Condensation in Single-walled Shelters: Contributing Factors and Tips for Reduction

Bummer :(

Hi Chris

> While everyone seems to agree that perimeter venting is essential, there doesn't seem to be unanimity about peak vents.

I assume that 'perimeter' => ground level and 'peak' => top level.
In that case, I would argue from snow experience that you need both. Well, at least you need somewhere for the fresh air to come in and somewhere for it to go out, carrying water vapour with it. In still conditions this usually means the airflow will be driven by heating from your bodies, so a low inlet and a high outlet are what's needed.
However, in windy conditions the inlet can be high as well. The problem then may be to limit the incoming gale and spindrift of course :-)

Two nights in the snow a couple of years ago illustrate this very well. On each night we had the vents at each end of our double-skin snow tent open, and the tent fly was an inch or two off the snow as well.
The first night was still and we were in a valley. In the mrning the inside of the tent fly was caked with ice. The inside of the (breathable) inner tent had ice on it as well. Sigh: a heavy tent to carry.
The second night had a gentle breeze blowing all night and I pitched the tent end-on to the wind direction. In addition I was on a slight shoulder well above the valley. (Not as sheltered in case of a storm, but I gambled …) In the morning the inner and outer layers of the tent were DRY.
I attribute most of the difference to air flow.

Under more severe conditions I have shut the top windward vent right up and relied on the ground-level ventilation. I had to: the spindrift coming in the top vent was building up on the inner tent and starting to melt – and drip onto my head. As I remember the inner tent dried right out and the outer tent was reasonably dry on the inside in the morning. Mind you, the outside of the fly was another matter!

I fail to see what all the hullabaloo is about condensation on the shelter, at least for 3-season backpacking. I get condensation on my tarp about half the nights I camp. I don't like it, any more than I like heavy dew on the grass in the morning. But I fail to see how either condensation on the shelter or dew on the grass is a major problem. If the temperature is near or above freezing, then there is plenty of body heat to burn off any moisture that drips onto your sleep gear or gets onto your clothes. If the temperature is well below freezing, then the condensation will freeze and hence drippage isn't a problem.

The real danger is condensation that occurs INSIDE your sleeping gear, which is mostly a problem at temperatures below freezing (there is usually enough body heat to avoid this problem at tempatures above freezing). There are basically two ways to deal with this. First, a vapor barrier will solve the problem completely. But this is a nuisance for many people. Second, by using a good double-walled tent, you can often raise the ambient temperature inside the tent sufficiently that the dewpoint is moved outside the sleeping bag. But this isn't guaranteed to work, so you need to be prepared for condensation inside the sleeping gear (either use polarguard, which is minimally impacted by condensation, or else be prepared to get back to civilization in a hurry if using down).

John,

I know this was a while ago, but nice mods on the Gogo! You get some nice tension from the pole replacement, as well as a bit of weight savings. All of us here at NEMO are impressed with your handiwork.

FYI, we are furiously working on an alternative airbeam construction that will cut down on the bulk of the current construction. Look for a great ultralight tent to come out in the spring using this technology.

Connie