I’m in the startup stage of rebuilding a house that was burned down. Actually it looks like I got the one next door too which burned in the same incident. More job security :-). So, this got me to thinking about fire resistance and flame spread ratings. I noticed that the original builder sheathed the homes with Thermo-Ply. I use 7/16″ OSB and Tyvek house wrap instead. My initial thought was how can that ~1/8″ cardboard be very fire resistant at all… Then I started doing a little research and found that it wasn’t so black and white.
I started by looking for flame spread ratings. I found this on OSB (and other wood products). I couldn’t find anything giving flame spread ratings for Thermo-ply. On their web site they say “Thermo-ply¯ can also be used as part of a 1 hour fire rated wall assembly.* ” and then it says something about “individual evaluation reports(ICC-ES, BOCA, ICBO, SBCCI for code compliance“. OK – so what does that mean? I guess paint could be some small part of a 1 hour rated fire assembly too… 😉 Sounds like a dodge to me.
Naturally I thought my method was better :-), but now I’m wondering…
Thoughts?
Replies
Individual materials are not rated. The have a flame spread and smoke accumulation rating but not a wall rating.
Type X drywall does not have a one hour rating alone. It is UL rated as a one hour assembly. It has to be screwed correctly with the right length screw and taped properly and penetrations have to be made correctly to get the one hour rating.
Same with any material.
Jason
Thanks. That makes sense. Still, I wonder why the Thermo-ply mfg doesn't publish a flame spread rating.
Have you looked at their materiaal data and safety sheet ? They are required to publish and most are onlline as PDFs
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The following is the Fire resistive info on thermoply's website, from the ICBO report.
It looks like you are allowed to use it opposite 5/8 TypeX in place of the 1/2 Gypsum Board.
2.4 One-hour Fire-resistive Construction:2.4.1 Exterior Wood Stud Wall: Thermo-Ply gStructuralh orgSuper Strengthh sheathings may be installed under exteriorcement plaster described in Item 18-1.3 in Table 7-B of thecode, provided the length of the fasteners attaching the metallath is increased by an amount at least equal to the thicknessof the sheathing.2.4.2 Limited Load-bearing Exterior Wood Stud Wall:The wall construction consists of 5/8-inch (15.9 mm), Type Xgypsum wallboard complying with ASTM C 36, applied to theinterior face of 2-inch-by-4-inch (51 mm by 102 mm) woodstuds spaced at a maximum of 16 inches (406 mm) on centerfor the gStructuralh (Stormbrace) sheathing, and a maximumof 24 inches on center (610 mm) for the gSuper Strengthh (24o.c.) sheathing. The wallboard is applied in accordance withdetails in Item 17-1.3 in Table 7-B of the code. The exteriorside is covered with 21/4-inch-high-by-33/4-inch-wide (57 mmby 95 mm) face brick, with cored holes, applied to the studsas anchored veneer in accordance with Section 1403.6 andItem 18-1.5 in Table 7-B of the code. Unfaced friction-fit glassfiber batt insulation, 31/2- or 35/8-inch-thick-by-151/4-inchwide(89 or 92 mm by 387 mm), R-11 or R-13, 0.89 pcf (1403kg/m3) density, must be placed within the stud cavities. TheThermo-Ply sheathing may be used in lieu of the 1/2-inch(12.7 mm) gypsum sheathing specified in Item 18-1.5. Themaximum wall height is 8 feet (2438 mm). Allowable bearingloads cannot exceed the following, whichever is most restrictive:1. 1,800pounds (8 kN) per 2-inch-by-4-inch (51 mm by 102mm) stud.2. Design stress of 0.78 FŒc, as set forth in Section 2307.3of the code.3. Design stress up to 51 percent of the FŒc or FcÛ permittedfor the stud species and grade.
