Spray foam in my step van - will it break apart?

[Chuckles]

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

 

[Almost There]

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!

 

[Chuckles]

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!

 

[rvwandering]

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 -

 

[Chuckles]

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.

 

[LeeRevell]

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.

 

[rvwandering]

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.

 

[Optimistic Paranoid]

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

 

[Patrick46]

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.

 

[66788]

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.

 

[Chuckles]

TonyAndKaren - Thanks for sharing your experience, yes I see the bulging and that is something I definitely want to avoid. I have decided to add additional studs to the rear part of my vehicle, I think that will be safer whether I choose foam or polyiso boards.

John - I'm trying to get a good balance on insulating for heat/cold, but since it's a lot easier to heat a vehicle than it is to cool, I'd say staying cool is more important. Everything I have read said spray foam is better, but maybe they were focused on keeping the cold out?

Is the off-gassing of spray foam really an issue? I guess I need to research that.

Patrick - Yep, I love the fact that this truck is so solid ... and simple. It's an engine, on a frame with a good solid aluminum box on the back!

Thanks everyone for your feedback so far! I'll be making my decision by the end of this week. I'm currently heavily leaning towards spraying as I like the idea of a quieter van (hardening the rattling walls) and all the surfaces and nooks and crannies being filled in.

 

[GrantRobertson]

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?

Hey, 66, I can answer that question. Reflective or "radiant" barriers only work by reflecting infra-red light. This polyiso foam usually has such a reflective barrier on one side.

Assuming there is an air gap, here is how the whole thing works:
1) The outside walls get hot from either the sun or just the outside air.
2) Because the walls aren't touching the insulation then they cannot transfer heat to the insulation through basic conduction.
3) Because the air gap is small, it is difficult for convection currents to get going, so the heat cannot get transferred by convection.
4) All that is left is infra-red radiation. But the reflective barrier bounces most of that back too.

So, why do we even need insulation at all? Because that air in that air gap will eventually get as hot as the wall itself and begin to conduct heat to the insulation directly. However, even though the air is the same temperature as the wall, it doesn't actually hold nearly as much heat energy because of all the, you know, empty space between all the air molecules. Therefore, the air transfers a lot less heat energy to the insulation than the wall of the truck would, so it does at least provide some insulation. Better than if we had just glued the insulation directly to the wall.

The super-efficient, closed-cell structure of the polyiso foam takes care of that last bit of heat and keeps it from getting to the inside. Of course, this assumes that NONE of that hot air can leak into your space. That is why air-tight barriers, often referred to as vapor barriers, are so important.

 

[gypsychic]

Hey, 66, I can answer that question...

That is the best, most concise, easy to understand explanation I have read yet. Maybe I needed to read all the other stuff to really understand your explanation, but yours was the one that really cemented it for me. Awesome-Thank You!

 

[GrantRobertson]

That is the best, most concise, easy to understand explanation I have read yet.

Thank you for the compliment. My technical writing skills have been honed by decades of participation in everything from dial-up BBSs, to internet newsgroups, and now to web forums. I hope to eventually build a web site that compiles and neatly organizes all the information RVers and vandwellers need to know in order to build, repair, restore, and enjoy their RVs and vans. However, I am still trying to figure out a way to do it that would compliment what Bob is doing here rather than compete with it. (If you want to discuss that further, we should probably start a separate thread.)

Thanks again,
Grant

 

[flying kurbmaster]

Hi Chuckles, re noise, I have a step have like yours only smaller, it was crazy noisy when I first got it, now that the rear is insulated and finished, spray foam in the front wheel wells, insulated under the floor, a divider wall, a second layer of insulation on the engine compartment, removed from a more modern truck, sections of insulation and wood on the inside side of the engine cover, a new exhaust system, rubber matting on the front floor, all helped but it is still noisy. I have been doing some research as to how certain cars are quieter then others. I have found out that it is in the quality of the soundproofing stick on stuff they install under the carpet underlay, in the door and side panels and on the firewall. They are made a variety of material, led being one of them. I am now thinking of lifting all my flooring in the front area finding a dead Mercedes riping out these strips and installing them on the firewall and under the flooring, just a thought before you get too far along, insulation quiets things a little but don't expect miracles, I don't want to discourage you as you can make big gains on an empty truck, every little bit helps, perhaps acoustafoam would be an option for the from area. ceiling, above and around windshield, inside doors, engine cover firewall, the stuff is not cheap, they use it in heavy machinery and tractors so it must work to a certain extent. good luck I use ear plugs on long hauls

 

[compassrose]

The heat barrier on the foam sheathing needs to have an airspace barrier in order to work correctly. That air space can either face the interior (your interior living space operates as the air barrier) or a consitently maintained airspace next to the metal skin of the vehicle (use plain old packaging bubble wrap to maintain the airspace). Thermal breaks are important to maintaining the thermal envelope. I will suggest to you what I suggest to everyone that does not have deep pockets...

Foam sheathing on the walls (face the shiny barrier, if there is one, which ever way you want, just install it right). Canned foam (like Great Foam brand) to fill in the larger gaps and tape all your seams. Use furring strips to attach your interior wall covering (thermal break) rather than attaching directly into a metal "stud" (creating a thermal bridge).

