The most value-engineered siding furring strips over thick rigid foam… but what width?
mackstann
| Posted in Green Building Techniques on
Assuming labor is free, I’ve found that the cheapest furring strips would be 15/32″ plywood. It’s quite a bit cheaper than 1×4’s (less than half the price, close to a third, if ripped to 2.5″), and can be narrower than 3.5″ without worrying about splitting like 1×3’s or 1×2’s would. Also, it just barely meets the 7/16″ penetration requirement that James Hardie has.
But how wide should they be? 2.5″ seems like a reasonably safe width, but I’m curious if anyone has real-world experience with smaller furring strips, and can comment on how small is too small.
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Replies
Nick,
2 1/2 inches sounds OK to me. But I must say that I am surprised that James Hardie is happy with only 7/16" inch penetration of fasteners. If ring-shank nails are an option, I would select them over smooth-shank nails.
I also use 19/32" for less nail "bounce" and at $17.5 for a 4x8 sheet ripped at 2.5", I get 19 furring strips @ $0.92. That's half the price of locally sourced 1x4" strips at $1.98 per. I do use "used" ring shanks from Habitat's ReStore for next to nothing (sometimes they clear the shelves for 25 cents a pound.
Cheers,
PK
Thanks for the real world experience, Paul.
Martin, the 7/16" number was surprising to me too, but it is your article and you even followed up about it in the comments. :-) In their documentation, the 7/16" number is given for OSB sheathing -- it doesn't say anything about furring strips. The nail is also required to be quite a bit longer and penetrate well past the inside face of the OSB. But you said the rep was confident that that requirement also applied to furring strips, so I am taking that at face value.
I don't live in a very windy place, and I'm surrounded by trees and houses in an urban area, so I feel fine going with the bare minimum requirements for wind resistance.
But I would definitely be using ring shank nails.
Nick, With Hardiplank it isn't the wind that will cause the problems, it is applying enough pressure at the fasteners to hold the board tight to the one below. I think you risk having gaps with what you propose.