Best insulation

[ConnorJDavis]

Hey everyone! I am getting close to insulating my school bus and wanted some suggestions on what to be looking for and what is the best insulation for a school bus??

[o1marc]

Spray insulation is commonly preferred, but price is high. Rigid board is used most often.

[john61ct]

Polyiso boards for most of the thickness, with a 1/2" of XPS facing the cold side if extreme.

Spray for sealing the gaps, getting a well-sealed envelope and moisture barrier is just as critical as R-value.

Heavy curtains to create smaller partitioned spaces.

Nothing reflective except for windows.

[shaymcquaid]

I’ll second the polyiso foam board.
Check FB marketplace or Craigslist for sources.

[dzl_]

Originally Posted by john61ct

Nothing reflective except for windows.

What do you mean by this, and what is your reasoning?

[john61ct]

Many people are duped into thinking that Mylar sheet products like "Reflectix" and/or bubble wrap have some sort of value to add to proper insulation.

A near-total waste of time and money in a space-limited mobile context.

They can help with the vapour barrier part, but much cheaper drop-cloth plastic does that just as well.

However, the ability to prevent most solar radiation from penetrating glass can be useful in building (usually removable) blackout / insulation covers, when pointing out only of course.

[dzl_]

Originally Posted by john61ct

Many people are duped into thinking that Mylar sheet products like "Reflectix" and/or bubble wrap have some sort of value to add to proper insulation

Ahh yes, I see what you mean now. And even with glass, I see a lot of people using it to "insulate" their windows on cold nights, but afaik, that reflectix is pretty useless in that situation (though if its tightly fitted i guess its probably as effective as double paned windows would be).

A near-total waste of time and money in a space-limited mobile context.

They can help with the vapour barrier part, but much cheaper drop-cloth plastic does that just as well.

However, the ability to prevent most solar radiation from penetrating glass can be useful in building (usually removable) blackout / insulation covers, when pointing out only of course.

To be honest, I'm still trying to wrap my head around the different modes of heat loss/gain and how to properly address each vector. Its a hell of a lot harder, and you have to get a lot more creative in a bus than in a traditional home.


I think you are right about the overuse and misuse of reflectix and the high levels of misinformation about how to properly use it.


That said, beyond blocking solar radiant heat, I think it has a few other limited uses. I think if your heat source primarily 'radiates heat' (woodstove, catalytic heater) strategic use of reflectix or some other radiant barrier to keep heat in and direct it in a useful direction would be useful. But even this in many cases would probably be a marginal gain.

[musigenesis]

An interesting aspect of foam insulation (either spray or boards) is that the blower gases (used to make the little bubbles in the material) have a lower thermal conductivity than air. Over time, these blower gases migrate out of the foam and are replaced with regular air, which results in a lowering of the material's R-value. The rate at which this happens is dependent on a variety of factors, like thickness of the material, temperatures it's exposed to etc., but it's in the neighborhood of a 10-15% loss after 5 years (other types of insulation do not experience this kind of degradation, since they incorporate regular air from the start). Not really a huge deal since it will still have a better R-value per inch than the alternatives, but interesting. (A side note though is that occasional exposure to high temperatures - as would be pretty common with a bus left out in the sun from time to time - will accelerate this degradation.)

Polyiso is also interesting because most insulations have a declining R-value with increasing temperature, but (at least within the range of temperatures experienced by people) polyiso's R-value actually increases with temperature, meaning it only achieves its R-6.5 per inch value at temperatures above 60F (in colder weather it's still as good as XPS, though, so this is not a reason to not use it in cold climates). It's almost certainly the best hot-weather insulation there is per inch (not counting aerogel).

I've been looking at rock wool as well, at least for the ceiling because it would be easier to form it to the curved ceiling. I found an ad on CL not long ago from a guy dumping enough 2" CavityRock to do my entire bus for $300. Unfortunately, as with all good Craigslist things it was immediately gone - although his ad is still up to torment me.

[EastCoastCB]

I'd use foam in the ceilings and roxul in the walls. And foam board on the floor.

[banman]

Anyone have any experience with this?
I like the idea -- seems promising...

https://havelockwool.com/van-insulation-products/

[musigenesis]

Originally Posted by banman

Anyone have any experience with this?
I like the idea -- seems promising...

https://havelockwool.com/van-insulation-products/

The rigid foam and the glue used to install it are petro-chemical based products that shouldn’t exist in your van.

Uh, what do these guys think vans are made out of in the first place? Unicorn horn and dragon saliva?

[ACamper]

I like any insulation that is not fiberglass..

[EastCoastCB]

Originally Posted by musigenesis

Uh, what do these guys think vans are made out of in the first place? Unicorn horn and dragon saliva?

