Managing Condensation in a Single Skin A-frame

[Roger Caffin]

Close enough to how I sew it. I don’t bother with the tilt though: almost vertical seems to work fine for me.

Cheers

[Sam Farrington]

“(I know, you don’t want to hear from mid fanatics, just ignore this, I iterated on a number of A frame and tunnel designs and moved to mid : )” Jerry – Hope that impression was not from me. The mids are much easier for MYOG than curved shapes, and have lots of room in the larger models for 2-4 people. I suppose that’s why they are so popular, especially for MYOG. But I would put a large A-shaped awning vent over the door, as some have done, and definitely have some kind of a floor for rainy weather. On my current solo tent, such a vent is very effective. Ryan Jordan put up a good article of a trek in the Uintas of southern Utah with a bunch of mids. Lots of wind due to the open terrain, and plenty of rain on occasion. The lightning also can be very dangerous, so much that I once had to hightail it out of there. Above timberline, I would prefer something with a lower profile, especially if the poles were metal. Also, as my Shelties can attest, I am always a “bull in a china shop” in the wee hours.

“Plus, a net inner IS NOT a double wall tent.” Walter – OK, but the net inner keeps the condensation off me, and if there is enough space between the outer wall and the net, and the set-up is taut enough, I can touch or press against the net without getting me or my gear wet. But this was on dome designs that sloped to the ground without much horizontal surfaces up top:

“As for the idea that the inner tent is to stop you from moving too far – I have to ask how it does that at 3 am when you are fast asleep.” OK, Roger, your got me. Have to admit that the taut net inners that keep me dry have been tents where the net inner pitched first (tautly, but first) – those dreadful ‘pop-ups’ to use your expression.
But that is no reason not to design a net inner that goes up along with the outer and is just as taut. Currently, that’s the goal here.

“And despite the dire warnings, most people do seem to manage fine in single skin A-frame designs – even in the PNW.” Geoff, do you think Dan was blowing smoke? I don’t. Also don’t think we are that different when it comes to creature comforts. That’s why Dan saw a number of trekkers heading for town. That is ‘social’ backpacking, and enjoyed by many, especially on the AT and the like, where shelters abound, and the trails sometimes go very near lodging, such as the Long Trail Lodge, one of lots of examples. The other kind of backpacking is quite different. Sometimes many days in the mountains without seeing a soul, and several days travel to the nearest road. There, the challenge is to make a shelter with the desired comforts that is both sturdy and light enough. I think we’re getting closer.
Please also note that it is a characteristic of human nature, and BPL, that having spent a good chunk of change, not too many vent about an unhappy choice. Once in a while you hear about a lousy new car someone bought, but not often. This thread is a bit more focused on fixing some of the problems, however, which is what I like about the MYOG forum.
Your ‘drip-lip’ seems a little like a variation on Z-Packs’ approach of a netting floor with a WP floor thrown over it. (How the netting survives, I’ll never know.) If your netting is not also for bug protection, you might want to make it less tightly woven to promote drainage. And suspect there may even be ways to design a larger vent on a tunnel with only one vestibule pull-out. Since I find ‘side-entry’ tents to be much more comfortable, haven’t pondered that overly.
But doubt you will find true happiness with A-frame designs. At least put a little bow in the frame as illustrated in Roger’s second photo, above. A little bowing goes a long way, especially compared to a sagging, cat-cut, profile. Also, a number of models, Lightheart Gear to name just one, use top strut-like connectors to increase the area underneath the two hiking poles.

[Geoff Caplan]

Hi Sam

“I doubt you will find true happiness with A-frame designs”

I’ve a couple of threads running on this project, and there’s a recurrent view that A-frames are miserably cramped. I’ve logged hundreds of nights in A-frames, and that’s simply not my experience. I don’t feel any need to introduce complexity to expand the space, and a properly cut and guyed design won’t sag significantly, especially when built in silpoly.

Here’s Chad Poindexter, a much bigger guy than me, in his trekking-pole Yama (which has similar dimensions to my A design). Lots of room to cook or chat at the entrance, and my tent won’t have a pole obstructing the door:

And it’s even fine for two – here’s a couple of guys in their trekking-pole MSR:

Not quite as spacious as a tunnel, but plenty liveable enough for most needs.

