The purpose of shelter is to create a micro-climate where you can control your core body temperature. The clothing on your back and the material you surround yourself in both offer cover to protect you from the elements, both in a wilderness environment and in an urban one (your home).
In this issue we will be looking at heat loss/gain mechanisms, clothing, man made and natural shelters.
The Rule of 3’s
The military and many other organisations use the rule of 3’s (which could be a rule of 2’s) to highlight the order of what to prioritise in a survival situation (both wilderness and urban), what is important and what is not. The order is not set in stone and depends on the situation, the environment you are in, your condition and your resources.
- 3 minutes without air (basic life support/first aid) if you are not breathing or bleeding out you’re dead!
- 3 hours without shelter (clothing, shelter from the elements, core body temperature)
- 3 days without water (the human body on average can only go without water for 3 days)
- 3 weeks without food (the human body can go without food for up to 3 weeks depending on the individual and is therefore the last of importance in a short term survival situation)
Heat Loss/Gain Mechanisms
There are five ways that the body loses heat to the environment, they also work in reverse to gain heat.
The direct transfer of heat from one object to a colder object. Without an insulating layer such as a foam mat, a person will quickly lose heat to the cold ground or a large rock.
Water conducts heat away from the body 25 times faster than air. Wet clothing will also conduct heat away from the body at a fast rate.
The continuous movement of air or water over the body stops it from being able to equalise to the same temperature of the body so the body keeps losing heat. Eg. wind chill.
Direct heat loss from the body to its surroundings. If the surroundings are colder than the body, the net result is heat loss. We lose 60-70% of our body heat through our head and neck. The naked human body starts losing heat to the environment at 28 degrees celsius. In hot climates we gain heat in the same way from the sun.
Occurs when water (sweat) on the surface of the skin is turned into water vapour. This process requires energy in the form of heat from the body. This is how our body cools itself. One quart of sweat will take approximately 600 calories of heat away from the body. In hot climates, conserve your sweat, not your water.
When you breathe in (inhalation), air is warmed by your body and saturated with water vapour. When you breathe out (exhalation), this heat is lost. E.g. in cold air your breath can be seen.
Heat loss/gain mechanisms
Clothing is your first line of defence against the elements. Your choice of clothing is dependent upon the activity that you are undertaking, what environment you are going into and being prepared for unexpected changes in the weather.
Cold and wet Climates
What your clothing is made from is very important. Wools and synthetics should be your first choice in a cold, wet environment. Wool retains approximately 70% of its insulative value when wet, is moderately fire retardant and smells less making it your first choice, particularly for a base layer. Sheep like it too.
Synthetic/polyester moisture wicking materials are light and dry very quickly so if conditions are wet this is important. Your clothing can also become wet through sweating which is something you need to avoid in cooler environments or if the temperature suddenly drops in a warm one e.g. the desert.
Generally speaking you want to avoid wearing cotton near your skin in cold wet environments as cotton stays wet and is hard to dry, causing you to lose heat through conduction to the damp clothing.
A useful acronym is COLD
Clean – keep your clothing clean. If it becomes dirty it stops breathing and doing its job.
Overheating – avoid overheating. If you sweat in a cold environment you can die if you can’t get your clothing dry. Avoid cottons.
Loose and in Layers – it’s the air trapped between the different layers that keep you warm. If your clothing is too tight those air pockets will be compressed and you will be colder.
Dry – keep your clothing dry.
Layering for colder climates
- Base layer of wool
- Warm intermediate layer (wool or synthetic)
- Optional thicker warm middle layer (wool or synthetic)
- Waterproof and wind proof outer layer that is breathable.
Remember to include a warm head covering and wool socks.
In warm to hot climates the focus is keeping yourself cool. Loose fitting cotton material is ideal for this. Take a look at what people in Arab nations wear to keep themselves cool.
During the day in very hot climates you want your clothing to retain moisture (sweat) to keep you cool through evaporation so in this case cotton is good. Synthetic moisture wicking garments are not good in hot climates as they wick the moisture away from you when you need it to keep you cool, making you feel hotter.
However when the temperature drops at night as it does in the desert you don’t want to be wet from sweat so you need to make sure you are dry before that happens and have a warm layer at hand.
You need to also select your clothing based on the activity you are undertaking. For example, if you are doing strenuous trekking in an alpine environment above the tree line, your choice might be to wear clothing that is synthetic, lightweight, waterproof, wind proof and breathable. However, this same clothing in a woodland or close bushland environment will get ripped and torn so something more durable and tough would be needed.
The Swedish company Fjallraven make a line of clothing that is specifically designed for outdoor use. It is made using Fjallraven’s durable wind and water resistant G-1000 fabric. Their clothing is functional, very durable and comfortable and is designed and manufactured with a number of different outdoor activities in mind.
Some of the garments I use regularly that are great for bushcraft and use in the Australian bush are the Vidda Pro Trousers, Singi Trekking shirt, Vidda Pro jacket, Keb wool shirt and Pine micro fleece top.
