Insulation - reality vs. internet "truths"?


Discussed insulation with a friend, which made me think a bit about the issue. Surely there is no subject that has so many “truths” given by confident bloggers (none of whom actually have any deeper knowledge in the field, background as a civil engineer or similar… ) I would love to hear your views on my “assumptions”.

Vapour barrier : I have read different opinions about the Vapour barrier, where some say that you shouldn’t have one as the metal exists. But according to building engineering, the sheet is on the “wrong” side of the temperature gradient, so that in itself is hardly an argument. The argument is also that you build moisture into the wall, which is true, but… The volume of one “side” of my van (metal to inner wall) is about 3.5x1.9x0.05m => 0.33m3. On a normal day that means there is about 4grams of water in the wall, a volume that hardly even if it falls out 100% causes any problems with mould or rust. Given that the Vapour barrier is tight, I see no problem whatsoever with 4g of water being in the wall. Far from any amount that could create rust problems. An interesting question is how much rust 4g of water can theoretically create, don’t know, but can’t be much?

If you don’t use a Vapour barrier, you are constantly feeding new moisture that can fall out, which can then lead to problems given that you have a point in the wall (metal or insulation) where condensation occurs. Of course, you can use insulation material that does not consist of air or can absorb moisture, but to succeed in filling a wall with cavities etc. to 100% I see as difficult.

Insulation: Nothing to do with moisture per se, but the insulation material creates a temperature gradient (from the outside temperature to the inside), where moisture (given that there is moisture) will fall out when the temperature gradient passes the dew point. In theory, solid materials without air in them are better, but since there are cavities in the car that can’t be filled, the material doesn’t really matter, given that you have a Vapour barrier. But of course, if you don’t have a Vapour barrier, there may be a point in having that type of solid material as there will be no moisture where the dew point is. Maybe two different design philosophies but with the same result. But can you really say from a theoretical/practical point of view which one is better? Even if you have a solid material, you have to ensure that no moisture can get into any cavity or hit a cold surface.

What are your reflections, are there “truths” that are in fact myths, things that are purely theoretical but never become a practical problem?


If we look back through time, the old ice houses typically had 3-4 foot thick walls & roof filled with sawdust, bales of hay or straw, dirt, mud, or sand. Whatever was easily available in the area. This allowed them to keep ice year round without any additional cooling. That’s effective temperature insulation.

Unfortunately, that isn’t practical for vehicles, or even most homes. Off grid desert dwellers often use double walls & roof, where the outside walls are vented top, bottom, and all sides. This keeps the inner walls always shaded, and doesn’t allow heat build up between the outer walls & roof and the inner ones. This method too, is pretty effective against heat.

For vehicles, shade will get you much farther than any amount of insulation. Insulation might buy you a little extra time, but your money will be better spent on active heating & cooling systems. I’ve spent winters down to -60°F and summers over 120°F with no added insulation, 360° of uncovered & untinted windows, quite comfortably inside with my climate control systems. My heat has never required any power, and my new Peltier powered heat/cool pump is powered by a liquid candle rather than electricity.

For my bus, which I’m currently using, I need two swamp coolers, one in front, & one in the back. Since they basically draw no more power than just a fan, their power usage is extremely minimal. (Both combined use less power than a single 12v compressor fridge.) [The peltier heat/cool pump isn’t enough for the bus, or tempertures much below freezing…]

You can’t stop or prevent condensation, you can only hide it. Moisture leads to mold & rust, and the best we can do is remove it via ventilation. Dry heat in the winter can help, but it still requires ventilation to prevent the moisture from being trapped inside the vehicle. To be totally successful, everything inside the metal walls needs adequate ventilation.

I don’t worry about insulation for temperature control, but it is very useful for sound deadening. Mostly for the floors & wheel wells, and the roof to lessen the sound of rain or hail. Wall insulation depends on the specific vehicle for me… I do prefer a smooth, quiet ride.

In both my bus & my van, I can create a virtual wind tunnel from front to back. Both while driving or while parked. This can do a really good job at keeping moisture levels in check.


"Be the reason someone smiles today!" ~ Van_Dweller