Its just "eco" salesmanship. I'd avoid using anything organic like wool or shredded up denim jeans. Those are the two that pop up from time to time.

LOL at the toxic glues part.

That's the best they can do to try and sway a customer from foam haha.

[gastone]

Originally Posted by musigenesis

Uh, what do these guys think vans are made out of in the first place? Unicorn horn and dragon saliva?

My BIL built out a Dodge Pro-Master and went with wool insulation. I'm not sure of which manufacturer. He and his wife live in Idaho and camp/hike/rock climb regularly. They've been very satisfied with their choice.

Of course the scale of a van ain't exactly the scale of a full size bus. Then again, I might be able to afford spray insulating my bus, but no way could I afford to do it to my house.

[dzl_]

Originally Posted by EastCoastCB

Its just "eco" salesmanship. I'd avoid using anything organic like wool or shredded up denim jeans. Those are the two that pop up from time to time.

I agree about the "eco salesmanship," but I don't understand why you would avoid using any organic insulation as a blanket rule.

I don't have any expertise or first hand experience with organic insulators in vehicle or building applications. But in the outdoor industry (where performance is super important) natural insulators (most notably merino wool, goose down, and quiviut) reign supreme. Outdoor companies spend millions and millions of dollars developing synthetics to compete with or outperform these natural insulators, but even companies like Patagonia who spend massive amounts developing synthetics and are on the cutting edge of synthetic design and innovation are just barely beginning to bring synthetics to a level where they can compete with natural fill.

This is not to say that synthetics are inferior (it depends on your use case) or that the experience in the outdoor industry translates directly to Skoolies or building. But I would push back against your blanket dismissal of natural insulators in general. For many use cases they are still top of the line.

Wool is an extremely effective and time tested insulator for many use cases. I have never considered using it as insulation in a bus or a home, as many of its strengths are less important in that context than in the outdoor industry and i'm a little skeptical for its suitability for this application, but I would hesitate to write it off entirely based on it being 'organic' without some good evidence of its inferiority for the application.

In terms of denim, I believe that is a form of cotton right? If so, I definitely wouldn't be using it in an application where moisture will likely be an issue (such as a Skoolie) unless its been treated with a hydrophobic conditioner and your heat source will sufficiently dehumidify the air.

It occurs to me after writing out this whole comment, that I may be misinterpreting yours. And that your advice to avoid 'organic insulation' is not a blanket generalization but advice based on specific design goals and the specific types of organic insulation on the market for home/vehicle insulation. I interpreted your comment as a blanket dismissal of 'natural' insulation in general, but I see that in a previous comment you recommended roxul which I believe is a mineral wool. correct? My apologies if I misunderstood you, I'm leaving my comment as is, as it still probably adds value to the discussion.

[dzl_]

And on another note, I am curious to learn more about Roxul and why you recommend it for the walls specifically. It seems XPS and and closed cell spray foam (and sometimes Polyiso) are the normal reccomendations around here. This is the first time I've heard mineral wool being reccomended, and I'm intrigued.


I was considering using it for doghouse and firewall insulation as it is extremely heat tolerant (1400-2200 degrees), but had not considered using it more extensively, and don't really know much about it.

[EastCoastCB]

If its organic it can rot and mold. Even non-organic stuff can get wet and grown nasty stuff. But organic stuff just seems foolhardy to me. Totally different story in a building, but it seems like a real bad idea in a mobile metal can. I get TONS of condensation inside my buses down here.

Roxul is non-organic, hydrophobic and fireproof. It also is GREAT at sound deadening. Seems like it would be good for walls. The roof I'd want foam so that all that heat from the sun beating downs could be negated as much as possible. Here in FL ya gotta keep cool.

[john61ct]

You do **not** want to use any material critters can even nest in, never mind eat.

If that's prevented by soaking it in poison. . .

[Shorty22]

Floor: foam board
Walls and ceiling: rockwool
Windows: cover with foam board / reflectix thermal curtains

This is my formula for a well insulated bus that will be long lasting, healthy for indoor air quality, and have minimal petroleum products.

[ol trunt]

I ended up with a mix of inorganic and organic insulation. I have 2" of foam board in the walls, the under floor and as much of the roof as was possible. The balance of the roof is a combination of polycarbonate and tent material--pretty good at letting hot air out during the summer and also pretty good at letting hot air out in the winter I might add. Now for the organic stuff. I stitched up a heavy goose down comforter to match the contours of the pop up and suspended it with straps and snaps from it. Wifey is afraid to leave the propane heater on at night (what's a boy to do) so it's just the two of us heating up the tin can at night. Readings from my indoor/outdoor thermometer show that the comforter maintains the interior heat at ten degrees above what we were dealing with beforehand.
Jack

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