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Discussion Starter #1
Hello DIYers

Due to a rather large topic & one of many opinions, I have started this thread in hopes to create logical conversations, sharing ideas, & amicable debate concerning the Van Build Envelope
 

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Those are too general to provide the whole picture. Here in the Sonoran Desert we have many months of near zero RH BUT have a month or more of monsoon season where the RH may stay 80-100%! This fall has been the wettest I have seen in my near 20 years here with >50% for a week at a time, over and over.
 

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Discussion Starter #4
So the idea here is how do we control the interior of our vans “practically“. For those of you who have knowledge in this area please post your ideas here. We can discuss theory, science, & best of all practicality.

Here are some of the topics I can think of for discussion. Please add to this list if you have more relevant topics;

Relative Humidity
Thermal Bridging
Dew Point
R Value
water and/or air vapor barriers
conductivity of materials
thermal expansion
drainage channels
air circulation
mold
rust
insulation
surface panel & floor materials
 

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Discussion Starter #5
Those are too general to provide the whole picture. Here in the Sonoran Desert we have many months of near zero RH BUT have a month or more of monsoon season where the RH may stay 80-100%! This fall has been the wettest I have seen in my near 20 years here with >50% for a week at a time, over and over.
Thanks RD

I have enjoyed reading your posts over the past 6 months I have been on here & really appreciate your perspectives. You have posted here some of your life education/experience, & I think in general you are bright & from my perspectives “on target”. I also think you are a realist & have practical ways at looking at various items. Opinionated ?? ... Well that would be me calling the kettle black ?

Yes - Way too general, I totally agree. I am thinking there are some members here that dont really know or even care what relative humidity is. So it is just a starting point. It is a beginning to show our environments change drastically and that is just one of the challenges to designing and creating ceiling, walls, and floors in a tin can that has 1/2 a chance of longevity

Also to attempt (as fleeting as that attempt is), to condense this topic onto 1 thread to share design/build ideas

I hope it stays civil
 

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Discussion Starter #6
When I began my build I looked at the internet to see what other DIYers were doing. The 2018 PM is the 1st RV I have ever owned. As an adult I have no RV experience. I have noticed over the years that many RVs smell moldy musty, some have rotted or rusted out, it seemed to me there was a real issue with longevity due to rot or corrosion.

So before I started building I attempted to analyze the major differences between building structures with foundations & our PM tin can exterior envelope.

One of the biggest differences is the hopefully water & air barrier metal van structure. Houses & Buildings in general (now), depending where you live have a gravity cavity building envelope rainscreen system. Where I live, there was billions of dollars spend repairing buildings that suffered from the NRC and Federal Building Codes, & Provincial Building Codes, & Municipal Codes, & Architects, & Engineers, & Builders all producing a product that leaked (water ingress) & molded & rotted. However this is not our vans

Our vans challenge for envelope is the thermal conductive, environmentally exposed, perfect condensation able, non-water vapour permeable “metal skin”

So how do you build best practices and practically to overcome this issue?
 

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I understand that most do not use their vans in the coldest temperatures, but as a reference, and perhaps as a starting point for discussion, I will describe our first trip in the van when it was still a bare metal box. Christmas in Wyoming, 2014, traveling at ~ minus 25°F. (Thank you, heated side mirrors.) The van heater kept us warm in the cab area, even with no curtain, but over the entire interior of the cargo area, we had a solid thick coating of rime ice. It sublimated with no evidence of passing through the liquid state.

Last year, I unexpectedly encountered rime ice at about 8°F in the channels below the rear side windows which I had not yet insulated or enclosed. Given that these areas were open to the warmth and humidity of the interior, I must assume that rime ice can form on any metal surface thus exposed, as in the van surface of any uninsulated channel. Here again, it must have sublimated, because I saw no evidence of there having been liquid water.

i recently removed my kitchen counter which sits below the window behind the driver. It had been in place for three years. Again, there was the channel that I had not insulated, but this one was isolated from the living space by the counter. Here, there is evidence of water drops in the accumulated dust on the metal “window sill”, but no harm done. There is no suggestion of moisture on the underside of the Baltic birch counter, which probably had two coats of varnish.
 

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RV8R,
Thanks for the kind comments, and yes I have opinions! I wasn’t being critical but wanted to relate the issue that going to the desert might seem like the answer but we have our moisture issues here too. You can probably drive out of RH issues but we find in reality that is not practical. For us the condensing issue is important and of course releasing our own moisture is a huge factor. For us venting all the time to get to ambient and heating when we can to lower internal van RH has worked even in S Mississippi in early summer. We cook inside but do not boil, no shower, awning windows open and vent open some at night. So far so good.
 

