Originally Posted by TygerCub
Speaking of insulation... most folks on this forum work their insulation from the inside, losing valuable inches of living space. Has anyone thought of putting insulation on the OUTSIDE and reskinning the bus with the original panels, instead of doing that to the inside?
I've actually given this a lot of thought and worked out a lot of the details with my dad and a good friend of mine that usually shoots holes in most of my plans.
Things to consider (or at least, things I keep in mind while planning)...
. The strength of a school bus during a rollover is related to the design of the body. There's the steel tubes that run up and over and down the other side. There's the skin on the inside. There's the skin on the outside. Then there's the rub rails. Yes, even the windows are somewhat important to the structural integrity.
. When insulating, you want a thermal break. Metal to metal contact is a thermal bridge, allowing easy transfer of heat from one side to the other.
. You must choose wisely when you choose your foam, as some variants of foam will act like a sponge when any moisture is nearby. moisture behind your metal will end up being a bad thing.
. School busses are built to protect kids. Many of them are held together by 30 gazillion screws or rivets or a combination of the two. Think about that for a minute.
My first thought for insulation involved removing the outer skin, extending the ribs with wood, insulating, then installing the skin to the wood ribs. Wood would still be a thermal bridge, but not as bad as metal to metal. After looking closely at my bus, I realized that type of project could turn into a suicide mission. Did I mention the 30 gazillion screws and rivets? Perhaps I should mention the 30 gazillion screws and rivets!
Seriously, there are 30 gazillion screws and rivets
holding that stuff on!
Also, I realized that doing that would reduce the strength of the bus. Let's face it, wood is not as strong as steel.
I basically abandoned the idea for a while. Then one day while sitting in the yard staring at the bus, I had an epiphany. Why not add a second skin?
I figure that using wood ribs *not* directly over the existing metal ribs will deflect the heat bridges. I can screw into the wood ribs from the inside of the original skin. I can mold the wood to fit over the rub rails and other strength adding bends in the sides. Then, on the outside, I could use some kind of thin metal or even fiberglass to be the outer skin. The outer skin would be nice and smooth (mostly), and have no importance to the structural integrity. Also, with the bus being already close to 8' wide on the exterior, you can add 3" per side and still be in the 8'6" clearance.
There are still a LOT of logistical details involved. These include sourcing large sheets of skin and finding sufficient help to manhandle them into place and screw or rivet them in place. With wooden ribs, I believe it would be screws.
The outer skin would not need to be as tough as the original outer skin.
An expanding foam insulation would give a good bang/buck for insulation value as well as adding a lot of sound deadening. Plus, it could help keep the skin smooth with the pressure when installed.
My current hope for my own bus is to be able to do this to the outside, and a 1" to 1.5" interior insulated wall, resulting in 4 layers. That would be new inside, original inside, original outside, and new outside. That's 3 layers of insulation between those 4 layers of "wall". This provides multiple thermal breaks and keeps the original structural integrity. Hopefully it'll help keep the weight down, add lots of noise dampening, and of course, insulate quite well.
Yes, I know that sounds extreme. I'm planning to build my bus to be able to survive wintering in alaska and summering in florida. If I can make it efficient enough for me to survive those extremes, then I know it will do quite well where ever I find myself. I don't expect anyone else to be as extreme about this as I currently plan to be.
Bear in mind I'm just barely started on my conversion. Time, money, and energy constraints might prompt a change of plans. Or the harsh onset of reality... nah, can't let that affect anything!
Also, for the roof, I'm considering making it closer to 4" to 6" thick between the original skin and the second skin.
On the side, there are several compartments that would not mate well with a second skin. It took a bit of thinking to come up with a good solution for that. We're thinking we can bring the second skin in a taper to the first skin at the bottom of the rub rail that is along the original floor. Extra insulation like that just isn't needed for my storage compartments, as my plan involves having plenty of storage inside thanks to a roof raise.
I realize my final bus is going to look a bit funky. Hopefully it won't be distasteful. But even if it is, I hope a nice paint job will help disguise any blemishes.
TygerCub, if you want to deal with the 30 gazillion screws and rivets, then by all means, don't let me stop you.
Keep thinking outside the box. Even bad ideas can prompt good ones, and I've seen you posting a lot of good ideas.