Rigid foam without logo
joenorm
| Posted in General Questions on
I am building a small workshop. I have fiberglass batts in a vented vaulted roof.
I’d like to next install rigid foam on the underside of rafters as an air barrier. I may just leave it that way for years so I was wondering if there is rigid foam, preferably white with a vapor barrier that has no logo, or more likely just a logo on one side.
Any thoughts on this? Thanks
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Replies
Dupont Thermax has a version with white foil facing. Two versions, actually--one with standard-duty foil and one heavy-duty foil. You can also get unmarked white tape from 3M for the seams. I specify these for unfinished basements.
If code or not, if inspector approved or not, rigid foam has very poor ASTM E84 rating for fire and smoke spread. FSK covered or not.
With chemicals, or tools, or whatever you'd expect in a "work shop" including a crafting hot glue gun...I'd shy away from anyone who recommends a product to you as ALL rigid foam makers have a requirement to cover with a thermal barrier (drywall, rockwool, metal, hardboard, structural plywood). Fire protective paint has not been made that I'm aware of for rigid foam applications.
The lower ignition barrier for attic and crawl space (unused) is a US code thing, but it is not a manufacturer approved thing.
Ryan, the Thermax I recommended and specify on many of my projects has been tested to comply with thermal and ignition barrier requirements. No other covering is needed. I believe that there may be one other rigid foam product on the market with the same ratings but it's not something I have used.
https://www.dupont.com/products/thermax-sheathing.html
https://www.dupont.com/content/dam/dupont/amer/us/en/performance-building-solutions/public/documents/en/thermax-sheathing-pis-43-D100094-enNA.pdf
Thermax has a Class A rating under UL 723 (ASTM E84) for surface burning characteristics. That's the best rating.
Thermax' flame spread rating is 25; the IRC requires it to be under 200.
Thermax' smoke-developed rating is under the required 450.
Tyvek, backwards would be white and is approve for inside.
However, no rigid foam is approve exposed indoors without ignition or thermal barrier per E84, even Thermax.
Thermax E84 is actually poorer than Formular NGX, and you can't leave NGX exposed either.
https://alleguard.com/products/construction/rigid-board-insulation/envirosheet/
No logo - white
https://www.menards.com/main/building-materials/insulation/foam-board-insulation/r-8-expanded-polystyrene-2-x-4-x-8-foam-board-insulation/1632118/p-1444435971902-c-5779.htm?exp=false
No logo - white
If you look at the Thermax technical sheet, it's E84 flame spread and smoke spread at 25 and 130...
Johns Manville ISO is flame 20-30.
Look at Foamular NGX, 10 and 175.
Rmax EPS is flame >75.
So there is nothing special about Thermax compared to real world E84 postings of others.
"Sheetrock" Type X 5/8 is 15 and 0.
It is simply not possible that DuPont has a truly safe plastic foam product left exposed. The tech spec shows it.
I don't understand what you're saying in your first sentence.
The chart in the PDF is a little confusing; ASTM C1289 covers the physical qualities (US) and ASTM E84 covers surface burning characteristics. In other words, the bottom row should be separate from the rest of the chart.
Edit: I see the problem: you're mixing up the US column and the Canadian column. In the US column, flame spread is 25 and smoke developed is <450. Canadians use a different system, with a reported flame spread of 25 and smoke developed of 130.
No other foam (with possibly one exception) meets BOTH the flame spread and smoke developed ratings. This is well-known information; I've had dozens of projects approved with Thermax exposed on the interior, it comes up regularly in presentations and articles by industry experts, etc.
I agree that having a more solid barrier such as drywall would perform even better than the foil-faced foam alone.
I was going to type something large, but if you look at Thermax, Hunter, JM IC, OC XPS NGX has a better E84 number flame spread than those. Sure, the billowing smoke is far greater. But the flame spread shouldn't be better.
Owens states NGX XPS must be covered. It seems the attic and crawl space code carve outs or risk mitigation calculations (house is burned down down once it reaches these areas or something), but that doesn't quite square that a flash fire can rapidly occur in both areas first.
If a local inspector follows local code, smoke and fire are agnostic to both their opinion. I don't see how this claim stands given the fact sheets prove all foam is below true assembly ignition or thermal barriers.
Tyvek backwards would "white" anything and is acceptable inside. Paint could be put over it. But none are truly safe or would be acceptable to code to the results on a data sheet.