Furring

[bill1952]

I'm working on my porch and am replacing vinyl (soffit) ceiling with 1x6 edge and center bead t&g pine. The existing ceiling joists are 2' on center (and parallel with planned direction of 1x6).

Does the IRC have requirements for the span of 1x3 SPF furring? It's a question raised by another builder, not a building official. Were it 5/8 gwb, I might be concerned, but the 1x6 is so light, it seems not a problem. Less than 4 psf, so just over 9 pounds uniform load on a 24" on of 1x3 flat.

All I could find was max spacing for furring of 24" in R702.6.2, which while for walks, is referenced from chapter 8 for ceilings.

I am going to mock it up - attach one furring strip and hang weight on it - at least 4 or 5 times the pine. Don't know if I'll put my 210 pounds on it or not. I prefict fasteners would be failure point.

I think once more I'm guilty of over thinking.

 

[wwhitney]

I think once more I'm guilty of over thinking.

In that vein, R503.1 covers lumber sheathing for floors. It says 11/16" is the minimum thickness for joists 24" o.c. If that's for a 40 psf live load (ignoring self-weight and weight of flooring above), we get that full coverage 1x lumber is good for 40 psf when supported at 24" o.c. (for some unspecified deflection criterion).

Now if you install your 1x3s (2.5" net) 24" o.c., that's about 10% coverage. So it should be good for 4 psf when supported at 24" o.c.

Of course, that's just the bending strength/stiffness of the strapping itself. You'd still need to calculate the load on the connections. Which for a 4 psf imposed load, and arbitrarily bumping it up to 5 psf for the self-weight, gives 20 lbs per 2' x 2' tributary area. There's one strapping/joist crossing per 2' x 2' area, so you'd need a connection that's good for 20 lbs in withdrawal.

Cheers, Wayne

 

[bill1952]

Interesting. Thank you. Furring wiil be on 16" centers so 2.5/16 * 40 is 6.25 pdf. Seems like lots of safety margins.

I was thinking 2 structural screws at each joist. no 8 x 1 1/2 seems way over.