Insulation inquiry.

[OwllieDriver]

Will be doing spray foam insulation for our 40ft conversion. I have 2 questions.

1. 1inch or 2 inch of spray which is best? We dont plan on being in the cold but I've driven through thick slush in Arizona. Whether cant be controlled and you can only drive so far

2. Doing a solar system, should I install that before I spray foam or after? Which way is best and safest.

[Danjo]

I think everyone will say, as much insulation as you can.

I’ve seen people blowing insulation on their wiring. I’m against it myself since hinders heat dissipation from the wiring. It also makes it more difficult to do repairs or modifications later. I’d install EMT or PVC raceway, adding junction boxes where you want them, and then spray insulation.

[musigenesis]

Originally Posted by OwllieDriver

1. 1inch or 2 inch of spray which is best? We dont plan on being in the cold but I've driven through thick slush in Arizona. Whether cant be controlled and you can only drive so far

Seems that most people use spray foam in between the ribs of the bus and flush with them on the walls and ceilings, so the thickness there depends on how thick the ribs are (for example 1.5" in an International or 2" in a Blue Bird). And then the floor is usually XPS foam board since it's rated 25 PSI and spray foam is not (you'd have to put "joists" of a sort in and then spray foam in between them - which I don't think I've ever actually seen done in a build).

I think the most effective way to spray foam the ceiling would be to run 1X furring strips front-to-back on the ribs and then spray flush with them, so the overall thickness would be 2.25" (on an International with 1.5" deep ribs), mainly because you would then get at least some insulation between your living space and the metal ribs (in home building, metal studs are estimated to lower the effectiveness of the insulation in between them by 30%-70% because of the severe thermal bridging).

2.25" is a lot of spray foam, however - you're likely looking at three of the kits for just the ceiling and walls (so around $2000). I'm going with XPS everywhere myself, because it's so much cheaper and I can do it myself.

[DrDanger]

I would recommend doing at least enough foam to cover all exposed metal (ribs, chair rail, etc.) to minimize thermal bridging. For me this meant adding firring strips to the walls and ceiling to give ~3/4-1in coverage over the metal. https://www.skoolie.net/forums/f11/p...tml#post386420


I laid conduit on the wall and then foamed over that so that I could pull new wire or replace old wire as needed. You can drill/cut through it so if you don't know exactly how your solar/electrical system is going to be laid out you can do the foam now and then add your cables later.

[dzl_]

Originally Posted by OwllieDriver

1. 1inch or 2 inch of spray which is best? We dont plan on being in the cold but I've driven through thick slush in Arizona. Whether cant be controlled and you can only drive so far

I mean if we are talking about which is best don't rule out 6 inches.. I kid, but point being more = better (up to a point). But that's not really the factor that determines your choice. Its specific to your bus, your climate, your budget, your priorities, and even your height.

2. Doing a solar system, should I install that before I spray foam or after?

I've no experience here, but I'd guess you'd want to take care of as much of the cutting and screwing and running wires through walls floor and ceiling as you possible before spray-foaming. This would apply to everything, not just solar/electrical. Seems like it would be much easier, and easier to correct any mistakes you make.

[kazetsukai]

Originally Posted by dzl_

I've no experience here, but I'd guess you'd want to take care of as much of the cutting and screwing and running wires through walls floor and ceiling as you possible before spray-foaming. This would apply to everything, not just solar/electrical. Seems like it would be much easier, and easier to correct any mistakes you make.

Eh? Seems like spray foaming first would be easier to me...


Thinking how I'd do a second rig, I'd first demo/rust remediate, then delete the windows, then spray foam, then decide on the layout and plan wiring/electrical/new windows so that the spray foam was most effective/applied everywhere on the shell, and anywhere I cut into I have to seal back up.

