For those of you that make the use of snow trenches while backcountry camping in winter:

1. What do you use for "roofing"? If you use a tarp set up, what kind of tarp are you using?

2. At what temperature do snow blocks become practical? I tried making use of them once (for roofing), but at the temperature (-3 deg Centigrade), the blocks would break/crumble easily and they wouldn't instantly freeze to each other.

3. Do you use a bivy bag? If so, which one? How is it for condensation?

Thanks...

This was a good tutorial:
http://www.youtube.com/watch?v=LKIfTB5H8vg

In the past I've just pitched my tarp and piled some snow around three corners to seal it off, then made an ice/snow wall at the entry:

pic

Last year, Don, a little older guy than I, built a trench, more like a pit to me. He had an entrance and covered the hole with a blue tarp, anything like that would work. Step or two leading out from his entrance. He had taken one or two classes with the Sierra Club. His pack covered the entrance opening and he had a raised bed inside to sleep on, leaving a cold sink as the floor. Andy, just excavated a den for his dog and himself. To fit in, I just dug down a foot for my tent and piled the snow around the edges. Don has another trip with the SC this winter, no plans with us guys yet.
Duane

There are some things _not_ to do.

I saw one beginner snowcamper who dug a trench. Maybe 30" wide by 8' long and maybe 24" deep. For a roof, first he wanted some supports, so he laid his cross country skis and poles across the top, binding side down. Then he laid a tarp over the skis. Then he piled up snow onto the tarp. Effectively, this made an insulated roof.

There were some problems. The weight of the snow forced the skis and poles to bend abnormally. That made the ceiling inside get low to his face. The warmth of his body rose up through the snow, causing the roof snow to freeze hard. When it was time to leave, he could barely get his skis out.

--B.G.--

1. Dig the trench only long enough for your head and torso (Entrance at one side of your head)

2. Then dig a "leg tunnel" for your legs.

3. cover the torso trench

**-> you need to make the trench "floor" either level or a little slanted toward your foot. Very important and sometimes forgotten - that is until you are snug in your bag with blood draining to your head.

This is the fastest way I know to get a nice snow/tarp shelter because it minimizes the amount of snow you must shovel. Plus the tarp will have enough material to make a "door" with your pack sitting on or leaning against it to keep it closed.

BTW, I think and eVent bivy bag would be the best way to go. Best breathability, least condensation.

A surplus Army GTX bivy is the cheapest.

Edited by Danepacker on 01/04/2012 16:57:50 MST.

Thanks Eric, that makes sense, only shoveling out space for your legs. If you cover up too much though, you are gonna have condensation on gear/clothes. Don liked the Sierra Club method with the bench and the low, cold sink.
Duane

Eric,

Assuming you have a couple of meters of snow, how far do you dig down for your quick trench (I take it from the name, not too deep?)? Do you have a cold well of any sort?

Edited by NightMarcher on 01/04/2012 08:44:13 MST.

A couple of meters?! Heck I'd just carve out a snow cave with that much snow!

@ Chris,
I don't dig down more than 3 ft. 2 1/2 ft. is actually enough and that's about halfway up your thigh, for quick measurement.

I've done this several times and it takes about 45 minutes to make it from start to complete finish.

And, BTW, I do use my skis & poles for the trench tarp supports. I only cover the tarp edges with snow about 1 ft. wide on the three sides. Use the snow you excavated for this purpose.

Then, of course you need to dig a small "kitchen" for your stove and a bench to sit on opposite the stove. One ov the benefits of having deep snow.

>"2. At what temperature do snow blocks become practical?"

Chris: I play with igloos and snow forts a fair bit at home with the kids.

It does have to be a decent bit below 0C or the snow is moderately plastic and will "flow" overnight. -5C is probably okay. It depends if you're adding heat from underneath by cooking, breathing, etc. or if you have a lot of ventilation.

The biggest issue is how consolidated the snow it. Snowflakes that have tumbled in the wind get rounded into little spheres and pack much more densely and are much stronger than snow that fell and frozen in place with any wind. Those desposits can have very weak layers within them.

So while you can find that more compacted snow downwind of a ridge or log or other obstruction, that's not a place to be while the snow is falling and the wind is blowing because it will get more, heavy snow deposited again.

Interesting tidbit from my Arctic Engineering class: When wind moves snow around, 90% of the mass travels within 1 inch of the ground. Yes, vision can obscured for many vertical feet. But all the mass is in the heavy, rounded particles rolling / tumbling along the ground. Look closely at wind-blown deposits and you can see how that happened.