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Discussion Starter #1 (Edited)
I just picked up some polyiso and have some concerns. To my surprise it was faced not with foil, but with a fiberglass paper. Polyiso is very hard to find in the area right now, and this was a delivery from Salt Lake, very good price. I decided to take it, head home and do some reading.

Apparently, it's an ideal product for roofing due to its rigidity. But, it's faced in a surface not friendly to moisture and will inhibit mold (obviously). Has anyone used this with success?

I really don't want to do a vapor barrier in this project out of sheathing as I've done it before and didn't enjoy the work. I also question its effectiveness in a van. I'm thinking I screwed up and this is something I should avoid. My only other thought is to paint the polyiso with something like Sherwin Williams Moisture Barrier paint, that allows less than 1 perm...

Ugh.

Edit: Or, I salvage what I can and do an outer layer of 1/2" foil faced EPS, with great stuff in the gaps...
 

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It is not a problem. There are all sorts of fiberglass faced sheathing materials out there used for interior and exterior use and they hold up great - drywall, insulation board and so on. It does resist mold very well, have used the drywall version in wet and basement areas before.
 

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I think I used what you are describing;

I purchased 2" & you can see it in the following thread (I had foil faced 1" also)

Like @cahaak I do not see any issue with using it other than the 1" is easier to work with and install.




66685
 

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I just picked up some polyiso and have some concerns. To my surprise it was faced not with foil, but with a fiberglass paper. Polyiso is very hard to find in the area right now, and this was a delivery to the from Salt Lake, very good price. I decided to take it, head home and do some reading.

Apparently, it's an ideal product for roofing due to its rigidity. But, it's faced in a surface not friendly to moisture and will inhibit mold (obviously). Has anyone used this with success?

I really don't want to do a vapor barrier in this project out of sheathing as I've done it before and didn't enjoy the work. I also question its effectiveness in a van. I'm thinking I screwed up and this is something I should avoid. My only other thought is to paint the polyiso with something like Sherwin Williams Moisture Barrier paint, that allows less than 1 perm...

Ugh.

Edit: Or, I salvage what I can and do an outer layer of 1/2" foil faced EPS, with great stuff in the gaps...

Regarding a vapour barrier; You could not create a good vapour barrier if you tried. The whole thing about the vapour barrier is this - You should not even try to create a vapour barrier as the van skin is a vapour barrier in itself but unfortunately it is on the wrong side of the insulation.

If you feel you do not know anything about insulation and vapour barriers you are right at home with the majority of DIYers on here (from what I can tell). If you have not already read it take a look at this thread I started. I created this thread in order to have a conversation about one of the most misunderstood things of DIY van building.

If you have questions regarding vapour barriers or insulation or van envelops; "I'm Your Huckleberry"


Regarding your Polyiso fiber-glass faced board - I am sure it is fine
 

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Discussion Starter #5
I think I used what you are describing;

I purchased 2" & you can see it in the following thread (I had foil faced 1" also)

Like @cahaak I do not see any issue with using it other than the 1" is easier to work with and install.



66690



View attachment 66685
That's good to hear. Thank you.

Here are some pictures of what I purchased. Look similar?

66692

66693
 

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That's good to hear. Thank you.

Here are some pictures of what I purchased. Look similar?

View attachment 66692
View attachment 66693
Mine was 2” & white looking compared to your photos (which look greyish), but the small dots were on mine as well. As long as it is fiberglass & not paper then I would assume it is mould resistant.

You want to build with as little mould food inside your ceiling, walls, & floor as practical. Mould needs 3 things to grow; spores / moisture / food (& you cant eliminate the spores so do as much as practical to remove the moisture & food). Wood & paper are mould food. If you do use wood seal it or coat it with a mould killing sealer like Kilz.

Sealed plywood panels are in fact vapour barriers, however they are not continuous ( that is they have joints ). If your van has high relative humidity you will get condensation on the windows & metal thermal bridges far before It happens on sealed plywood panels that are on the warm side of the insulation (interior exposed panelling etc).

You don’t really have to overthink it (insulating a van). Just use polyiso in the walls & ceilings / xps high load on the floor (if you want better than polyiso on the floor) and fill in the gaps with ”Great Stuff” & keep the mould food to a minimum. Do not insulate behind the plastic triangle rocker plates (that is a drainage cavity). That design will probably outlive the van. Seal any plywood panels & coat the backside with Kilz (I used Bullseye 123, but it is the same thing).

Good Luck !!
 
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