Can I Turn a Septic Tank into an Emergency Bunker Shelter?

Photo from Butts Precast Concrete Products, Inc. (

We used to live in a city where natural disasters just aren’t a thing.  But now we live in a place where we could be at risk for at least one type of natural disaster we could shelter from.  Premade storm shelters and bunkers are quite pricey and we like to find ways to save money rather than spend it.   One option that came to mind is using a new concrete septic  tank as a storm shelter or bunker.  So we researched it and now share those findings with you.

Using a new concrete septic tank as a bunker or storm shelter can certainly work whether you want your shelter above ground or underground.  It is a less expensive option than pre-made storm shelters, but that means you will need to put some work into modifying it to work as a shelter.  You will need to be able to make modifications such as adding a door, ensuring some form of ventilation, providing at least minimal bathroom facilities, and electricity or at least a reliable light source. 

There are many scenarios for which someone wants a storm shelter or bunker for their family.  Maybe you want to escape a tornado, maybe you want to escape bad people doing bad things.  Maybe you just want a place to store your goods that will withstand heavy winds, or a fire, or that you can bury underground to keep your private things out the prying eyes and hands of those who would like to steal your stuff.   A new concrete septic tank is a good option to consider, but may not be right for every situation and every location, so let’s take a look at some pros and cons for using a (new!!) concrete septic as a storm shelter or hidey hole.

Pros and Cons of Concrete Septic Tanks as Emergency Shelters

First, let’s look at reasons a concrete septic tank would be a good option for a storm shelter or bunker, either above ground or buried below ground

  • Concrete is fire proof.  Your valuables will be safe from fire whether above or below ground.  That’s not to say delicate items may not be damaged by prolonged heat exposure.  If your shelter is above ground, in a thick forest of trees, and they burn in a forest fire, there will be heat building up in there.  But if you place it away from anything that will burn much, then yes, they should be safe from fire.  Bury it underground and fire becomes that much less of an issue.
  • Concrete is wind proof.   A concrete septic tank is designed to withstand hundreds of pounds of pressure from contents within it pushing out and from the ground outside it pushing in.  So yeah, it will withstand very high winds if above ground and it won’t be an issue at all if below ground.
  • Concrete is relatively bullet proof (of course there are some huge rounds that will destroy about anything, but we’re talking your run-of-the-mill shooting scenario.) 
  • Concrete  is extremely durable.  A concrete septic tank, when used as a septic tank underground, will last a good 40 years or more. 

But concrete is not perfect, so let’s look at some downsides that might affect your decision to use a new septic for hiding, storing, and sheltering.

  • Concrete can crumble.  If not mixed or poured properly, or if too thin for the use it’s designed for, concrete can crumble over time.  You’ve probably seen that in sidewalks, driveways, basketball courts, or other outdoor uses.  (But septic tank walls are at least 4” thick.)
  • Concrete can crack.  You’ve definitely seen that in sidewalks, and the like.  However, a sidewalk is a single slab and thinner than a septic wall, but still could be an issue.  Buy your septic tank from a reputable precast concrete company if you do this.
  • Concrete can be susceptible to moisture, and therefore mold.  If you are in a very wet area – above or below ground – use precautions against moisture like sealing, moisture barriers, and if above ground, not setting it where water will pool after a rainstorm.
  • Concrete is not absolutely crush-proof.  If your shelter is above ground and near a large tree, it will not necessarily withstand the tree falling on it in a tornado or heavy storm.  But neither will a house or shed remain undamaged, right?
Photo from

The concrete septic tanks will come in many sizes and dimensions.  You’ll need to contact the precast concrete companies in your area for specifics on dimensions, but we can give you a general idea of what you might find, for preliminary planning purposes.  

Keep in mind, too, that concrete tanks are heavy! 

This chart of septic tank sizes below shows what you might expect to find as far as size, dimensions, weight and cost.  But this will vary, perhaps greatly, with your location, vendors available to you, and the current cost of concrete.

Gallons Dimensions ** Weight Approx Cost
1500 10’ L   x  6’ H  x  6’ W 12,000 pounds $2000 – $3000
2000 14’ L  x  7’  x  6’  14,000 pounds $2500 – $3500
2500 14’ L  x 7’  x  6’ 16,000 pounds $3000 – $4000
3000 14’ L  x 7’ H  x  7’ W 18,000 pounds $4000 – $5000

** These dimensions are outer dimensions.  Concrete septic tanks walls are at least 4” thick, so each dimension will be at least 8” less than stated.

