Why use tarp shelters? The biggest reason ultralight backpackers use them is to reduce pack weight. The lightest tent you can find will be close to three pounds. Some of the newest ultralight tarps weigh just seven ounces.
Weight isn't the only advantage of tarp shelters, though. They also give you room to move, and you can easily look around. You can quickly take them down when you're ready to go. If it's wet, just shake it off and it will fit in an outside pocket of your backpack. Even if they were the same weight, I'd still prefer a tarp over a tent for most trips.
The lightest of my own tarp shelters weighs 16 ounces with all the strings. That seems heavy now, when I look at the new ultralight tarps out there. Integral Designs Sil Tarp 5' x 8', for example, weighs just 7 ounces.
The Bozeman Mountain Works Stealth 0 Catenary Ridgeline Ulralight Backpacking Tarp weighs an amazing 5.7 ounces. With a name like that, you know it has to be expensive. Of course, almost any backpacking tarp will be lighter - and cheaper - than the lightest tents out there.
How To Use Tarp Shelters
You'll probably need a bigger tarp than you think. A seven-foot roof may seem like it will cover your six-foot body well enough, until a blowing rain soaks your feet. Proper use is even more important than size, though.
Pitch the low side into the wind. Keep all sides low if a storm is coming. Evenly tighten guy lines. Use rocks, trees, trekking poles and whatever else helps. Pitch the tarp tightly, to keep it from flapping in the wind too much, which can loosen the strings or cause the tarp to tear.
If you haven't used tarp shelters before, experiment until you can quickly set up in several different enviroments. Bring lightweight stakes, until you learn how to use sticks and trees and rocks. No stakes means less weight to carry. I've always found something to use, even up high on the tundra.
You might have to treat the seams with a sealant occasionally, or at least when you first buy your tarp. Buy seam-sealer anyplace that sells tarps and tents. You'll need string or cord of some sort for tie-downs. I put varying lengths around the tarp, so I can untie and use the long ones where I need them. Sometimes that tree will be a little too far away.
I use 4' by 7' pieces of plastic for groundsheets. They're opened-up giant garbage bags that weigh 2 ounces. They're disposable, but I've used one for a week in the Rockies, and they're cheap and easy to replace. Whatever you use, lay your bag on it, to be sure you'll have room. You don't want to be touching the wet ground just because you moved a little. On the other hand, if it's too big it will catch rain out near the edge of the tarp, and funnel it back to you.
Mosquitos keep a lot of ultralight backpackers from using tarp shelters. Repellant is a partial solution, as is using the tarp only when it isn't too buggy. A headnet helps, but keeping the rest of your body covered when it's warm isn't pleasant. Pitch camp in a high, breezy place and you'll have fewer bug problems.
There are also mesh shelters you can pitch under your tarp. The lightest I've seen weighs 1 pound, 7 ounces. With a 7-ounce tarp, you'd be under 2 pounds for a shelter, and it comes with a floor, so you don't have to bring a groundsheet. Ultralight tarps and tarp shelters, by the way, weigh less than 20 ounces, a standard I just invented, but it seems reasonable.
