Insulation Dams and Vent Chutes? – GreenBuildingAdvisor

Hello!  As I mentioned in a previous post, I received an extreeeemely high quote for blown-in cellulose insulation in our vented attic, so I think I will have my builder do it (he has a blower and does it all the time, but he’s not high performance). 

We have a vaulted area, where the ceiling drops from 13′ to 9′ over a 40′ span (and the head space in the attic goes from 7′ down to the raised heel trusses which are 29 5/8″ tall at the outside wall).   We are putting in 21″ of insulation, leaving 8 5/8″ of “head space” to get to the top of the heel before any settling occurs.  Do we need vent chutes with that setup?  

Also, we had 1/2″ plywood put up on the ceiling to hold the insulation in (strapping is next) because we need to get that in ASAP before winter gets too bad and we are too far out from drywall.  Do I need to worry about the insulation “sliding” down the slope (4′ over 40′) and put in some sort of intermediate insulation dams, or would it be okay as-is?  We have the open web trusses, and plywood is slippery.  I’ve uploaded photos that shows a bit of the vaulted area (prior to plywood and after plywood).

We’ve built dams for where the side of the slope transitions to flat so we can retain the full 21″ at the transition point without it slumping over into the flat area, but not sure if we need to worry about the slope as well.

Thanks so much!