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Old 06-09-2004, 11:24 AM   #15
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The key is to keep a dehumidifyer constantly running. which means a hole for the water to run out and a way of dealing with the heat from the dryed air. know that problem- still havent figured it all out. But plan to have a dehumidifier on board. I often find the airconditioner needs to run longer and really make it colder than I want- just to get rid of the humidity- especially when it's 99% outside! Perhaps in a smaller space the dehumidifyer will work- best for no mold is to keep it at about 30% .Suz
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Old 06-09-2004, 11:29 AM   #16
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how about "tyvek" stapled to the underside of the plywood floor?

I can tell you that steel frame members don't "breath" very well when there's soaking, ringing wet fiberglass nestled up against it.

Friend of mine used the 2" foam boards, attached with long screws and fender washers. didn't ask how he dealt with the plumbing, though. another thing he did was removed the plate that covers the rear frame x-member and forms the front "wall" of the bumper storage compartment, in an effort to increase airflow.
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Old 06-09-2004, 01:16 PM   #17
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Tyvek isnt viable for me, i'm sure it's fine with others. My husband wants to use the woven fiberglass with paper wrap, but I don't He also wants to use the insulation made of cotton (used jeans micro shredded) and borax. Seems to me that would be a sponge and mold grower too. So far we haven't agreed on anything. Foam cell boards are too chancy for me too- after all a small airstream is just a big oven- outgassing like crazy! We still havent' come to a solution but we still have the floor ,plumbing, electrical etc to do! time to "discuss" suz
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Old 06-09-2004, 01:28 PM   #18
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Ms. Suz
Prehaps you would find a more direct solution working from the other side. Unless you are planning on extended stays in sub 32 areas you may not need much insulation under the floor. Put it on top of the floor. Subfloor, insulating lay of an acceptible foam board, finish floor. I know there is a sensitive foam out there, I think it's soy based. So you give up an inch, big deal. The keeping cool challenge is tha damn thing couldn't be designed more like a solar oven if they tried, except painting it black. It's the walls not the floor that are the keeping cool problem. No?
Just a thought.
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Old 06-09-2004, 04:10 PM   #19
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Isn't there a one way flap valve used in boats, almost like a valved scupper? Could be used to vent the belly pan...

Kevin
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Old 06-09-2004, 05:19 PM   #20
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The nature of reflective insulation...

There is a an excellent explaination of the benefits of different types of foil installations at the following web-site:

http://www.tvmi.com/rfoil/physics.htm

Some thoughts or conclusions that I have after gleaning from the above site and others are the following:

1.) Even though an airstream has a relective skin it is not nearly as relective as highly shiny foil insulation. In the case of my belly pan I doubt it is all that effective as a relector (and never will be). If it is true that the aluminum skins are really that reflective and that such a large percentage of heat loss is reflective then we wouldn't be talkaing about the need to insulate at all.

2.) A very well polished airstream skin will in fact have less heat gain in the summer.

3.) Where the foil should be placed for best effectiveness depends on whether we are trying to keep heat out or keep heat in the trailer. I think this means that the outer surface of a well polished unit will help keep heat out but does not really help keep heat in. Maybe we should polish the inside of the skin as well?

4.) Foil seems to work best when its relective surfaces are not in direct contact with anything but air.

5.) There are 3 types of heat transfer mechanisms that all need to be considered to some degree (conduction, convection, radiation). Evidently 65% to 85% of heat transfer through walls is by radiation and up to 93% through floors.

6.) Reducing heat loss is not just a case of having a high R-value since R-value seems to only apply to heat transfer by conduction.

Some practical application thoughts:

If it is true that 93% of the heat loss through the floor happens through radiation then it seems like underfloor insulation could be accomlished quite well without actually sealing up the floor to air flow. What appears to be needed are at least two reflective surfaces - one pointing toward the interior and one toward the ground - somewhere in the underfloor cavitity. It seems to be preferable to have an air gap above and an air gap below the foil. Since the underfloor area seems to be quite capable of getting really dirty I think I would want to keep the foil near the top and try to block dust from getting onto the top surface of the foil (reducing its reflectivity). So I think the question still is how best to mount foil an inch or so below the floor. Maybe using sticky back foam tape might work? I think I would still want to have the area above the foil mostly sealed but still leave a weep hole or two for condensaction to drip out. It might make sense to staple a layer of foil directly to the bottom of the floor and add another layer about 1" below the floor. The layer on the bottom of the floor would help prevent moisture from attacking the floor and would give an extra barrier to summer heat gain.

From the examples given in the tutorial I sited above I think it would be great to have two layers of foil in the wall cavities. It is interesting to note that their example wall was only 1-1/2" thick. Again would sticky back foam tape be a good machanism for suspending the foil in the middle of the cavities?

I like the idea of some sort of proactive ventilation mechanism for under the floor. My son-in-law suggested installing a small fan under the floor that could be used to power vent the area. I am also aware that you can buy round louvered vent covers with a built in screen that are designed to be used in the soffit of your house (on the bottom side of your roof overhang if you are not familiar with the term soffit). The ones I am thinking of are made out of aluminum and are about 3" in diameter as I recall. The louvers are all nicely pointing in one direction. I think I will at least consider using some of these vents and maybe the fan too.

Malcolm
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Old 08-16-2017, 01:02 AM   #21
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Choices for under floor insulation and ventilation

Malcolm,
With your floor removal underway, have you made any decisions on how you will insulate and ventilate the under-floor volume as you discussed in thread 11881 about 13 years ago?
My 2001 Bambi has a new uprated Dexter axle, and I need to decide on the insulation/ventilation system to use before replacing the belly pan material. My floor and frame are in good shape, but the old fiberglas insulation was completely removed.
I'm considering a 2-in thick rigid foam mounted to the floor with standoffs and formed to allow 3/4in air space, and provide for condensation or water drainage to the bellypan. I likely will plan to use a small grid vent in each floor section bellypan segment, similar to a soffit vent, to assure sufficient drainage while minimizing air flow and blocking insects and vermin from entering.
Any thoughts or considerations you could provide would be welcome.
And best of luck on your restoration project.
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