Jan 7, 2008 at 2:57 pm #1226623
Does the addition of a full floor decrease the condensation. I know that when a house is built over a crawlspace and a 6 mil poly vapor barrier is used on the ground there is less humidity in the crawlspace. And it is required to install a 6 mil pvb before pouring concrete for a slab floor. So it seems that stopping the vapor from the soil is a good idea. Is this why picking a site in a forested area is better? Is is because the trees are drawing moisture from the ground?Jan 7, 2008 at 5:22 pm #1415209
@johng10Locale: Mid-Atlantic via Upstate NY
It's not because the trees use moisture from the soil.
Pitching you tent in the forest is better because:
1. A field has vegitation that supplies extra moisture at night.
2. The leaves on the trees hold some of the heat close to the ground & colder equals more condensation.
3. The pine needles, leaves, and other "forest duff & litter" prevent rain from splashing up under the fly / tarp and also forming running streams that could flood over the groundsheet.
The tent bottom or groundsheet (2mm plastic) serves the same purpose as the vapor barrier in your house construction example.
Pitching a tarp over grass, and then using a small groundsheet does result in moisture from the grass rising at night & possibly condensing on the underside of the tarp (if it's cold or humid enough).Jan 7, 2008 at 5:48 pm #1415214
@fairweather8588Locale: The Desert
"2. The leaves on the trees hold some of the heat close to the ground & colder equals more condensation."
I had first hand experience with the phenomenon about 2 weeks ago. My buddy camped in the open without trees to speak of, and he awoke with frost on his down bag (d'oh!)
and his water bottles were partially frozen. Now here's the proof in the pudding… I was no more than 12 feet away partially enclosed on one side by a Sugar Sumac and on the other by an Alligator Juniper. No frost, no ice, no worries! his thoery was that he would catch the sunlight first thing, while I would freeze in the shade. Ha, sucka!Jan 7, 2008 at 6:04 pm #1415218
Another point to remember is that the closer your face is to the fly the more condensation you will have (from your breath)
FrancoJan 7, 2008 at 7:53 pm #1415235
@eaglembLocale: AZ, the Great Southwest!
If it was a clear night, I expect a fair amount of the cooling was from black body radiation.Jan 8, 2008 at 1:36 am #1415262
@archnemesisLocale: England, UK
If you cover all the ground beneath you with a vapour barrier then that will help matters somewhat – unless you fully enclose the sides as well in which case matters will be worse.
One of the things I did last year was to create a fully enclosed single-skin non-breathable tent. The condensation was unbelievably bad – even with vents in the tent.
By separating the base from the tent – so that there are gaps all around then condensation is very little – even if more ground is exposed.
Most of the vapour comes off you at night. You are the main heat source and the main water source.
If you pitch a tarp in your garden with no ground-cloth beneath it you will find almost no condensation. If you then sleep under it you will see some condensation.
Airflow is king. Covering the floor area is very secondary.
I tend to use a bath-tub floor under my tarps. It weighs less than a bivy bag, and gives me more dry-space. With a bath-tub floor you can also cover more of the ground for a given weight.
A good test to run to make yousrelf happy would be to pitch a flat tarp in the garden and under one half of it cover the ground and the other leave the ground exposed. See what happens…Jan 8, 2008 at 5:16 pm #1415359
I have been tarping for a year. I'm sorta new to it. I just got a tipi style tarp to help with winter issues. I did fine all last year using a poncho tarp as primary shelter with a myog bivy, but opted for some extra room this winter. But, unless I have ample space at ground level for air flow, I get a lot of condensation. And one thing I was really looking forward to was more complete wind protection from the tipi style. But as it seems I must have the base of the tarp elevated to allow for air flow- and that also allows for wind chill. I know there is no way to get around this, but what I want to do is take steps to eliminate as much 'cause' as possible and experiment with having one side elevated and one side lowered to the ground (on leeward side). I am hoping this will stop the issue because as it stand I am having to bring my bivy along with me to keep condensation from wetting me -darn it!
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