Although not at the implementation stage, I've been trying ,to figure out a cost effective method to insulate the floor trusses between the garage and the second story. The garage is subterranean, with the exception of the front (obviously) and will likely never get below freezing even though I'm in zone 6B. Second story is subterranean as well again except the front. All is ICF. Trusses are 16" centers and are 24" overall depth. Garage is 30' x 90'. Foam would be prohibitively expensive in my mind. I'm thinking of netting the ceiling and blowing fiberglass the full depth. Not dense packing as I don't need that benefit when 24" of depth and the temperature of the garage is moderate. I know I can't control uniformity as well as I would like to, but does this make some sense, or are there other suggestions?

Fully insulating the space is a good move, but it needs to be air sealed. That could be your drywall, if it's done well with no gaps or holes, or you could install a fabric such as Majpell. (http://performancebuildingsupply.com). A blower door test in the space above prior to insulating the walls and roof will give you some assurance that the space is tight and will heat easily.

It'll probably be the drywall in my case. Whoch isn't as bad as one thinks as really the ICF foam on the next level overlaps the flooring with the way I set trusses on the thicker wall below. And they were foamed to the floor as they were placed. Yes a blower door test is in order. Nearest contractors are three hours away in Albuquerque which is a bummer. The framer I was using on the shell said I was building this so tight that I was going to have trouble closing doors! Not with an HRV I replied. Most everybody thinks housewrap takes care of everything.

Net and blow is probably the better option. Boy, those are tall trusses. As bob said pay attention to air sealing the garage ceiling as the garage door will probably leak horribly. If that air has nowhere to go, it becomes a non-issue.

Yes, I've never seen a garage door that seals well. The height of the trusses were the result of a
long span (31') with a 1/360 stiffness, the desire to have plenty of space for ducts, plumbing, and more importantly, trying to reach a final elevation on the backside as we are built into a slope that tops out. As I have only the two 2/0 SER cables penetrating the ceiling in the garage, and Romex for lighting, I'm thinking I can get a good seal with the drywall. By paying attn to those few penetrations.

L/360 floor is unacceptable to alot of people, especially if the entire thing is clear spanned 30'. L/480 is a little better, L/720 even better. Having the underside drywalled will help eliminate the vibration that some people mistake for bounce, but depending on design you may not like the feel of the deflection.

The entire second floor is clear spanned over the garage with walls between it and much of the third floor. The fourth floor has considerable clear spans over the third. None of it feels bouncy once the rat runs were installed. Jumping up and down feels like a rock. while I specified 1/360, I just gave them the number of trusses. They didn't know I was putting them at 16" OC. So in actuality, the system is far stiffer.

Nash,
Out of curiousity do you have perpendicular runs of 2x material anywhere midspan, like in the duct rectangles or a vertical upright? If so was it spec'd on a print?
I think that would help stiffen the floor.

Do you know if they spec'd l/360 based on 24" oc or maybe you're actually quite a bit under the l/360 maximum span, cause Im not kidding l/360 IS NOT rock solid if you jump on it or have a bunch of people walking over it, you can usually go underneath and measure the deflection with a tape measure when the truss or joist approaches its maximum span. The company I usually use has a l/480 min design and I dont hear much for complaints.

Sorry to drift your thread, its just a topic most people dont completely get, yet it really affects homeowner satisfaction.

Green
It does have perpendicular runs. We call them rat runs here. Man. calls them strong backs. They were recommended but not required. Again I just specified the length and L/D to them. I am assuming they designs based on a 24" spacing as is normal for floor trusses. Can't find any mention of that in the paperwork. I put them at 16". If so that would explain why my floor is as stiff as it is. I don't like a bouncy floor at all either. It's horrible to feel and hear stuff clattering. And for those that are old enough to remember, have the stylus skip when playing a record. 😜😜