Why I'm Choosing Rockwool over Spray and Rigid.

TucsonAZ

Skoolie

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Join Date: Aug

Location: Lost

Posts: 106

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Coachwork: Bluebird

Chassis: All American

Engine: 8.3 Cummins

Why I'm Choosing Rockwool over Spray and Rigid.

Additional resources:
Hydrophobic silica
Overview of DIN Standard Hydraulic Fittings

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Sometimes I'm seeking out information and it takes forever and many sources to aggregate the data needed to make a fully informed decision. This is why I'M choosing Rockwool, all decisions are a balance of acceptable risks, rewards, time, finances for the person making them as well as other factors. This may not be the correct decision for you but here's the information I've gathered to lead me to my conclusion and hopefully it helps you.



I'll start with why I'm not using other options:


1) Fiberglass batts. Low R-Value and issues if it does get wet.



2) Polyurethane AKA Spray Foam AKA Soy Something or other (if they're attempting to greenwash it). Two part spray foam is the "Holy Grail" of insulation and, if you can live with the down sides (which are extreme) it's an amazing option. It's seamless, ties things together structurally, has a high R-Value and many other advantages.


The reality of this though is that no matter how hard you attempt to get a perfect install, no matter how good or experienced the installer. You ARE NOT going to get the zero VOC off gassing they're able to do with the tiny samples submitted for testing that actually cures in 48-72 hours. In the real world where a tiny difference of output between the A and B nozzles, more or less humidity, higher or lower temps all play a part in the final product you're looking at a solid 2-3 years of off gassing and that's best case. I'm not going to get into the specific chemicals or health concerns, I'll just say it isn't worth the risk for me in such a tiny space that requires so much effort to build.



This may totally be acceptable for you and your wants, needs, lifestyle, health concerns and so on. This is certainly the best option if you don't have the same worries I do and I can see why it's appealing enough that people choose it even with the incredible risks. And I know many of you don't even notice the off gassing, but that doesn't mean it isn't there.



3) Rigid Foam Board. This of course comes in XPS, Polyiso, EPS and so on. I think it's a good choice and mitigates some risks of 2 part foams, it does have some off gassing over a long time but it's low and within what I would call acceptable. It does still have flame retardants and the dust can be an issue but again this can be mitigated with boards that have a radiant barrier or are being used under subfloor.



My issue with this is getting a good, solid insulation envelope. Let's assume 3 inches of polyiso. If this were not a bus and all walls were flat I would choose it. But in a bus where we're having to accommodate a lot of curves with more cuts and needing so many seams and gaps I think it drastically drops the R-Value from what would be R20 in a 3" thick Polyiso to my speculation maybe an R12 or something. You can fill gaps with 1 part canned foam but I still think you're dealing with huge losses, a higher cost, and a lot of time and energy.



Don't get me wrong, this was my first choice and I still may use it on large, flat spans and will on the floor for sure, but I don't think it should be the only thing you're focused on to the point you're using it in less than ideal situations.



4) Single part spray foam. Can you imagine this, I mean, it addresses a lot of the issues, no risk like in the 2 part spray foams but I think it's best left for gaps here and there and filler. Unless you're insane, and seeing as you own a bus you likely are so maybe give it a shot.


5) Rockwool Formerly Roxul. I've used this a lot, comes in 2.5", 3", 3.5" so it should be easy to work into a build. Cuts easily with an electric bread knife, easy to install, seamless roof install even with the curves and offers you a respectable R3-R4 per inch. It's totally safe and chemical free and really comes with no down sides.



If you go to an insulation cost savings calculator you will see there is certainly a difference with the higher spray foam insulation but insulation has a law of diminishing returns. For example, going from R2 to R4 is HUGE, going from R4 to R6 is big, but those two jumps right there will make more of a difference than going from R6 to R20 and cost you much less. Basically think of it like this, every time you add R2 you double the gains but it's like halfing a number, if you start with 20 and you half it, you end up with 10, 5, 2.5, 1.25, 0.625 and you quickly see that your 50% off isn't making nearly the difference it did in the beginning but with insulation it's costing you time, money, and space. With insulation you hit a point of diminishing returns around R12 before you have to start making other compromises to gain more and those gains start doing very little.


At that point, I think you're better off adding a roof coating, higher SEER AC units, more solar and so on. After all, we have limited space so let's retain as much of it as possible and expend our energy and resources wisely.



I am actually going to try to get R15 Rockwool in the ceiling, I'll see how I feel about that, given the 2" stud depth it will cost me 1.5" of headroom, coupled with an 1" loss on the floor and I can live with that for my height and needs.



Soooo, those are my thoughts, I'll update in a year to see if I'm going to stand behind these decisions but I've built other units and worked with insulation a lot so I'm comfortable enough with this to move ahead given the ease of install and comfort I have in it being chemical free with no off gassing risks. I only got one life, I can buy 100 busses ( :

Why insulate:

There are many reasons to insulate walls, for heat retention, soundproofing, fire-blocking, and just for fun. I live in sunny San Diego where it rarely gets wet and it never gets truly cold. So while most insulate to keep comfortable in the winter, we&#;re insulating to keep cool in the summer and to reduce the noise of the airplanes overhead as well as the sounds from nearby rooms.

I used a few different insulation products:

R-15 Bat Insulation: All insulation has an R-value, which is a measure of how well a barrier resists the conductive flow of heat. The higher the R-value, the better the insulation will do to keep the cold air our and the hot air in (or vice versa). Often, to get a really good R-value, the insulation needs to be really thick, or it will get costly like spray foam insulation. The insulation I used is in the sweet spot of being efficient and not crazy expensive - plus it&#;s exactly the required R-value our city code calls for. I installed the R-15 insulation in the exterior walls of the kitchen and bathroom.

Soundproofing Insulation Bats: For the interior walls, we opted to add soundproofing insulation. It isn&#;t really necessary, but hey, while the walls are open, it&#;s the time to do it. We also thought it would be smart to dampen the noises between the kitchen and the bathroom since the toilet is literally on the other side of the stove.

Foam Sealant: For all the small holes, cracks, and gaps, I sealed them with expanding foam before installing the bat insulation over the top of them. I used a combination of fire-blocking and door foam. I&#;ll explain more below.

Learn more about R-value and insulation in this video.

1. Seal the gaps

Before filling the wall cavities with the insulation bats, I went around with expanding foam to fill the gaps to the outside, into the attic, or into the crawl space. Openings like gaps under the window or next to pipes are big culprits for heat transfer, so I filled them with some foam that sprays out like a really sticky mousse, then grows and hardens into a firm mushroom shape.

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