In addition, a well executed A-frame:

• Can use the strong straight poles you’re already carrying (unlike a dome, hoop or tunnel)
• Is as easy as a tunnel to pitch in wind (you use the same technique)
• Has a tight footprint
• Is great for getting a through-draught
• Can be fitted with well sheltered vestibules for ventilation, cooking and gear
• Works well for floors, draught and bug-protection (all essential where I camp)
• Puts the space where you want it, above your head and feet when sleeping
• Handles weather well enough to be used on the South Col
• Uses fabric efficiently so can be very lightweight.

The other main option with straight poles is the mid. I have extensive experience of the TrailStar, which in my view is about as good as a small mid can get. But it has issues:

• Huge footprint, which is a problem in the woods and tight alpine pitches.
• A challenging pitch at the end of a long day, especially in wind
• Difficult to get in and out of without wet knees (or worse, when there’s livestock around…)
• A draughty open door which you sometimes have to reposition in bad weather.
• No sheltered vestibule, so you have to cook inside
• No cross-ventilation
• The central pole means much of the space is unusable and you’re jammed up against damp walls with silnylon in your face.
• Very difficult to fit out with a bug and draught nest – involves a lot of faff and you end up with a small and awkward living space tucked in a corner of the cavernous tarp
• Because there’s so much wasted space, the combined weight of tarp and nest is more than I want to carry.

To balance all that:

• Superb in the wind
• Great views
• And IMHO the most beautiful tent ever made.

More conventional small mids are difficult to protect from draughts and bugs, have little space above your head and feet, are difficult to ventilate and have door drip lines that overhang your sleeping bag and imprison you in the rain. These problems don’t apply so much with bigger mids, but then you’re stuck with more weight, a high profile in the wind, and a huge footprint.

I’m going to get soaked without a net inner

There are thousands of people using small single-skin tarps and tents in challenging conditions, and the great majority are perfectly fine with the condensation. As I’ve said before, it’s been a non-issue in the TrailStar. For example here’s a video of a guy in his Lunar Solo on the Pyrenean High Route during a typical storm. He’s “Completely sold on a single skin tent – you don’t have the faff of having a damp inner to deal with – you just wipe it over”  https://youtu.be/aR18cJHhg7Y?t=4m17s This has been my experience, and Roger’s too. A mesh inner adds weight and complexity, and is very difficult to keep tensioned in an outer-first design. It doesn’t offer much protection from draught, dust or spindrift, and as Roger says, there are easier ways to keep your bag away from the walls. Dan’s issues were in a tent that is somewhat notorious for poor ventilation. Many others beg to differ.

The people who say they are happy with their A-frames are social hikers or bullshitters

Oh come on – the reviews I’ve read are from thru-hikers on alpine routes – people like super-hiker Cam Honan, who uses a ProTrail when it’s too gnarly for a tarp. I used A-frames most weekends for a decade in Scotland, and we can match the PNW when it comes to rain and bugs…

Your design obviously works for your preferences and conditions, but it wouldn’t work for me at all. As I tried to say above, we all have different preferences and use-cases. I’ve no doubts at all that a single skin A-frame will work OK for me – I’m simply looking for ideas on the best way to execute it.

[Roger Caffin]

I am going to limit my comments here.

That MSR A-frame that looks so roomy: you do realise that it is twice as high as a tunnel? That is going to collect a lot of wind. And that huge unsupported fabric side is going to handle high winds rather poorly. To be sure, it might stay up if the fabric is strong, the poles strong, the guys strong and the stakes good.

On the other hand, it might be fine and airy in mild weather below the tree line. Horses for courses.

Cheers

[Geoff Caplan]

Roger

Twice as high as a tunnel? I think you must have misread something – that’s an MSR Twin Sisters at 1100 mm high:

It doesn’t have any guys at all, so it’s not really designed for wind. But they used it for a tour of Iceland and it seems to have done OK.

[Jerry Adams]

“Jerry – Hope that impression was not from me.”

I was just trying to be humorous about something, I forget what now…

I don’t think you can have one design that’s best for everyone.  It’s good to brainstorm different ideas, try things that seem like it would work for an individual.  But, it can get annoying if someone is always bringing up the same idea (mids).

 

“you do realize that it is twice as high as a tunnel? That is going to collect a lot of wind.”

Like that plot of wind speed vs distance above ground you posted in some article, yeah, the wind speed is higher as you get higher.

But, especially for a single pole mid, the cross sectional area is smaller as you get higher.  Especially at the peak, the cross sectional area gets so small it doesn’t “catch much wind”.

[Tipi Walter]

The single-wall vs double-wall condensation question will be discussed forever it seems.  And every location is different from every other location.  My experience in the mountains of TN/NC/Virginia will be very different than campers in Calif or Arizona or Montana or even the PNW.

