Having an underground room can come in handy for a variety of reasons. Children love to have secret rooms for play. If the room is near your house or attached to your basement it can serve as a tornado shelter. It can also serve as a fresh vegetable or fruit storage area like the old-fashioned root cellars. Some people like to have an underground room for an emergency fallout shelter. How do you build an underground room?
Dig a hole a little larger than the final dimensions that you want your underground room to be. This will allow you to add some structural supports to prevent a cave-in and injury. First, you dig straight down and then you will want to tunnel out. Another option is to dig a very large hole with a backhoe.
Frame up 4 walls using treated 2x4s and 10D nails, as well as a ceiling if you choose to dig a large hole with a backhoe. See Resources below for more information on building a wall. Cover the ceiling frame with treated plywood sheets.
Decide if you want to make a stairway coming up out of your room or if you want to use a ladder with a hatchway. Then place the top soil back over the room, except the entrance area, and plant grass so your room is hidden.
Find an area in your basement or crawl space that you can open up. This is another option for building an underground room. This can be more convenient to access if you intend to use your room for severe weather shelter, root cellar to store fresh crops, or a fallout shelter.
Remove some of the blocks or stone to create an opening. Be careful not to remove a supporting wall. You may still need to dig the room out from outside using a backhoe. If so, frame your room using treated 2x4s as described in a previous step. You will also need to decide if you want an outdoor entrance as well or just the indoor entrance to your underground room.
You can use bricks, treated lumber, or pour concrete to make a square or rectangular frame on which to mount your door or hatchway. Then you can make doors, a hatchway, or purchase prefabricated doors. You could make double doors, like the ones pictured, use a simple sheet of plywood, or make a hatchway if you are trying to keep your room secret.
Reinforce your walls using concrete, brick, cement blocks, or treated lumber to prevent a cave in or possible injury. If you have a large hole open at the top you can frame your walls before installing them. If you have dug a hole and tunnelled over, you will need to build from inside your room.
You may want to insulate your room, add air vents, and other amenities depending on your purpose for the room. Some people add storage shelves that they fill with nonperishable food items, emergency bedding, and other necessary supplies.
Prefabricated steel shelters are available to install after you dig the hole.
If working underground, before reinforcing the walls, run a hose down for an emergency air supply. Too large of a room can become unstable over time. It may be better to build more than one if you need more room. Site your underground room in a place away from drains or other areas that may catch water You may want to consider installing a sump pump or other drainage alternatives if you have a high water table.