Furring with plywood / 2×4 for vertical metal siding and roofing
mason_
| Posted in General Questions on
My plan is to use strips of 5/8″ plywood installed vertically on the 16oc studs to act as a rainscreen, then to install horizontal furring strips of 2×4 or 1×4 that the metal siding will be installed onto.
Is that best practice? Is there a better method I am not aware of?
Can I use 3/4 ply for the horizontal furring instead of 2x4s?
My wall buildup is; 2×6 framing, rockwool batts, Zip sheathing – taped, 2″ polyiso, furring, then vertical metal siding.
Thanks,
Mason
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
I would use 3/4" plywood for the vertical furring strips, which is commonly done since the plywood is less prone to cracking and splitting compared to 1x4s. I would think 3/4" plywood would be OK for the horizontal strips too if ripped to a reasonable width, and assuming the lightweight siding materials I'm thinking of. Others here may have more experience with metal siding (I don't ever work with it) than I do though so I'd watch for some others to respond before finalizing your plans.
Bill
Thanks for the recommendations Bill, I'll use 3/4" for the verticals instead of the 5/8", glad to hear its common. The metal siding and roofing is going to be 26ga. standing seam.
For the horizontal furring I was planning on ripping it to 3" - 4" to give enough area for the standing seam clips to attach to, I think that gives enough extra space around the clips to avoid splitting, etc.
I will talk to my metal supplier as well to see if they can make any recommendations.
Mason,
As Bill said, plywood (5/8" is fine) and 1"x4"s. 16"oc for the horizontals, but check your manufacturer for spacing of those. With no loads you can probably go 32" to 36" oc.
The stack up for a roof may be different depending on what the the roof assembly consists of, and what type of metal panels you are using.
Deleted
The roof will have 4" poly over the sheathing, then the vertical 3/4 ply, and a horizontal furring member spaced to the manufacturer's recommendations.
Since 1x4's are commonly used (actual size 3/4" x 3.5") it would seem to make sense that 3/4 ply ripped to the same size should work, but I'll reach out to my metal supplier to see if they can attest to that or not.
Mason,
A similarly sized strip of 3/4" plywood doesn't have nearly the resistance to bending that 1"x4" does. Plywood strips are fine against the sheathing or foam. They hold fasteners well, but for the suspended layer you want to use lumber. Another advantage is being able to use much longer lengths.
I would consider a second layer of sheathing instead of the two layers of strapping for the roof. The vent space just adds complication with little benefit.
Note that plywood will be much better at resisting bending when the strips are ripped parallel to the grain in the highest number of plys.
If we just use 3 ply plywood as an example (because it's easy to talk about), the center ply will have the grain perpindicular (90 degrees) to the outer two plys. Plywood is made by stacking sheets of wood with every ply having the grain 90 degrees to the previous ply. With that 3 ply example, if you rip the strips so that the grain goes the "long way", parallel to the LENGTH of the ripped strip for TWO plys, it will be a LOT stiffer than if you have only ONE of the three plys with the grain parallel to the length of the strip.
Either way though, the 1x4 is still going to be stiffer than the plywood, but it's also a lot more likely to split when you're nailing/screwing stuff to it.
Bill
Mason,
As Bill said: all sheathing has a direction of span marked on the sheets indicting which way it needs to be oriented for strength. It is always in the long (8 ft) direction.
Does the metal profile allow for water to drain? It may not need any furring strips.
Bill,
7/8" corrugated technically meets our rain-screen requirements for walls, altogether most people do mount it on strapping.
Thanks Malcolm.
I was thinking of a vertical plank siding like.
https://luxarpro.com/v-groove-steel-siding/
Bill,
That looks like it would work really well.
Slope on the lower end so we are using standing seam