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Discussion Starter #9
I understand that most do not use their vans in the coldest temperatures, but as a reference, and perhaps as a starting point for discussion, I will describe our first trip in the van when it was still a bare metal box. Christmas in Wyoming, 2014, traveling at ~ minus 25°F. (Thank you, heated side mirrors.) The van heater kept us warm in the cab area, even with no curtain, but over the entire interior of the cargo area, we had a solid thick coating of rime ice. It sublimated with no evidence of passing through the liquid state.

Last year, I unexpectedly encountered rime ice at about 8°F in the channels below the rear side windows which I had not yet insulated or enclosed. Given that these areas were open to the warmth and humidity of the interior, I must assume that rime ice can form on any metal surface thus exposed, as in the van surface of any uninsulated channel. Here again, it must have sublimated, because I saw no evidence of there having been liquid water.

i recently removed my kitchen counter which sits below the window behind the driver. It had been in place for three years. Again, there was the channel that I had not insulated, but this one was isolated from the living space by the counter. Here, there is evidence of water drops in the accumulated dust on the metal “window sill”, but no harm done. There is no suggestion of moisture on the underside of the Baltic birch counter, which probably had two coats of varnish.
Interesting “real world” experiences. Thanks for reporting your findings. You pioneers in the PM builds will be able to provide much needed data for us who follow in your footsteps ?

You have a nice build MsNomer & a great understanding of wood and the need to seal it ?. That coupled with some extreme enviromental swings, I consider your data reports & experiences valuable on this topic
 

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Discussion Starter #10
RV8R,
Thanks for the kind comments, and yes I have opinions! I wasn’t being critical but wanted to relate the issue that going to the desert might seem like the answer but we have our moisture issues here too. You can probably drive out of RH issues but we find in reality that is not practical. For us the condensing issue is important and of course releasing our own moisture is a huge factor. For us venting all the time to get to ambient and heating when we can to lower internal van RH has worked even in S Mississippi in early summer. We cook inside but do not boil, no shower, awning windows open and vent open some at night. So far so good.
You are welcome, I truly think you are a thoughtful & helpful guy (Yes opinionated, but in my mind that is what we need here). Thank You RD

I did not take your comments on RH as being critical, I totally agree.

Venting !! At least the HVAC type is very very important !! Many people heat their houses & don't want to vent due to the heating bill, but they do not understand the science & also dont know it costs more to heat moist air rather than hopefully dryer fresh colder air. This is a major item to reduce interior RH & hopefully reducing the dew point condensation on the metal skin

This is really the info we can collectively provide, discuss, and debate. Interior use & venting hot moist air to the outside & bring in cool (hopefully dryer air) heat it up let it suck up the interior moisture & vent it out again

not boiling steam into the inside of the van. All great use precautions to get longevity from our vans

Thanks RD

If you have more keep them coming

Anyone else?
 

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Discussion Starter #12
Don’t cook or shower in your van unless absolutely necessary. Always keep your roof vent and a window opened enough if possible to provide air flow thru the van.
Thanks KOV

I totally agree; keep introduction of moisture to a minimum as much as practical & Vent “thru flow” as much as practical ??
 

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I won't get into details because I haven't gotten to that bridge yet, but my shower stall will be sealed up like a submarine on all 6 sides. It will be ventilated by pulling outside air and venting directly outside. Everyone has their feature(s) that they are happy with "good enough" and everyone has their feature(s) that they go above and beyond on. For me it will be the shower that I cross the "unnecessary" line on.
For fresh air supply in a conditioned space, it's always ideal to add filtered fresh air to the return side of a forced air system. This not only allows the the outside air to be filtered twice, but allows it to be conditioned and also creates a slight positive pressure in the envelope.
Our vehicles work the same way. If your van is insulated well, the forced air system pulls outside air and conditions it. Whether AC or heat, that will lower RH inside the van.
Granted you don't use the recirc mode.
 

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I haven't seen them widely used (possibly due to cost) but there is a device called a "low temperature dehumidifier".

A normal dehumidifier works by cooling the air (like an air conditioner) and condensing out moisture. It is intended for use in warm / hot weather and isn't effective for lower temperature use.

A "low temperature" unit is designed for conditions such as a winter in the pacific northwest. Cold, damp air - not only nearly saturated, but also carrying water as an aerosol.

It works like a freezer. The air passes over a coil that literally "freezes out" the water, then re-warms it with the waste heat. Just like in a freezer, the coil is periodically allowed to warm up and the water drains out.

Don't be fooled by the ones that work on a thermoelectric effect - not nearly as powerful as the ones that work via a compressor.

I don't own one, but have seen then for sale on the usual on-line platforms.
 

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Another thing that I discovered is the dreaded plastic triangle subterranean cavern dilemma. A lot of people believe that this is some form of deliberate drainage system to drain away interior moisture. However, I'm certain that the holes in the bottom are for draining when the shell is dipped in the liquid rust proofing/primer. Because they are plugged afterward to prevent water from getting in. The gaps where the spot welds are, near the rear wheel well, simply have sloppy gaps and are not intended for drainage. Actually, it appears they attempt to seal them with the undercoating, but usually do a sloppy, poor job. With the rake of the van, they only allow for water to enter when flung off the rear tire (many posts on water accumulated in that area and not draining at all). I would suggest thoroughly drying and sealing this area, as once it's covered up with insulation, paneling, cabinetry, etc, it's a good place to have excessive moisture permeating up into your walls and insulation, creating condensation on cold walls and mold in insulation and wood furring strips.
And rusting screws and screw holes.
 

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Discussion Starter #16
I haven't seen them widely used (possibly due to cost) but there is a device called a "low temperature dehumidifier".

A normal dehumidifier works by cooling the air (like an air conditioner) and condensing out moisture. It is intended for use in warm / hot weather and isn't effective for lower temperature use.

A "low temperature" unit is designed for conditions such as a winter in the pacific northwest. Cold, damp air - not only nearly saturated, but also carrying water as an aerosol.

It works like a freezer. The air passes over a coil that literally "freezes out" the water, then re-warms it with the waste heat. Just like in a freezer, the coil is periodically allowed to warm up and the water drains out.

Don't be fooled by the ones that work on a thermoelectric effect - not nearly as powerful as the ones that work via a compressor.

I don't own one, but have seen then for sale on the usual on-line platforms.
Thanks HarryN

I agree cooling the air to the “dew point” gets water vapor to a liquid water state & the if you can drain off the liquid water out on the interior you end up with cool dry air, which when warmed up can hold more moisture, which you can then vent outside (or repeat the chiller process).

Cost is one item for these “dehumidifiers”, however my concern would be what type of energy do they need & if they are practical in a van

Do you have some product links you could post here?

Dryzair chemical dehydrators work but you have to be diligent in emptying out the collected water otherwise it will re-vaporize and be re-introduced into the air as vapor moisture
 

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Discussion Starter #17
Another thing that I discovered is the dreaded plastic triangle subterranean cavern dilemma. A lot of people believe that this is some form of deliberate drainage system to drain away interior moisture. However, I'm certain that the holes in the bottom are for draining when the shell is dipped in the liquid rust proofing/primer. Because they are plugged afterward to prevent water from getting in. The gaps where the spot welds are, near the rear wheel well, simply have sloppy gaps and are not intended for drainage. Actually, it appears they attempt to seal them with the undercoating, but usually do a sloppy, poor job. With the rake of the van, they only allow for water to enter when flung off the rear tire (many posts on water accumulated in that area and not draining at all). I would suggest thoroughly drying and sealing this area, as once it's covered up with insulation, paneling, cabinetry, etc, it's a good place to have excessive moisture permeating up into your walls and insulation, creating condensation on cold walls and mold in insulation and wood furring strips.
And rusting screws and screw holes.
RnR

Great Point;

Theory is; condensation on the metal van skin walls and possibly ceiling will drip down into these rocker cavities. Factory drain holes may not drain properly & factory sealing may be substandard.

I have mixed thoughts on insulating this cavity, but think it is best left uninsulated & the thermal bridge at the plastic triangles be kept on the cold side if the build design allows floor/wall insulation at the interior base

Regardless, if one did insulate that cavity, a non wicking, non mold food insulation should be used over a choice of denim.
 

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I would not insulate it.
I'm convinced that it was not purposefully deigned to collect and drain interior moisture. I don't think anyone at FCA really cared if water leaked in or drained out of that space, to be honest. And to me, the logic would be the same as cutting a hole in the bottom of a boat to let water out. Any gaps or holes in that area do a better job of letting water in than draining out and any condensation on the walls would end up running down, over the top and onto the floor.
I would not insulate it, but I would definitely suggest sealing it to prevent water from getting in from the outside and evaporating up into the walls. You probably won't prevent every drop, so definitely don't insulate it.
 

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My Pinto (yea I know) collected so much water in that similar space because they had closed it off and water got in from the front wheel wells that it would slosh when you drove. I fixed it with a 3/8 inch drill by putting 3-4 holes in it and never had a problem with water in it again. I have seen this in other cars too. I am a believer in that being a drain and unlike a boat in the water there is a place for moisture to drain. Perhaps it makes no difference if you don’t get condensation in the walls, or don’t let it drain down, but if you fill it and it gets wet in there it will be a problem. I have several places I can easily get to the covers and mine appear dry.
 
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Your scenario with the pinto is identical to the promaster.
Water gets in from being thrown off the tire in the wheel well and then has no way to drain out. If you can't seal it and stop the water from getting in, then you should remove the plugs or drill a hole in the lowest point to let it drain back out.
I opted for sealing it.
 
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