We are hoping to put our trusses up in a week or so for our new sugarhouse. We spec'd the trusses to space the ones around the smoke stack at 4' (we were told to double the trusses on either side).
With our 2x6 we ran metalbestos and it worked great. A you get larger that is a challenge. I like the idea of the double wall, insulation blanket, and you could add some cement board on spacers too.
Mike
Tapping since 1985 (four generations back to early to mid 1900s). 200-250 taps on buckets and then tubing in the mid 90s. 2013- 275 taps w/sap puller 25 gal. 2014-295 taps w/sap puller 55 ga. (re-tapped to vacuum theory) 2015-330 taps full vac. 65 gal, 2016-400 taps 105 gal, 2017-400 taps 95 gal. 2018-additional 800' mainline and maybe 400 new taps for a total near 800 taps. 2x6 Leader WSE (last year on it) supported by a 250 gph RO.