For a large scissor truss (top chord 31″ above bottom chord), we want around R-70 but no more
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For a large scissor truss (top chord 31″ above bottom chord), we want around R-70 but no more. How do you ‘contain’ the blown in, or how would you use batts?
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Damp sprayed cellulose blown in netting works. The damp sprayed goods have water activeated adhesives to keep it from sliding down the slope over time. If vented above it'll dry a a reasonable rate after installation even at R70 levels.
Dana, are you talking about netting above or below the insulation? I assume above, but it seems like it would be difficult to net that plane within the truss chords. As much as I hate batts, it seems like something that holds its shape is going to be a lot easier to do.
Yes, batts are easier to install, but will be guaranteed to have gaps. It's next to impossible to do a really GOOD job with R70 worth of batt in any open web truss.
If it can be installed from above you don't really need the netting, just depth gauges and a competent insulation crew, but that would be a pretty awkward installation in most scissor trusses.
The answer might be to have a carpenter install backing, then baffles of thin plywood or maybe rigid foam, then the wet cells. You could ask the truss company to factory-install something to make the baffling or netting easier, but they might look at you funny.