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Old 07-24-2020, 12:53 PM   #1
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Wall insulation - lots of prep questions

Hey folk! We've got the bus mostly gutted. It looks like I'll be able to get 1.5" foam boards in the walls and still not cover the chair rail (or 2" and only cover a bit of it).

When y'all gutted your walls, did you trim down the protruding screws that anchor the outside rub rails? Or just push foam directly onto them?

Any particular glue to use for polyiso foam? How do I minimize squeaks when driving?

The stuff I'm using has an aluminum face. Should I put that "face in" so it's rubbing on wood instead of steel?

I'm not adding any wiring inside the walls (no need, it's a very simple electric layout), but did you put anything over any 12v wiring (running lights, stop sign, etc.) before putting in the foam? How about at the back, where the tail lights are... Did you insulate directly over the light housings? Cut access holes?

Thanks a million!
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Old 08-25-2020, 10:46 PM   #2
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Unhappy Air space

I hope you haven't insulated yet the way you described.
You should leave an airspace between the outer steel and the insulation. Read some of the other threads to understand why. Steel conducts heat and cold and will lower the r value received from insulation.
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Old 08-26-2020, 05:40 AM   #3
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In order to reflect radiant heat (which is different from heat transfer via conduction and convection), the foil layer needs to be facing the source of that radiant heat (which in the case of a bus would be the steel roof, heated well above the ambient air temperature by direct sunlight) with an air gap of at least 1". The only way you could achieve that would be to attach the insulation foil side up to the ribs at ceiling level, using the 1.5" gap between the ceiling and the roof as the air gap. This would cost you an inch and a half of internal head room, and it would only give you an additional insulating benefit of about R-2, and only in summer when the bus is in direct sunlight.

Since you're installing your foam in the gaps between the ribs with no air gap, it doesn't matter which way you point the reflective layer. This does not mean the insulation is worthless since it's still an inch and a half of polyiso, which should give an R-value of about 10. It just means that the foil layer is worthless in your scenario.
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Old 08-26-2020, 07:13 AM   #4
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I would not leave an air gap between the skin and the insulation. The insulation will have a higher R value than an air gap as heat will transfer through the air gap by convection. An air gap would also provide an area for condensation on the sheet metal. You should be able to find an adhesive that is compatible with the foam board and steel. I would try to get a thin layer of adhesive across the entire surface of the insulation for no gaps. Face the foil side in to keep radiant heat in the bus for when your trying to heat it. The area that will transfer the most heat is your ceiling and wall ribs if insultion is not placed between them and your interior wall or ceiling.

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Old 08-26-2020, 07:42 AM   #5
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Quote:
Originally Posted by TJones View Post
Face the foil side in to keep radiant heat in the bus for when your trying to heat it.
There's very little radiant heat involved in an interior at 70F or below, and the reflective side would not have an air gap since it would be covered by the ceiling. It would make no difference whether the board was installed foil side up or foil side down.
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Old 08-26-2020, 11:02 AM   #6
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At the present I'd agree with TJones and the others. However, before I poohoo your thoughts Bill&Angel I'd ask that you take the time to find and post links to the threads you refer to so we all can review them. I've been reading this forum for over ten years and while I could have missed something I've never seen a post that encourages leaving an air gap.
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Old 08-27-2020, 09:29 AM   #7
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I used 2” polyiso in my walls/ceiling. Works well with no air gap. More important than an air gap is addressing thermal bridging imho.
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Old 08-27-2020, 10:17 AM   #8
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I insulated my walls with 1.5 inch foam board.

It has air space, but I was not worried about it.. The walls are under single pane windows and the metal bus frame studs run down the wall every 24".
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