Spiral Shelter Office

As things heat up in the Middle East and the potential for trouble spilling into the rest of the world increases, I bet there are a few folks wondering how a simple shelter could be built without a permit, in a backyard, and serve as something like a home office on a daily basis.

Well even if that scenario hasn’t crossed your mind yet, let me share with you a design concept for a stout yet tiny earthen building.

The Shelter Office design is a modified spiral made from earthbags. The walls pictured here are about 2-feet thick and the roof is a 7 1/4-inch thick reinforced concrete slab with 2-feet of earthbags on top.  The main room is just 55 square feet, which is just enough room for a desk, chair, rolling files, and a bit of storage hidden behind a false wall.

Even in the unlikely case of a distant nuclear war, this little building could shield you from most of the radiation from fallout outside the front door. The entry hall of the Shelter Office has a right angle turn and two doors.

Radiation can penetrate thin walls and doors, but it can’t turn corners. So gamma radiation  coming from fallout outside would penetrate into the entryway between the doors but wouldn’t turn the corner into the main room. The entry hall would also have a drain in the floor, to allow the occupants to shower off before re-entering after short trips outside.

On top of the walls is a row pipes encased in the concrete bond beam. Two layers of thick plexiglass would be embedded in breaks in the pipe to provide a clerestory right at ceiling level. The clerestory would allow natural light to enter the Shelter Office. Gamma radiation would stay at ceiling height. Gamma radiation isn’t like a gas or cloud – it’s more like an beam of energy that can pass through thin materials in a strait line. So as long as you can temporarily block it from reaching you, you can wait out it’s dangerous effects – which in the case of a nuclear blast degrades very quickly.

On top of the clerestory would sit a 7 1/4-inch thick reinforced concrete slab roof, strong enough to support itself plus two additional feet of earthbags above. The entire exterior and interior would be stuccoed to protect the earthen walls and provide an aesthetic look & feel. The very top of the roof would need to be slightly sloped to shed water and would be coated in a roofing sealant.

Inside would be a false wall behind the desk with hinged doors. Behind the doors would be pre-positioned emergency supplies like food, water, camp fuel, a hand-cranked electric generator, radio, and other items stored in metal storage boxes.

Mounted on the wall would be a NBC (nuclear, biologic, chemical) air filter that runs on a 12-volt DC fan and battery. This would provide fresh filtered air inside the shelter when the doors were closed.

When the doors are open the wood boards that are normally used as desk & shelves would be used as bunk beds instead. Sleeping bags and pads would be stored there too.

Construction Steps

The Shelter Office could go together quickly and on a low budget. For details about building earthbag homes see this step-by-step construction guide. There’s also an excellent article written by Dr. Owen Geiger on Instructables for an earthbag building about this size. Before building anything be sure to check with your local planning department for guidelines and restrictions.

Step 1: Lay a foundation. Also shown here is a concrete floor. Rough plumbing for the entry way drain would need to be added before the foundation is laid.

Step 2: Earthbag walls stacked up. Rough wiring and plumbing would be installed as the walls are laid. Air pipes for the air filter would need to be added at this point too. Rough bucks (not shown) would be installed at the doorways to secure the doors.

Step 3: A concrete bond beam poured with clerestory pipes and plexiglass.

Step 4: A rectangular reinforced concrete slab roof would then be poured in place. This would require some stout forms during the concrete pour (not shown).

Step 5: More earthbags would be added above if one wanted to make the structure double as a fallout shelter.

Step 6: The exterior and interior are stuccoed and complete.


Building with earthbags is one of the fastest ways of building with dirt. Other earthen options are adobe, cob, and rammed earth. Earthen buildings store a lot of energy in their walls.

Thermal mass is not the same as insulation. Insulation is a thin layer that blocks heat transfer. Thick masonry walls allow the heat to pass through, but it does so slowly. Heat passes through earthen walls at about a rate of on inch per hour.

So as the sun beats down on the exterior of an earthen wall, the heat begins to slowly move through the wall. If the wall is about 12-inches thick, 12 hours later the heat of the day will finally enter the interior, warming the building through the night.

If you wanted to build a home office like this with 1-foot thick walls and leave the earthbags off the roof you could. It would make a fine office. In the event of nuclear fallout it would still provide a lot more protection from radiation than a stick-framed building – assuming you didn’t add windows. Three feet of dirt (or ten halving thickensses) is considered ideal for a fallout shelter.

The cost of earthbags structures can be very low. 1000 15″X27″ Woven Polypropylene Bags cost about $300 (as of September 2013) – which is my guess at how many bags you’d need for a structure this size. The other things you’d need are bailing wire, barbed wire, 6 yards of concrete for this roof design, rebar, some lumber for the concrete forms, stucco, doors, and some basic tools. I suspect this could be built by a frugal owner-builder for as little as $3,000.

In many places small outbuildings like this can be built without permits. The thick walls and roof might raise a few eyebrows from neighbors. Savvy neighbors will notice its potential usefulness as a fallout shelter, but others might just admire it’s southwestern modern charm. So if you’re looking for ideas for dual-use structures and having a stout home office in your backyard brings you a sense of security, consider something building your own shelter office.


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