"That space right there might save your life"

[registror]

two layers can have an insulating effect, in that radiation moves from hot object to cold object. If the object is not as cold, then less radiation is draw to it.. Convection currents can also be set up with such an arrangement

[AdamantAnn]

Many older manufactured homes have had something called a "roof over" installed. It's basically a metal roof over the original roof. It's somewhat louvered. I don't know details about it's exact construction but I do know it made the house sooo much cooler her in FL and made the building materials last years and years longer than their counterparts who don't have one. Concept definitely worth noting. Thanks guys!

[Nik]

Hence tents' fly-sheets ??
Diverts unwanted solar heat away from inner tent, shelters inner from wind-chill, lets condensation and driven rain drain beyond inner to gulleys...

Been there, dug them, collapsed and secured canopy, double-guyed, double-pegged main & fly, cross-tied poles etc to roof rack & fenders of car. Woke to forecast howling gale. Noticed rippling ground-sheet as surface run-off flowed beneath. Whispered, 'River, stay awaaay from my door', went back to sleep...

Okay, ours was a braw Marechal steel-framed family tent but, the following morning, that previously crowded field held only us and a tiny 'hooped' bivvie-tent. The latter had torn free, was now wedged half-way up the tall perimeter hedge. For the passionate young couple within, the earth really had moved...

My brother and I helped the field-keeper pull dozens and dozens and dozens of pegs from the many razed pitches...

[Applejack]

Grizzly, that makes a lot of since about the dead air space between the two tarps.

[GrizzlyetteAdams]

Thanks for bringing this thread to light. It makes a ton of sense.

The First Americans used the same principle in their tipi design. Years ago I used to sell tipis (Primitive Panther brand) and lived in them from time to time, and experienced first hand the marvelous design of the Plains Indian tipi. It is truly an all-weather home.

There is a "dead air" space between the tipi and its inner liner. I was amazed at how well the air convection effect that the liner had on the temperature inside the tipi. It had a cooling effect in summer and a warming effect in winter.

I can see how useful that airspace would be between two tarps!

[Applejack]

This was interesting and has a lot of merritt to it. You guys that have been in the military might already know about this one.

[lalakai]

aaahhhhh....thank you. another trick added to the bag.

[Applejack]

Don't know why it would work except that the poncho above the lower one would help keep the lower one more shaded and therefore keep the air below the upper poncho cooler thereby keeping you cooler under the lower poncho. But hey if it works I am all for it. I will have to remember this one be it for my tent or tarp to give this a try.

[methusaleh]

This post is inspired by the recently-revived lightweight tent thread. Someone mentioned using tarps as an excellent lightweight solution.

When I was an Infantryman, we carried the notorious poncho and poncho liner. Or shall I say, two ponchos when the mission loadout permitted. Every milligram of weight counts when you are in a Light Infantry unit! We went to extremes to reduce the weight of our kit sometimes. But "the mission drives the gear" no matter what.

Anyhow, I referred to having two ponchos on purpose, and that is where the title to this piece comes in.

I don't remember where or whom it was, but a wiser, seasoned soldier somewhere saw some of us young and less-experienced guys setting up hooches with ponchos in a sunny and hot environment. He came over and struck up a conversation, asking who had a second poncho. Even though it was a training environment and weight discipline wasn't as tight as it was when we were operational, nobody had a second poncho, nor thought that there was a reason to. Some people carry some silly extras during training, but a second poncho wasn't in anyone's mind at that level in that unit.

The older gentleman smiled, and asked us to follow him to view his hooch. He had two ponchos rigged up parallel to each other and roughly a foot apart, one directly above the other. Both were guyed similarly and peaked in the middle, as we did to encourage moisture runoff. I think all of us green guys sort of looked at each other, as if to silently say, "alright, so what, this guy wants two ponchos above his head, why should we care?"

"That space right there might save your life," said the older soldier, pointing between the ponchos. He went on to explain some complicated scientific stuff about convection or advection of air, something like that. Bottom line is, on a hot and sunny day, the space between the ponchos greatly helps with cooling and will help keep a resting person cooler. Naturally all of us acquired second ponchos to try out the trick the next time we were in the field, and it seemed to work.

That was over 20 years ago. I am not sure of the reason why, but that extra layer above your tent or hammock seems to work. If I have a conventional backpacking-type tent, I will rig up a tarp or even a good ol' military poncho about a foot above the roof. I swear it works to keep things cooler and somehow move the air.

My two cents, would appreciate what others might add or comment.