Hummm... I'm a little surprised I missed that - well, OK maybe not surprised... anyway... translating, it sounds to me like they get a 1 hour wall if the exterior cladding is either stucco or brick. I'm not really impressed:
2.4 One-hour Fire-resistive Construction:2.4.1 Exterior Wood Stud Wall: Thermo-Ply gStructuralh orgSuper Strengthh sheathings may be installed under exteriorcement plaster described in Item 18-1.3 in Table 7-B of thecode, provided the length of the fasteners attaching the metallath is increased by an amount at least equal to the thicknessof the sheathing. this sounds like a stucco exterior
2.4.2 Limited Load-bearing Exterior Wood Stud Wall:The wall construction consists of 5/8-inch (15.9 mm), Type Xgypsum wallboard complying with ASTM C 36, applied to theinterior face of 2-inch-by-4-inch (51 mm by 102 mm) woodstuds spaced at a maximum of 16 inches (406 mm) on centerfor the gStructuralh (Stormbrace) sheathing, and a maximumof 24 inches on center (610 mm) for the gSuper Strengthh (24o.c.) sheathing. The wallboard is applied in accordance withdetails in Item 17-1.3 in Table 7-B of the code. The exteriorside is covered with 21/4-inch-high-by-33/4-inch-wide (57 mmby 95 mm) face brick, with cored holes, applied to the studsas anchored veneer in accordance with Section 1403.6 andItem 18-1.5 in Table 7-B of the code. Unfaced friction-fit glassfiber batt insulation, 31/2- or 35/8-inch-thick-by-151/4-inchwide(89 or 92 mm by 387 mm), R-11 or R-13, 0.89 pcf (1403kg/m3) density, must be placed within the stud cavities. brick veneer exterior exterior The Thermo-Ply sheathing may be used in lieu of the 1/2-inch(12.7 mm) gypsum sheathing specified in Item 18-1.5. Themaximum wall height is 8 feet (2438 mm). Allowable bearingloads cannot exceed the following, whichever is most restrictive:1. 1,800pounds (8 kN) per 2-inch-by-4-inch (51 mm by 102mm) stud.2. Design stress of 0.78 FŒc, as set forth in Section 2307.3of the code.3. Design stress up to 51 percent of the FŒc or FcÛ permittedfor the stud species and grade.
It's worse than that. The way I read it it's.
TypeX--2x4xmax24"oc(with Fiberglass insulation((no cellulose or Sprayfoam)))--Thermoply(only blue thickness)--Stucco--Brick
So your 1 hour rating is really the TypeX layer
Thanks for helping me unravel this part of the puzzle.
I'm still not getting to the info I want though. Basically, I want to be able to tell the customers that the way I construct homes (with OSB sheathing and Tyvek) is better in a fire than the cardboard sheathed homes with no housewrap. I just need to find some kind of data, etc, to back that claim up, since now it is only an hunch...
Basically, I want to be able to tell the customers that the way I construct homes (with OSB sheathing and Tyvek) is better in a fire than the cardboard sheathed homes with no housewrap.
That may be a tough row to hoe, documentation wise. I would think that if you really wanted to build fire-resistant houses, you would have to go the way of multi-family dwellings, with the exterior wrapped in Dens-glass.
And think about the eves.
And think about talking to a Architect and Lawyer also!
Yea - maybe I'm barking up the wrong tree...
I wasn't contracted to build a fire resistant house - just trying to look for some sales points or how I can do the right thing for little to no expense. If they wanted a more fire resistant home it wouldn't be sided in vinyl :-( Hardie would be the way to go. I'll build whatever people want to pay for. I guess it wouldn't make sense to build that in an all vinyl neighborhood.
BTW - my co also builds multi-family. For example, we are using Dense-glass on the party walls of a TH product that we are in the start-up stages of. So, yes I familiar with rated wall assemblies.
Matt, IMHO, you'd be better off selling the OTHER advantages of OSB/Tyvek vs. Thermoply. Things like structural rigidity, water resistance, nail-holding ability of the sheathing, ease of future remodeling, etc.Bill
Yea - I think you are right. I was just trying to look at different angles.
I'd look closely at the eves and roof at them. If there was a house on fire next to another one the eves would probably catch fisrt. The way they extend out closer to the fire and the horizonal surface under the eves would catch alot of heat. Once it gets into the roof shealing it is in the trusses and you know how dry they are if you've even been in an attic.
Matt,
Flame spread and fire rated assemblies are two different things.
Flame spread ratings have to do with interior finishes. One reason you can't find a flame spread rating for Thermo-ply is that it is not likely to be used as an interior finish material, so it wouldn't be worth paying a lab to test it. Here's an excerpt from the OSB link you provided. NFPA 101 primarily applies this classification to interior wall and ceiling finish materials. Roof coverings must meet a different set of criteria.
If you are looking for a rated wall assembly that includes Thermo-Ply , the link you posted to Thermo-ply shows one.
http://www.covalencecoatedproducts.com/docs/pdf/products/brands/CodeReport/esr-1122.pdf
>> Flame spread ratings have to do with interior finishes. <<
Thanks for making that point. I had missed it.