The APA advises against Thermo Ply - are they biased or does the stuff just actually suck? 3

[jacktbg]

So I was out walking a job site a while back and noticed Thermo-ply in lieu of actual WSP - an engineer we were with pointed out that the APA said some thermo ply homes may be under designed for lateral loads by as much as 39 percent. That kind of makes complete sense when you hold the stuff in your hands - you can tear it apart with your bare hands, try doing that with wood sheathing!! I understand that a weird composite material might have the tension strength much stiffer materials have but it's apparent just by playing with it that the compressive strength is absolutely awful, which is what the APA test in their product advisory seemed to indicate too. The stuff in compression might as well be cardboard, and part of a racking load on a set of studs is most certainly compression right?

Given the data out there about it being so dreadfully worse than plywood/osb per length, and the fact that I have not seen any further testing of it to refute the APA's claims (other than claims from like Ox itself claiming the APA is biased and/or they didn't like aspects of the test, even though they didn't bother to reproduce them...) I am left wondering, why does the IRC still allow it to be used equivalently to WSP/CS-WSP!?

This is on top of the fact that we all know the proper nailing patterns are often not being followed anyways and probably slip past inspection. I am SO curious if I'm the only one who finds the whole thing sketchy or if the industry as a whole kind of agrees and recognizes it as an issue. Is the problem that everyone is afraid to put out a negative opinion of Dr. J as an accredited lab? Every other product I have seen and or tested which is accredited by them is the same way - seemingly way overstated claims about products who similar manufacturers make, and those other manufacturers always have more conservative claims.

I would not build my own house with flexible sheathing in a wind-prone region, that's for sure!

Here's the APA studies I referenced alongside Ox's rebuttal:

https://www.texasinspector.com/files/SP-1186_Flexible_Sheathing-unlocked.pdf

https://www.apawood.org/apa-updates...nderperform-in-independent-laboratory-testing

https://www.oxengineeredproducts.co...reasons-to-explore-continuous-insulation-2-2/

 

[ChorasDen]

I'll go on the record and say that I have basically no confidence in these products with regard to equivalent, or even marginal, performance when it comes to designed systems. I am not familiar with the design of thermoply systems, as it is not a product that is common or requested in area that I work, but after quickly glancing through the links that you provided and the DrJ report, I do not see a robust method for code acceptance of this product.

If they (OX Engineered Products) believed the claims and felt the product was robust enough to meet the requirements for usage in shear walls, they would meet the ASTM standards and produce an ICC-ES report, which is the current gold standard for engineered products and alternates to the building code.

To add, I am currently employed by a wood products manufacturer that produces wood sheathing panels compliant with APA voluntary standard PS-2. Statements made here are my own, I have no bone to pick in this fight other than not trusting the claims made by OX Engineered Products.

 

[ChorasDen]

To add, taking a look at their research report 1004-03, it doesn't pass the 30k foot sniff test. They make rather bold claims in tables 3 and 4. Table 3 shows Thermo-Ply green without gypsum wallboard has an ASD design wind capacity of 190plf for 24" o.c. studs (what is the stud Specific Gravity value?).

Table 4 indicates seismic performance, and shows Thermo-Ply green with a seismic capacity of 230plf. Why is the seismic performance 21% higher than wind performance, that's counter-intuitive to how wood structural panels behave. On Table 4, they indicate 1/2" gypsum as part of the assembly, but also indicate an R factor of 6.5, which does not apply to gypsum wallboard shear walls (gypsum shear wall requires an R of 2 per ASCE 7-16 Table 12.2-1, which will dramatically increase design lateral loads on the structure). So they are claiming either a)their panels outperform for seismic load when compared to wind load or b)they are including contribution of interior drywall for capacities, but publishing an incorrect seismic response factor.

