If you're going to be outside for more than 24 hours, or in dangerous conditions, shelter is crucial. In most cases, finding water should be your first priority, but shelter is a close second. Extremely cold weather can be fatal in as few as three hours, but even in milder climates, having somewhere to stay comfortable and dry is essential.

One important principle of outdoor survival is that you should use your limited time and energy as efficiently as possible. Finding or repurposing an existing shelter is always preferable to burning valuable hours and calories building one, but we'll cover both in this guide.

To Search or to Build?

Whether you're building a shelter or looking for one, you're expending time and energy. To determine which is the better plan, assess your surroundings and the resources available to you. Ask yourself: “Is it likely that I'd be able to find shelter in less time and with less effort than it would take to build one with the available materials?”

Also, consider whether you'll be moving every day or staying put for a long time. The best course of action depends on the details of your situation. If you're lost or in trouble, you'll generally want to stay put only if someone else knows roughly where you are and will be looking for you. Otherwise, you'll need to stay on the move and try to find someone who can help.

Finding Pre-Existing Shelter

Before you set about transforming nature to fit your needs, consider whether someone or something else may have already done the work for you. If you're in an area with a temperate climate and lots of vegetation and wildlife, odds are good that there's an animal den or terrain feature nearby that you could make use of.

Conversely, if you find yourself in a barren desert, there probably haven't been many mammals (human or otherwise) creating shelters before you came along — and there also may not be much to work with in the way of building materials. In such cases, your best bet usually is to search out caves or rock formations, or to construct rudimentary shelters that don't require many materials.

Search Out Man-Made Structures

You might be surprised at how easy it can be to find abandoned, man-made structures. At least in America, much of the land has been used by humans at some point, especially in regions with plentiful resources. If, historically speaking, there's been a lot of human activity in the area, climb a tall tree or a big hill and look around for old houses, farms, villages, or mines in the area.

If finding man-made shelter doesn't seem likely, consider searching out a cave, large overhang, ravine, canyon, or abandoned animal den. Large trees, both living and dead, can make cozy shelters, too.

Move Into a Cave or Animal Den

Use caution when investigating caves, dens, and other places that animals may find tempting — they could still be there. Before venturing into a confined space that may or may not harbor an unhappy grizzly bear, look around the area for tracks, droppings, and other signs of recent animal activity. If you don't find any, toss some small rocks into the shelter or otherwise try to elicit a response from any animals inside without appearing overtly threatening.

Of course, the risks you take and the manner in which you search for wild animals will depend on many factors, such as your knowledge of the animals you're likely to find, whether you're armed, and whether you need food. Always err on the side of caution and avoid conflict when possible; if you aren't confident in your ability to deal with whatever may be sleeping in that cave, it's probably best to move on unless your need for shelter is critical and immediate.

Shelter in Canyons and Ravines, or Under Overhangs and Ledges

A protruding shelf of rock or packed earth can make a passable shelter for a night or two, as can a shallow indentation in the wall of a ravine or canyon. Such overhangs are most commonly found in areas with lots of uneven terrain. Before crawling under one, though, thoroughly investigate its stability and ensure that it won't fall on you.

If possible, find an overhang at the base of a cliff, tucked into the side of a wide hill, or otherwise situated such that potentially unfriendly people and animals can approach only from one general direction. Leave yourself at least one other exit, but try to avoid shelters that can be approached from all sides.

If you intend to build a fire, do so outside of — not under — the overhang, so as to ensure adequate ventilation. If it's cold outside, line your sleeping area with boughs, leaves, or whatever else might help to keep you off the ground and retain some heat.

Sleep Under a Big Tree

Deadfalls (large, dead or dying trees that have fallen over) can make excellent short-term shelters. Their exposed, vertical surfaces make great backstops for a lean-to or tarp tent (see below), and the depressions they leave behind when they fall can provide some extra protection from wind. Of course, the tree itself is also a convenient source of wood for building or for making a fire, provided it hasn't rotted.

Living trees can provide shelter, too. Large trees with many thick branches can make nice roofs, under which you can set up a lean-to or dig a sleeping hole as needed. Beware of “widow makers” (heavy, dead tree limbs that could fall at any time).

