overall assembly they represent, and then take the inverse. For our sample wall, section A is 94% (ie 22.5" out of 24"), and so section B is 6%. The basic formula is:

Uwall = Ua*Pa + Ub+Pb + Uc*Pc +

.... where Ux is the U value of a section and Px is the section's percentage of the whole.
For our wall, Uwall = (1/34.9)*.94+(1/16)*.06 = .0307, which is a R value of about 32.5.Standard framing factors are much higher than the sample wall section shown above--the range from 12% to 20%--that is two to three times more than the sample above. While this does reduce the whole wall R-value, the effect isn't terrible:

Doubling the framing to 12% results in: (1/34.9)*.88+(1/16)*.12=R30.6
Increasing the framing to 20% results in : (1/34.9)*.8+(1/16)*.2=R28.2

So, the difference between a theoretical wall with no studs and a wall with 2x4 studs at 24" centers is a reduction in R-value of around 7%. For a typical wall with additional framing for doors, windows, etc., the reduction in R-value is between 12% and 20%.

Due to the difficulties noted in previous posts with using the T studs for window and door framing, I would guess the typical increase in R-value for walls employing the T studs would be 10% or less.

I saw a few sites stating the energy losses through walls, for a house without wall insulation, 35% of the total losses, but that included air leakage, as well as conduction. The percentage for conduction losses only through an insulated wall would obviously be much lower. I saw one source indicating that losses were reduced by about half by insulating the walls (I can find and post it, if anyone disputes that assertion). Taking half of the 35% multiplying by the 10% leaves us with a less than 2% increase in energy efficiency by using the T Studs. I'd say there's undoubtedly more cost-effective ways to accomplish greater energy efficiency.

Edit: Near the end of the article, there is a calculator for heat losses with sample calculations that seems to confirm some of my assumptions.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Tstuds - Engineered Lumber

Rod, forgive me for only breezing that link, but isn't your chosen example a double-stud wall, where there is effectively no thermal bridge? In that article, they are constructing a wall with two 2x4 walls framed a two inches apart, and filled with dense-packed cellulose insulation. This leaves insulation between the inner and outer studs, albeit 7" less than in the remainder of the wall. Indeed, in that scenario, increasing the framing density does not result in the same amount of performance penalty as a standard single-stud assembly. In contrast, when the wall's studs bridge directly from the interior finish to the exterior sheathing, the performance penalty is more severe.

RE: Tstuds - Engineered Lumber

Upon closer reading of the article, you are correct Craig_H. It appears that they used a similar R-value for the wood as other sources (it appears they used an R-value per inch of 1.0), so using their R-values and calculation method [Rwall = 1 / (Pa/Ra+Pb/Rb+Pc/Rc)], the change in R-value for a wall with 2x6 studs vs. a T stud wall (both at 16" O.C.) is 12.6%. That assumes R=1.5 for siding, sheathing, and drywall and R=12.5 for the 2.5" thermal break in the T stud. (R=17.36 for the wall with 2x6 studs; R=19.86 for wall with T studs).

Using the corresponding U values for the wall in the calculator near the bottom of the article, without changing any of the other values, yields a change in energy loss of 3.33%. However, the infiltration value (.2 air changes per hour) is very low for residential construction. From the College of Architecture at the University of Texas at Austin, found this note: *In winter, use 0.5, 0.85, and 1.3 ACH, respectively, for tight, medium, and loose construction. In summer, use 70% of winter values. Using the 0.85 value, the change to T studs reduces overall energy loss by 2.5%.

For the house in the calculator, with 0.85 ACH value and 2x6 stud walls, a change from high-performance double-pane windows (U=0.3) to triple-pane windows (which can achieve U-factors as low as 0.15), would lower energy losses by about 9%.

Rod Smith, P.E., The artist formerly known as HotRod10

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