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Full Version: Spray foam in my step van - will it break apart?
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First, let me say thanks to everyone on these forums. I've been reading for weeks and the forums have been a huge help. A couple weeks ago I purchased a 16' 2004 MT35 Freightliner step van that I'm converting into my stealthy roaming house.

I'm currently trying to decide between polyiso vs closed cell spray foam for my insulation. I plan on 1 1/2" on all walls, 2" ceiling, 1" floor.

My concern about the spray foam is the aluminum walls flexing as I'm driving down the road or someone punching the outside of the van and causing the spray foam to break. If I did polyiso, I would plan on having about 1/2" of dead air space between the exterior aluminum walls and the polyiso which should protect the boards from this type of damage.

The professional who is going to do the spraying says it will not be an issue, but I know he's never sprayed a truck like this before so I think he's just guessing.

Thanks!

Charlie
I think he's just guessing as well.

I remember back in the 80's a few vanners tried spray foam, probably not closed cell, but spray nonetheless. It wasn't but a couple of years before they could be heard complaining about the squeaks going down the road. And this was in regular vans as opposed to a step van so they had a much harder shell than you will have.

Is the cost comparable? I would have imagined the cost of having a professional spray job would be, well, costly!
Yeah, definitely a huge difference in cost -- it's double the price of me installing polyiso. Surprisingly though, professional installation is about the same cost as buying the materials and spraying myself.

I'm leaning towards saying yes, but I'm hesitant on saying yes because of breaking up concern as well as the extra cost, but I do like the other benefits -- like reducing road noise (the truck is crazy noisy right now), and of course the convenience of driving it in, and an hour later having all the insulation done!
I think that it would be fine. Your step van is not that dissimilar to our little class C. We have an aluminum frame with lauan substrate riveted to the frame and an exterior covering of fiberglass sheets glued onto the lauan. The aluminum walls on your step van should be stiffer than our wood and fiberglass.

During the construction we had foam sprayed in the walls, ceiling and floor. We've driven 80,000 miles in five years in all types of weather and over some very bumpy terrain and haven't developed any squeaks in the body of the motorhome. The only problem that we had was where the cabover of the motorhome attached to the truck body. It wasn't done right and after about a year the foam broke loose and we had a horrendous squeak from foam rubbing on foam. Taking off some of the trim pieces, scraping out the loose foam and securely attaching the cabover to the truck body solved the squeaking problem.

Interior with sprayed foam -
Tonyandkaren, based on your description of your motorhome I would guess your walls are stronger than mine...

My studs are 4 feet apart (for a 16 foot cargo area, there are only 3 studs between the driver seer and the rear door). In fact, the last stud doesn't even come to the ceiling. So when I put about 75lbs of pressure on the wall (near the back), the wall will push in about 3/4" with a loud sheet metal noise.

I'm not sure if my step van has less studs than most step vans, but I'm guessing most motorhomes have more studs and have sturdier walls.
You could add some framework (wood or metal) to it to stiffen it. That would give you more options with mounting furniture and appliances too.
Chuckles - From your description and photo it does look like our walls are stronger. Lee's idea of adding more framework to stiffen up the walls is good especially because it will add additional spots to anchor things when you begin your finish work.

Another thing to be concerned about is that the pressure of the foam expanding may cause the walls of your van to bulge a bit. It's just cosmetic but the fiberglass on our motorhome is very shiny so the bulging is obvious in some lighting.
Are you trying to insulate to keep heat in during cold weather, or to keep heat out from a hot desert sun?

If the latter, I believe that polyiso boards, with a reflective heat barrier on one side, installed with a half inch airspace, will be far more effective than straight insulation.

Also, some spray foams can off-gas, causing problems for some people who are extra sensitive.

Regards
John
Your stepvan will do just dandy with this process!!

I've owned 7 stepvans, and they're all built with industry in mind. A camper is nothing compared to the strength of you stepvan's body and framework.

They spray foam inside all the big luxury coaches, so what does that tell you??

I'd do it to mine if the cost was more reasonable.
(01-09-2015, 05:29 PM)Optimistic Paranoid Wrote: [ -> ]Are you trying to insulate to keep heat in during cold weather, or to keep heat out from a hot desert sun?

If the latter, I believe that polyiso boards, with a reflective heat barrier on one side, installed with a half inch airspace, will be far more effective than straight insulation.

Also, some spray foams can off-gas, causing problems for some people who are extra sensitive.

Regards
John

Just curious as to why you recommend a 1/2 inch airspace? When I buy an iced cold drink in a styrofoam cup that is 1/8 inch thick, I don't feel any cold penetrate the styrofoam. Why wouldn't butting it up against the aluminum do just as well?

Looking forward to your answer.
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