When I removed the belly pan and fiberglass insulation, I thought I would replace the fiberglass with "styrofoam" insulation.
I've got two questions:
1. Is using this type of insulation a good idea for this application? and
2. I plan to screw it in place by driving a screw (complete with wide washer) through the insulation and into the flooring about one quarter of an inch. Is this a good idea assuming number one is acceptable?
Someone in a previous post, indicated the floor needs to breathe. How much, I don't know. I'm in a similar situation as you right now, and hope someone posts a good answer.
Was cost a consideration to you? While it won't break the bank, it seems styrofoam would be more expensive.
Perhaps my use of the term "styrofoam" is too loose. When I say "styrofoam", I mean housing grade insulation which is approved for installation in residential and commercial buildings. Every time I pass a constructions site I see either pink or blue insulation boards in 4X8 sheets (about 3 inches thick) and think how nice that might work under the floor.
On a previous SOB, I used the foil-bubble-foil stuff stapled in place. I understand Airstream now uses this material on Limited models with slideouts. The stuff is light and can't soak up water. The fact that Airstream is using it says it should be safe for the floor.
I can vouch for the efficiency of the foam-bubble-foam stuff. My whole Scamp was lined with the stuff and it was a super snug trailer.
__________________
John W. Irwin
2005 Classic 28 "Sabre-Dog III"
2004 Silverado 2500HD Duramax/Allison
WBCCI Region 9 Webmaster, #9632
I think we are discussing the same type of generic foam insulation. I like the idea that it won't hold water, too.
Ken
I've got to admit that I, too, thought of not replacing the insulation. I have never camped below 31 degrees, so I don't think I need all that added insulation. However, the next owner may want the added protection. Since re-insulating the unit is pretty simple, I will go ahead and do it.
I am intrigued by the issue of the flooring needing to breathe. That sounds reasonable, but does it breathe adequately from the other side? What about laying down floor tiles with glue? I have a feeling that the breathing issue may not be as strong a concern as some people think.
I'm sort of thinking like Rick on this subject, but I'm not really sure.
I have a few questions I can't seem to clear up in my mind.
Conventional thinking on insulation is
a.] The vapor barrier goes toward the heated side.
b.] Insulation should have adequate ventalation on one side to keep it dry
The question is if the insulation is between the floor and the belly pan where is the "vapor barrier" and where is the "air space" for ventalation?
This brings up another question: If your insulation gets wet for what ever reason does it not dry out by the water vapor going through the wood floor? Does this cause rot?
Is there a better way, maybe styrofoam?
Nothing clear in this head.
My take on this is that the belly pan is not sealed air tight, also with the tank connections and vent stacks and what have you going thru the floor, there are plenty of opportunities for vapor to escape. I like the idea of a vapor barrier, but wonder if it is necessary. I like the idea of the batt insulation only because it is easy to stuff around things. The styrofoam (FWIW know as extruded polystyrene) has the advantage of not absorbing water, doesn't lend itself well to nesting critters and won't absorb and hold odors. Downfalls; it is quite noxious if burned, and being ridgid is hard to fit in and around things. That being said...want to guess what I insulated the roof of my house and barn with?
I've been in my trailer down to about 10 degrees and did not seem to miss the insulation...
As far as breathing goes what that refers to is you don't want your belly 100% sealed - it should breathe - otherwise any mositure in there would stay there + you would get condensation.
This was something I had concerns with several years ago because the belly on my 59 was not 100% sealed - I was told not to over vulcum........
Aaron: I think it's the other way, expanded polystyrene (3.8) has a higher R-value than fibreglas (3.2). Extruded polystyrene R-value is 4.8, and sprayed polyurethane R-value is 5.9.
The problem is along the lower seam, behind the rubrail, water comes in quite easily.
From the factory they are somewhat sealed with double edge tape which holds for maybe a few months, perhaps a couple of years. If any of the flooring is exposed anywhere near this seam the water wicks into the plywood and you have rot. Then insulation gets wet also and further contributes to the problem. Aluminum starts corroding at the rivets and then the belly starts falling off while the steel framing turns to rust.
The more I think about it the recent AS models had a lot going for them with the abscence of a bellypan. If I had anothe Airstream I would pull all the insulation out and put a bunch of "soffit-like vents" in the bellyskin, keeping it well aired out.
Originally posted by markdoane Aaron: I think it's the other way, expanded polystyrene (3.8) has a higher R-value than fibreglas (3.2). Extruded polystyrene R-value is 4.8, and sprayed polyurethane R-value is 5.9.
I used 2" polyisocyanurate rigid insulation with foil backing under our newly installed floor. I used panel adhesive with a few screws as you propose to hold it in place overnight. The stuff has less noxious off-gassing than polystyrene, it doesn't absorb water, and it has high R-values (7-10). I used spray foam in cracks around edges of panels with advice from Geof to increase R-values further. It was tedious cutting and fitting the polyisocyanurate insulation into so many odd sized panels. I used 1-1/2" in the walls and managed to get it to bend okay. The trailer didn't heat up nearly as much in the hot sun last summer (no A/C). Might make a difference in the floor, too, if you're on hot pavement?
Doug
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I was thinking of Expanded Polystyrene. 
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