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Old 09-18-2019, 09:10 PM   #21
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I agree with you, but I think he's talking about spray foaming the outside, which is an interesting concept that I've never heard of.
"You can get just as much insulation up there with practically no effort if you spray foamed the roof instead of the ceiling."
I was referring specifically to spray foaming the outside. It will not be effective.
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Old 09-18-2019, 10:39 PM   #22
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I see, I live in Phoenix now so thatís good information.

How was your spray foam? Just the ceiling, walls, or both? Closed cell or open? Did you paint your roof white? Radiant barrier?

I ask because, and Iím not personally accusing you at all so donít misinterpret, it seems like people want to stick a heater or ac in their conversions with some insulation and call it done. No real rhyme or reason besides ďreplace the fiberglass insulation with foamĒ.

Open cell foam wonít do much in a bus with a black roof for instance. Radiant barriers make a HUGE difference in an insulation plan along with that white roof paint, and some of the open cell people donít even bother to seal the bus of air infiltration which closed cell does but open cell doesnít.

Just some observations after watching YouTube videos and reading about peopleís builds.

People are quick to half do insulation and then just add another AC. I view the bus like a yeti cooler or a styrofoam cup. Itís an extremely insulated container (in theory) where you determine the air leaks. Like windows.

Look at how many people rip the ceilings out and remove perfectly good fiberglass. Why? Why not have that fiberglass dead space and that metal ceiling that you can stick magnet hooks to? You can get just as much insulation up there with practically no effort if you spray foamed the roof instead of the ceiling. Plenty of buildings use a foam roof, done right your bus can too. Bonus? You donít loose ceiling height with all those furring strips and wood planks, and any roof leaks just need minor attention and the foam itself finishes the sealing and repair.
that's my plan if my bus needs more insulation - spray the closed cell foam on TOP of the roof rather than under the ceiling - less labour, less cost, and at least as good a result
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Old 09-18-2019, 10:54 PM   #23
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I actually did some research on bus A/C systems and fouynd that the insulation and heat and A/C system is designed to make a 20* change over ambient. When it's cold outside the passengers are usually bundle up for the conditions, so it doesn't need to be hot inside during the winter, only warmer than the outside. Vice versa for when it's hot and the A/C is on. This is not acceptable for long term occupancy when a more efficient way can be done. Ya, it's easy to just add more to the underside of the ceiling, but then you have the headroom clearance raise it's ugly head to deal with. It's a bit more work up front to remove the ceiling, insulate, and build from there with little headroom loss and better insulation in the big surface that sucks heat and cold out.

1. I’m talking of sealing the roof, not the ceiling, no loss of height, no loss of structural rigidity (yes those steel sheets are a part of the reason why a school bus can roll with little damage. Those “roof raises” that are so “dangerous” are not really different from removing half of the roof structures metal.

2. 20 degrees over ambient is standard for any hvac. House, bus, it doesn’t matter. The difference comes from the amount of times the doors on a bus open vs a house. Of course the bus will have a much harder time reaching temp
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Old 09-18-2019, 10:58 PM   #24
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Spray foam roofs are very common now on new buildings, quite a few apartment buildings here in Phoenix use them.

It’s a 3lb closed cell, denser so it can be walked on, or have a ac compressor on it. (Ac’s on roofs are common here especially apartment buildings.

The thing with them? They work, and do I mean they work. They seal the roof and insulate it all at once. If we can build decks on a roof or a solar grid on the roof, we can figure out how to make a low lying very adhesive product already designed for roofs work on a bus.
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Old 09-19-2019, 12:12 AM   #25
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There is a single wide trailer nearby that was coated with spray foam from the outside then painted. It wasn't pretty but it has held up for years. As long as the foam is protected from the sun, the foam is good. Course it did burn up the other day- that couldn't have been pretty either
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Old 09-19-2019, 12:39 AM   #26
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1. Iím talking of sealing the roof, not the ceiling, no loss of height, no loss of structural rigidity (yes those steel sheets are a part of the reason why a school bus can roll with little damage. Those ďroof raisesĒ that are so ďdangerousĒ are not really different from removing half of the roof structures metal.
I've not yet seen any evidence proving roof raises lessen the structural rigidity.
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Old 09-19-2019, 12:49 AM   #27
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Really? Because it seems to be common knowledge in the community, from what I read. And a large part of the reason insurance companies decided to drop skoolies.
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Old 09-19-2019, 01:04 AM   #28
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Really? Because it seems to be common knowledge in the community, from what I read. And a large part of the reason insurance companies decided to drop skoolies.
It's common misconception is more like it. No one has provided any evidence to back up the claim. I agree there may be some reduction in strength due to the lever action of the longer ribs in a rollover scenario. But I think due to the massive "fudge factor" build into a bus , that percentage less is still far exceeding what is safe. I've spoken to a lot of insurance comapnies in the last year about insuring skoolie, never was roof raise ever broght up as a reason for non compliance.
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Old 09-19-2019, 11:04 AM   #29
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I see, I live in Phoenix now so that’s good information.

