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Old 05-17-2020, 04:52 PM   #1
Mini-Skoolie
 
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Got another one...

Ok, so here's my question. I am seriously debating whether to use spray foam insulation or foam boards. I initially was thinking spray foam all the way but now I'm trying to weigh the pros and cons like price, R-value, etc. I know there is a serious difference in R-value between the two but here's my situation: 1. I plan on keeping my windows (I love the look and having that view everywhere seems amazing to me). (btw, that could change but that is the plan for now). I know there will be heat/cold loss in the windows so I initially thought the better R-value in the insulation may offset a little in the windows. 2. My wife has assured me she will not visit a place where the temperature is below 40 degrees F at night. An occasional dip is ok with her but she does not like to be cold. So with staying in those types of climates we probably will not use a fireplace and hopefully will be fine with the combination of extra blankets and other small heat sources. So has anyone done a comparison of heat/cold retention/loss to see if the more expensive spray foam truly is a better choice given my current predicament/situation? Since I'm keeping my windows, does it really make a difference? And, how comfortable have you guys been inside your buses with your situation. I know this was a long one, but really trying to figure out what is the best option for me. Thanks again everybody!
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Old 05-17-2020, 05:26 PM   #2
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I went with 2" spray foam on the roof and 3" XPS boards on the walls. I'll probably add 1" of EPS to the roof also. Spray foam is much more expensive, but you can get into small spaces and it adds leak protection.

If you add spray foam, you'll go from 5 to 6.5 r-value per inch which is fairly marginal in my opinion. However, you'll quadruple or more your cost....

For spray foam, paying a professional is almost certainly cheaper than doing it yourself with spray foam also. It took me 3x $600 kits just to do my roof. For that price, I could have had a pro do the walls too and probably have had a more consistent job.

How big is your budget?
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Old 05-17-2020, 06:04 PM   #3
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There is no difference in R-value (per inch) between spray foam (at least the kind most commonly used) and XPS foam board - they're both 5 per inch, because they're both essentially the same substance once installed. Polyiso foam board has a higher rated R-value (6.5 per inch, although this actually declines with temperature so polyiso is slightly worse than XPS in cold weather) and you can also do polyiso spray foam with the same higher R-value (although I don't believe this is available in the cheap kit form).

The main advantage of spray foam over board is that if done correctly it will provide a (largely) waterproof barrier with no air gaps that could impair insulation performance (although it's not that difficult to install XPS foam board very snugly); it's also a lot easier to apply it to the curved ceiling. IMO spray foam is way too expensive and difficult to apply, while the benefits over foam board are too marginal.
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Old 05-17-2020, 06:23 PM   #4
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Quote:
Originally Posted by Mako View Post
Ok, so here's my question. I am seriously debating whether to use spray foam insulation or foam boards. I initially was thinking spray foam all the way but now I'm trying to weigh the pros and cons like price, R-value, etc. I know there is a serious difference in R-value between the two but here's my situation: 1. I plan on keeping my windows (I love the look and having that view everywhere seems amazing to me). (btw, that could change but that is the plan for now). I know there will be heat/cold loss in the windows so I initially thought the better R-value in the insulation may offset a little in the windows. 2. My wife has assured me she will not visit a place where the temperature is below 40 degrees F at night. An occasional dip is ok with her but she does not like to be cold. So with staying in those types of climates we probably will not use a fireplace and hopefully will be fine with the combination of extra blankets and other small heat sources. So has anyone done a comparison of heat/cold retention/loss to see if the more expensive spray foam truly is a better choice given my current predicament/situation? Since I'm keeping my windows, does it really make a difference? And, how comfortable have you guys been inside your buses with your situation. I know this was a long one, but really trying to figure out what is the best option for me. Thanks again everybody!

We used 3" foamboard in the walls, and 1/2" insulation over the metal ceiling. We kept our windows and made insulated shades that roll up from the bottom and are held at the top with tension rods. Like you, we love the look of the windows and how it really opens the space up (that was the appeal of a bus over an rv). If you're not planning on going where it'll be below 40 at night, then it shouldn't be a problem. We have a Chinese diesel heater installed and it keeps things toasty even on the coldest nights. An added benefit to keeping the windows is that it warms up nicely during the day due to the greenhouse effect, and it's easy to cool down due to all the ventilation, esp. with the back door open.
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Old 05-17-2020, 06:40 PM   #5
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Quote:
Originally Posted by Biscuitsjam View Post
I went with 2" spray foam on the roof and 3" XPS boards on the walls. I'll probably add 1" of EPS to the roof also. Spray foam is much more expensive, but you can get into small spaces and it adds leak protection.

If you add spray foam, you'll go from 5 to 6.5 r-value per inch which is fairly marginal in my opinion. However, you'll quadruple or more your cost....

For spray foam, paying a professional is almost certainly cheaper than doing it yourself with spray foam also. It took me 3x $600 kits just to do my roof. For that price, I could have had a pro do the walls too and probably have had a more consistent job.

How big is your budget?
My budget is fairly good (between 35,000-40,000). I plan on having someone doing my roof raise which I heard can be up to $10,000. I could afford the spray foam, just wanted to know if it is actually worth it. Sounds like the added waterproofing would be worth it.
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Old 05-17-2020, 08:13 PM   #6
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The trade-off with foam board is that you invite condensation and mold formation between the foam board and the bus body.
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