Build a Mini Root Cellar that Actually Works

Reader Contribution by Steve Maxwell
1 / 2
2 / 2

Some kind of food storage space is as important to the self reliant gardener as a hoe and shovel. But food storage is also where many people have trouble.  While it’s true that millions of homes across the continent include a small cold room off the basement for storing food, most of these cold rooms don’t actually work – at least not without the upgrades I’ll tell you about here.

The kind of cold rooms I’m talking about extend underneath the concrete front steps of homes. There are other styles of root cellar storage, but this blog is all about making under-the-steps basement cold rooms work. What is the usual problem with these things? Too cold in winter and too warm in summer, cold rooms fail for one main reason: they don’t have enough soil cover to function as the miniature root cellar they claim to be.

Why Some Cold Rooms Don’t Work

If you’ve got an under-the-front porch cold room at your place, you probably know all too well what the major problems are. It’s not unusual for frost to penetrate the top 25 percent of the structure during winter. On its own, frost on walls might not seem like the end of the world, but when it melts and runs onto the floor, it comes close. Besides soaking the floor, the added moisture boosts airborne humidity high enough to promote mold and mildew. You might even get significant amounts of water pooling on the floor of your cold room because of melted frost. Not good.

Poor warm weather performance usually goes hand-in-hand with a cold room that’s bad in winter, too. Without the moderating effects of enough soil around the structure, cold room temperatures are likely to get way too high in summer for effective root cellaring.

Water leakage into under-the-steps cold rooms is the third most common cold room headache, and it has several sources. Liquid water can seep in through the walls of the structure, or down from the top, through or around the precast steps. Despite its solid appearance, ordinary concrete blocks and poured concrete aren’t fully waterproof. Many times they’re not even close.

How to Make Your Cold Room Work

The good news is that there are three specific things you can do to make your cold room a pretty decent food storage zone. It won’t be as good as a full-blown root cellar, but it will work way better than it does now.

Boosting your cold room is all about stabilizing temperatures within the space. You need temperatures to stay just above freezing in winter, and to be as cool as possible during summer. So how do you make this happen? After waterproofing the cold room so it doesn’t leak water, there are three key steps:

Step 1: Bank as much soil as you can around the sides of the cold room. Soil is your friend when it comes to food storage. It works to keep things above freezing during winter, and as cool as possible during hot weather.

Step 2: Install vapor-proof insulation on the cellar ceiling and partway down the walls. It’s very important that this insulation prevent the movement of air through it.

Step 3: Install a door capable of keeping heated basement air out of the cold room space. An exterior insulated door meant for houses is perfect as a cold room door. Anything less and all the rest of your modifications won’t make a difference.

After banking as much soil as possible around the walls of your cold room, fasten 2-inch thick sheets of extruded polystyrene foam to the ceiling of your cold room using construction adhesive, then part way down the walls.

How far down? A foot or so lower than the outside level of the soil. Extruded polystyrene is smooth textured and typically blue or pink in color. Don’t use the white, beady expanded polystyrene foam. It’s cheaper than extruded, but air can pass through it, leading to condensation forming behind the foam during cold weather. 

You’ll need to cover your foam to keep it in good condition and meet building code requirements. Cement board is an excellent option for this.

Need more help? Download free cold room renovation plans It shows you everything you need to do so your cold room actually works as your own miniature food self reliance zone.

Steve Maxwell, “Canada’s Handiest Man”, is an award-winning home improvement authority and woodworking expert. For more than two decades he’s been helping people renovate, repair, build and maintain their homes. Find him online at Maxwell’s House blog and read all of Steve’s MOTHER EARTH NEWS posts here.

All MOTHER EARTH NEWS community bloggers have agreed to follow our Blogging Guidelines, and they are responsible for the accuracy of their posts. To learn more about the author of this post, click on their byline link at the top of the page.