 

[XR250]

Mostly used by Tract Builders in my area. They staple it. The installation is horrendous. At least the sheetrock will provide the stability needed

 

[jacktbg]

I am trying to word my response carefully too - I too am an engineer (currently a lowly mechanical engineer, formerly a fairly low level residential structural engineer), working for a steel structural component manufacturer (among other things). I don't remember the engineering firm I used to work for ever specifying T-ply on the walls, but talking to old engineering coworkers who work there now, they are a little sketched out by it too - because they call out WSP or CS-WSP on their prescriptively designed homes per the IRC, but because of the IRC provision allowing this stuff to get used in lieu of and equivalent to even CS-WSP builders can just swap it. And I don't think the engineers can throw a fit over their builders swapping their plywood out for it without implicitly questioning the claims DR J makes and risking getting into this whole legal battle.

I have no dog in this fight either outside of the fact that my company cares extremely deeply about building safer, stronger structures and if homes are being built with this stuff to their limits, people and their property could be at really high risk during high wind events. Again, we don't even produce wood products, but this "Dr J" org has verified some really hard to believe loads for some of our competitor products as well (I say, at risk of oversharing) but I'm genuinely worried about states like Texas where this stuff is everywhere, and where just this week there are huge wind storms ravaging the area.

When I became an engineer, I sort of assumed that the IRC and the testing/accreditation labs had all of these technologies and methodologies super under control and that they kept cost-cutters from doing anything that could really compromise the safety of people who are buying these low-budget fast built homes and buildings. And it feels like there's this taboo around what we can say even though in my opinion there's some pretty good evidence to suggest that T-ply and other flexible structural sheathing products truly don't cut it. After doing some digging, it really seems like everybody kind of knows on some level that this product is a little dangerous, but nobody wants to be the company that has to take the stand if some accredited lab or Ox were to sue for defamation (again I'm not a lawyer but even at other companies that's the sentiment I get).

What really gets me is the defense the company has that "For over 50 years Alternative Structural Sheathing products have been accepted and used in the building industry accounting for more than 5,000,000 new homes." - which if strength properties are overstated, makes my concern far bigger, not far smaller.

I'm glad to hear I'm not the only one who read the APA report, 1004-03, and Ox's response and was left Un-reassured. At any rate, it's been used for 50+ years and it's been almost 10 years since that APA report, maybe nothing ever changes...

Probably should add the obligatory P.S. that this whole thread is of course my own opinion and not representative of who I work for either.

 

[XR250]

I mean, the stuff is great for criminals. All it takes to break into a vinyl box is a razor knife.

 

[Klitor]

Cant blame them. In a way not much has changed over the years.
The word for burglar in ancient greece being "wall digger" because of shoddy mud outer walls.

 

[lexpatrie]

I've seen it used as roof sheathing at least once, and as I recall it had tile on it. Apartment. I made a point of discussing it in my report and suggested it be replaced.

Jack - if your former colleagues want, they are within their rights or rather their obligations, (i.e. protecting the health, safety and welfare) to forbid the substitution if they think it's inadequate.

 

[jacktbg]

@lexpatrie That's really good to know! And I totally agree. To be clear, the engineers did not tell me that they couldn't keep them from swapping it out, they more or less just expressed some uncertainty about the decision and sort of an "it depends on who you ask" as far as whether the IRC provision makes sense. It's probably not a legal thing to your point, so much as it is the fact that these builders desperately want to save money and there's a whole carve out for it in the IRC, so telling someone "you're gonna lose a few million dollars because we don't want you using this product that everyone around you is using" is probably a hard sell. My assumption that there was some legal reason not to push back is exactly that, an assumption, it just felt like that might be a fear a firm would have.

And to be fair, Ox is right that it HAS been used in millions of homes, so even if there's a big question mark and or asterisk on the use of it, it's certainly not out of the ordinary. (This home was also in a relatively medium wind zone in Atlanta, and probably exposure B or C.) What really worries me is that I see all sorts of pictures of it being used in texas in massive open fields and it just sets off alarm bells in the back of my mind - as I said above, especially given this year's absolutely insane storm season.

It just really seems like after enough years of people not being sure about it, a better (more comprehensive) set of testing would come out either supporting or discrediting it by now. I'm a little shocked that more code officials don't require an ICC-ES report, per Choras's recommendation above, to OK their builders using it in lieu of the sheathing there.