But there’s enough tent reviews online highlighting the problem of single wall tent condensation to at least say there can be a problem—just as you could find similar reviews with double wall tents.

We had this discussion on Whiteblaze recently and I found several examples of tent condensation in a variety of tents—check out the links—and test the limits of how far you want to delve into this subject—

http://whiteblaze.net/forum/showthread.php/121016-Tent-How-big-is-too-big?p=2096531&viewfull=1#post2096531

Beyond all this, I agree with Geoff on several points—A-frame tents use straight strong poles, they offer a small footprint, they work well with floors.

And he’s right, Tipi tents are the most beautiful but I’m biased since I lived in a Tipi for many years.  The only reason I would ever discard my “regular” backpacking tents (think Hilleberg) for another Tipi tent is because of their beauty.  That’s the only reason.

I miss my old A-frame because it brings back many good memories of camping at hundreds of different sites.  If I had it now in my greedy hands I’d certainly start using it again, if for no other reason than the good mojo it brings.

But my current tunnel tent, like I said, is really just a modified A-frame with bent A’s (the hoops) tensioning out the side walls.  Break the curved poles at the top (god forbid) and you end up with an A-frame, fore and aft.

Then again, while I’m a sucker for Tent Discussions and love tents in all their configurations—mainly because they represent a cozy home in a forbidding wilderness—a black cozy hole in a snow-plastered blizzard—the important thing is that we use these tents as much as possible in all conditions.

What does it matter if it’s a mid or a tunnel or an A-frame or a tarp or a wedge or a 3 or 4 pole dome etc?  Test your fave, put it thru the wringer, struggle thru a windstorm, get condensation, use it 500 nights, THEN provide a full report and we’ll read it.

[HiLight]

Since this has gone a bit afield of the original topic, and since Sam mentioned BD’s single wall tents, I thought I’d throw something about those into the mix.

I’ve used an older BD HiLight tent for several years in a variety of conditions, and I’ve been generally pleased with it. Condensation does collect inside at times, but I’ve never found it to be much of a problem to quickly wipe it down in the morning. It’s a simple, robust structure that I’ve lightened by adding CF poles and a few other changes. While not terribly light by BPL standards, it’s under 3 lbs and capable of handling a wide range of weather.

I was wondering if anyone had made a MYOG attempt with a similar design. The HiLight’s 2.5 straight pole system would be relatively easy to fabricate (the BD FirstLight is even simpler), and I believe the shape offers some of the benefits of a tunnel (vertical sides) and an A-frame (headroom). If I was sewing one, I’d definitely sleeve the poles, and add a drip bead at the junction between the bathtub floor and walls. If desired, a true vestibule could be incorporated easily on the door side, and sheltered storage could be added to the opposite side. BD sells one, but I think a simpler design that incorporated trekking pole supports would work well, too. Non-storm draft isn’t an issue, as an entire side of the tent can be opened. Storm ventilation could be improved by extending the side flaps that tie into the half pole, with vestibule extensions added, as needed.

Geoff, I’ve used the HiLight “for lightweight use in exposed mountain and desert terrain,” and found it does a pretty good job, but there is room for improvement. I’m not sure if any of that will help you reach your design goals, but as I read through the thread, I found myself evaluating what I use against what you’re creating, and those thoughts came to mind. Good luck with your design process, and I look forward to more of this discussion.

>>>>>>>>>>>

I removed hot links from the above so it would actually be displayed when I reposted it. I believe this problem is still in play: https://backpackinglight.com/forums/topic/some-content-causes-posts-andor-comments-to-disappear/

The continuing forum issues are breathtaking.

[Roger Caffin]

Hi Geoff

Well, I looked carefully at the photo and even more carefully at the MSR illustration you posted. If the 1.1 m measurement is correct, then the figure they have crouching inside the tent must be of a very small child.  Something looks seriously wrong there.

So I got my wife to measure how high the top of my head was when I crouched as in the diagram. My head was 1.25 m above ground, and I am only 1.65 m tall. And the diagram shows lots of clearance from the top of the figure’s head to the apex of the tent. That diagram is so misleading as to be fraudulent.

Some sites label it as a ‘minimalist UL tarp for mild weather’. Fair enough.

Cheers

[HiLight]

Hobbit. perhaps?

[Geoff Caplan]

Roger – you’re right about that plan illustration – I just measured myself in the same position and the top of my head was 104cm, so that must be a very small person! Still, I think it’s more likely that the measurement is right and the manikin is wrong – the tarp is held up by single trekking poles, so the height would be 130cm at the max.

