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Old 01-07-2020, 05:57 PM   #1
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Fiberglass insulation?

Hey everyone!


So I am getting ready to start demo on my bus tomorrow and have been doing as much research up to this point and I have a question about insulation. I have seen a lot of people doing closed foam insulation with is super nice, but a little pricey.



Then I see a lot of people using foam board and expansion foam to fill the cracks, but I am curious why no one is using standard fiberglass paper backed insulation? I am estimating from the outer skin to the inside of the studs will be about 3" so R13 would fit.



Is there a reason people are not using it?


Thank you in advance!
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Old 01-07-2020, 06:34 PM   #2
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I think you want the thinest wall possible, bus walls are only 1 inch thick,not 3. don't think you need or want to pad it out. Every inch counts inside.

foam boards are twice the r value then fg and you are not buying a house load (even though it cost way more)!
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Old 01-07-2020, 06:38 PM   #3
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Originally Posted by matthews2001 View Post
I think you want the thinest wall possible, bus walls are only 1 inch thick,not 3. don't think you need or want to pad it out. Every inch counts inside.

foam boards are twice the r value then fg and you are not buying a house load (even though it cost way more)!

I have not pulled the inner skin off, but I am guessing the ribs are an 1" and then flat 2x3 or 2x4 adds another 1.5" I have a thomas so my walls are not straight so I am going to lose a tiny bit more space than most.



The fiberglass is rated R13, but most of the foam board I have seen is R4-7
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Old 01-07-2020, 06:52 PM   #4
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Quote:
Originally Posted by asquarecan View Post
I have not pulled the inner skin off, but I am guessing the ribs are an 1" and then flat 2x3 or 2x4 adds another 1.5" I have a thomas so my walls are not straight so I am going to lose a tiny bit more space than most.



The fiberglass is rated R13, but most of the foam board I have seen is R4-7
I was pricing XPS board at home Depot today. 2 inch board was listed as R-10. Inch and a half was $3 cheaper and valued at R7.5. so doubling that gives you a little more then the batt insulation.

I kind of have the same question though. I think it's a matter of condensation and mold. I took out my ceiling and the bat insulation that came with the bus was in good shape. But the compressed stuff that they had in the walls was really bad.
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Old 01-07-2020, 07:12 PM   #5
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Quote:
Originally Posted by asquarecan View Post
I have not pulled the inner skin off, but I am guessing the ribs are an 1" and then flat 2x3 or 2x4 adds another 1.5" I have a thomas so my walls are not straight so I am going to lose a tiny bit more space than most.



The fiberglass is rated R13, but most of the foam board I have seen is R4-7
XPS foam is R5 per inch, so 3" would be R15, a bit better than fiberglass. The superior performance of foams is partly due to the fact that the blower gases used to create the tiny bubbles have a lower thermal conductivity than regular air (which is mostly nitrogen); over time these gases leech out and are replaced with regular air, lowering the effective R value and making it more like fiberglass.

One downside to fiberglass insulation is that if it gets wet it loses most of its insulating capacity. If you get a leak with foam you still have to deal with the leak, but you won't also get your wall freezing up in the spot because of suddenly-ineffective insulation.
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Old 01-07-2020, 07:46 PM   #6
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Originally Posted by musigenesis View Post
XPS foam is R5 per inch, so 3" would be R15, a bit better than fiberglass. The superior performance of foams is partly due to the fact that the blower gases used to create the tiny bubbles have a lower thermal conductivity than regular air (which is mostly nitrogen); over time these gases leech out and are replaced with regular air, lowering the effective R value and making it more like fiberglass.

One downside to fiberglass insulation is that if it gets wet it loses most of its insulating capacity. If you get a leak with foam you still have to deal with the leak, but you won't also get your wall freezing up in the spot because of suddenly-ineffective insulation.



That makes a lot of sense! I figured there was a reason, but couldn't figure why! I will go with the foam board then! Once I get it gutted and framed I will determine the correct thicken and seal her up as good as possible!
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Old 01-07-2020, 07:58 PM   #7
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That makes a lot of sense! I figured there was a reason, but couldn't figure why! I will go with the foam board then! Once I get it gutted and framed I will determine the correct thicken and seal her up as good as possible!
If you click on "User CP" you can edit your details, like where you are in the country and what kind of bus you have - helps people tailor their answers to your specific concerns.

If you're going with 3" of insulation (which is great, the more the better, but 3" seems pretty rare in the skoolie world because of how much headroom it costs), one option is reclaimed polyiso foam, which is often available in a 3" thickness, and relatively cheap. Polyiso is R-6.5 per inch (at higher temperatures, anyway - it's more like XPS in cold weather) so almost an R-20.
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Old 01-07-2020, 08:07 PM   #8
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I have a Thomas. The ribs are 1 1/2” on mine.
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Old 01-07-2020, 09:18 PM   #9
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Originally Posted by musigenesis View Post
If you click on "User CP" you can edit your details, like where you are in the country and what kind of bus you have - helps people tailor their answers to your specific concerns.

If you're going with 3" of insulation (which is great, the more the better, but 3" seems pretty rare in the skoolie world because of how much headroom it costs), one option is reclaimed polyiso foam, which is often available in a 3" thickness, and relatively cheap. Polyiso is R-6.5 per inch (at higher temperatures, anyway - it's more like XPS in cold weather) so almost an R-20.



Now that I officially have a bus I will need to update that! I will see how much space I have. I will do the math and see if spraying it will much of a cost difference. I just want it to snug and warm.
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