Building a Shelter

If you must build a shelter, choose a site with as many of the following characteristics as possible:

• Dry
• Flat
• Ground soft enough to dig but firm enough to support stakes or braces as needed
• Adequate drainage away from your sleeping area (if rain is likely)
• Protected from wind and direct sunlight as needed
• Not next to water or animal trails
• Not on top of, underneath, or close to precarious overhangs or other environmental hazards
• Can safely accommodate a fire (if one is needed)
• Highly visible (or well-hidden, depending on whether you want to be found)

Building Short-Term Shelters

Building long-term outdoor shelters tends to be a meticulous and time-consuming process, but when a short-term shelter will do, here are four quick and easy shelters to get you through one or two nights at a time.

Lean-To

Pros: Easy to build with materials common in many regions

Cons: Doesn't provide much protection against animals or the elements, may require an axe or saw

Lean-tos are among the oldest and simplest temporary shelter designs. They're great for deflecting wind and rain, but they don't retain warmth very well. If you have the time, and if it's going to be especially cold, consider building a leaf hut instead.

First, gather or cut (again, conserve energy when possible) three poles or branches, about six feet long and as thick as your arm. Two of them should have forks at one end wide enough for the third to fit into. If you can't find any forked branches, cut the forks yourself with an axe or hatchet, and cut the contact points of the third pole into wedges to make it narrow enough to fit.

Brace the two forked poles against a large tree, hill, or rock face at a 45-degree angle, with the forks facing up, then fit the third pole into the forks to make a frame. Gather or cut smaller, straight branches and use rope or plant fibers to fasten them to the frame in a vertical row. Then, pile leaves or grass on top of these ribs to block wind and rain. (Wet foliage is acceptable and even preferable for this purpose; it's less likely to blow away.) For extra waterproofing, make shingles out of large strips of bark.

Leaf Hut

Pros: Retains heat well without a fire, provides better protection than a lean-to against wind and rain, no tools required

Cons: Requires careful site selection, dangerously flammable

Find or cut a thick, sturdy branch ten to twelve feet long. Elevate one end about three feet off the ground by propping it on a flat rock or in a forked tree trunk. This end will be the entrance, so if possible, face it away from the wind.

Next, gather a few dozen branches ranging from one foot to three feet long and create walls by leaning them against either side of the support pole. For added stability, strip bark or twist plant fibers into rope and tie the branches in place. Periodically crawl inside and lie down to gauge the width; there should be only about six inches of free space on either side of your body. (Less empty space means your body heat will be retained more efficiently.)

Finally, pile leaves against both sides in layers about three feet thick. When you're finished, the interior should be dark and well-protected against wind and rain (though it won't be completely waterproof). If you build a fire, do so well away from the leaf hut and extinguish it completely before you go to sleep.

Tarp Tents

Pros: Extremely quick and easy to build, good protection against water and light wind

Cons: Poor heat retention, requires a tarp/cloth/canvas

If you're fortunate enough to have a large tarp or canvas, you can construct a tent in a matter of minutes. There are dozens of designs to choose from; we'll introduce two of them here.

If you have a large rock or fallen tree to work with, wrap and secure one end of the tarp over the top, stake the other two corners to the ground at a 45-degree angle, and you're done.

Alternatively, drape the tarp over an elevated support pole (see leaf hut, above) and stake the four corners to the ground to create a quick pup tent.

Snow Cave

Pros: Quick and easy to build, retains heat, tools not required (but they are helpful)

Cons: Potentially dangerous — may collapse if not dug properly

In a snowstorm, you need heat and shelter quickly. A snow cave is an ideal short-term solution. Once you've got one dug out, consider building a longer-term shelter such as an igloo or quinzhee if you'll be staying put for a while.

To safely dig out a snow cave, you'll need to find a large snowdrift, and the snow needs to be the right consistency — thick and dense enough to retain its shape when you start digging. If you've ever built a snowman, look for snow of that consistency or a bit thicker. Loose, powdery snow won't hold its shape well enough and will simply collapse when you try to dig a cave under the surface.

Start digging at the lowest possible point in the bank. Dig an upward-sloping entrance tunnel about five feet long. The sleeping chamber itself should be above the entrance (to retain heat) and should be in the shape of an upright bell to maximize its structural integrity. The ceiling should be about three feet thick, which is thick enough to support its own weight but not so thick that you'd be unable to dig yourself out if it does collapse. If there's still heavy snowfall, though, make the ceiling thinner; more snow will pile on top of it soon enough.

Finding shelter is critical in survival situations. While your location and access to supplies can play a role in determining the kind of shelter you search for or build, there are always plenty of options available for keeping yourself safe. No matter the case, it's important always to stay calm, survey your surroundings and create the best possible safeguard to ensure your survival and safety.