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Old 04-02-2015, 08:52 PM   #11
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Quote:
Originally Posted by nat_ster View Post
Phone your local spray foam contractors and ask them what kind of foam they spray. You only want closed cell, synthetic foams. No open cell, biodegradable types.
I want to re-iterate this: call a professional to do the spray foam!! I wasted money on doing it myself, largely because I wanted the experience (I could have done without the experience). Someone who does it day-in and day-out as their occupation will do a MUCH better job with less waste than a first-time DIYer.
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Old 04-03-2015, 07:11 AM   #12
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from Nat_ster-
Quote:
the expansion and contraction of the Styrofoam you mention is so little, it's not even a concern for me. The steel the bus is made from will likely expand and contract at close to the same rate as the foam.
I found a 'solution'.

From buildingscience.com
"Foam Shrinks, and Other
Lessons: Correction"
11 May 2012 Joseph Lstiburek

http://www.buildingscience.com/docum...Foam%20shrinks

"So what happened...? Foams, all of them, expand and contract due to temperature as do pretty much all materials. Some materials even expand and contract due to moisture changes... when foams are hot they get bigger. When they are cold they get smaller. All of them.

...So, bottom line, all foams move. All of them have joints that open up. All of this can be addressed by using a flexible material to handle the movement at joints or by using multiple layers with offset joints or by a combination of both."

Re:flexible joining material:
"What if you only have one layer of rigid insulation on your walls? Well, nowadays we have tapes and sealants and membrane strips that can withstand the movement. This is a big change over the past twenty years. When I did my barn the first time I tried to deal with the joints with a mastic. That particular mastic did not work. Today, there are all kinds of mastics that can work and in fact do work."

Here is a link to their index of articles including topics like air and water barriers and ventilation etc:

http://www.buildingscience.com/index_html

And the original article. There is a lot of good technical details about construction in here. It is about a retrofit of of a super-insulated barn/office after 16 years. What worked, what failed. Granted, it is based on a stationary building with breathable exteriors, but the details about ant/bug barriers, materials, and building products that lasted (or didn't) is quite informative.

http://www.buildingscience.com/docum...a-foam-shrinks
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Old 04-03-2015, 12:59 PM   #13
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Lightbulb Polyiso insulation- r-value decreases with temperature change. Test results here.

For anyone considering Polyiso insulation-

(This information is from the linked article below)

Polyiso Pro - it has one of the highest published R-values per inch.
HOWEVER- the FTC's R-Value rule requires that R-value tests be conducted at a mean temperature of 75F (23.9C) and a temperature differential of 50F (27.8C). This means that insulation is _usually_ tested with the cold side at 50F (10C) and the warm side at 100F (37.8C).3

Wouldn't you like to live in a climate with so little temperature variance???

So what happens if you have 2-2" polyiso boards for a 4" total, rated aprox R-24 on your mobile residence which can see 144*F solar heat in summer (apparent R-value decreases by 5) and negative temps in winter (apparent R-value of 4" at 0*F decreases by 7). According to these test results, you will need a more Polyiso to have the same apparent R-value, especially in cold climates. Another solution/suggestion is to use a hybrid insulation approach (I like this idea) - install cold temperature-tolerant insulation on the outside/cold side of the polyiso insulation to increase the mean temperature of the polyiso for maximum R-value effectiveness.

Source- Test results and explanations from Building Science:
Info-502: Temperature Dependence of R-values in Polyisocyanurate Roof Insulation — Building Science Information
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Old 04-03-2015, 02:20 PM   #14
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I used polyiso to insulate a thermal storage tank for a hot-water storage system on a wood boiler I installed a few years ago. It's very strong - around here, it meets code for roof overlayments (which is important because we can have high snow loads). Strong enough to be the underlayment under a 4'x8'x4' (around 800 gallon) tank full of water without compressing.

However, given my (admittedly limited) experience, I personally wouldn't recommend putting it in a bus. It's rigid almost to a fault, IMO it's harder to cut cleanly than other foams (I found a hacksaw blade worked best) and it absorbs water more than other foams. It might make good flooring, though.

