Insulation questions

[chuckd]

Gary, be careful in recommending dead air space, one of the best is a vacuum.  The problem with a dead air space, is that it is not dead.  There are thermal currents set up by sun and shade, light and dark paint etc.  This moving air then transfers heat by convection on the various surfaces involved.  "Dead air space" is one of the reasons that bubble foil R values should be carefully looked at to determine the testing protocol used.

fyi chuckd

[Chaz]

I think what I did works well, as well. I bought foam board in 1/2", 3/4', and 1" thicknesses with the foil back. I cut it to fit snug in all the different spaces and would use whatever thicknesses, combined, to get as much in as possible. Then if there were voids, I used the expanding foam. That will also "glue" the board to the ribs, etc. (nasty sticky stuff! It's basically Gorilla glue that expands)
By doing it that way, I "think" it is "just about" as good as spray foam (I have that in my house) and for a LOT less money!!! I think the foil is a plus.
Just my way. Your mileage may vary.
  Chaz

[artvonne]

 Fiberglass inside a Bus is bad? I scrapped over 20 Buses back in the late 80's, including a 1947 GMC 3751, and a 1953 GMC 4104, and a bunch of Transits, GMC Fishbowls and AM Generals. All those Buses had fiberglass batt insulation, I never saw a single one that had rust or corrosion from condensation. I currently have a 1975 MCI MC5B, that still has all of its original fiberglass batt insulation and the only place ive found corrosion is where a hole was drilled through the outside skin and water soaked the insulation. It hasnt caused trouble in 36 years, why tear it out?

  I have also read that spray foam insulation is not recommended for metal buildings because of high cndensation/corrosion issues, and that potential damage will remain unseen until it at an advanced stage which could lead to structural failure. I cant see that foam boards would be any different, the stuff just sweats and soaks anything its in contact with. Honestly, foam may well be to Buses what fiberglass was to wood boats in the 1950's. Time will tell.

  I'm sticking with fiberglass and other types of porous breathable insulation as well as to keep the cavities well ventilated. May not be as sound proof or offer the greatest R value, but the Bus might still be around 10 or 20 years from now.

 

[robertglines1]

Main reason for their reasoning in metal buildings is all the UN sealed seams every few feet. eliminate water entry/seams and no problem.

[niles500]

House wrap (Tyvek) is a selective barrier - while it is resistent to water it is not resistant to water vapor - this is the reason it is on the exterior of the structure - if water or water vapor gets into the wall cavity from another source (plumbing or structural leak) the house wrap allows the water vapor to escape - visqueen (polyethylene) when properly installed (ceiling sheets applied first then tucked under wall sections and sealed with tape) is an absolute water and water vapor barrier and should only be applied on the climate controlled/conditioned side of the wall - FWIW

When you say "dead air space" what your really refering to is "isolated" dead air space - a frame structure with 2x4's foam sealed drywall on one side and foam sealed sheathing on the other with no insulation is also considered "dead air space" by definition - that insulation you add in the cavity is isolated or encapsulated air pockets encased in a nonconductive material - that is what gives you the R value - FWIW

[artvonne]

Main reason for their reasoning in metal buildings is all the UN sealed seams every few feet. eliminate water entry/seams and no problem.

  But your forgetting condensation from living inside breathing, cooking, showering, and heating. Every RV ive owned had warnings that the vehicle was not designed for long term use. They are built too tight and condensation cant escape past the metal skin, so instead the interior walls get saturated and they rot and mildew from the inside out if used that way. As long as they dont stay too closed up and you air them out after use they last for years. That was actually a discussion when they started handing out trailers to the refugees after Katrina, those trailers wernt designed to be used as long term living quarters.

  Certainly the majority of Bus conversions are for limited use, spending most of the time parked and empty. But for those living in them as a home they could see problems down the road. I know many have used spray foam and foam boards, and it may not ever be a problem, but I dont think we know enough about it one way or the other. I know fiberglass is not any problem at all as long as it can breath, and thats what I intend to use. At least until I see more data on foam to show its safe.

