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Old 03-03-2014, 04:24 PM   #1
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Insulation added to outside of roof?

So I have this hare-brained idea of adding insulation to the outside of the roof, in order to maximize both insulation efficiency and headroom without doing a roof raise. I thought the best way to go about it might be to laminate thin layers of a flexible insulation panel, such as 1/2" Styrofoam (several thinner layers would be more flexible than one thick layer), and then coat it all with fiberglass, then a top coat of Hytech Bus Kote. This should eliminate the problem of thermal transfer through the metal structure of the roof. I'm thinking four layers of 1/2" foam sheets would be enough. The down side as I see it would be the potential for delamination and the altered appearance of the bus.

Has anyone ever tried something like this? What were your results? Any advice?
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Old 03-03-2014, 07:40 PM   #2
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Re: Insulation added to outside of roof?

In some commercial and industrial applications, a 6 pound spray foam is applied directly to the outside of the steel roofing.

Spray foam is painted with a UV stable latex paint. Repaint every 5 to 10 years with a sprayer.

For reference the spray foam used in homes is 2 pound, and the great stuff cans are half pound density. They use 6 pound so they can walk on it, and to take hail.



Anything else would be a nightmare to secure well enough to drive down the road.

Nat
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Old 03-04-2014, 09:29 AM   #3
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Re: Insulation added to outside of roof?

Thanks Nat. That looks like the easiest way to do it, but how would it look on the bus? I was hoping to make it look nice and smooth and original looking. I think the spray foam would require a lot of sanding/shaving to make it look decent. I hadn't thought about the density. Good point.
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Old 03-04-2014, 10:19 AM   #4
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Re: Insulation added to outside of roof?

The initial install would need to be done carefully and neat as possible. I think as long as the edges were strait and defined, and thickness was consistent, it would look alright.

It would not take much. 1 inch would do wonders, and over 2 inches would be just wasting.

Nat
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Old 03-04-2014, 10:56 AM   #5
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Re: Insulation added to outside of roof?

How do you think it would hold up to the vibration and wind from driving? It is intriguing to me that they actually do this on buildings, but they don't have to deal with vibration and constant 60+mph winds.
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Old 03-04-2014, 11:05 AM   #6
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Re: Insulation added to outside of roof?

I really like this idea! It would be especially do-able if you will have a roof rack on top, so there is even less concern about appearance, or possible damage from the environment or walking on it.
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Old 03-04-2014, 11:06 AM   #7
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Re: Insulation added to outside of roof?

The adhesion is good enough, and the 6 pound density is quite strong.

I'm sure it won't, but If the surface started to get tattered, we could give it a thin coating of fiberglass.

I was going to use this process on my bus, but decided with my roof deck, roof raise, and 6 inches of attic insulation, it won't be needed.

I was going to share this Ida last fall when I first saw it on a job site, but got busy and forgot. I'm glad some one asked.

Nat
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Old 03-04-2014, 11:13 AM   #8
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Re: Insulation added to outside of roof?

Very interesting indeed. I can especially see where this would be a viable option with a roof deck. I'm having a hard timing getting the picture of a roof covered in great-stuff foam out of my head, but I realize that is NOT what it would look like
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Old 03-04-2014, 11:27 AM   #9
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Re: Insulation added to outside of roof?

Quote:
Originally Posted by JakeC
I'm having a hard timing getting the picture of a roof covered in great-stuff foam out of my head, but I realize that is NOT what it would look like
Lol, yup I can see that being a little traumatizing. It looks more like elephant skin.

Some pics from Google.





This one has 3 inches of foam over normal corrugated roofing tin.



Nat
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Old 03-04-2014, 12:44 PM   #10
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Re: Insulation added to outside of roof?

That is pretty dang cool. Definitely nicer than the picture in my head, lol!!
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Old 03-04-2014, 01:02 PM   #11
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Re: Insulation added to outside of roof?

LOL, just kidding...kind of. This wil probably cost more than you paid for your bus.
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Old 03-04-2014, 02:14 PM   #12
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Re: Insulation added to outside of roof?

Quote:
Originally Posted by crazycal
This wil probably cost more than you paid for your bus.