Interior hollow core flush doors make great interior "walls". They are sturdy yet lightweight, can be easily trimmed to fit against walls, and come "finished" on both sides (I painted mine). They cost roughly $1 per inch (mine have been costing me slightly less than than). When installed 90* (perpendicular) to the side walls of the vehicle, they add a great deal of structural stiffening without adding much weight.

The inside of a hollow core door is a heavily glued paper honey comb the framing is 1" thick around the sides. Try to get wood framed (you will see where the wood was joined) as the composition stuff is extremely hard to cut and drill.

I bought two 28" hollow core doors for $24 each yesterday at work so I can make my clothes closet. I can't build a finished wall that cheap. We figured it out a few years back when we started using the doors as walls. Only thing is you do have to plan ahead for anything that you would want the wall to support. Our walls really don't support anything. And the ones that do use the 1" framing around the edges of the door. They paint up nicely (mine are all painted bright yellow).

 

[66788]

Hey, 66, I can answer that question. Reflective or "radiant" barriers only work by reflecting infra-red light. This polyiso foam usually has such a reflective barrier on one side.

Assuming there is an air gap, here is how the whole thing works:
1) The outside walls get hot from either the sun or just the outside air.
2) Because the walls aren't touching the insulation then they cannot transfer heat to the insulation through basic conduction.
3) Because the air gap is small, it is difficult for convection currents to get going, so the heat cannot get transferred by convection.
4) All that is left is infra-red radiation. But the reflective barrier bounces most of that back too.

So, why do we even need insulation at all? Because that air in that air gap will eventually get as hot as the wall itself and begin to conduct heat to the insulation directly. However, even though the air is the same temperature as the wall, it doesn't actually hold nearly as much heat energy because of all the, you know, empty space between all the air molecules. Therefore, the air transfers a lot less heat energy to the insulation than the wall of the truck would, so it does at least provide some insulation. Better than if we had just glued the insulation directly to the wall.

The super-efficient, closed-cell structure of the polyiso foam takes care of that last bit of heat and keeps it from getting to the inside. Of course, this assumes that NONE of that hot air can leak into your space. That is why air-tight barriers, often referred to as vapor barriers, are so important.

In theory this sounds good, but in reality, how do you explain the cold drink with ice in the 1/8 inch thick styrofoam cup not transferring the cold as there is no air gap in this application?

I think the foam stuck directly to the metal of the van is fine. I painted the inside of my window van's windows black on the driver's side and then added 2 inches of foam insulation. Touch the outside of the black window on a summer day and you will get burned. Touch the inside of the foam directly behind the window and it's about the same temperature as the ambient air. That's not theory, that's real life fact.

Reflectix can't do that, but styrofoam can.














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[ccbreder]

hard foam insulations don't need the air gap.

 

[GrantRobertson]

how do you explain the cold drink with ice in the 1/8 inch thick styrofoam cup not transferring the cold as there is no air gap in this application?

Perhaps we haven't been quite clear enough. No one is saying that you need an air gap for insulation to work. But you do need an air gap (actually an optical gap like glass or clear bubble wrap will do) if you want any reflective or radiant barrier to do any good.

The person who first discussed installing that polyiso insulation with an air gap did so because polyiso almost always has a reflective surface adhered to one side. If one wants to take advantage of the extra benefit that reflective barrier provides, then one must install said polyiso with an air gap and with that reflective surface facing said air gap.

Personally, when I have used the stuff, I have often skipped the air gap because all I was concerned about was the superior insulating properties of polyiso over the pink foam.

Reflectix can't do that, but styrofoam can.

You are correct. Reflectix is mostly good for when you have some surface that will get pretty hot (like the body of a van or truck sitting in the hot, Arizona sun, and you don't want that heat to be radiated (via infra-red light) directly into the inside. It doesn't really protect one from cold at all. If you plan on being in predominantly cold climates, then Reflectix as the outer layer is an absolute waste. Now, one could derive some benefit by using Reflectix as the inside layer of their wall "system" and letting the Reflectix reflect the infra-red from their bodies and other items inside the cabin back towards the inside of the cabin. While the effect is not nearly so great as when reflecting all that heat from the body of the vehicle back towards the outside on a hot day, you would be amazed at how much difference merely having your heat reflected back toward you can make. That is why those reflective, emergency blankets work so well.

Keep in mind that no insulation stops the transfer of heat (or cold) completely. It just slows it down. So, sometimes, if you can ALSO use a reflective barrier, such as in Reflectix or one side of most polyiso, then you can reduce heat transmission even further.

Finally, remember that the human hand is a very poor judge of how much heat is leaving an object. Our senses quickly get used to the temperature of an object we are holding. Keep in mind, even though you can't "feel" the cold from that styrofoam cup, the ice still melts over time. That means the heat from the air got into that cup somehow. Hint: it wasn't all just in through the top.

 

[Almost There]

Okay, I have another question - If I'm using foil backed polyiso sheets is there any point to also using reflectix? Or should I use reflectix and skip the foil backed polyiso in favor of one that doesn't have it.

Does one work better as a radiant heat barrier than the other..


And yes, that's more than one question...