James:
For those looking to create stable and “passively” cool storage in a basement, the book “How and Why to Build a Wine Cellar” by Richard Gold is a well-thought, meticulously engineered solution to many of the same issues faced by those seeking to store food at stable, cool temperatures. Regards, – Ben
JWR:
I have spent much of my adult life in the construction industry and through experience and educational seminars, etc. I have acquired a substantial amount of knowledge concerning moisture intrusion into structures.
Water is the main source of problems in construction. Keeping it in, keeping it out, and getting it out once it is in. The components of a building that are constructed of concrete such as basements, foundations and slabs on grade are very susceptible to moisture intrusion. Concrete acts as a wick and when dry will actually attract moisture and move it through out the structure under the right conditions. For example a twenty-inch concrete column sealed on its sides and standing in water will wick moisture hundreds of feet straight up. A concrete basement floor set over a wet subsurface will continuously wick that moisture up through the floor and allow it to evaporate into the basement atmosphere, i.e., damp basement. For several hundred years this condition has been referred to as “rising damp”. The modern term for it is capillary action.
To construct a dry basement in damp ground conditions requires some planning and a little ingenuity. Choose as dry and well-drained location as possible to build the structure. Once the excavation of the basement is complete you should proceed with water management measures as dictated by the conditions of your location. If you have a substantial amount of groundwater or springs under the excavation you will need to install a drain system around the outside of the foundation and under the floor to move this water away from the basement. There is a lot of information available on how to do this. If located in a hillside it is easy to install a gravity flow system, dumping into a dry well down hill from the basement. The only other alternative is to dump into a sump pump installed in the floor of the basement and pump the water out away from the house.
Now comes the important part. Once the drain system is completed and the forms for the foundation and floor have been constructed you will want to lay down heavy-duty plastic vapor barrier on the ground under all areas where you will pour concrete. The barrier should cover the entire floor, pass under the foundation and up the outside wall as continuous as possible. Where you need to make seams, overlap the barrier at least five feet. Applying a sealant between the layers at the seams is advisable. The concrete will be poured over the vapor barrier only after it has been completely sealed from the outside of one wall to the outside of the opposite wall. Once the foundation and slab are poured and the outside walls are constructed, the vapor barrier protruding out from under the foundation is pulled up on the wall and adhered using the standard basement wall sealant. The entire outside of the wall is then coated with sealant. You should end up with basement that is totally encapsulated in a plastic vapor barrier. Most builders that attempt installation of vapor barriers ignore the foundation because it takes a little finesse to do this right. This leaves a path for capillary action to bring moisture into the basement.
Now that you have a dry basement don’t forget to properly ventilate it. It should be tied in with the rest of the house ventilation system. If you construct a safe room in one corner it will still be necessary to supply some ventilation to that room or it will become very musty.
I am presently planning the construction of a small house for my wife and I and will construct a safe/storage room as an extension of the basement, which will extend out from under the house. It will basically be an underground concrete room next to the house joining the basement wall and will be totally sealed from moisture as I have described. I will be able to easily hide the entrance through the basement wall in the back of a utility room. Being outside of the house footprint will also protect it from fire in case the house would burn down or otherwise be destroyed.
Hope you find this useful, – JR