Anyone seen or used Tstuds (thermally broken studs) yet?
paxsonalaska
| Posted in Green Products and Materials on
Has anyone here looked at Tstuds yet? They’re basically a sandwich of two 2×3 studs filled with foam. The idea is to make a stud assembly with an integrated thermal break that can serve as a direct replacement for standard 2×6 studs. The concept is pretty interesting, since you could reach a reasonably high whole-wall R value without external insulation. I’m building a home in Alaska and external foam insulation is hard to incorporate here because of very high wind and seismic requirements coupled with condensation issues.
Their website is here:
https://www.tstud.com/
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Paxson,
A decade ago there were several companies making thermally broken studs in the US. They all went out of business. It would be interesting to know why. Lack of market acceptance? Price? Approvals? In theory it seems like a good idea to me, but I'd want to know what went wrong, or at least speak to someone who used them before committing.
I'm a bit confused by your reasons not to use exterior foam. Seismic and wind-resistance are independent of the foam, which isn't part of the load-bearing structure of the house.
Thanks for the reply. I was hoping that someone here had some experience with the Tstuds (or a similar product) but maybe there's a reason they didn't catch on.
As to exterior foam: we have had a LOT of building failures in Fairbanks and Juneau because of condensation caused by inadequate exterior foam insulation, and "doing it right" is complicated and expensive. Our code and climate requires an interior vapor barrier, and exterior foam eliminates the possibility of drying outward. The muni might accept a semi-permeable interior vapor barrier like MemBrain, but it's still chancier. Moreover, our climate requires that exterior insulation must comprise at least 2/3 of the wall's insulation value in order to avoid condensation on the sheathing. Products like Zip-R sheathing are instantly out because they don't have enough insulation. I'd probably have to do two layers of two-inch exterior foam. While possible, that would significantly increase cost and complexity, and I don't like the idea of hanging heavy fiber cement siding through four or five inches of foam.
I also tried to price out Rockwool exterior insulation, but the quotes I got were incredibly high and I was told that the 1/3 2/3 rule still applies. Another factor here is that I have a high-efficiency woodstove and access to more or less unlimited firewood in the immediate vicinity, so a lot of my home heating is arguably close to carbon neutral anyway.
The Tstud looks interesting because I could use a robust, proven, highly permeable conventional wall design that still performs better than normal, even if it's not up to PH standards.
Paxson,
It does sound a bit daunting to get exterior foam to work there. Perhaps a more forgiving double-wall assembly might be easier? The reduced thermal performance of conventional studs isn't as important when there is a gap between the walls.
I'm naturally conservative, so I'd prefer not to be a first-adaptor of new products. There is a lot of Coming Soon on their website.
I have Hardie cement fiber siding over 3.75" of exterior polyiso, with a 3/4 furring strip separating them (rainscreen). Siding nailed to furring, furring screwed into studs using (8"?) Headlok screws.
It has been up for nearly 5 years and is rock solid. I don't think you should be intimidated by this type of assembly in general, though seismic considerations I can't speak for (in NY).
Even if you don't want to use the full class III enabling level of exterior foam, I'd use a lesser amount of exterior mineral wool or EPS. The benefits are clear.
Unfortunately I can't use small or moderate amounts of exterior foam because of sheathing condensation issues in my climate (zone 7).
Yes you can. Condensation doesn't cause a moisture accumulation problem with some outward drying and some blocking of interior vapor flow. But feel free to post exactly what you think the problem is.
So you reject the notion that foam needs to be a certain thickness depending on climate zone that Martin suggests?
Malcolm,
The main reason for minimum R-value rules for exterior rigid foam is the fact that exterior rigid foam prevents outward drying. With a continuous layer of exterior mineral wool, there is no reduction in the outward drying potential, so minimum R-value rules don't apply.
Martin,
I think Jon is suggesting the rules for foam don't need to be observed, not that they don't apply to mineral wool.
Martin,
I contacted Rockwool to ask whether the normal cavity/exterior insulation ratios could be ignored when using Rockwool exterior insulation, due to the Rockwool's high permeability. I was told, "Being vapor permeable allows walls to dry quicker but will not prevent wall components from getting wet" and that the normal ratios should still be followed.
This string of replies reads like they came from an automated bot generating random responses. I'm very confused.
> you reject the notion that foam needs to be a certain thickness depending on climate zone
Of course. One can build walls that work well with less (or more) than typically recommended exterior foam - one just needs to have the right interior and exterior permeance. For example, a couple of inches of less than recommended R value EPS will provide some sheathing warming (beneficial) but can still provide a interior/exterior perm ratio that works well (ie, minimal moisture accumulation).
