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Just got my top put on the Van and am thinking insulation.  I am concerned about the condensation traps I will be creating by using the rigid polyiso as much as I can and still having air pockets next to the fiberglass top, metal walls and framework of the van.   I am so tempted to fill all the van frame areas and other nooks and crannies with the spray cans from Home Depot.  I understand that is a bad idea due to moisture retention and eventual sloughing-off of material as the van bounces down the road for the next 500,000 miles. Smile

Has anyone used SHREDDED polyiso?  I have looked on line for it with not luck.  I will be calling polyiso manufacturers on Monday.  I also thought of shredding it myself in a paper shredded but doubt that is very feasible.  I know people cut it up in little pieces and pack it in.  I just thought an easier way would be with it already shredded.
Knowing nothing would packaging peanuts work?
I have absolutely no idea where all the 'condensation issues with insulation' in vans came from.

RV manufacturers and van enthusiasts have insulated moving vehicles for decades with no problem with condensation. I've personally owned customized vans for 41 years and have never experienced a condensation issue nor have any of my friends nationwide.

Our vehicles are opened many times a day in actual use. Short of staying in your van in high humidity regions for days at a time while cooking and breathing in there without opening any ventilation of any kind, it is extremely unlikely that you will create a humid enough environment between the walls of the van and the insulation to create any problems. If you're doing that you have more problems than just condensation... Rolleyes

The inside of the walls of the vans are painted with the same paint that is on the exterior. Your van gets wetter on the outside than it ever will on the inside.

Use sheets of polyiso and forget about trying to cram it in to all the nooks and crannies, like down the holes in the ribs. It's called 'good enough'. You're not going to get 100% insulation no matter how hard you try and just like those homes that were built with total wrap sealing, it creates it's own share of problems if you get it too tight.
To answer your question directly, no, I don't know anything about using shredded polyiso.

I'm in the middle of a build-out myself, and I've given quite a lot of thought to insulation, condensation, vapor barriers, dead airspace, you name it.

While I don't doubt that some problems do occur, more and more I am beginning to suspect that a lot of these "impending disasters" are just theoretical or are overstated.  I think we can spend way too much time worrying about this stuff, when we should just pick something and build.

Think of all of the DIY builders of little campers and house boats and so many other things in the last 100 years who faced these kinds of design issues with a lot less knowledge and simply built.  Very few things blew up or societies crumbled as a result. I think the Internet is on the verge of turning us all into research addicts bordering on constant design decision paralysis.

If I turn out to be wrong, and mushrooms start growing from my walls, I'll just try to make sure they're the right variety, pick them, chop them, and make an omelet.

Stepping off soapbox now.

hmm, omlets....not where I thought you were going with that...
I have a conversion van. When I put the roof fan in I seen from bottom layer to top, fabric, 1/2" open cell foam, 3/8 plywood. There is a lot of space above the plywood. I don't like the idea of pulling out all the interior to insulate, so I am thinking about drilling a hole in each area between the ribs, and blowing in Cellulose. I can put a led light in each hole to plug it back up. If it settles over time, just shove some more in.

The cellulose is already treated for mold and fire.
VJ, read AlmostThere's post again. One of the problems that you will repeatedly run across in these vehicle conversion forums is the quest for Absolute Perfection. It doesn't exist. So just relax and decide which way is the best for your conditions, expertise and wallet, and go with it.

DannyB, Cellulose absorbs moisture, and it doesn't let go of it easily or quickly. If there is some sort of spill or leak, you might have to rip it out, and that's usually not easy on the road. (I'm not talking airborn moisture.)
(12-19-2016, 04:28 PM)TrainChaser Wrote: [ -> ]DannyB, Cellulose absorbs moisture, and it doesn't let go of it easily or quickly.  If there is some sort of spill or leak, you might have to rip it out, and that's usually not easy on the road.  (I'm not talking airborn moisture.)
I guess I will have to make sure the roof don't leak. With most any insulation if you have a leak you can have mold and corrosion. Every insulation has some sort of drawback, otherwise there would be only one type of insulation sold. I am not a fan of foam. I used it once in a house I had. Carpenter ants loved the stuff. They don't eat it, they just tunnel through it for nests. I had tongue and groove pine ceiling with very little insulation, (about a half inch of some kind of tar product), and wood shingles. When I redid the roof, I added 3 1/2" of foam on top of the pine. I was gone for a week and when I returned there were piles of foam dust in a few places. Ants were excavating, pushing out the foam where there was a gap in the tongue and groove. Cellulose has boron as a fire retardant and bugs don't like it much. 

If you do not allow moisture to travel, (as in a sheet of foam), if moisture does get on the wrong side, it isn't going to dry out easy.
EPS or Extruded Polystyrene (aka Styrofoam) is the most vapor-permeable of the rigid insulation, if that is of any use to you.
(12-18-2016, 01:37 PM)BradKW Wrote: [ -> ]hmm, omlets....not where I thought you were going with that...

See, all that Key West degeneracy polluted your mind and had you thinking evil or illegal things. ;-)