Condensation mitigation in single wall (duplex-style) tent

[Luke T]

Hello,

I’m designing a duplex/smd lunar duo style tent and I’ve seen various different approaches to ventilation in this style tent and I’m wondering about what is actually effective (apart from campsite choice and sleeping with one or more doors open).

The main difference I’ve observed is that the lunar duo has small vents at the top, but tends to be pitched a little lower to the ground, but the pictures I’ve seen of the duplex are all pitched higher off the ground.

Being the the pacific northwest, condensation is just inevitable sometimes, so I’m also interested in the behaviour of moisture once it’s on the tent walls (if condensation flows down the walls but doesn’t touch my sleeping bag it’s less of an issue). Does material choice have an effect on this? At this point, I’m considering both silnylon and silpoly for the fly.

Lastly, I’m wondering if the positioning of the mesh that connects to the bathtub floor might make a meaningful difference. For the lunar duo, these mesh panels go up vertically from the bathtub floor on the left and right:

versus, the duplex, where the mesh connects perpendicular to the floor:

My suspicion is that the vertical mesh panels might wick condensation as it flows down the side panels and cause it to drain into the bathtub, vs draining outside the bathtub and on the ground, but I have no clue if that theory is grounded in reality.

Thoughts?

[Sam Farrington]

“(if condensation flows down the walls but doesn’t touch my sleeping bag it’s less of an issue)”

Wishful thinking?  I’ve always experienced condensation on the inside of single wall tents, and sleeping and other gear has always gotten wet from it, no matter how well ventilated the tent.  It can be partially avoided by a more spacious (and therefore heavier) tent, and reduced by using Mylar and other materials that develop it less.  Condensation seems to be a personal choice – to tolerate or not tolerate it.

In the past, Sierra Designs produced several single wall tents as ‘partially’ double wall because they had net doors inside the vestibules.  Others expanded the double wall portion a bit.  Those tents were taken off the market after a few seasons.  Tarptent tried net barriers over a portion of the single wall Moment.  Now they sell a full double wall Moment.  Why fool around.  Extend the double wall to all occupied portions of the tent (maybe not in the vestibule(s) outside netting doors).  On a solo tent, this means 2-4 square yards of tent surface, protected by inner net or woven material weighing well under one ounce per square yard.  Two to three ounces is too much to stay dry?  Is that what is meant by ‘stupid light’?  For some, obviously not.  For me, I’m built for comfort, not for speed, as the saying goes.  Which of us is having a better time after a week or two of trekking, the one who saved three ounces, or the one who stayed bone dry in the tent?  Isn’t that what tents are for?

 

[Roger Caffin]

I know what Sam means, but I have to say we have very rarely ever had a condensation problem. There was one time in fog, when the condensation on the outside of the tent matched or exceeded the condensation on the inside, but normally – no problem. The secret is shown here:

VENTILATION!
A small through-flow of air will eliminate the problem. This is the back door – the windward end. We leave it open until bad weather forces it closed – and even then we normally still leave it open a bit. The same applies to our double-skin winter tents.

The problem with so many other tent designs is that they have no real provision for a through-flow of air. Tiny little vents just don’t cut it – as many have noticed.

Cheers

[Jerry Adams]

There are times when I get condensation regardless of ventilation, like if I leave the door open all the way to the peak of my mid.  Or if I just suspend a piece of fabric in the air as a test.  Especially if it’s near 100% humidity, and there’s radiative cooling because the sky is clear, the tent will cool down another 10 degree F, condensation happens.

The mid has steep walls so condensation drips down on the inside.  Your tent walls aren’t quite so steep but that should still work.

I have no floor so the condensation just drips onto the ground.  If your netting flowed down to the ground rather than onto a bathtub floor it would work better.  I have no idea though whether this is a problem in your case, just throwing stuff out there.

The peak of my mid is 60 inches so when I sit up in sleeping bag to get up I can avoid touching the walls with my head and getting it wet.  Also, if you touch the inside of the tent, sometimes condensation will start dripping down from there.

Some people take a small towel to wipe off the condensation.  There is synthetic material that absorbs a lot of water but wrings out good.

[Roger Caffin]

If condensation does happen, it seems to dribble down to the netting sidewalls and go through them. The netting does not guide the water onto the bathtub floor. Strange, but it works. Not often though.

Yeah – we carry a small sponge ( 5 g?) to wipe the walls down just in case. If the lee vestibule is over wet ground it can get a bit wet so I give that a wipe. The main body of the tent, over us, seems to stay that bit drier.

Cheers

[Sam Farrington]

Hi Roger,

The photo in your March 17th post appears to show dry inner walls in a single wall tent. At one time, I used a single wall, tunnel shaped shelter made from a Gerry tarp with pole sleeves and a floor added:

There were short awnings that cinched over the front and rear guy-outs, but are rolled up and not visible in the photo.  But otherwise, most of the ends were open.  That is a lot of ventilation.  Nevertheless,  most of the time the walls collected a lot of condensation on the insides of the lower walls, soaking sleeping bag shells and other clothing and gear.

Northern New England is well forested, at least along the trails, and can be quite humid.  Maybe the climate is dryer where you are.  Otherwise, it is hard to explain the variance between your experiences and mine.  In any event, wanted readers to be aware of what can be expected in the way of condensation in single wall tents used in many places.

[Roger Caffin]

Hi Sam

One occasion when we had a LOT of condensation was by a large creek, in a forest with steep valley sides, a cold night and a thick fog. Sounds a bit like NE, doesn’t it?

It might be worth bearing in mind that we have two bodies asleep in my blue tent, not one. That is double the heating. I suspect that is significant. Hum – I wonder how a Cloudburst 3 goes with 3 sleepers?

Yeah, it’s a problem under some conditions. The side-walls on my blue tent seem to be steep enough that most condensation passes the netting side walls and continues to ground OUTside the bathtub groundsheet.

Cheers

[Author]

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