My wife and I lived in place with no underground rooms (such as a basement of a cellar) since we have been married. As I have matured and my desire for disaster preparation has increased, I began to realize the importance of having an underground room for storage (particularly food storage and other things necessary for survival in the event of a short term or long term TEOTWAWKI ) and protection from disasters such as heavy storms, tornadoes, nuclear activity, etc. My career in construction, specializing in masonry and excavation, made this goal one that was easily attainable and I would like to share some things that I incorporated as I built and prepared this space for those possible emergency situations.
We were in need of a master bedroom addition on our small home. So I decided to incorporate our underground room under it. I will talk about the stages along the way that you will face so that you (working with the people that you may need to hire) can be prepared and have a head start.
The first step is to obtain the proper permits (a step that I decided to skip, as I live in a lenient county in a very rural area). I chose to keep my project as low key as possible. But I thought I should include this step because life could become very difficult in some areas where building inspectors and codes are strict. Be sure to know where all underground utilities and wires are at on the property before moving forward with excavation. Severing gas and electrical lines will most certainly ruin your day. [JWR Adds: There are free line-locating services provided by most utilities. In the US, just call 811 . See this site  for “pre-dig” numbers for Canada.]
After excavating, I poured the floor. If you are not experienced placing and finishing concrete, you will want to seriously consider hiring professional help. If you decide you have the skills and strength to take on this task, make sure you have all the tools and adequate manpower to help. Make sure to adequately reinforce your concrete (I always use steel reinforcing bar (“rebar”) of at least 3/8” diameter). I poured my floor approximately 6 inches thick. You may want to pour concrete footers and lay up (or pour) your walls on the footers, leaving the floor to pour later. I opted just to pour a thick, adequately reinforced floor, and lay up my walls on it. Wanting to have some space for a root cellar, I left the floor in that area a dirt floor (to increase humidity, important for root cellaring). I used standard 8x8x16 block for the walls. You could form and pour your walls with concrete if you prefer. I poured the cells of the block with rebar and concrete for reinforcement (making sure to leave adequate rebar extended to tie the ceiling and walls together). Remember, concrete strength is always unpredictable without the use of reinforcement. For the root cellar, I left lower and upper ventilation for circulation, also important.
As I planned, I decided to go with a seven foot ceiling. I decided this because I wanted to be able to drain water without the use of pumps, and this made it possible. Rain and groundwater can be your worst enemy, and I did not want to depend on a pump and electricity to take care of removing water. I put a drain line in the dirt section of floor in the root cellar and sloped the concrete slightly towards the drain. A pump may be necessary for your situation. If it is, you may want to consider using a sump pump capable of being run by a battery backup. Do not forget to put your sump pump pit in before pouring your floor and slope your concrete accordingly. Proper grade around the perimeter of your underground room will greatly reduce the risk of water problems, especially when combined with properly installed gutters (if your underground room has a room above it like ours does). Also install a waterproof coating on the outside of the walls and a perimeter drain. Again, the perimeter drain would best be drained by gravity, but if this is not possible, drain it into your sump pump. Always backfill with an adequate amount of gravel. This will allow water to infiltrate down to the perimeter drain freely and will help keep your perimeter drain from being plugged. I have been in this kind of work for many years, and I have seen many water problems caused by improperly installed perimeter drains that have eventually filled with silt over time.
I decided to go with a concrete lid, heavily reinforced with ½” diameter rebar, to top off our new 16 ft by 20 ft underground room. You will want to find out how much reinforcement and how thick the concrete will need to be in order to span the distance you need. Also critical is the placement of the rebar in the concrete. When spanning an open room, you will want to place the rebar towards the bottom of your concrete. Make sure to be vigilant to make all the necessary rebar connections. Not many different building materials do worse in an earthquake than un-reinforced or improperly reinforced masonry and concrete. When it is necessary to overlap (“lap”) your rebar, make sure that the length of the rebar lap is equal to 40 bar diameters of the size rebar you are using. For example, if using ½ diameter (#4) rebar, your rebar lap will be 20 inches. If you decide to go with a concrete lid, make sure to adequately brace your forms. A collapse (or even a sag) would be a disaster for sure. I used sheet metal roofing under the concrete, which ultimately become the ceiling of my room. Make sure to leave some fasteners to anchor the sheet metal to the concrete, or the metal will sag when the forms are removed.
Since I wanted a dry and canned food storage (low humidity) area along with a root cellar, I built insulated walls to separate the two rooms. I decided to build my own shelves for these rooms (you may want to buy yours). Nonetheless, I took into consideration a few things. One was to make them very sturdy. Bulk food can be heavy. Another consideration was to attach them to the walls and make a lip around the outside edge of the shelves. That always unexpected earthquake could deplete your food supply quickly, especially glass containers. I also liked the idea of building my own shelves so that I could build them to best suit my needs with the shelf heights and widths that were best for my particular situation. This room would also be a great spot for your freezers. You may want to consider a DC freezer with some solar panels and batteries or a propane freezer for those times of extended power outages. Freezers may not be a necessity, but they sure would be a welcome luxury in those times without electricity. This would also be a good spot to keep an adequate supply of drinking water.
Last thing I will leave you with to consider is your consideration for a dehumidifier. You will want one for your dry storage area. Moisture and stored foods do not go well together (not to mention moisture’s effect on guns, ammunition, other steel items, clothes, blankets, etc). Some dehumidifiers operate better in lower temperatures, so do your research.
Since the completion of our room, this space has proven to be well worth the time and resources that it took to build it. One day it may be crucial in the sustaining of our lives for any number of reasons. Hope this article leaves those who read it with some helpful advice to think about.