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Old 06-18-2012, 10:36 PM   #1
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Best type of floor insulation?

When I gutted our 66 Overlander to replace the rear floor, I didn't find very much insulation under the floor (partly due to mice). Now that the vinyl is down and I am going back together, I was wondering the best way to insulate the floor. I there a better product out now, such as spray foam, that would work better? If I do use fiberglass, what is the best thickness and how do I hold it in place? Also, since it was in bad shape when I tore it apart, I don't know how to treat the area under the floor that vents the refrigerator? Any help would be appreciated!

TomE
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Old 06-18-2012, 11:20 PM   #2
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DON"T PUT FIBERGLASS BACK IN. what ever you do. It attracts moisture like no tomorrow. I used 2" blue foam or Pink. We use it on our endless pool to insulate it. It doesn't absorb water and has an R value of 10 3" has has an R value of 15.

Spray in foam would be the best, as it fills all the cracks and knocks. I think home depot and lowes sell do it yourself kits, or can order them. But I don't think they are cheap.. I cut the foam and put it up with screws and washers. you can see what I did here: http://www.airforums.com/forums/f44/...ml#post1163026
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Old 06-19-2012, 07:40 AM   #3
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The rigid foam is what a lot of folks use. I like RMAX which has a reflective foil on one side. Spray foam holds in water and any place I have seen it used on old cars there is a hole there where it rusted out. In the 60's and 70's expanding foam was used in some cars to seal voids. The space above the fender on my 73 VW was one place that had that stuff. They would always rust out there.

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Old 06-19-2012, 09:01 AM   #4
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The rigid foam is what a lot of folks use. I like RMAX which has a reflective foil on one side.
It seems that when installing radiant barriers they need an airspace to work properly. For roofing, the video below says an inch. 1" is not really practical in Airstream walls, so perhaps some airspace is better than none. Here's a video explaining the air space.
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Old 06-19-2012, 01:01 PM   #5
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I am not big on using Radiation Barrier and nothing else. The stuff works great when new and installed with air space on both sides but it may degrade over time when the reflective layers get dirty or eaten away by water. I used Liquid nail blobs to fasten my RMAX panels to the floor. This provided a little gap between the foam and the floor. I use 1/2" RMAX in the walls by installing two layers. It touches in a few places but for the most part there are gaps between the panels. It is easy to slit it with a knife and bend it to just about any shape.

Perry
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Old 06-19-2012, 01:48 PM   #6
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I used rigid foam on mine. Just cut it tight enough so it can't slide around. If you use rigid, make sure it is closed cell, so it won't hold water. If your not sure, put a hunk in a bucket of water overnite and see if it gets wet. I think the pink/red stuff at H. Depot is closed cell.
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Old 06-19-2012, 02:25 PM   #7
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I used rigid foam on mine. Just cut it tight enough so it can't slide around. If you use rigid, make sure it is closed cell, so it won't hold water. If your not sure, put a hunk in a bucket of water overnite and see if it gets wet. I think the pink/red stuff at H. Depot is closed cell.
It is, I got some Blue at my local Ace Hardware. Works great
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Old 06-19-2012, 09:42 PM   #8
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Sheet foam is most commonly available in 3 types:

1) Expanded Polystyrene EPS (the white bead stuff)

2) Extruded Polystyrene XPS (pink (Owens Corning with the Pink Panther), blue (Dow), yellow, green, etc. Color is about brand only not function or performance.

3) Polyisocyanurate (foil faced and the foil may be shiny like your AS or white, etc). Foil face is for protection of the foam and fire resistance.

Don't use EPS, even the good stuff can eventually retain moisture.

XPS is great because it is very resistant to moisture. This is what is used underground around buildings, etc. It can be had in higher densities. Under your floor, density is not important. R-5 per inch.

Polyisocyanurate is less moisture resistant than XPS. Foil face can be glued, but foil to foam bond is not super strong.

IMO there is no role for radiant barrier in your floor so the foil on the Polyisocyanurate isn't really a big help. (I would use it in the walls of an AS, however). BYW, a radiant barrier alone in your floor is, IMO, worthless.

My '68 overlander has the original spray foam under the plywood floor. Where I can see it, it is still in good shape. Stay tuned, demo on my AS soon.

Modern spray foams are certainly better in many ways over those from 1968. Spraying it will give you the best air seal and the most insulation value per inch possible. It will also cost the most. Use closed cell foam. Spray kits are available online and sold by coverage.

A cheaper alternative would be to use XPS sheet foam and then spray foam around all the edges and gaps with can foam. If you use multiple layers of sheet foam, stagger the joints. Standard construction adhesive will eat the foam so use PL300.

