Fire retardent OSB

Is fire retardent OSB typical in duplex dwellings? I find lots of FRT sheathing (plywood) in older duplex(s). I am pretty sure the blackness I found todayis mold/mildew although I want to be sure it is not charcoaling. Thanks everyone and long live NACHI :stuck_out_tongue:

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Looks like mould! Is it active now or was it just in the first year or so while the building dryed out from damp wood/concrete and excess mositure migrated to the attic.

I tell clients to check the attic in colder winter weather and call me if there is excess condensation/frost on the sheathing…then we can work on the causes.

There are attic moulds that are green or white when active and leave a black stain like in your pics after they die. Active molds of any colour can be wiped off with a finger, so that’s a good test. Be careful scaring people when there’s just a bit of old stain on the OSB. Call for improvements to ventilation if the soffits are blocked, weatherstrip seal on the hatch, stuff like that.

John Kogel

What makes you think it’s “fire-retardant” (resistant) OSB, as opposed to standard OSB?

I havent had much experience with Fire retardent OSB. I have seen quite a bit of FRT plywood that is deteriorated (looks black with white charcoaling). Just wanted to know if this new fire retardent OSB ( ) does the same thing as FRT plywood deterioration.

It is my understanding that mould (dead mould) can re-activate under the right conditions.

Asked again.

Moisture, temp and food. There are mold spores in the air.

The charcoaling/deterioration of FRT plywood sheathing sometimes blends in with mold/mildew staining. I am curious if anyone has had experience with fire retardent OSB and if it blackens the same way as FRT plywood sheathing does when it starts to deteriorate from high attic temperatures.

Jeff, at least we know the product was manufacturered in 1996 August, but I do not see the Class “A” stamp anywheres.

Marcel :slight_smile: :smiley:

That’s why I asked :wink:

It is Exposure 1 classification, which is French Canadian for Class A. Just kidding, Monsieur Marcel. :stuck_out_tongue:

Bonsoir, French Canadian? No Franco-American Yes.

I think that is just a fancy word for mutt in the Lingual World. ha. ha. That’s what happens when brought up to close to my Canadian friends of New Brunswick. :wink: :slight_smile:

Marcel :smiley:

OSB = Mold candy

And comes in colors too!



Brown mold on plywood roof sheathing](
Marcel :slight_smile: :smiley:


That is just gross.


If you let water continually get at any wood product (except preservative treated and rot resistant species), it’s going to support mould/rot. It’s just that OSB came on big in the last 20-25 years when building practice common sense went out the window (poor/non-existent flashing details) , houses got more airtight at the walls/windows (housewraps creating more stack/chimney effect for moist air to rise to the attics) without compensating with good interior venting practice (bath fans dumped into attics)…all these other items/problems were blamed on the OSB…Hell!, it couldn’t be me, the builder, causing this mould/rot from not knowing what I’m doing and that buildings have changed in nature…gotta be the poor sheathing.

I’d use OSB board any day…though not on walls…insulation sheathing only!!!

I agree Brian, OSB is not the problem.

Keeping moisture and water away from it is.

Knowing how to prevent it from moisture and water is.

Having builders know how to keep moisture and water from it is.

Not enough education on building science for builders is.

Until that is corrected, we will continue to have problems.

Education is the key word here.

Let us all Members/non-members chip in and educate some of these clients.

Marcel :slight_smile: :smiley:

I know guys!

But everytime it ROTS around here they blame the stucco. :wink:

Thread drift, I think we need to get back on track for this Member which was Fire Rated OSB. :wink:

Any contributions anyone?

Marcel :slight_smile: :smiley: