vapor barrier

[paulbevilacqua]

I am trying to decide if putting a vapor barrier on both sides of the insulation is a good idea if I have vents installed in the interior walls letting air flow through the walls keeping it insulation drier, any feedback would be appreciated, thanks

 

[ZacLee]

Have considered closed cell sprayed urethane foam? That provides twice the insulation value per inch compared to fiberglass. It should also function as a vapor barrier.

 

[John61CT]

Two would be overkill, and so is active ventilation in the cavities.

Spray foam works great, long as you do get complete adhesion and coverage of the panels and the temp range supports proper curing so you don't get excessive off gassing lofter, some people are very sensitive to the fumes.

With rigid foam panels, making sure all metal is otherwise covered, and then a 'reasonable attempt' at stopping any airflows between the living space and the bodywork, that should be fine.

Not getting it perfect will allow any condensation to evaporate when you really heat things up.

The real key is ventilation, no way around it, you need a lot all the time bodies are breathing and sweating in the enclosed space. MaxxAir, Fantastic Fan plus an intake opening at the other end, pretty much 24*7 year round.

And avoid adding more than needed, open up while booking, don't use unvented propane for heat etc.

More extreme measures would only be needed if staying put in humid tropics or places like the PNW.

 

[paulbevilacqua]

I am going to install 2 ceiling vent fans and will probably keep them open most of the time even when the wood burning heater is going but haven't decided what insulation to use yet. I was going to go with recycled denim but the R value isn't high enough and really don't want to use fiberglas even if it has a very good R value, I am open to suggestions on insulation (by the way I'm doing this on a bus), the spray foam is very messy but good I just hate the thought of having to shave it. another possibility is shredded plastic

 

[John61CT]

Do not use anything a creature would consume or nest with! And for sure not fiberglass.

Rigid board, XPS facing the cold, then polyiso to get max R-value per inch lost. Spray foam sparingly to fill gaps and help hold the panels in place.

Maybe even bulk spray the sheet metal, leave a dead air space behind the panels, that's where a VB could go.

And you're not ventilating "even" when burning wood, but especially then.

Also when cooking, bathing, burning propne inside the space.

 

[user 37446]

Have considered closed cell sprayed urethane foam?  That provides twice the insulation value per inch compared to fiberglass.  It  should also function as a vapor barrier.

Spray foams, being used in attics of houses up north (Canada) are getting a bad reputation.  There are CBC documentaries about entire homes having to be demolished due to the off-gassing.
[font=arial, sans-serif]

Here's a recent (2017) EPA fact sheet on dangers of closed cell spray foam: 
https://www.epa.gov/saferchoice/health-concerns-about-spray-polyurethane-foam


Then there's the documented vanner concerns about its use rotting out the vans walls... here's a recent good thread:
https://www.mountainproject.com/forum/topic/111576774/insulating-a-van

 

[ZacLee]

This problem is extremely rare and likely caused by improper mixing of the foam components.

 

[John61CT]

Also very common for people to fail to precisely follow instructions - temps really do need to be in range, not spray too much too thick or it never cures.

But yes, rigid foam, only using small qty of spray for filling nooks and edges is better and probably cheaper.