A shelter will protect one from potentially disastrous weather, help prevent hypothermia, and allow restful sleep. It will also boost how you feel emotionally, as it will become a base or home. Therefore, in typical survival situations, a shelter should be able to be moved with you, if possible, and be set up quickly. If one spends too much time on a shelter it takes away from other survival tasks.
Immovable rocks, animal nests, and other obstacles and hazards should be avoided.
Dry watercourses may be flat, sandy, and comfortable to sleep on, but they will flood in a storm.
Sunlight provides warmth (which is not always welcome), and can help one to wake up in the morning. However, sunny, open areas are vulnerable to wind which causes convection of one's body heat.
Heat transfer: an excessively large or well-ventilated shelter will not retain warmth well.
Flashing (weatherproofing) to provide protection from elements. A cave can provide a very useful shelter because it can provide protection from wind, rain and snow and maintains a constant internal temperature. Unfortunately, caves can present additional problems such as ground water, dampness, disease, and wildlife. Histoplasmosis, Blastomycosis, and Coccidiomycosis are several fungi found in caves that can infect the eyes and lungs of cavers. If bird or bat droppings are prevalent, you may want to find a different survival shelter to avoid these fungi. Bats often roost in caves and through their bite they can transmit rabies and other terminal illnesses. Bears also make dens in caves, so before you settle down in one, you should check it thoroughly for signs of inhabitance.
The simplest and most mobile shelter is a tarp, supported by make-shift frame work or rope. Large leaves, such as ferns or fir branches, can be added to a latticework of branches. Ferns on a shelter provide insect repellent. Branches propped against a fallen tree make a simple and effective refuge, but animals such as ants and snakes may nest under the tree.
A more advanced shelter is known as a debris shelter, which can be constructed without modern tools or implements. It consists of a central ridge pole supported by two forked poles. This ridge pole supports a lattice of branches, which is then finished by leaves or other insulating material.