How was your spray foam? Just the ceiling, walls, or both? Closed cell or open? Did you paint your roof white? Radiant barrier?

I ask because, and I’m not personally accusing you at all so don’t misinterpret, it seems like people want to stick a heater or ac in their conversions with some insulation and call it done. No real rhyme or reason besides “replace the fiberglass insulation with foam”.

Open cell foam won’t do much in a bus with a black roof for instance. Radiant barriers make a HUGE difference in an insulation plan along with that white roof paint, and some of the open cell people don’t even bother to seal the bus of air infiltration which closed cell does but open cell doesn’t.

Just some observations after watching YouTube videos and reading about people’s builds.

People are quick to half do insulation and then just add another AC. I view the bus like a yeti cooler or a styrofoam cup. It’s an extremely insulated container (in theory) where you determine the air leaks. Like windows.

Look at how many people rip the ceilings out and remove perfectly good fiberglass. Why? Why not have that fiberglass dead space and that metal ceiling that you can stick magnet hooks to? You can get just as much insulation up there with practically no effort if you spray foamed the roof instead of the ceiling. Plenty of buildings use a foam roof, done right your bus can too. Bonus? You don’t loose ceiling height with all those furring strips and wood planks, and any roof leaks just need minor attention and the foam itself finishes the sealing and repair.
We gutted the bus, removed windows, raised roof, resided window openings, installed RV windows then sprayed closed cell polyurethane foam.

The whole bus was painted Arctic white.

I used the Mylar bubble wrap for my windshield cover. I found that it performed notably better when on the outside of the windshield.

I also made window inserts from 1" foam insulation board.

I am not sure how well an exterior foam roof would fair on a bus. After six years of bouncing around the country I managed to accumulate a number of scratches on the roof. Sometimes you can't avoid low hanging tree branches.
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Old 09-19-2019, 11:55 AM   #30
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I was referring specifically to spray foaming the outside. It will not be effective.
But the metal roof is now under a couple inches of spray foam insulation, so it presumably wouldn't conduct heat to the interior metal ceiling panel. What am I missing?
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Old 09-19-2019, 12:23 PM   #31
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So you think a roof painted white doesn't heat up at all in the sun? You might want to get a thermometer and find out if that's true or not.

I went up on the roof of my first bus bare footed ONCE. It was August in AZ....

I did about 15 seconds of happy dance, climbed back down and put on some shoes.

The bus was painted with Arctic White Imron.

The white paint definitely helped with the heat but did not eliminate it by any means.

A member here did a pretty decent test of various roof paint/coatings.

He cut his ceiling metal into squares and coated each one with a different product. Then he laid them out on sawhorses. After a suitable time for them to warm in the sun he measured the temperature of the underside of each one.

IIRC: he used Rustolium, Buscoat, Henry's and some others. The Buscoat Was The "winner" by a tiny margin. Running a very close second was white Rustolium with sawdust mixed in it.