HiLight – thanks for the input. Looks like your tent is pretty much a Bibler, with a bit more headroom and a big vent. Don’t really follow you when you say it could be adapted to trekking pole supports, though – seems like the bendy poles are integral to the concept? As you say, it would be greatly improved with a porch. It looks as if you’d have to zip right up with any kind of wind-driven rain, and there’s no real shelter for cooking and gear. Similar to the issues with small solo mids. Not a design that would work well in European conditions, I suspect, though the reviews on the US website are pretty positive.

Innovative single skin fabric

Someone asked whether there are any innovative fabrics earlier in the thread. I meant to mention something that Crux are using on their single skin mountain tents – https://www.crux.uk.com/product/x1-raid

It’s a membrane fabric with an activated carbon inner face that they claim greatly reduces condensation. They describe the fly as: Waterproof and breathable X-tex, 120 g/m², 50 denier, polyester ripstop 10,000 mm hydrostatic head PU/activated carbon”. It’s claimed to be waterproof, but that might mean waterproof in the way the Event is waterproof?? The PR is that:

Using <b>X-tex </b>means that unlike other single-skinned tents when climatic conditions cause condensation to form on the inner wall of the tent, the X-Tex fabric actually absorbs the moisture which prevents dripping (a serious problem with other single skinned tents). The fabric stays dry to the touch whilst absorbing this moisture and continues to breathe at a significant rate, as it doesn’t rely on water molecules remaining as vapour to pass through it.

I researched this a little, and I’m pretty sure that this is from 37.5, the oddly named company that supply Rab with their baselayer fabrics. Doubt it will ever be on the MYOG market, but interesting.

[HiLight]

Geoff – BD seems to be moving away from the Bibler name (it’s still in the small print), but yes, the HiLight is a lighter version of the (Bibler) Ahwahnee. The main sore points with the current design are the lack of pole sleeves (makes the pitch fiddly), and the lack of vent protection in storms, as you mentioned. I may address both of those issues myself at some point, because they’re both problems that a bad storm could exploit. Btw, I meant that trekking poles could be used to support a simple MYOG vestibule, rather than adding another pole, as BD does with their design. The basic form & framework are proven, but finding the right fabric for a MYOG version that would be durable, workable, and light enough might take some time.

Speaking of which, I’d have to see some durability tests before going forward with that activated carbon fabric. Sounds like something that might work early on, but I imagine the absorption properties might degrade quickly with wear & contamination. I also wonder how quickly all of those little carbon passageways release the moisture. I suspect that a good ventilation design will still trump magic fabric in the battle against condensation. Still, it’s interesting tech that I’d like to see Richard Nisley examine.

https://www.outdoorline.sk/en/content/75-x-tex-fabric – @richard295

[Roger Caffin]

Waterproof and breathable X-tex, 120 g/m², 50 denier, polyester ripstop 10,000 mm hydrostatic head PU/activated carbon
Blimey! That’s more of a UL pack fabric than a tent fabric!

Cheers

[Geoff Caplan]

Roger: the floor is lighter, at 70gsm despite a higher denier, so that coating must be heavy. Still, the smallest would just fit two good friends at 1.5 kilos, which isn’t too bad for a bomber high-mountain tent.

HiLite: for your fabric, take a look at the new silpolys at Ripstop By The Roll. I’ve had some advice from a very experienced designer that silpoly and silpoly PU are the best options: they don’t sag in the wet and they have much better UV properties than silnylon. Silnylon is stronger in the lab, but after UV degradation the silpoly wins out. With proper reinforcement, the 20d should be fine for the walls and the 40d for the floors, unless you want full 4-season strength in which case you’d probably want 40d on the fly. Hilly use 40d on their arctic tents, so there shouldn’t be any need to go heavier. He recommends the PU coating for both as it can be well sealed with heat-tape. I’ve checked with RSBTR and they are using the right kind of long-lasting PU.

As for the Crux fabric, I share your skepticism about its longevity. Except that Crux have a strong rep and have been selling this for a few years now to a very demanding customer base, so they must have confidence it has some staying power. I wonder if it works in lighter weights – it’s far too heavy for a backpacking tent, though it might be great for a small bivy…

[Jon Fong / Flat Cat Gear]

I did not see anything in the search results, but has anyone added a chimney to manage condensation?  Not being a tent builder, it seems like adding a fabric flue (say 4″ in diameter and a few feet tall) could add sufficient venting to reduce condensation.  And it may not weigh very much.   Just spitballing here.