Man made shelters
There are many different kinds of man made shelters on the market including various kinds of tents, lightweight tarps, hammock systems, emergency blankets and swags. Some are designed to be used with vehicle camping such as swags (which are too bulky to possibly carry) and some are designed for lightweight hiking. Below are a selection of systems that in my opinion are the best for emergencies, bushcraft and lightweight hiking.
“No matter what kind of man made shelter you choose with the exception of a swag, you will need some form of insulation mat (either blow up up or closed cell foam) to sleep on to prevent heat loss through conduction to the cold ground. 3/4 size is all that is necessary”
Garbage Bag/Drum liner
Large, un-pleated heavy duty garbage bags (hard to find in Australia) are one of the most versatile pieces of kit you can have with you. Uses include: a raincoat (a hole cut in it for your head), a moisture barrier or ground sheet, water carrier, filled with leaves for insulation to stop conduction to the ground, water proofing, a flotation device or cut open and made into a lean-to shelter using a few simple knots and hitches. This can also be combined with a disposable space blanket to make a heat reflective lean-to to keep you warm and dry.
Garbage bag/space blanket lean-to emergency shelter
Re- useable Space Blanket/All weather blanket
These are much more durable than the flimsy disposable space blankets and can be used as a heat reflective blanket, a ground sheet or configured into a couple of different types of shelters as they have built in grommets and eyelets in the corners. The shiny aluminised Mylar side can be turned out to reflect the sun in hot weather or turned in to reflect your body heat or the radiated heat from a fire. They also come in a range of colours so you can also use them as a signalling device to attract attention.
A student on a course erects an emergency all weather blanket
Hootchie/Light Weight Tarp
A lightweight tarp or hootchie as we call them in the Australian Army is arguably the most versatile light weight shelter there is. Suitable for most climates (not windy), they can be configured into a range of shelter types (A frame, lean-to, pup tent etc) or connected with others (of the same type) to make a larger shelter. A few simple knots and hitches are needed to use them effectively. In wet weather you just set them lower and in clear weather you can raise them.
A light weight tarp shelter allows you to connect with nature in a way that an enclosed tent does not and if you have not tried sleeping under a lightweight tarp than you are really missing out.
To sleep under a lightweight tarp you will also need: a ground sheet, 3/4 insulation mat, sleeping bag and a bivvi bag (water proof sleeping bag cover).
Australian Army hootchie/tarp
Hammock and tarp
Hammocks are designed to get you off the ground which is preferable in hot wet tropical areas where there are lots of creepie crawlies. A built in bug net is also advisable in these areas. Hammocks are also preferable in areas of uneven ground like the side of a hill. You will still need some form of insulation under you such as a half inflated sleeping mat to prevent cold spots and heat loss through convection. In recent years there has been a surge in interest in cold weather hammock camping with a number of elaborate cold weather cocoons and sleeping systems available. Personally I find many of these over complicated and impractical to carry because they are too bulky.
Hammock and tarp
If you don’t have a manufactured man made shelter with you, you will have to build one using the resources you find around you in nature. There are many different natural shelter types which can all be thatched with an array of different natural materials. Some of these include: lean-to, wickiup, dome huts, various group shelters, debri huts, A-frame shelters, raised jungle shelters etc. Unlike what the reality TV shows portray, building a natural shelter is time consuming and can take anywhere from 3 hours to 3 days to build depending on the thatching material and resources you have at your disposal and the type of shelter you are building.
A few general principles include:
- correctly siting your shelter
- sturdy framework to support thatching
- 45 degree roof angle to achieve water run off
- thatched in rows from bottom to top with 1/3 overlap to achieve proper watershed without leaks…similar to roof tiles.
- when thatching with palm fronds, use dead ones as they will not shrink and leave holes
- an improvised bed to get you off the ground to prevent heat loss through conduction
One man leaf debris hut (NSW)
Lean-to thatched with cabbage tree palm fronds (NSW)
Raised Jungle Shelter thatched with cabbage tree palm fronds (NSW)
Siting your shelter
No matter what kind of shelter you have or need to make whether it be man made or natural, it must be safely and correctly sited. Here are some guidelines:
- Look up, look down, look all around
- DO NOT site your shelter under dead fall, a branch that could come crashing down or a sick looking tree. These are known as widow makers for obvious reasons!
- Do not site your shelter at the very bottom of a hill a valley or a localised low spot if possible. Cold air sinks and those areas will be significantly colder.
- Do not site your shelter on a game trail or ants nest. You may get a surprise in the middle of the night.
- Site your shelter on flat even ground so that you get a comfortable nights sleep.
- Allow for water run off if heavy rain. Where will the water go or pool?
- Do not site your shelter in dried up creek or river beds. Rain a long way away can cause flash flooding and is very dangerous.
- In hot climates, try to site your shelter in the shade to allow for extra cooling.
- Do not site your shelter too close to water as many insects breed in water. Running water will also prevent you from hearing predators or someone looking for you.
- Site your shelter with any breeze blowing across the front (90 degrees) to blow any smoke away.