In my experience, the earth shelter is the ideal wilderness home. In this post I'll first discuss what makes the earth shelter so effective and advantageous. Then I'll cover the various methods for construction and lastly, special considerations that need to be made based on available materials and environmental conditions. There are a lot of subtleties when picking the location, depth and geometry of the shelter.
Earth shelters cover a wide variety of styles and materials but what they all share in common is that the majority of their structure is covered in earth. Some are buried so deep that the roof is at ground level. Others are built in not much more than an indentation and others into the side of a hill. They all share the same advantages of being highly secure, robust, cool in the heat and warm in the cold weather. Even without a fire, the interior will not dip below freezing when properly constructed, and a very small fire will keep it warm throughout the winter.
The construction process is basically identical with each style. First, once the style of earth shelter is decided upon, the appropriate amount of earth is dug up and set outside the building site. Around the perimeter of what will be the walls it is a good idea to ram the earth down and create a solid footer. If stone is available, dry stack it on top of the rammed earth. If enough stone suitable for dry stacking is around, you can continue the walls up a high as you like, all the way up to the roof beams if possible. The stone needs to be thought of as a retaining wall with it slanting away from the center of the structure. Circular construction will be the strongest and most durable using the inherent strength of compression, as in an arch. Always remember to dig in an air intake for the fire-pit that feeds to outside the shelter.
If the stone walls continue up past the level of the ground, use the removed earth and build up a berm behind the stone. Pack it down hard to keep everything in place and to maintain compression. If the site is dug down into packed earth with a high clay content, one can actually leave the walls bare. If you do this and the pit is deep enough, you can rest the roof beams directly on the earth. Bare earth is prone to disturbance and will be a constant source of dust and debris.
Wood poles can be used for the walls as well. If so, dig a trench inside the pit around the perimeter to set the poles in. They need to be as close to touching side-by-side as possible for strength and to ensure no earth finds it's way through the cracks. A layer of leaf-litter, grass or foliage between the wooden frame and the earth is always a good idea. It will prevent dirt from falling through the cracks and add to the longevity of the frame by keeping moist earth from being in constant contact wood. The exposed interior of the shelter will largely keep the wood dry and a fire will keep the earth on the other side of the frame dry even in wet country as long as it is adequately applied.
For an entrance, build a frame similar to what you see in the above picture. The top of the entrance in that picture is flat, which in my experience is a mistake unless there is a MASSIVE amount of earth on top of it. For water to flow well it is always a good idea to have a pitch to every part of your shelter. If in an area where there is peelable bark, and it's the right time of year for the sap flow to be at peak, bark makes an excellent barrier between the wood frame and the earth, especially where the pitch isn't ideal such as over the passageway.
I've always preferred an extended passageway for an entrance rather than a regular doorway. It will protect the door and the interior from weather far more effectively than a conventional entrance. Behind the outer door, towards the interior, you can hang a wool blanket or fur-on hide and further insulate the shelter. It will serve as a mud room for boots and wet coats when initially entering your shelter and if wide enough, be a place for storing firewood.
The floor of the entrance should always slope down to the outside of the shelter or otherwise you could be dealing with flooding. If the depth of the shelter prevents this, make the covered entrance extra long. The first portion extends upwards out of the shelter to above the grade of the land outside of the shelter. The last half of the entrance-way then slopes down, creating an internal "hill" keeping the flow of water from coming down into the shelter.
For the roof, a central frame is commonly built to support the roof beams and provide a smoke hole or at times, an entrance. These posts and beams that make up the central frame need to be the most substantial of all wood used in the shelter's construction. For the posts, I like to use natural Y's, the crook opening to the top in line with the center of the post. If the Y is off to the side, the crook is only as strong as the Y and doesn't fully utilize the strength of the pillar structure of the post. If Y's aren't available, notch the posts and beams together and ideally spike or dowel them.
The roof beams need to be substantial as well. Due to the high number and closely laid proximity of them, they only need to be about half the diameter of the central posts. As you can see in the above photo, lay as many down as possible. The first ones are the beams that extend all the way to the smoke hole, the remainder filling in the gaps. These need to be notched where they make contact with the frame and can also be spiked or doweled. The next layer would be much smaller poles laid between the roof beams in a horizontal fashion. It is best to cover the roof as you go up, first with a layer of horizontal poles, next with some type of debris and lastly, with earth. If you try to lay all the horizontal poles first, they will slip and pop out of place as go up.
By covering the roof with all the proper layers as you work towards the top center, everything is held in place. This is where building up the walls as you go comes in handy, everything is locked in and there is no chance of shifting. The debris layer can be leaf-litter, grass, peeled bark panels, or even the bark shavings from the wooden frame. Do not put the debris all the way up to the smoke hole. It is possible that a spark from the fire could catch on the edge and you could have a low level smolder travel down through the debris layer that can be very difficult to put out. Also precipitation can soak into this layer if exposed around the edge. I like to end the debris layer at least a foot (.3m) from the edge of the smoke-hole.
If you live in an area of heavy rainfall, it is a good idea to build a frame on the roof over the smoke-hole to guard against excess moisture penetrating the structure. If a large enough fire is built, a lot of times the updraft will keep out the moisture, but in the warm months you would not want such a large interior fire. The roof of the frame needs to be as fireproof of a material that can be found. Large, thin flagstone is my favorite and bark panels would be my next choice. If neither of these are available, build the cover with very closely laid poles and cover it in a similar fashion as the earth shelter. The smoke-hole cover should look like a miniature gazebo.
Now let's get into special considerations. Always build the earth shelter on a natural rise. The floor of the shelter should be no deeper than the surrounding land below the rise except in all but the most arid regions. In wet, mountainous country, there is a likelihood of underground water-flows, pathways that feed springs. These might not be apparent, they can be present at times in only wet weather. Before deciding on a building site, make sure you do plenty of reconnaissance after heavy rain during the wet season. You don't want water pouring from your walls or coming up from your floor, else you'll end up with one of those useless underground mosquito breeding pools so popular on YouTube.
In a wet environment it is best not to have the shelter dug so far into the earth. The pitch of the roof also needs to be much steeper. The drier the environment, the flatter the roof can be. Remember though, most deserts have a monsoon season. A good pitch to the roof is always a good idea. The Sami build an earth shelter called a Goathi that has a very similar shape to a Tipi. Such a steep pitch is ideal for wet weather, but is will also need a higher amount of maintenance. The steeper the pitch, the greater the erosion, hence the poles on the exterior similar to a debris hut to help mitigate erosion. If you can have grass or moss growing on the exterior so that the root system holds the soil in place, all the better.
In my opinion the apex of the earth shelter is the stone turf houses of Iceland. The permanence of stone and earth combine to make a shelter that will last countless generations with minimal maintenance. If there ever were Hobbit Holes these were it.
It is my plan to build such a structure this year at an old quarry from the late 19th century that I found on the property. It is a level site located on the mountain side overlooking the New River with a massive amount of flat stone ideal for dry-stack masonry. These structures are not the typical "bushcraft" shelter, but are for long-term wilderness living. It is my opinion that what people commonly call "bushcraft" has become more about wilderness survival with a side of handicrafts. My goal is to introduce a depth of knowledge and a symbiotic relationship back into bushcraft to allow for long-term wilderness living. My next post will be about this shift.