[OwllieDriver]

It's a 40ft bus so I'm assuming about 35ft of insulated area. Assuming the bus to be 6ft tall (hopefully) going to get it next weekend. As well as factoring in the non-insulated area space of the windows. I've calculated a rough estimate of 35x8 for the roof and 35x5 (2) for each of the walls. For a total est. spray area of 700. The kit I found from Foam It Green is $627 for approx 600sqft and $330 for a 200sqft kit. This is for 1" of spray. Might try to find a padding insulation that will work with spray foam. I'm sure this makes a difference, we will have a wood burning stove as a furnace.

3 things that no budget was really created for was staying warm, energy, and kitchen appliances.

[Danjo]

Originally Posted by OwllieDriver

It's a 40ft bus so I'm assuming about 35ft of insulated area. Assuming the bus to be 6ft tall (hopefully) going to get it next weekend. As well as factoring in the non-insulated area space of the windows. I've calculated a rough estimate of 35x8 for the roof and 35x5 (2) for each of the walls. For a total est. spray area of 700. The kit I found from Foam It Green is $627 for approx 600sqft and $330 for a 200sqft kit. This is for 1" of spray. Might try to find a padding insulation that will work with spray foam. I'm sure this makes a difference, we will have a wood burning stove as a furnace.

3 things that no budget was really created for was staying warm, energy, and kitchen appliances.

Spray foam is going to create a more airtight envelope (dont forget you have all that window space anyway!), but with the budget, is rigid foam going to be a better option? You may want to check costs. And those with spray foam please feel free to argue on its behalf

[OwllieDriver]

R-tech 1.5in x 48in x 8ft is roughly $14 each per current search and with out discount. I see that rigid foam is closed cell which is the desired insulation. The total area needing to be insulated if done with rigid is 1,015ft. Using 9ft as comp for the curved ceiling, 8ft for the deck, and 6ft for the walls. At 35ft length living space. With that math I wont need to calculate mistakes.

Foam cost comes to $910

[FatBoySTL]

Originally Posted by musigenesis

...And then the floor is usually XPS foam board since it's rated 25 PSI and spray foam is not (you'd have to put "joists" of a sort in and then spray foam in between them - which I don't think I've ever actually seen done in a build).

If I'm interpreting this correctly, this suggests that you do NOT need to joist the floor if you're putting down foam board. Would you just lay it down, lay the plywood on top of it, then through-bolt the whole thing to the chassis/body, creating an unframed foam sandwich?

[Oscar1]

Originally Posted by Danjo

I think everyone will say, as much insulation as you can.

I’ve seen people blowing insulation on their wiring. I’m against it myself since hinders heat dissipation from the wiring. It also makes it more difficult to do repairs or modifications later. I’d install EMT or PVC raceway, adding junction boxes where you want them, and then spray insulation.

What he said!
It is actually in our federal building code not to spray foam over wires for this very reason.
Installing conduit before foaming is the way to go.

[musigenesis]

Originally Posted by FatBoySTL

If I'm interpreting this correctly, this suggests that you do NOT need to joist the floor if you're putting down foam board. Would you just lay it down, lay the plywood on top of it, then through-bolt the whole thing to the chassis/body, creating an unframed foam sandwich?

Some people just lay the foam board down and the plywood on top of that with no glue or fasteners and call it a day and it seems to work out (there's usually enough stuff built on top of it that it can't come up anyway). Others glue the layers down and/or run screws from the plywood through the foam and through the metal floor. Joists are not necessary in terms of holding up the plywood since the foam board will do that (if you were insulating the floor with fiberglass or rock wool or the like, you would need joists to support the plywood).

I want a mechanical connection between my plywood and my steel floor (more to support the rusted steel floor with the plywood than the other way around) rather than glue, but I don't want fasteners that make additional holes in the floor (although I don't think this is really that big of a deal) and create thermal bridging. So I'm doing a weird thing where I weld 1" bolts to the floor and then screw 2" pieces of wooden dowel down onto them through the foam board.

So far I've done this in one place on my floor, and it's a lot less difficult than it sounds: https://www.skoolie.net/forums/f11/r...tml#post379129

[Native]

I will add that the fastening system Musigenesis came up with is both unique and genious.......