Hey ya'll. Looking for a way to meet code while useing wood planks for my interior sheathing. I plan on ordering 6 inch osb sips and using 8'" wide poplar planks i had cut @ a local sawyer from a downed tree. If i understand correctly the wood interior wall covering will not meet the flame spread code. How can i achieve the interior wood look i want without using drywall or MGO. Any help much appreciated. Thanks Michael

How about using a rock-wool mat behind the wood to meet the requirement. Talk to your inspector for ideas. If he comes up with an economical solution with your guidance, you are one step ahead of the game.

Maybe you should revisit the codes again, just to be sure. Section R315 of the IRC requires wall and ceiling finishes to have a flame spread of less than 200 and a smoke developed index of less than 450. My tables provided by the Western Wood Products Association shows poplar to have a UL flame spread rating of 170-185. Which should allow its usage as interior wall (or ceiling) paneling.

wes, couldn't one also use plywood given that it's thick enough to have the proper flame spread rating?

And what about the seams for poplar planks or plywood either one - would they need to be tongue and groove or are butt joints acceptable? Seems like the inspector always wants to see drywall seams taped to pass electrical inspection - not sure why that is.

My experience has been with T&G wood. And, yes, according to my tables, 3/4" plywood will meet the flame spread ratings listed. Most are actually lower than solid poplar wood.
The information I have does not address the butt joint/T&G issue, only the actual materials ratings. However, IRC section R702 discusses in length the use of plaster and drywall as interior wall coverings. Subsection R702.5 deals with 'other finishes' namely wood paneling. The only requirement listed is that if the paneling is less than 1/4" thick, it must be backed by at least 3/8" drywall. Anything thicker than 1/4" is OK.

Wes, you are the man! All this time i was worried about nothing. After your post I looked through the charts for flame spread and it seems even osb would pass. Thanks again. Always so helpful. michael

wes, I'm looking at my IRC at R702.5 and trying to interpret it - they only reference wood paneling and hardboard paneling (I'm guessing MDF) for other finishes. What about stamped steel (think of those old stamped "tin" ceilings) - do you have any idea if gypsum board would be required underneath? Some of the manufacturers specify furring under the tin ceilings that have a deep profile. I wonder if I could just place furring directly on the joists and do without gypsum board?

Jelly,
I would check with 1: the tin ceiling mfg. and 2: local building officials.
I thought most of those tin ceilings required a solid surface behind them. Howevr, I have no specific knowledge about these products.