I don't remember all of the details but I made the decision when I read the results that I am simply going paint the roof white.
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Old 09-19-2019, 05:59 PM   #32
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that's my plan if my bus needs more insulation - spray the closed cell foam on TOP of the roof rather than under the ceiling - less labour, less cost, and at least as good a result
The reason people are against this idea is because of the conductive qualities of metal. Unless you spray foam the ENTIRE outside of the bus, heat and cold will conduct straight through the walls of the bus, into the ribs, cross into your metal ceiling, and radiate from there into the living area.
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Old 09-19-2019, 06:13 PM   #33
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The reason people are against this idea is because of the conductive qualities of metal. Unless you spray foam the ENTIRE outside of the bus, heat and cold will conduct straight through the walls of the bus, into the ribs, cross into your metal ceiling, and radiate from there into the living area.
Ahhh...thanks for the explanation, I can totally envision the path of thermal bridging now.
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Old 09-19-2019, 08:27 PM   #34
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You insulate the roof and only the outside edges now conduct heat, so you insulate the walls too (obviously) so you have a small ring around the bus that is thermally conductive. By small I’m talking the thickness of the sheet metal. That clearly is less than an exposed metal roof (to the sun) that has a couple dozen u channel ribs stretching the width of it.

As far as roof paint, you used the wrong one. As I said I work in phoenix, on an apartment building, with a spray foam roof that was painted white. It’s max 130 degrees on a 115 degree day. That’s only 15 extra degrees on the top side of the foam.

They aren’t spraying roofs on new construction for no reason. It works, it completely seals any unwanted air exchange and water leaks, and you don’t lose interior space.
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Old 09-19-2019, 08:35 PM   #35
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Itís max 130 degrees on a 115 degree day. Thatís only 15 extra degrees on the top side of the foam.
Damn!! I will solve this problem by avoiding any place that is 115*!!!!
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Old 09-19-2019, 08:36 PM   #36
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You insulate the roof and only the outside edges now conduct heat, so you insulate the walls too (obviously) so you have a small ring around the bus that is thermally conductive. By small Iím talking the thickness of the sheet metal. That clearly is less than an exposed metal roof (to the sun) that has a couple dozen u channel ribs stretching the width of it.

As far as roof paint, you used the wrong one. As I said I work in phoenix, on an apartment building, with a spray foam roof that was painted white. Itís max 130 degrees on a 115 degree day. Thatís only 15 extra degrees on the top side of the foam.

They arenít spraying roofs on new construction for no reason. It works, it completely seals any unwanted air exchange and water leaks, and you donít lose interior space.
Yeah, but I don't imagine these new buildings you're talking about have metal walls that conduct directly into the interior ceiling; buses do.
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Old 09-19-2019, 08:39 PM   #37
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I’m fine with having to be the first to try it lol, but I’ve seen enough spray foamed roofs with that white paint with those little glass beads in the hottest major city in the country to know that it’s far superior to anything else.

Still looking for a bus though, and storage is an issue. So I’m thinking I won’t start for another year on an actual bus, just buying some of the bigger items in advance.
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Old 09-19-2019, 08:42 PM   #38
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just buying some of the bigger items in advance.
Oooh, save the receipts.....don't ask me how I know
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Old 09-19-2019, 08:45 PM   #39
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Yeah, but I don't imagine these new buildings you're talking about have metal walls that conduct directly into the interior ceiling; buses do.
A regular insulated bus does too though, thatís the point. Every reinforcing rib is directly attached to the metal skin on the top. Putting insulation between them is great but still leaves them exposed. Putting a ceiling on like wood with furring strips helps keep the heat directly off the ceiling, but itís not air tight and will conduct heat. EVERYTHING conducts heat, r value addresses conduction but not convection or infrared. Having that fully sealed insulation which closed cell inherently is, is a large factor that is completely ignored by r value ratings.

Would you rather put water in a cup with an inch of fiberglass for walls or 1/8 inch styrofoam? Which had the higher r value?
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Old 09-19-2019, 08:53 PM   #40
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A regular insulated bus does too though, thatís the point. Every reinforcing rib is directly attached to the metal skin on the top. Putting insulation between them is great but still leaves them exposed. Putting a ceiling on like wood with furring strips helps keep the heat directly off the ceiling, but itís not air tight and will conduct heat. EVERYTHING conducts heat, r value addresses conduction but not convection or infrared. Having that fully sealed insulation which closed cell inherently is, is a large factor that is completely ignored by r value ratings.

Would you rather put water in a cup with an inch of fiberglass for walls or 1/8 inch styrofoam? Which had the higher r value?
Is the cup open cell foam?
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