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Full Version: mylar and dead air space, adhesion method ?s
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I'm considering mylar due to cost of Reflectix. My plan has been to apply to the outside face of the CT plywood walls facing out to keep exterior heat out. Is the 1" space between the mylar and the outer metal skin adequate as dead air space, or do I need to apply a layer of bubble wrap on the mylar? Just not sure how "dead" or static the air should be. What's a good adhesive to use or do I staple it on? As cold season approaches I plan to put up the polyiso on the interior side of plywood walls in a way so as to be able to easily take down in the hot season and fall back on the existing mylar along with shade and ventilation fan and ramp (porch) and side door open. All openings will have screening to keep bugs out.
3M Super 77 would do well as an adhesive for it. A paint roller or a wooden rolling pin will both work for smoothly attaching whatever you use to the wood.

I'm just not sure that the single layer of mylar is going to do much for you.

Reflectix is two layers with essentially bubble wrap sandwiched in the middle which obviously has some method to it otherwise it would just be a single layer of reflective material. I'm no engineer but I can't help but think that it was designed that way because it works.
http://www.cheaprvliving.com/forums/foru...php?fid=33

This has been covered at least twice.   Wink  See what will work for you.
Thanks Almost There. I'm still in planning stage and want to repel as much of the outside and trailer's metal skin heat as much as I can. I was thinking about insulating but I think that would only work if I was using AC (to keep the cool in). I will have a tarp covering 2 ft above the roof and spanning over the door side area and also shading the other side of the CT out a few feet at where it meets the ground. I wonder if mylar is only effective as a light reflector, not radiant heat barrier. Maybe Reflectix will have to be my only option. I don't mind heat, esp dry, as long as the air is moving. I've never had air conditioning....only fans in St Louis/KC summer heat/humidity. Humidity is the devil.
(06-08-2015, 11:24 AM)GotSmart Wrote: [ -> ]http://www.cheaprvliving.com/forums/foru...php?fid=33

This has been covered at least twice.   Wink  See what will work for you.

I already browsed but couldn't find much specific to my question re mylar.
Personally, if you have to cut costs on something, personal comfort is NOT one of them.

When it comes to the choice of a fan that you have to reach to turn off or one with the remote, hell, I need the exercise - I can walk 3 feet to the fan and turn the darn thing off - savings $$.

Sweating in the night when you're trying to get to sleep and the trailer is still too hot - worth bucks to me!

Oh, and be very thankful that you're buying it at US  prices - it's just about half what I paid for it up here!

I'm not putting in any conventional insulation, just the reflectix with the air gap between it and the sheet metal. There will be an air gap between it and the finished walls of the van anyways so I want to see if it reflects enough heat from the heater back in to the van. Partly experiment and partly because I can't find 1/2 or 1" polyiso up here. But then I plan on following the good weather anyways.
To answer your question, mylar is the same stuff used in space blankets, so there is no question that it works against relective heat transfer. It just offers no protection from convection or conduction transfer. 

The one inch space between the outer skin and the plywood inner wall isn't really dead air space.  True dead air space means there is no room for convection transfer.

I believe the space between the outer skin and mylar-faced plywood would quickly get very hot, and the mylar would NOT prevent the heat from coming in via conduction and convection.

Regards
John
Optimistic Paranoid, that was the confirming answer I was looking for....thanks. So bubble wrap adds the dead air space then. Going to use Reflectix instead.
Insulation DOES help keep heat from the sun out especially if you have a dark colored van and good ventilation. It helped a lot in mine. The only time it's really going to hurt you would be on hot nights.

I'd forget the mylar, just get some rigid insulation with foil on one side. Put it between the plywood in the gaps.

Personally, I'm just using bare polyiso and no plywood on my new conversion. It worked well when I tried it before with the blue rigid foam. If it starts to get damaged I'll find some thin plastic or hardboard to put over it.
Thanks Reducto. I was afraid to insulate for hot weather thinking it would retain the heat more unless I ran the roof fan a lot, but in order to ventilate well all doors (and windows not yet installed) will be open so I'll be pulling heat thru the CT all day anyway so no way around it I guess whatever I do. I do want to keep the sun from pounding heat thru the walls/ceiling and the 1st line of defense will be a silver tarp 2 ft over the top and also shading both sides using emt frames. Wind will be my problem there, less so if I switch to mesh tarps. 2nd line would be a radiant barrier like Reflectix. The polyiso I intend to install will be bare but I'm considering hanging canvas coverings from the top of the wall or something similar with some design over it to protect it and have some degree of a finish look. I suppose one could stretch over and adhere fabric to the polyiso so the walls have a consistent finish. Anyway this heat/cold issue looks to be a work in progress.
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