Modifying a Concrete Septic Tank into a Storm Shelter or Bunker

Now that we know a concrete septic tank can be used to create your bunker, storm shelter, or emergency shelter, and if you’re still considering it for your family’s needs, you will need to consider how much work will need to go into it to make it storm-worthy and safe. 

Here are a few things to consider, but probably not an exhaustive list since your needs and wants will be different from the needs and wants of Tom in Texas, Andy in Alabama, and Charlie in California.

Photo from

Obviously you need to be able to get in and out of your shelter, bunker, or storage room.  Septic tanks do come with access holes on the top and they may be up to 24 inches in diameter. 

You need to figure out how to close and secure the lid from inside your shelter and also how to be able to open it if it were to become blocked, say from a large tree falling on it.  Being able to open towards the inside allows you to be able to (hopefully) move the blockage, or at least get air and signal to rescuers once the danger has passed.

For some of you, that 24” access hole is plenty to be able to get in and out with just a ladder inside.

But if that won’t work for you for some reason, then you will need to plan to cut out and install a doorway.  Again, think about getting in and out.  If the door swings out, then you may be blocked by debris in a tornado.  If it opens inward, you can at least open the door and try to clear the blockage.  

If you create a roll-up type door, that may be the best of both worlds, but it may have less integrity than a swing open door.   

Maybe a hatch door would work – the type where you remove it completely to crawl in and out.

You have many options to choose from and work with.

You’ll want a means of opening the door from the oustside as you go in, but also to latch and unlatch it from the inside to keep the door shut tight, as well as securing it to your liking from the inside.  You might have a very different system if you’re just trying to keep safe from a tornado vs. keeping out very, very bad people.  And zombies.  Someone always has to mention zombies, so there it is.

Electrical Lighting
You may not want to run electricity into your bunker, but you will need some kind of reliable lighting system inside.  Closed up inside that container will be as dark as dark can be.  In fact, plan for at least two methods of providing light inside, if not more, so you have backup systems should one fail

Getting fresh oxygen inside your emergency shelter is a must.  Concrete septic tanks will come with usually two access holes on top, as well as two smaller holes on either side of the tank.  One is for the inlet pipe, and one for the outlet pipe.  Figure these will be 3” or 4” openings that you may be able to utilize for your ventilation plans. 

This will take some careful planning if you bury your shelter underground and don’t want the ventilation openings to be seen, damaged, or blocked. 

Features to Consider for Your Concrete Storm Shelter

Now that we looked at modifications to the actual structure to make it able to keep you safe through the emergency, here are some things that you ought to think of to modify inside.

Remember, this isn’t an ultimate “how to” guide to turn a septic tank into a shelter, but a jumping off point to help you see if it’s something you want to pursue.

Bathroom Facilities
Whether you plan to be in there a short while or a long while, the “need to go” can strike at any time, so you’ll want a plan for everyone to be able to go, probably with a little privacy, and a means to close or cover the contents to avoid unwanted smells.  A 5 gallon bucket, a toilet seat, and a bag of sawdust is a cheap way to get the deed done.

As mentioned above, you’ll want at least one reliable source of lighting, but two or more sources is even better. 

Connection to the Outside World
Depending on the emergency you’re sheltering from might depend on the kind of connection to the outside world that you want.  Do you want to call on your cell phone?  Do you want an emergency band radio?  Do you want a peep hole or periscope of some kind? 

Consider your communications / observation system early.  Will your plan work in a concrete box?  Will it work if you bury your shelter underground? 

Creature Comforts
Everyone inside will want a place to sit, and probably to lay down.  Remember that concrete is susceptible to moisture, so in case that ground floor gets wet, moist, or otherwise uncomfortable, consider something  like folding cots (but measure for size and the number of people sheltering).  Might be seating is all you will be able to do.

Other things to consider having stocked already:  weapons, food, water, trash bags, first aid, essential medication, fresh batteries, diapers and baby wipes, deck of cards, pens and crossword puzzles, etc.

Photo from shelters

If a DIY Septic Tank Bunker is Too Much

I know thinking of how to do something on the cheap and then realizing all that is involved in making it come to fruition can be overwhelming.  Sometimes we just opt to buy the pre-made whatever-it-is.  After all, time is money and avoiding frustration sometimes has a price worth paying, too.

You probably know about pre-made concrete shelters, right?  They are more or less fancified septics.  A septic tank is just a concrete box, same as a shelter.  But the pre-made shelters already have a lot of these things we discussed, such as an entrance, conduit for electric, stairs, and possibly other items, depending on how much of a set-up you want to purchase.

Kelly Albertson

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