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insulation and such and so forth
#31
I don't think having an air gap does anything as far as reducing heat. The original insulation on the roof of my van had an air gap and when I touched the roof all I felt was heat. 
When I removed the original oem insulation and installed the foam, it was a major improvement. As far as the ribs I just put foam over them, no need to fill them in. 
To me hotgluing the foam to the metal skin makes for a neater and more solid installation. Heat reduction is noticeable.

oem insulation on astrovan it was just hanging loose.
   

rtech foam on roof , this is the first layer, you see how I cut in small pieces to install. Cutting into small sections works best with hotglue which drys quickly. It lets you work around obstacles. The second layer you can use to cover up some small gaps between foam sections.
   
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#32
(12-25-2017, 10:01 PM)wistful vista Wrote: Is it necessary to attach insulation to the inside skin of the van?  Couldn't we just attach polysio to the ribs, shiny side towards the van skin, leaving a couple inch air space between the polysio and the van skin?  

To insulate for heat, it is not needed to attach anything to the inside of the van skin. 


Moisture/dampness/high humidity air  can however become an issue. Especially in colder climates.
So, if the metal has a temperature, lower than the dew-point, then condensation will happen on the inside skin of the van, if air can get in touch with the metal of the skin. 
 
With condensation comes the possibility of mold. 

So the only reason for all this talk, is in order to possibly find methods, where the condensation can be eliminated, even at lower temperatures. Or in other words, to find methods where the humid air, will not be allowed to pass a sealed inner envelope. 

And if one does not want to use an inner envelope (which will always be breached to some extend), is it then possible to expand the thickness of the outer envelope, so to speak. 



So the length of the discussion is actually not primarily about heat insulation, but about avoiding condensation.
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wistful vista (12-26-2017)
#33
Yes gluing in itself does not change insulation performance. Gaps between the envelope layers does nothing, either way.

But you don't want gaps between you and the body panels, increasing R-value even 6" does little good if you letvair from the body panels infiltrate to the inside.

Effective insulation must be a continuous skin like that photo
(12-25-2017, 11:20 PM)jonyjoe303 Wrote: The second layer you can use to cover up some small gaps between foam sections.

Only "dead air" gaps between layers help insulate, but not nearly as well as if they were filled with foam.
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#34
If your foam envelope is continuous that also acts as a vapor barrier against condensation. Closed-cell foam without gaps does this by itself, but an additional skin of heavy plastic will help as well.

Shiny side out if you have a dead air gap between that and the body panels.

Otherwise doesn't matter which way you point it.
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#35
(12-25-2017, 10:01 PM)wistful vista Wrote: As a Newbie here, I have a couple of questions on this topic (at the risk of being seen as hijacking the thread):

Is it necessary to attach insulation to the inside skin of the van?  Couldn't we just attach polysio to the ribs, shiny side towards the van skin, leaving a couple inch air space between the polysio and the van skin?  This would seem to negate the necessity of filling in the ribs.  I was thinking of also attaching sound deadening material such as Dynamat or Hushmat directly to the inside skin (for sound deadening purposes, not insulating purposes) .

Hijack away! Great question!!!![Image: smile.gif]
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wistful vista (12-26-2017)
#36
(12-26-2017, 02:09 AM)MrAlvinDude Wrote: To insulate for heat, it is not needed to attach anything to the inside of the van skin. 


Moisture/dampness/high humidity air  can however become an issue. Especially in colder climates.
So, if the metal has a temperature, lower than the dew-point, then condensation will happen on the inside skin of the van, if air can get in touch with the metal of the skin. 
 

Thank you for your advice. Smile
So, to be clear, if only insulating for heat, it is not necessary to have insulation attached to the inner skin of the van;  but if (also) insulating for cold, then it is necessary to have all of the inner skin of the van insulated/covered?

If I got that right, I still have the following questions:

If I place Dynamat sections directly on the inner metal walls of the van and then cover the metal walls with rigid insulation, there would still be air gaps between the insulation and the metal where there is no Dynamat;  therefore would it be better to forgo the Dynamat all together?

With or without the Dynamat, I was thinking about putting 1/4 to 1/2 in polysio directly on the metal walls, followed by 1 in polysio mounted on the ribs.  This would leave the metal skin covered, give an inch or two air gap (air is also an insulator), and cover the ribs. 
Would this work?
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#37
Makes no difference heat vs cold, that's just a question of direction the heat's trying to migrate toward.

Dynamat is only for dampening sound. May not be needed if you're doing a thorough thermal insulation job, but of course would be a pain to add later. Note it will affect total weight.

No need to cover all the steel with it, as I keep saying gaps between layers are not an issue, as long as the "envelope skin" is as continuous as possible.

It works just by adding weight, so a big piece in the middle of each exposed section is fine. Tons of howto's on youtube, different brands work the same, some people get by with regular home depot roof liner.

Air gap as insulation is very ineffective compared to just going thicker with the polyiso, and useless with an imperfect vapour barrier.

3-4" in a single layer would be ideal if you could. If you want multiple laters then 1/2"-1" of XPS outside of the polyiso will help against extreme cold, polyiso superior R-value only applies to moderate temp ranges and against heat.
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wistful vista (12-28-2017)
#38
As usual, we are allowing perfection to be the mortal enemy of good enough. All too often perfectionism paralyzes and nothing gets done. It's not all or nothing!

Unless you are going to be in extreme cold, I'd use spray glue to glue sheets of polyiso that you've cut to fit against all the sheet metal of the van between the ribs, and not do anything else. It's far from perfect but it is still going to help a lot. It'll be plenty good enough! If you want it to look good, put the wall covering of your choice over the ribs.
2015 GMC Savannah 2500 van, 480 watts of Solar Panels--and a wonderful furry best friend named Cody. I'm out to change the world!
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ColoRockiesFan (12-29-2017), tnvangirl (12-29-2017), bethiebugs (12-29-2017), wistful vista (12-28-2017)
#39
(12-28-2017, 08:38 PM)akrvbob Wrote: As usual, we are allowing perfection to be the mortal enemy of good enough. All too often perfectionism paralyzes and nothing gets done. It's not all or nothing!

Unless you are going to be in extreme cold, I'd use spray glue to glue sheets of polyiso that you've cut to fit against all the sheet metal of the van between the ribs, and not do anything else. It's far from perfect but it is still going to help a lot. It'll be plenty good enough! If you want it to look good, put the wall covering of your choice over the ribs.

Thank you so much! This breaks things down to the most basic need and feels more doable as a good start!!!! I very much appreciate it, as I tend to get befuddled when things get complicated and discouragement rushes in. Oh! relief. I CAN do that!
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#40
(12-29-2017, 07:10 AM)bethiebugs Wrote: Thank you so much! This breaks things down to the most basic need and feels more doable as a good start!!!! I very much appreciate it, as I tend to get befuddled when things get complicated and discouragement rushes in. Oh! relief. I CAN do that!

I agree 100%.  All too often we let the perfect be the enemy of the good (or as Bob says, the "good enough"). 
It looks much more doable.

Now, if I could only understand electricity . . . Confused
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GeorgiePorgie (12-29-2017)


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