No idea of the cost...haven't gotten that far yet. But I definitely need to keep the budget reasonable. If it costs too much I'll have to nix the idea.
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Old 03-04-2014, 02:32 PM   #13
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Re: Insulation added to outside of roof?

Unfortunately, nothing good is cheap.

6 pound foam is $3 a square foot by 1 inch thick.

8' wide X 40' long = 320 square feet.

$1056 for 1 inch thick.

$1584 for 1.5" thick.



As long as your not walking on it, 2 pound would do fine.

2 pound foam is $1.10 a square foot by 1 inch thick.

$352 for 1 inch thick.

$528 for 1.5" thick.


As the density go's up, the coverage go's down. 4 pound go's half as far as 2 pound, ect.

Nat
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Old 03-04-2014, 06:34 PM   #14
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Re: Insulation added to outside of roof?

That 2 pound sounds affordable. The 6 pound seems steep though.

Hat tip to Lorna for turning me on to this article:

http://www.busnut.com/artgm04.html

Interesting point the author makes about expansion and contraction. I wonder if this issue could cause spray foam to delaminate from the exterior bus skin?

Probably wouldn't be any cheaper with that aluminum cover but might look better. I wouldn't need to insulate the outside of the end caps because they're made of moulded fiberglass and I could fill them with insulation when I remove the flasher lights.
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Old 03-04-2014, 11:52 PM   #15
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Re: Insulation added to outside of roof?

Quote:
Originally Posted by nat_ster
Unfortunately, nothing good is cheap.

6 pound foam is $3 a square foot by 1 inch thick.

8' wide X 40' long = 320 square feet.

$1056 for 1 inch thick.

$1584 for 1.5" thick.



As long as your not walking on it, 2 pound would do fine.

2 pound foam is $1.10 a square foot by 1 inch thick.

$352 for 1 inch thick.

$528 for 1.5" thick.


As the density go's up, the coverage go's down. 4 pound go's half as far as 2 pound, ect.

Nat

I was going to guess a couple bucks a foot. I was checking prices recently and it was expensive. Then you need to do the fiberglass.
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Old 03-05-2014, 04:22 PM   #16
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Re: Insulation added to outside of roof?

Quote:
Originally Posted by Locutus
Interesting point the author makes about expansion and contraction. I wonder if this issue could cause spray foam to delaminate from the exterior bus skin?
Spray foam is basically plastic. It will contract and expand at the rate of the substrait it was sprayed onto.

So far I have never seen spray foam delaminate from anything. It even sticks to plastic vapor barrier.

I had to do two small demo jobs where a home owner made a big mess of wiring, plumbing, and studs behind a planned kitchen counter.
I started trying to remove individual wires, pipes, ect to make the needed changes. Even using a keyhole saw, utility knife, claw hammer, ect.
It was so hard to get apart, it took 4 times as long. My 10 pound sledge hammer, and the reciprocating saw were the main players. I had to cut the foam vertically between every stud, then smash the studs out with the 10 pound hammer. I had to remove everything they had done because everything was encased in a semi flexible, impact absorbing mass.

If all homes were built with this stuff, they would be 50% stronger. In our blue prints, when a home calls for foamed walls, the engineer will sometimes remover sheeting from interior wind thrust walls due to how stiff the structure becomes.

Nat
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Old 03-13-2014, 08:34 AM   #17
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Re: Insulation added to outside of roof?

didn't someone glue down 1/2 poly panels and then free floated a thin aluminum skin over it?(only attached at sides above windows and front/back)
the edges over lapped to move with expansion/contraction

It was down years ago and was still working after atleast 10 years on the road
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Old 04-22-2015, 09:02 AM   #18
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I keep thinking about going with this spray on roof foam. I love the idea and it seems like what I need. I am hoping cost is a regional thing. Since I am in Central FL but plan to travel, I could get prices based on location and wait until I get where it is cheaper.
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Old 04-22-2015, 09:05 AM   #19
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Since I'm right near you, maybe we could get another bus owner or two to join us on trying to get a volume discount.
Worth a shot. I will be wanting insulation in a couple months.
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Old 02-13-2016, 06:38 PM   #20
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Has anyone actually used spray foam on the outside/ rooftop? How has it worked... sounds interesting
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