[HiLight]

Geoff – Thanks for the advice. I should make my tent modifications a winter project and add it to the list.

[Roger Caffin]

I’ve checked with RSBTR and they are using the right kind of long-lasting PU.
Tell us more about this idea of ‘the right kind of PU’. I have been wondering about TPU but I have not had time to chase it up.

Cheers

 

[Roger Caffin]

it seems like adding a fabric flue (say 4″ in diameter and a few feet tall) could add sufficient venting to reduce condensation. 
I am sure it would, but how do you keep it pointing upwards? I tried this on two of my domes many decades ago and they always flopped over and flattened.

Cheers

 

[Geoff Caplan]

Roger:

I posted about the PU coatings here: https://backpackinglight.com/forums/topic/silpoly-tarp-durability/#post-3415289

To summarise, I contacted one of the most experienced freelance designers in the industry and he was kind enough to respond to points about silpoly made on that thread. Based on lab-work, wind-tunnel testing and experience in the field he’s a great proponent for the newly available silpoly PUs, saying they have many advantages over silnylons:

1. They stretch much less when wet, meaning that the shelter keeps its aerodynamic pitch.
2. They are much more resistant to UV.
3. Although silnylon is slightly stronger in the lab, it will be weaker after some UV exposure. In any case, with proper design both have plenty tensile strength to take big wind loads – the failure point is the poles, not the fabric (hence my interest in strong poles). And both are very vulnerable to puncture, eg from a falling branch. So the relative strength shouldn’t be a factor in the decision.
4. The PU finish seals well with heat-sensitive tape, making the seams the strongest and most waterproof part of the tent.

But he says that most silpoly PUs use a coating with poor durability and that you need to look for a polyether/PEU finish. I contacted RSBTR and they confirmed that their silpoly/PUs use this coating.

He’s putting his money where his mouth is, literally, by launching his own range of comfort-oriented backpacking tents with 20d silpoly walls. They did exceptionally well (for consumer tents) in what were, to the best of his knowledge, the most comprehensive multi-directional wind-tunnel tests ever conducted in the industry.

[Geoff Caplan]

Just spotted an interesting quote on the WhiteBlaze thread linked by Tipi. For thru-hikers, the tent of the moment seems to be the ZPacks Duplex, because its great space to weight ratio. The post backs up my feeling that good ventilation can help cut condensation, but that an always-open design can get pretty unpleasant in cold wind. Hence my quest for good but controllable through-ventilation.

My Duplex, for example, has far far less condensation than my StratoSpire2, even though the Duplex is a single wall and the SS2 a double wall.

Granted i really don’t want to spend many a windy night in the Duplex as it can get VERY drafty inside the tent, but it does show how well some tents (yes even single wall) are ventilated.

[Mark Fowler]

I am a fan of transverse ridge tents like the Duplex as I prefer a side entry.  I have a Solplex and a SMD Haven (asymmetric), both in cuben.  The transverse ridge gives better head space than a typical A or pyramid and reduces the size of unsupported panels.  The issue then becomes draft exclusion – does the tent pin to the ground around it’s entire perimeter or do the doors not reach the ground and leave a gap.  The asymmetric design also allows a good vent to be put into the steeper roof panel a la Roger’s design or else vents are placed in the side walls.

The transverse design allows for a short spreader bar to keep the ridge from sagging and the vertical poles can be spread to strengthen the walls. This may require short extension sections to achieve the required length depending on your walking poles.

If making a tent like the Duplex then the large door panels can be  solid fabric with a small mesh piece on top and the ends have fabric flaps to seal over the mesh if the conditions require it.

The A is a 1 angle arc, the transverse ridge a 2 angle arc, Rogers tents use a 5? angle arc.  I realise that the flat spreader bar creates a problem with snow accumulation but putting an angle in the spreader bar (now 3 angle arc) or using different pole heights (see the ZPacks Solplex)  can alleviate the problem.

[Roger Caffin]

Not sure about the 5 angles. They have 3 elbows or bends per pole. Perhaps that should be 4 angles?

Cheers

[Mark Fowler]

Oops! That’s what happens when you don’t check a photo and age is plundering ones memory.

[Roger Caffin]

What’s age?
What’s memory?

Cheers

[HiLight]

Geoff – I don’t know if you’ve seen the Sierra Designs High Route Tent 1FL. It’s a double wall A-frame, but there may be some design features that would work with your single skinner. Skurka has several posts about the design process on his site.

[Author]

Posts