If anybody is REALLY serious about using polyiso, if you're anywhere near the USA-NE area, I know a guy in New Haven, CT that sells this stuff for less than half what you can buy it anywhere else. He buys rejected lots from construction installations - if they get more than a few dings they're not allowed to use it there. He has 1"-4" thicknesses and posts them on Craigslist all the time. It sounds a little back-of-the-truck-ish, but the guy's legit.
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Old 04-03-2015, 02:44 PM   #15
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You guys are making my head hurt with all this stuff about expansion and contraction of Styrofoam.

So how much rigid Styrofoam do we need? This is my findings.

Last year late fall I installed my residential foam core entry door. Then I painted it black.

Sun came up one morning, it had been close to freezing that night. Black door was facing the sun.

Within a hour of the sun shining on the door, it was to hot to touch. One more hour later, you could not hold your hand within a inch of the surface of the door.

Back of the door stayed cold for 7 hours before the heat started to bleed through the 1.5 inches of rigid Styrofoam between the two metal surfaces of the door.

9 hours later, the backside of the door was still only only a few degree's warmer than the air temp around me. Then the sun started to set.

So how much rigid Styrofoam insulation do you need? No more than 2 inches by my findings. However 4 inches is always better than 2.

These are the kind of tests I'm interested in. All that other stuff just makes my head hurt.

Nat
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Old 04-03-2015, 03:18 PM   #16
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Polyiso insulation

Quote:
Originally Posted by taskswap View Post
I used polyiso to insulate a thermal storage tank for a hot-water storage system on a wood boiler I installed a few years ago. It's very strong - around here, it meets code for roof overlayments (which is important because we can have high snow loads). Strong enough to be the underlayment under a 4'x8'x4' (around 800 gallon) tank full of water without compressing.

However, given my (admittedly limited) experience, I personally wouldn't recommend putting it in a bus. It's rigid almost to a fault, IMO it's harder to cut cleanly than other foams (I found a hacksaw blade worked best) and it absorbs water more than other foams. It might make good flooring, though.

If anybody is REALLY serious about using polyiso, if you're anywhere near the USA-NE area, I know a guy in New Haven, CT that sells this stuff for less than half what you can buy it anywhere else. He buys rejected lots from construction installations - if they get more than a few dings they're not allowed to use it there. He has 1"-4" thicknesses and posts them on Craigslist all the time. It sounds a little back-of-the-truck-ish, but the guy's legit.
Thanks for sharing your experience tank swap. I will definitely look into that water absorption you mention. Not something I want to add on purpose. The Polyiso has the best published R-value per inch that I've found so far, but I'm still weighing all the other properties too.
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Old 04-03-2015, 03:34 PM   #17
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Quote:
Originally Posted by nat_ster View Post
So how much rigid Styrofoam insulation do you need? No more than 2 inches by my findings. However 4 inches is always better than 2.

These are the kind of tests I'm interested in. All that other stuff just makes my head hurt.
They make my head hurt too Nat, but for the life of me, I have been unable to fix my crystal ball and figure out which rigid insulation might be be the best choice, or which one might be inside your door that works so well in high temps.

I'm just trying to gather and share the facts until I figure out how to fix everyone's crystal ball. <wink>
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Old 08-23-2017, 02:42 PM   #18
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What about spray foam the undercarrage of bus
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Old 08-23-2017, 02:48 PM   #19
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Quote:
Originally Posted by jazty View Post
I want to re-iterate this: call a professional to do the spray foam!! I wasted money on doing it myself, largely because I wanted the experience (I could have done without the experience). Someone who does it day-in and day-out as their occupation will do a MUCH better job with less waste than a first-time DIYer.
Tobeamiss did a bang up job of spray foaming, and spent a fraction of what a "pro" would charge. Dave did his own, too.
The kits aren't too hard to use, and I'll bet the big dollar contractors will eventually either cease to be or have to adjust their egregious pricing.
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Old 08-23-2017, 03:33 PM   #20
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I found a spray foam guy did my bus for $750. Hes in northern illinois
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