Why is Rock Wool Board Better?
Rockwool Comfortboard 80 Review: Is It The Best Option? - Rmax
Here, we cover the major benefits of Rockwool, its shortcomings, and what other options are available to insulate your walls in your home or commercial project.
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Benefits of Rockwool Board
Rockwool has a number of things going for it. Here are some of the benefits of choosing Rockwool Comfortboard 80 to insulate your project:
Made from natural and recycled raw materials
Excellent fire resistance with no smoke production or flame spread
Termite and insect resistant
High compressive strength
Provides acoustic sound absorption
Where to Use Rockwool Comfortboard 80
Rockwool Comfortboard 80 is designed for use on the exterior side of the wall for continuous insulation. It's installed with 3-inch washers and nails, and is attached to sheathing over a vapor barrier or house wrap. Other applications can include foundation walls and under concrete slabs.
Disadvantages of Rockwool Insulation
Rockwool is a great option for some projects, however this type of insulation isn't always the best for every application. Some of the shortcomings of Rockwool Comfortboard include:
Weight
It's heavy, at over 50 lbs. per 4' x 8' board at 2' thickness, which makes installation laborious.
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R-Value
At R4.2 per inch, Rockwool Comfortboard 80 is a middle-of-the-road option when it comes to thermal R-value performance.
Cost and Availability
Rockwool Comfortboard 80 can be difficult for homeowners to obtain because it is not typically stocked in big box stores, so it can be a challenge to obtain, and pricier to purchase.
An Alternative to Rockwool
Luckily, there is an alternative to Rockwool Comfortboard 80. Polyiso is a comparable option to Rockwool when it comes to installing insulation on walls. Taking it a step further, polyiso outperforms Rockwool when it comes to installability, thermal performance, and price point. If you're looking for a less expensive, lightweight alternative to Rockwool'without sacrificing on performance, consider polyiso.
Easier Installation
Polyiso can be installed in the same locations and applications as Rockwool as a continuous insulation, but with significantly less weight bearing on your installers and your walls. Since polyiso is made out of foam, it's inherently lightweight and can be carried and maneuvered easily by a single installer without suffering from the fatigue of lifting heavy Rockwool boards, which may require two installers per board, or smaller board sizes.
R-Value Thermal Performance
It's hard to beat the thermal performance of polyiso. At R6 per inch, it's one of the best thermal insulation options for walls. With polyiso products like Rmax Durasheath® building envelope insulation, you can achieve an R21.8 with just 3-½' thickness, whereas achieving this same R-value with Rockwool Comfortboard 80 requires over 5' thickness.
Affordability
Polyiso insulation is affordably priced at just over a dollar per square foot for a two inch thickness. Rockwool, on the other hand, can be quite pricey at nearly two dollars per square foot at the same thickness. Since you're getting less thermal insulating power for the same thickness, that's a double whammy.
Availability
Polyiso is more readily available for purchase by ordinary homeowners, because it is available at building supply stores. Rockwool Comfortboard 80, on the other hand, can be a specialty item that is not stocked in stores and often requires a special order and larger quantities.
Tailored Performance
Polyiso has a unique advantage over most other wall insulation types, including Rockwool Comfortboard 80'it can be tailored to meet your project's needs by applying an appropriate facer. Because polyiso not only accepts, but requires a facer during production, it gives you the choice between different performance properties that you want to incorporate.
For example, if you're looking for an air and vapor barrier, you can find an all-in-one solution with Rmax's ECOMAXci® FR Air Barrier. Rockwool, on the other hand, is vapor permeable and requires a second product to add vapor protection.
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Why I'm Choosing Rockwool over Spray and Rigid. - Skoolie Forum
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 ( :
I have to wonder why you dismiss fiberglass so quickly, it has the same r value per inch (3.7 per inch) as rock wool, no chemicals, nothing toxic about it, and as far as getting wet it does not hold moisture. So seems to be even with rock wool.
If you prefer rockwool, that is fine but you leave the impression fiberglass is worthless
I don't think it's worse, they have different qualities and I think for a bus build it's easier to work with the RW in terms of patching in pieces and so on. I also think it's safer in general.
I love the analysis, even if I might quibble with some of the details.
THIS is how we learn as a community, so thanks for the detailed write-up.
On to quibbling:
R value is a linear measure of thermal transfer. R6 is half the resistance to thermal transfer of R12, and R12 is half the resistance to thermal transfer of R24. R49 is two percent less resistant to thermal transfer as R50.
So in your example, R2 to R4 is double the value, but R4 to R6 is 1.5 times the value. Maybe I'm missing your point, but I think that's how the math works.
Perhaps you are referring to the total cost of the insulation, the bang for the buck, in which case yes, the labor is constant so the less R value you install the more expensive per...well, maybe the less overall (life cycle) value you get in return.
Agreed?
Yes, it's like lumen, aperture, and so many other things where you have to essentially double it to see a noticeable difference. I think we're saying the same thing, I'll post a picture I found so others have a visual. I'm basically saying that by R-12 you've gotten the most gains you're going to get given the effort and cost involved. This is even more apparent in a bus build where more may require a roof raise, more framing and so on. When you're at R-12 going to say R-14 is of course a gain but not a "substantial" one.
In short, I'm saying add as much as you can with the least effort, if you're at R-12 by the end of that you should be good. At that point you can put the effort and money into higher SEER, roof coatings or something else.
I'm pretty sure I clarified nothing so I'll just post the picture lol