liv2learn,

You probably have a heated basement.

To build a cold room, ( not a root cellar) for storage, you are going to have to build a room that is insulated on the interior sides, and insulates the floor above.

Coldness, will rely on the concrete wall and floor in contact with the earth to moderate temps. In that regard, there is no difference between north and east.

Cold rooms need to be "dry" to prevent mold and fungi from forming and rotting what you want to store.

Root cellars are "unprotected" storage spaces dug in earth. Walls may be timber, the roof may be protected against rain and groundwater. Root cellars mimic the humidity and darkness of being in the earth, just like they were when they were growing, but moderate the temperature from the suface to a deeper earth temp.

Root crops keep better much longer and in much better shape in a "real" root cellar, than in a cold room, but they keep a long time in a cold room.

I guess I used the term "root cellar" in a very general sense. :-) Our basement is not heated. Our plan is to use metal studs to frame an area against the cement wall, using foam panels to insulate the areas that face air and the ceiling joists. I am a bit confused by the humidity issues because I have read that you need to have a fairly high level of humidity to keep root crops. Wouldn't that apply to a cold room too?

Liv2learn,

common concrete is not waterproof. It is damproofed by an exterior membrane, ( tar in the old days) with a sand or gravel ben for the floor.

Steel studs are a no-no in a basement. They rust in no time. Timber framing, insulated from contact with the concrete with a sill gasket is the best way to go.

Foamboard is an expensive insulator.

The best "bang for the buck" is a 2 x 4 or 2 x 6 stud wall, sheathed on the interior of the coldroom with a 1" polethelene foam with a radiant heat barrier, ( mylar film) facing into the cold room. Seams get taped with foil tape. Fill the stud voids with Rocksil, (mineral wool, rodent and pest resistant, water resistant, 98% recyled material, cheaper than Fiberglass batts). Sheath the exterior with a 1" polethelene foam with a radiant heat barrier, ( mylar film) facing into the basement.

With a 2 x 4 stud wall this will give you an R24 minimum* wall, (radiant heat loss is not easily measured), compared to R14 with batt insulation alone or R 20 with foamboard.

Basements are almost always "heated". In the old days this was done by just placing the furnace and hot water heater down there.

Insulate the roof of the cold room by placing a 6 mil poly barrier along the underside of the floor, lapping it around the joists. Fill the joist void with Rocksil, (8"to 10") and sheath it with 1" polethelene foam with a radiant heat barrier, ( mylar film) facing into the cold room.

Its a good idea to protect the foamboard with another layer of sheathing. Wood will work best inside the cold room, ( plywood, strandboard, tongue and groove), drywall outside the coldroom (greater thermal mass).

Use an exterior insulated door and frame for the entrance to the cold room, or build a well insulated and well sealed door.

Once built, you will find that the cold room will come pretty close to approxamating the ground temps, ( 56 degrees F average) and will have higher humidity than the rest of the basement.

You actually need 2 cold rooms, as carrots, apples, horseradish, radishes, etc need to be stored seperately from onions, cabbage, etc. The gasses given off by one, ripen and lead to rot in the other.

You will find that dependant on storage abilities, stuff will last over the winter. Different strains of crops, store differently. Walla Walla onions for example, will store for 3 months or less. Yellow Russian Onions will store a year or more. Yellow Transparents or Suncrisp Apples will make it a month or two, Cox Orange Pippins will last into the next harvest.

True root cellars are about twice as good as cold rooms for storage, but cold rooms beat refridgerators by about 12 times, and are a lot cheaper to run.

Thanks for the detailed feedback. I will pass this along to my husband who is building the storage area. We are trying to do this project using as much of what we already have as possible - for example, a free interior door rather than an insulated steel one, and hard foam board sheets which we have. We can always add insulation to the door. We also have extra recycled cotton insulation that was leftover from an earlier project, and that will probably fill the wall cavities. The joists are already filled with this batting.

We are trying to reduce the chances for mold in the basement because of allergies, so we tend to stay away from wood and cardboard, especially near the floor. The basement is damp is some spots and in some seasons; hence the need for the sump. If the studs are galvanized, will they still tend to rust?