> exterior rigid foam prevents outward drying
Sometimes yes, sometimes no. Unfaced EPS can allow significant outward drying.
Don't agree that less than recommended foam can work on a Zone 7 wall? - see here, Side bar 2, points 5 and 6.
I'm suspicious that some have fallen down a rabbit hole of "all walls with exterior foam need a Class III vapor retarder to work" and therefor "we need a certain foam/other ratio". But the former is incorrect (making both incorrect). Where are such ideas coming from?
What about the caveat in P0int 7 that "the interior surface of the exterior sheathing shall be maintained above the dew point temperature of the interior air." ?
I may be wrong, but aren't the recommendations for the type of interior vapour control all premised on having the sheathing above the dew point? And doesn't that mean an adequately thick layer of foam?
You only need to follow point 7 If you choose <= .1 perm exterior sheathing. Very unlikely for unfaced EPS or mineral wool. With higher exterior perms, "maintained above the dew point" is optional.
> interior vapour control all premised on having the sheathing above the dew point?
Only for the low exterior perm walls . You can build a good wall without any exterior foam at all. Or a little. Or a lot. Just follow the recommendations wrt interior and exterior permeance. And always air seal well.
A serious issue is when people who aren't willing to use the full amount of foam think that their only other choice is no foam. This is unfortunate and results in colder sheathing and typically higher risk. Keep perm values correct and any foam is better than none.
Jon,
That's very interesting. Thanks for the link.
Perhaps a moot point thanks to some interesting information from Jon, but linked below is a some data from a study by Building Science Corporation which showed ripping small channels in the layer of exterior foam against the sheathing greatly increased the drying capability. Perhaps worthy of exploration.
Unfortunately Building Science Corporation didn't post more information on that project on their website and I didn't hear back when I made a request.
https://www.buildingscience.com/documents/special/vancouver-test-hut
https://static.sched.com/hosted_files/phcc2018/bd/Knitting%20the%20Sweater_QuikTherm.pdf
I've had the opportunity to view their product and see a wall mock-up using Tstuds. My understanding is they have code approval in the US and are working on approval in Canada. Fastening schedules are different. There will be a Matt Risinger video that will be filmed in the next couple weeks with more information about the product. Not sure when the video will be released. One of their new products that will be released this fall is called BareNaked Tstud, basically the Tstud without the foam. It is intended to be used in a home that has closed cell spray foam applied in the field rather than the factory. There are a few good pics and videos on their Instagram account.
Thanks! I like the idea of the BareNaked Tstud. It would be great if you could use mineral wool insulation with it, but I'm guessing the closed cell foam might be needed for structural support. I'll check out their Instagram acct.
One problem I see is that they are too wide for standard batt insulation, you can use batts but it would be a lot of trimming. Your options would be limited to blown in/spray products.
For less extreme climate conditions, standard framing with exterior foam is simple enough, I don't think a specialty stud adds enough value.
You can also DIY something close enough by laminating some R6 ZIP strips onto a 2x4. Would be much easier to build with.
If you look at the https://www.tstud.com/testing-reports TER FINAL OF TSTUD under testing reports. Section 9.5 not approved for use in seismic zone D,E,F.
That might solve your problem.
Malcom has a good suggestion of a double stud wall. Goes up quick & can be dried in quick.
Hi Paxson -
I just spent quite a bit of time digging into the T-stud website.
I have some questions:
1. Why is there no engineer cross section of the T-stud? I had to dig into their TERs to determine that the way the T-stud achieves shear is through metal pins connecting the inside and outside wood framing members. How big are the pins? How often are they spaced?
2. How do you nail up the framing members? What happens when you try and toenail either the 2 by 3 or the 2 by 2 framing members?
3. Why is there both an open-cell and closed-cell foam version of the t-stud? Why would you bother to go with the lower R-value per inch open-cell t-stud; just based on cost?
So far, I see a thermal solution that has significant structural questions to answer?
Peter
Those are all great points Peter, thank you. It looks like the seismic data is limited too, which would present an unacceptable risk in my earthquake-prone area (we just had a 7.0 that wrecked a good number of homes this winter).
If they work, get the necessary approvals, and the owner has a good business plan, they will show up in our local lumberyards. That's when I'd look at using them, not when they get shipped from one location. These aren't a specialized piece of equipment, they are structural member. A builder needs to be able to quickly get various lengths, just as they can with dimensional lumber, or more recently TJ's and LVLs.
