How to Build an Underground Room in Your Backyard?

Many people today are finding that they can feel more secure with an underground space on their property. It can be used in emergencies or can be used for other purposes like storage. It’s not as hard as you think to create an underground room on your property. 

There are several steps on how to build an underground room in your backyard. You need to check with city ordinances, determine the space needed, find the location, and draw out plans before you start any work. Then, there’s digging, setting the walls, and the entrance. 

Reasons for an Underground Room

People want an underground room in their backyard for different reasons. The most common reason is to have a place to go in case of tornados. 

Underground rooms can be a great place to store water and food because they regulate temperature well. Food and water will keep longer stored underground than above the surface. 

Some people turn underground rooms into the ultimate man cave where guys can play poker or watch a game. That involves adding electricity and water for a bathroom but it’s a place where a man can get some peace.

Those who go all-out turn underground rooms into a personal gym when there’s no room in the house. This frees up space in the house for everyday living.

It may seem odd but underground rooms can also be used as guest room space. This is especially helpful when guests are staying long-term as it gives them and your privacy. Some people are renting them out to family, friends, or others in transition to make some extra cash.

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Getting Started

Building an underground room is a process that could take some time. Here are the steps to take.

Checking Local Ordinances

You will need to research not only local city or county ordinances but also need to look into local Home Owners’ Association (HOA) rules before proceeding with any construction. While most shouldn’t have any problems with an underground room because it is not visible from the topside, some may have questions or permits to pull before you build.

Some areas make it illegal to dig so you will need to check to see what the rules are. Rules may exist on how deep you can dig too, so check that out.

Pick Your Area

Choosing a good area for an underground room deserves some consideration. There’s proximity to the house to consider but there are also other considerations. It can’t be in a flood plain because you don’t want it to leak or for the room to flood. 

The ground should be level, although some build an underground room into a hill, like a cave. A grassy field works the best and you can’t build one in the sand.

The ground should have more dirt than rock and be able to drain well. 
You also have to make sure it’s not near water, electrical, cable, or other utility lines. A check on where the septic tank is also necessary. 

Another consideration is how far it is from utilities in case you want to tie into those for a complete room.

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Decide on Size

Building an underground room starts with determining how big you should make it. Local rules and regulations, your property, and HOA permitting may affect the size. The best shape is a square because that reduces collapse risk. 

Experts say never go any deeper than six feet underground because that increases the risk of collapsing. 

Looking at Layout

You will need to plan how to design the room even though it starts with a square. Other decisions include the type of wall needed, the furniture, shelves for food, and how to power it. 

Another item on your checklist should be ventilation, which is crucial. 

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Safety Checklist

Many things in underground rooms are options but some things should be a part of your safety guidelines.

These include how to build structural retaining walls, install outside HDPE perforated draining pipes to prevent flooding, build the roof opening and staircase, and how the roof will be supported to avoid collapse. 

Clearing the Site

The site will need to be cleared of all tree stumps, roots, and other topical items before you dig.  


Excavating the site is the biggest part of the project because you will need to get the dimensions correct. Smaller rooms will require more hand shoveling than using a machine. Hire professionals if it’s a larger room. 

An element of the dig should be to slope the walls where they’re wider than the floor. This reduces collapsing risk. Use a shovel to move along the wall siders to make a sloping shape. Smooth them out.
Cover the area with a tarp if you can’t finish in one day so pets or children don’t fall in and to protect it should it rain. 

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Secure Walls

Walls must be secured for safety. You can cover them with plywood but you may consider using braces along with the plywood to build a secure wall that will always hold the dirt back. 

Secured walls can be done by using two pressure treated 2 x 4 posts in the corners, or by using cement. After they are secured, you can use bricks or plywood to build a wall. 

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Pour floor

Most people like to use concrete for the floor of their underground room because it is leak-proof, is durable, and easy to install.

Building the Roof

Most people use plywood to build a roof. The most important thing is to make sure it’s sturdy enough to be an upper floor too. The roof should cover the room well and be bigger than the room. 

There are two types of roofs. The liftable room comes up when you pull on a rope. It can’t be heavy wood if you choose this open. A fixed roof has an entrance with a door to enter, similar to old storm cellars. It’s easier to walk down and get out since there isn’t a rope to pull. 


Are underground rooms safe?

They are safe if build correctly. Underground rooms also offer protection against extreme weather and are cheap to insure as part of the home. 

Do underground rooms add value to your home?

It can increase the value of your home as it’s extra space. Fully functional, decorated underground rooms will add more value than storm rooms. Making it a bedroom, family room, or adding a bathroom or kitchen will increase value.

Is it expensive to build an underground room?

It isn’t incredibly expensive to build an underground room, especially if you do it as a DIY project with a few friends. Wood can be expensive these days but it doesn’t take a lot to come up with a standard room. Installing electrical and plumbing can put a dent in the wallet.

How do you ventilate an underground room?

The easiest way is to install a fan that draws in air from the outside. Air purifiers may be suitable to use but they require electricity and you will still need an outside source of air. Air bricks and heat exchange units are other options. 

Can you decorate an underground room like any other room?

Yes, underground rooms can be painted but be sure to do that before the roof is attached. They can also have wallpaper and stickers, furniture, bedding, and everything in other rooms.