Rainscreen Over Ci and Advanced Framing
As someone who appreciates advanced framing for the benefits of reducing framing material in favour of more insulation I keep running into the same challenge when I work through wall assembly details. To me an ideal wall would be
2×6 studs 24″oc
1/2″ plywood sheathing
WRB
Continuous insulation (preferably Comfortboard)
1X4 furring as rainscreen
Engineered wood siding (preferably Eco-Side from KWP)
It is at the cladding level that things get tricky though. One of the siding produces I like is Eco-Side from KWP however it requires nailing at 16″oc with a min nail penetration of 1.25″ (including sheathing). When Ci gets beyond 1″ thick finding suitable nails to penetrate the furring, Ci and into the framing is a challenge not to mention that assemblies with Ci considerably thicker than 1″ are becoming more and more common.
I’m interested to know what folks are doing in these situations? Hardie and LP Smartside allow for nailing at 24″ centres but have similar nail penetration requirements. Part of me feels like simply ignoring the installation recommendations and using ring shanked nails to secure the siding to the furring only. As for the 24″ stud spacing, Hardie is an option for me but not my favourite material to work with. LP does not appear to be easy available in Ontario.
I’m interested to know if anyone has used KWP siding over advanced framing with a Ci+RS assembly?
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Replies
For generic guidance, IRC 2018 Table R703.15.2 has nailing patterns for furring at 24" O.C., so depending on your cladding weight and insulation thickness, you can use that for determining the appropriate fastening in terms of supporting the weight of the cladding. This table is assuming the siding is attached only to the furring.
Method 2 in James Hardie technical bulletin #19 details how to fasten Hardie products to wood furring over continuous insulation, and does include tables for furring at 24" O.C.: https://www.jameshardie.com/JamesHardieMainSite/media/Site-Documents/TechnicalBulletins/19-jh-over-advanced-framing-or-continuous-insulation.pdf Again, this method has the siding attached only to the furring (Method 1 attaches the siding all the way back to the studs, through the insulation).
The example of Method 2 in the above Hardie document uses a 1.25" nail to attach the siding to the 1x4 furring.
Hardie is the go to composite siding in my region, so I don't have any experience with the other products you mention.
It feels like a manufacturer that doesn't have a detail for fastening siding to 1x4 furring at 24" O.C. is a little behind the times at this point.
It seems like the secret for the shallow penetration needed to get the 1x4 furring to work with these various tables is finding the one that allows using an 11 ga. 1 1/4" long roofing nail.
Another option is nail strapping at 12OC with half the strapping nailed only the sheathing. Ring shank nails going into just plywood is plenty strong enough but I would check with your building department if it will fly. I've only done Hardie at 24OC and was no problem.