I believe the open-cell variation is something that was tested at one point, but doesn't match what they're producing now. Also, I believe the current iteration doesn't have metal pins either. They're wooden dowels.
The spacing and placement of the dowels is important. when building, you need to make sure they're aligned so that when you run a pipe or something, you don't break break cut any pins. There are definite quirks about how to build with them. I found this video rather informative: (https://www.youtube.com/watch?v=1ZSxnAqpG04)
I'm interested in them because they allow you to fit more insulation in a thinner wall. The property taxes here in northern NJ are absurd, unfair, and don't make much sense. ($30K for a 2600 sf house??). A reduced building footprint can be helpful in getting a lower assessment. However, finding a builder comfortable working with these things would seem to be challenging.
I'm curious but how would a thinner wall lead to a reduced building footprint that would achieve a lower assessment?
Also, where in NJ are 2600 SF houses have $30k in property taxes? I live in northern NJ. Property taxes are much higher than in other parts of the US but they aren't that high.
It is common in San Diego County that with strawbale construction (2 ft thick walls) that the sqft fees are based on interior sqft or some calculated equal exterior sq footage . It eliminates the thick wall penalty.
That's a crazy amount of property tax!
Here the square footage is based on the framed area, so I guess for tax purposes exterior insulation would be a better bet that a double wall.
But the assessed value of the property is based on a number of different criteria, not just size. The land value, upgrades over standard construction, outbuildings, decks, fixed fees for services for every lot that don't vary, etc. So I don't think a small increase of the wall thickness is significant. Even if it was calculated in, the increase from going say to a 2"x8" wall would be about 1.2%.
Matt Risinger just posted an episode on T-Studs
https://www.youtube.com/watch?v=mxDSulcLpAE
Looks like a truss of wood dowels instead of metal pins.
They're claiming R-20 and several times as strong as the 2x6 it replaces.
T-Studs were $2.50 usd per linear ft, before being shipped. In my situation (Southern New Brunswick, Canada), I also had to contend with the dismal exchange rate. This was for the closed cell version, as the naked was not available yet. Something to do with not being able to control/advertise an r-20 with different spray foam installers.
I too am striving for a vapour permeable wall system. Rockwool Comfortbatt in my area is over $2 sq ft on 2 x 6 construction, and the additional 2.5" of Comfortboard proved difficult to get. My supplier won't even order it in that size, would have to go with a 3" to be out past the exterior of my concrete wall, or change sheating depth). My supplier actually wanted to do 1.5" doubled up, price was about 2 bucks a bag difference.
Lately i'm leaning toward an open-cell spray foam from elasto-chem. The Wrapsulate product in particular, that can be applied to both interior and exterior. R value of 4.2 per inch, looks promising, just trying to get some pricing. If it saves on some labour, I think it'll make a nice air barrier, and teamed up with Smart Membrain, should allow for a relatively simple, permeable wall system. I'm just not totally sure on the best way to use furring strips if using Wrapsulate for my Fraser Pine Siding.
I saw the risinger video on this and it looked pretty good. from my perspective it's pretty much a prepackaged double stud wall assembly. I've never built a double stud wall before so I can imagine I'd opt for this with advanced framing spacing cause it looks like it would be a much easier build. (We'll have to see how to the pricing comes in though).
Thoughts?
On of the main advantages of double-walls is their increased depth, so that you can add more insulation to the majority of the assembly that is composed of cavities not framing. T-Studs may reduce thermal bridging of the framing, but they don't offer a wider wall.
Excellent point Malcom.
I think in the risinger video the TStud guy was saying they're coming out with wider ones. But yes, you'd be limited to their sizes.
Are there moisture/condensation concerns for the exterior part of the T-stud and the sheathing, which will both be outside all the insulation?
Paxson,
Just an aside from your original inquiry. I used an external foam product manufactured in Canada (Edmonton) that provides both thermal break, strength and integrity. I put 4" on a rebuild of my house and its been phenomenal. They have since come out with a 7" foam product. Worth taking a look at https://energywallsystems.com/is3000-is4000-insulation-series/
Paxson,
Just an aside from your original inquiry. I used an external foam product manufactured in Canada (Edmonton) that provides both thermal break, strength and integrity. I put 4" on a rebuild of my house and its been phenomenal. They have since come out with a 7" foam product. Worth taking a look at
https://energywallsystems.com/is3000-is4000-insulation-series/
It's been 3 1/2 years since this thread. I'm just curious if t-stud type products have become any more available and affordable than in 2019.
It seems like it would be ideal paired with dense pack cellulose insulation and would be a very low GWP assembly.