Insulation underneath floor

[Carlosclark]

Hey everybody, anybody ever put XPS board insulation underneath the floor in between the metal frame rails of the bus? My bus came with a wooden floor that I am replacing and plan to put the insulation there to save some head room as I am 6’3”

Any pointers on how to protect the insulation from road debris, salt, moisture, etc. ? Any other advice if anyone has done this before would be amazing too!

[kazetsukai]

Seems like it would be easier to spray in insulation underneath if you can.

[Danjo]

I was thinking that this wouldn’t work too well, but then I remembered The roof on my friends house. It is this sprayed on insulTing roofin FM that’s like a foot thick. IDK what the stuff is called.

[Carlosclark]

Originally Posted by kazetsukai

Seems like it would be easier to spray in insulation underneath if you can.

My main issue with spray foam is the cost, so if I went that route I would probably do it myself with the can stuff which seems to be far more effort than just cutting foam board to fit and dropping them in between the frame. Not sure if I was very clear in my original post but here is how my floor is.

[BlackJohn]

The underside of your bus would be better left untouched for maintenance and inspection purposes. Is your bus in that good of condition to bury everything under there?
A mechanics nightmare and you will pay dearly for removal of any or all of it.


John

[Carlosclark]

Originally Posted by BlackJohn

The underside of your bus would be better left untouched for maintenance and inspection purposes. Is your bus in that good of condition to bury everything under there?
A mechanics nightmare and you will pay dearly for removal of any or all of it.


John

Right that is another solid reason to avoid spray foam.

I have measured out the dimensions of all the spaces between the frame rails and there is at least 1” (2”-3” in most areas) before I get to any parts underneath the bus. So I would basically slot the individually cut pieces of XPS board into the spaces and then secure it to the subfloor (Advantech T&G) on top with adhesive. This way nothing from underneath would be covered. Only concerns I can think of is protecting the foam board from road debris/the elements but maybe I am missing something..

[ol trunt]

I guess I'd have to agree with BlackJohn in most cases as far as spray foam under the floor goes. Placing chunks of foam board under the floor also looks like a problem because of the difficulty of fitting it in and sealing the cuts and edges.

That said, do as I say not as I did. I seem to be getting away with my under floor foam board insulation. The reason for this is that I had the bus body completely off the frame which allowed easy installation of foam board with spray foam around the edges to keep moisture out. It also provided a foil heat reflective barrier from the road. I ended up with 2" of insulation in the floor with no loss of headroom. In my case all mechanicals and electrical are below the insulation so no worries.
Jack

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[Carlosclark]

Originally Posted by ol trunt

I guess I'd have to agree with BlackJohn in most cases as far as spray foam under the floor goes. Placing chunks of foam board under the floor also looks like a problem because of the difficulty of fitting it in and sealing the cuts and edges.

That said, do as I say not as I did. I seem to be getting away with my under floor foam board insulation. The reason for this is that I had the bus body completely off the frame which allowed easy installation of foam board with spray foam around the edges to keep moisture out. It also provided a foil heat reflective barrier from the road. I ended up with 2" of insulation in the floor with no loss of headroom. In my case all mechanicals and electrical are below the insulation so no worries.
Jack

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Wow looks great Jack thanks for the advice! What kind of foil did you use ? The stuff with bubble wrap in between or something else?

So if I put the foam board pieces in between the frame rails and they are not one hundred percent sealed won’t that be better than no insulation at all? Or am I horribly mistaken ?

[ol trunt]

My foam came foil backed on one side though I have used spray glue to attach aluminum foil to foam. Some spray glues attack foam board so do a small test. Loose fitting or unsealed foam will leave open all sorts of heat bridges and would nearly negate the value. Judicious use of Great Stuff or the like to fill the gaps will make all the difference. Also, any open spaces will serve to collect moisture to say nothing of critters. If I hadn't been able to seal things up as I did I wouldn't have used foam board under the floor
Jack

[BlackJohn]

Jack, that is some beautiful work you have done. There is a way to skin a cat I guess.
Op you need to leave room for wrenching in places too. And varmits will nest as will hornets etc.

Inside insulation where possible should do just fine in your territory.


I might do under as you say if the bus was parked, never to be driven, just shelter.


John

[Rucker]

Isn't all the metal frame a conduit for heat/cold? Not sure you'll see much of an R factor improvement. By way of example, on my shuttle bus, the fiberglass walls are only warm to the touch in direct sun but the window frames are too hot to touch. I have to insulate or protect the interior from both the glass and the metal frame...

[BeNimble]

Originally Posted by Rucker

Isn't all the metal frame a conduit for heat/cold?

Yep. While it would have some effect, just seems like wasted effort. Just an inch of floor insulation would make a much bigger impact and not much headroom lost.
In my opinion anyway.

[ol trunt]

BN, just for the record, although installing under the floor and sealing up the edges with spray foam is a PITA it actually is quite effective. After a long drive in the heat of the summer I used an IR gun I measured the temp of the floor on the uninsulated first entry step and the temp of the main floor under which is 2" of foam board. I found the insulated portion to be ten degrees cooler than the uninsulated step. While it is true using insulation on top of the floor would reduce the effect of thermal bridging, having the foil side of insulation pointing down under the bus no doubt reduces heat transfer to a good degree.

Our bus projects all end up being a series of trade offs. I'm tall so the loss of an inch or two of head room is important to me. Perhaps one inch of under floor insulation might not be worth the effort but the two inches I installed certainly was worth the effort.
Jack