Which is the better technique? Over R 13 2 X 4 walls without an interior vapor barrier, #1) 5/16 Hardie lap siding over 1/2 furring (rainscreen) over taped 1″ continuous XPS (no thermal stud bridging) . This would allow me to use a 10d nail for 1 1/2 framing penetration per IRC. #2) 5/16 Hardie over 2″ furring with 1 1/2 XPS (1/2″ Rainscreen). The furring would be screwed to the original sheathing for a code approved nail base but it would leave the thermal bridging of the studs at 16 o.c. or about 7% of the surface area. Since the R value of polyiso is 6.4 for 1″ and 9.6 for 1 1/2″ the 1 1/2 is about 30 % higher in value,But the details of sealing out for air infiltration are increased. This is in WA with an average Dec, Jan & Feb low temp of 33 degrees.
Thanks for the help
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Greetings sparky,
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I would imagine either way would be fine, obviously you'd get more insulation with more 1.5" XPS. I've checked Hardi Plank's website and they only reccommend 1" max for rigid insulation, and make no mention of needing a rainscreen (at least for my climate, I may be wrong as I haven't checked for WA). And, just to add a little more confusion, I've seen people do up to 2" of XPS with no problem.
If it were me, I'd do 1" XPS, furring strips to make a rain screen, and then hardi plank.
Do a search on this forum for the PERSIST system.
better off with foil faced polyiso continuous.
If you have to break it around furring, you lose the thermal break and the integrity of the rainscreen..
So go with 1/2" furring over 1" polyiso taped
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