Covered trench shelters utilize the massive density and inherent strength of packed soil to create a protective shelter suitable for protection against natural and wartime elements including biological and nuclear fallout. Trench shelters also provide excellent wind and blast protection.
Typical trench shelter plans fall into two categories, differentiated solely by the roof construction. A door-covered trench shelter uses common household doors to construct the base of the roof support system while a pole-covered trench shelter uses long logs, poles, or lumber. The door or pole supports are placed over the trench and then covered with dirt.
Before you begin
Determining the size of your trench shelter
When determining the length of the trench shelter, add about 3 feet to the length for each person that will be sheltered. If more than 10 persons are to be sheltered, construct a second trench shelter (end to end if space permits).
Materials required to build a covered trench shelter
Materials required include shovels and if the ground is hard, picks. Waterproof material such as shower curtains, plastic tablecloths, mattress covers, canvas, tarps, etc. will be needed to construct canopies over the two shelter openings (entrance and ventilation openings)
Additional materials could include canvas bags for sandbag construction and bedsheets or other sheets of materials to cover the roof, walls, and openings.
Choosing the best location for your trench shelter
The best location for the trench is at least 40 feet from any buildings that could catch fire. The ground area should be flat. Building the trench shelter under a tree offers additional protection but can add time to the construction effort since tree roots must be dealt with.
How to build a trench shelter
To begin, clear the ground and stake out the area you wish to dig. The trench should be about 3 feet wide and 5 feet deep. The length will depend on how many people are to be sheltered. Allocate about 3 feet of length per person. When digging, toss extracted dirt about 8 feet from the trench in a neat pile (it will be reused later).
Make sure the wall angle is flat or angled inward (wider at the top and narrower at the bottom). Any overhang will make the walls unstable and increase the potential of a cave-in. Walls can later be covered with sheets or plastic. If walls are covered, leave about an inch of earth exposed at the bottom. If wall-sheets reach the floor, they can be stepped on and pulled from the walls.
On one end, extend a narrower trench about 3 feet longer. This will be a ventilation trench that will help circulate air. The ventilation trench should only be about 2 feet wide and 3 ½ feet deep. Plastic curtains can be hung over the opening to protect against fallout and inclement weather.
On the other end, gradually narrow the trench width and dig steps for stepping into the trench. Threshold boards or small pegs can be used to stabilize the earth around the steps.
Cover the trench with doors, logs, poles, or lumber. Place the supports longways over the width of the trench. This will leave about 2-5 feet overhang beyond the edge of the trench. The more supports overhang the edges of the trench, the greater the area over which to distribute the weight of the roof.
Cover the roof supports with plastic if possible. Then cover supports with 2-5 feet of dirt. Remember, the thicker the dirt mound, the more weight and added pressure applied to the walls. If longer poles are used, more dirt can be added. Mound the dirt so it is shaped like a rounded dome over the trench.
Build canopies to cover the exposed ends of the trench. Alternatively, lay tarp on the ground across the opening. A canopy is preferred to allow ventilation.
Place sandbags around the entrance and ventilation opening. This will help keep water, debris, and fallout from entering the trench. If sandbags are not available, make an earth roll using bed sheets or sheets of plastic film. To make an earth roll, lay a few feet of sheet on the ground while holding the remainder off the ground. Cover the sheet with a layer of earth. Have a second person begin rolling up the sheet (and earth) as the first person releases more sheet, allowing it to fall onto the ground. Continue adding dirt and rolling up the sheet.
Finally, bank dirt/sand around the bottom edges of the sandbags or earth rolls.
Make sure you consider the effects of rain. Dig drainage trenches around the trench as needed to direct water away and around the trench.
The following illustrates the protection a trench shelter provides against radioactive fallout. The same protection exists on the opposite end where the ventilation opening is located. Notice that few radioactive particles enter the trench and that protection increases dramatically beyond the trench entrances.
Below are various drawings illustrating the total construction plan (and variants) of the basic trench shelter.