 

[EngDM]

I haven't done too much by way of residential construction, but am I reading this right that they are using a product that is 1/8" thick fastened with staples as a shear restraint?

I went through the Canadian tables they provide for wind, similar to ChorasDen, and they are showing that the ThermoPly nearly has more strength than 3/8" plywood, with staples that are 65% as thick? It just doesn't make a lot of sense that the company boasts that the product can be cut with a knife to easily rough out windows and doors, but also that it provides any shear strength whatsoever. As the wall racks I'd imagine those staples just rip thru it.

 

[geesaman.d]

I'm mildly amazed that homeowners who suffered major damage haven't sued for this. I sure would.

As for "this year's absolutely insane storm season", it's not a one-year risk. As steady as major storm event appearances can be, they intensity and frequency has been increasing year-over-year for some years now. The risk is only increasing as the storms get stronger and the homes get not stronger.

 

[Eng16080]

I have no experience with this product and just took a quick look at their wind/seismic report for the blue (highest strength) product. The in-plane shear numbers are hard to believe for what's essentially a 1/8" thick wood product stapled to wall studs. I also noticed that the panel's strength to resist out-of-plane wind loads is dependent on the installation of interior drywall, which seems questionable.

We should get the same people who tested this stuff to test plywood/OSB wall panels. Maybe we can get an allowable unit shear strength of 3,000 plf. That would really help some of my shear wall designs.

 

[XR250]

Yea, the whole concept seems ridiculous. They must have bribed someone to get an ICC report thru.
If sheetrock was not so good at bracing house, I imagine we would have a lot more failures from using this crap.

 

[lexpatrie]

The Dr. J Technical Evaluation report isn't directly linked, if anyone wants to read that without dredging....

Thermo-Ply® Red and Thermo-Ply® Red AMG Structural Sheathing, Report 1004-01, Revised March 20, 2024

I may be wrong, but based on my skim of the report and previous encounter with it in the field, (as roof sheathing, mind you) the wall version of this (which it's actually uh, listed for, as a braced wall replacement?), depends at least partly on the interior gypsum board. It seems this is a "combined" assembly. Without trying to impugn the material, it appears it's a mix of something approaching fiberboard, and the outside surfaces have plastic adhered to them.

"Thermo-Ply Red Structural Sheathing are composed of pressure-laminated plies consisting of high strength
cellulosic fibers. These fibers are specially treated to be water resistant and are bonded with a proprietary water
resistive adhesive. A protective polymer layer is applied on both sides of the panel, and foil facings may
additionally be applied on one or both faces."

I think the APA's interest in the material sprung from various wall failures following encounters with Tornadoes. I seem to recall a Bryan Readling report with that material blowing off an end wall. Might be one of these reports (Link to APA publications index), but I'd look for something closer to the advisory, maybe 2011 or so? Foam sheathing at least in the past had a tendency to blow off the end walls as well, I'd suggest most of those failures involved vinyl siding as well, but I don't mean that's a contributing factor.

Thematically this reminds me of the "dispute" between the various building codes and the American Fiberboard Association, when they had static testing values and the code wanted the newer dynamic testing protocol. They both had valid concerns.

 

[lexpatrie]

As a footnote, I'd be cautious of this because it doesn't have any explicit stud testing. Typically even in the IRC, the studs are considered braced in the weak axis by the sheathing/gypsum board. For wind blowing onto the outside wall, the outside face of the stud goes into compression bending and the support offered by the Thermoply would be undocumented by testing as far as I know.

 

[bones206]

I'm genuinely worried about states like Texas where this stuff is everywhere, and where just this week there are huge wind storms ravaging the area.

https://www.structuremag.org/?p=12933

 

[XR250]

Woulda been fine if the staples were installed properly LOL

 

[Huevo]

There are folks that have criticized these products publicly that have gotten cease and desist letters from the manufacturers.

This is one of those topics that bothers me personally on a deep level. Obvious structural complications aside, good luck achieving any reasonable level of air sealing and keeping bugs out.