[wal1809]

I am not a very big fan of foam over the engine compartment.  I have it in the top of all my bays but not over the negine.  Throw a piece in a fire and you might change your mind.  It is one thing to have a fire but another to have a fire with extra fuel.  When I burned the scraps after my project they burned like a Christmas tree.

[Scott & Heather]

Before we pink 1.5 inch foam boarded everything, we laid down a layer of Reflectix in the ceiling, walls, etc. Was well well worth it. Been in 100 degree temps this summer and a 13,500 BTU Coleman Mach III kept it at 75 degrees or less in here. Right now it's 84, and the thing is set to low about half way on the thermostat, and we're chilly. As for the engine compartment, I used actual firerock sheetrock over the plywood we laid. Sound proofed, and gives us 90 minutes to figure out we're on fire down there before it toasts us.

[artvonne]

Throw a piece in a fire and you might change your mind.  It is one thing to have a fire but another to have a fire with extra fuel.  When I burned the scraps after my project they burned like a Christmas tree.

  Thats something I forgot about. I know Celotex and some of the other foam type insulation boards have fire warnings, and state they are only to be used as exterior sheathing. I have no idea about spray in foam, but it is urethane so I assume it would burn.

[demodriver]

Normal spray foam from a can will go up like gas!!!  Nasty stuff!

[JohnEd]

I did a lot of research before deciding on which type of insulation to use on my conversion.  The conclusion was the fiberglass batting was out because of condensation getting it wet and ending up with absolutely no R value.  I didn't think I could totally eliminate condensation in a bus environment no matter how hard I tried.  The best choice is blown in expanding foam, but it only has a slight advantage in R value over pink, or blue board and cost a lot more.  I decided to go with Styrofoam board, packing in as much as possible and filling in any gaps and tightening it all up with expanding foam in a can. Now condensation is no longer a worry as far as R value is concerned.  I may have a little less R value than fiberglass and a little less than spray in expanding foam, but it's only about 1 or 2 R's.  Also take into consideration that huge hole in the front called a windshield, maybe the dash, or the whole front end depending on how difficult your particular bus is to insulate there, can you really take full advantage of the R value your insulation has to offer. Remember that R value is calculated in a laboratory setting under perfect condition, a bus does not even come close to that.  For me I feel I made the right choice for my budget and my intended use for the bus. 

What Mike said....all of it.  You could install fibre bats under the floor where no interior air will get into it.  I would still use foam board, though.  I put fibre glass bats in the little spaces between the foam boards and such in my roof.  I built a roof on top of my roof and that chamber is isolated from the interior and is sealled to weather.

[JohnEd]

Regarding the foam board insulation, how do you attach it to the metal roof? What type adhesive?

Boyce

Be careful here.  Many cemenbts/glues have solvents that disolve different foams.  Consult the mfr fo the cement that works.  I used contact cement cause it is dry when you press the parts in place.

John

[artvonne]

Normal spray foam from a can will go up like gas!!!  Nasty stuff!

  I imagine it would right out of the can, but what about after its dry/cured??

[Scott & Heather]

Normal spray foam from a can will go up like gas!!!  Nasty stuff!

  I imagine it would right out of the can, but what about after its dry/cured??

Not sure it really goes up like a gas...this guy has a hard time keeping it lit with a torch!

Burning Spray Foam Insulation

[JohnEd]

There are three families of this stuff that i can think of off hand.  One uses "two parts" and seems to cure like epoxy.....fast and it out gasses highly toxic when curing.  Second comes from a can and that stuff needs to out-gas it's solvent to cure and if shot into a confined space, pipe or plastic bag or some such, it stays wet "forever".  The third is a new stuff that is water based and that is water absorbent after it cures/drys.  I think there are also variants within each category.  I probably have some of these angles off but you need to either do all your homework or follow what others have done.  Whether it actually flames violently or not, much of this stuff will out-gas toxic stuff when subjected to extreme heat(fire) that will kill you in seconds or render you unconscious in less time.  In a motor home/bus it is the heat that kills in mere seconds.  You need to be out before you take your next breath after discovering a fire regardless of how nourishing the gas might happen to be.

John