With respect to frame damage concerns above, I would prefer to have a freshly painted frame encapsulated in closed cell foam over one surrounded loosely by sheet foam or fiberglass that can trap water.

Hope this helps.
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Old 06-19-2012, 10:33 PM   #9
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Really are you going camping in the middle of winter? I took the mousey fiberglass out of my 28 ' and decided that nothing had to be better then that. We have been out in below freezing weather (on the way to warmer) and don't see any problem with no insulation in the floor. At that temperature you don't walk around barefoot and with a couple of floor mats the floor is just fine. It's a lot better then what was in there when we bought the trailer.
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Old 06-19-2012, 11:56 PM   #10
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Radiant barriers help heat and cold do what physics wants them to, so radiant barriers are not very good at making heat and cold do otherwise.

Heat wants to rise - radiant barriers excel at bouncing heat up. Cold wants to fall, and radiant barriers excel at bouncing cold down.... but they are are only about 1/3 as effective in bouncing heat down and cold up. Still better than nothing but not the miracle the retailers make them out to be in bold print, and that 1/3rd is with their 2-inch closed air space gap. In a baffled wall cavity, to keep a chimney circulation from happening, expect about 1/2 of the peak R-value.

So for winter heating keeping creeping cold from coming through the floor alright - for keeping sun heating on the roof from rapidly cooking the interior alright - for keeping the interior heated air bubble from dumping its heat straight through the roof no so good, for keeping cooled summer interior air from trying to chill the ground under the trailer, not so good.

And a correct vapor barrier will trap 99% of the water vapor present, a few drops of liquid will make their own weather patterns until they dissipate.

The only reason to avoid all the foams is the toxic gasses produced rapidly when they try to burn, for that the fiberglass being almost inert takes category for safety and earned its place in an Airstream from the factory. When fire ratings are talked about the best foams will not support or feed combustion but they still produce some nasty gasses rapidly, none of foams are what you want inbetween you and a fire in an enclosed space although some are safer than others.

I am tempted to go with fiberglass below the windows mid-line (for sound deadening) and between the main frame rails beneath a 3/4" or so gap radiant barrier held against the floor, block foam for the outriggers where the largest chance of water intrusion collecting, and air-gap prodex and sheathing foam for the roof. I also have an insulating paint I'll be doing the entire shell interior with.
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Old 06-20-2012, 07:42 AM   #11
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Not entirely true. Heat is heat. The Radiation barrier reflects heat back where it came from. So if you put it in the floor it is going to reflect the heat back into the trailer. Multiple layers with air gaps provide insulation as well as thermal interfaces. The more intefaces the less heat transfer. I think combining the two methods of conduction (foam) and radiation (shiney stuff) is the best approach. It is true that in the summer most of the heat comes in from the sun. In the winter, a lot of heat leaves through the skin but some leaves through the floor. I am all for warm floors.

Perry

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IMO there is no role for radiant barrier in your floor so the foil on the Polyisocyanurate isn't really a big help. (I would use it in the walls of an AS, however). BYW, a radiant barrier alone in your floor is, IMO, worthless.
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Old 06-20-2012, 08:26 AM   #12
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It is true that in the summer most of the heat comes in from the sun. In the winter, a lot of heat leaves through the skin but some leaves through the floor. I am all for warm floors.

Perry

Yep, If it was up to my wife, she would have me putting In Floor heat in the trailer
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Old 06-20-2012, 11:43 AM   #13
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Not entirely true. Heat is heat. The Radiation barrier reflects heat back where it came from. So if you put it in the floor it is going to reflect the heat back into the trailer. Multiple layers with air gaps provide insulation as well as thermal interfaces. The more intefaces the less heat transfer. I think combining the two methods of conduction (foam) and radiation (shiney stuff) is the best approach. It is true that in the summer most of the heat comes in from the sun. In the winter, a lot of heat leaves through the skin but some leaves through the floor. I am all for warm floors.

Perry
Heat is heat? This is a gross oversimplification. Heat energy moves by conduction, convection, and radiation. Radiant heat requires a vacuum or air to move. Radiant heat can not move through the floor of your AS because it is solid. If you did choose to use a radiant barrier under your floor, you would need an air gap (2" is best), and a way to keep the reflective barrier from getting dirty (which significantly decreases its effectiveness). You would be much better off filling the air gap with insulation (2" of XPS=R10). The air gap is very good at letting convective heat and cold move around under your floor (commonly called leaks or drafts).

There is no role for radiant barriers in your AS floor. They border on being a scam in any application, but are especially useless in this application.
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