As far as two rooms or one, I think I can't ask for too much. I'll be lucky to get one room and find other little storage spots in the basement for other things. ;-)

Liv2learn,

mold needs two things, moisture in the form of condensation, and food. Pretty much anything will suffice for food. Gypsum and steel excepted.

Moisture in the form of condensation is caused by basically, having a cold surface that water can condense on. If mold is not currently a problem in the basement, as long as the cold room is well insulated, vapour barriered and well ventilated, mold will not be a problem.

You need to make sure that there is a vapour barrier on the warm side of the cold room.

For the ceiling, that means 6 mil poly wrapped around the joists and across the underside of the floor, then out across the king studs and taped to the exterior foam sheathing. With out a vapour barrier, the insulation won't do much for keeping areas warm (R5 instead of R14 for example), and will provide that perfect surface for condensation and mold growth.

For the walls, the foamboard on the warm side of the basement needs to have its seams glued and sealed, Tucktape or foil tape if mylar clad will do the job. That will provide a good vapour barrier.

It's a good idea to wrap the kingstuds and rim stud, along with any studs that contact the wall, with 6 mil poly and pull it outside, (into the basement) and tape it to the foam to prevent air intrusion along the concrete and ceiling.

Acoustic and vapour barrier mastic, ( a black, gummy caulk) laid in beads along these studs before they are installed will also help a lot.

Spray foam injected into the interior door will help insulate it, but by the time you add up the costs of a proper door frame, weather stripping, spray foam, labour,....... well, I can get a cosmetic damaged exterior metal clad insulated door and frame, for $69, suitable for use anywhere in Canada but the high Arctic. Might have a dent in it, more likely the primer coat will have been scratched.

Galvanised steel studs will still rust. The rust will start where the screws penetrate the galvanising and will rot them out in, (in housing terms) no time. 5- 10 years in a damp basement. Keep in mind as well that basements often flood. While floods will ruin carpet, wallboard, etc, they will not damage timber studs, metal studs however will be toast.

Neglected in my prior posts was ventilation. You need 2" of passive, or 1" of active ventilation for roughly every 32 square feet (4' x 8').

Active ventilation is easy. All you need is a cold air inlet near the floor, and a hot air outlet near the ceiling. For an 8' x 8' cold room, the easy way to do it is drill two 2" holes through the sill plate to the exterior. Run a lenght of ABS or PVC pipe through these holes.

For the hot line, run it from just outside the exterior cladding to just inside the foundation wall. Cut two small 2" circles of metal screening. Place them each inside a 90 degree elbow and glue one on each end of the pipe, inside and out with the elbow pointing down, so that the screen is wedged between the pipe and the elbow. The screens will keep out pests. On the inside, run just enough pipe from the 90 elbow down, to pass through the finished ceiling of the cold room.

Do the same for the cold line, but run it from the inside foundation wall, almost to the end wall of the cold room. Add the screened 90 elbows. Then glue a pipe that almost reaches to the floor.

Warm air will rise out the hot line, and cold air will flow in the cold line. Natural convection will power the ventilation system.

Recycled Cotton batting (Denim batts) will do fine for the stud voids and joists, just make sure that on the inside and outside of the cold room you sheath the walls well. The one major drawback of cotton is that rodents find it to be an exceptional nest material.

A lot of people think, well, I have a cat who is an excellent mouser,..... and while that is great for killing the resident rodents, it does nothing to repair the damage that the rodents made trying to nest.

Trust me on this one. I had to replace all the wall insulation and ceiling insulation in a house due to rodent damage. In one 24" x 8' wall cavity, there was less than 24" of insulation left in the wall, after the mice had finished shredding it for nest material. Half of the walls and all of the ceiling were like that. A R20 house was left with essentually 0 insulation when the mice were done. Might as well have been a tarpaper shack.

It's starting to sound like burying a sealed barrel in the back yard would be easier than building this room. ;-) But I'd be anxious about critters getting into it. Thanks for all the information. I'll pass it along to my "builder" (ie: spouse).