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We want a root cellar in the basement our new home. Throughout most of the year (except summer) the root cellar will have a temperature of 40-55 degrees F. and a humidity of 60-85%. Ventilation must be placed in the root cellar to keep air moving and keep the area cool--this is typically done with two PVC pipes sticking out of the foundation.

 

Our home will be very tight and ventilation will be controlled with a heat recovery ventilator. We are very concerned about high humidity levels causing mold problems in the walls and ceiling of the root cellar.

 

Specifications:

• The root cellar will be a 8x14 foot rectangle in the northeast corner.
• We plan to use insulated concrete forms (ICFs) for the basement foundation.
• The basement will be unfinished.

 

Questions:

• What is the best way to partition the root cellar off from the rest of the basement so its climate does not affect the rest of the home?
• What wall system should be used (SIPs?) and how should the walls be insulated?
• How should the ceiling be insulated?
• Does anything need to be done to the two exposed ICF walls?
• Is there a more modern way of ventilating the root cellar other than two PVC pipes sticking out of the foundation?

 

Thanks so much for your ideas and time.

 

-FMeyer

I always thought of a root cellar as one like my cousins had up in B.C.. A trap door in the kitchen pantry which lead down to a small hand dug underground cellar. It always remained cool there because of the constant temp of the earth below grade. There was no insulation there, and it was totally outside the conditioned space. Not enough info here...

FWIW
Mark

In my brothers house they have a "room" off the basement, under their front porch. It has four poured walls and spancrete above it for the porch. From the basement it has a regular exterior door through the cement wall. The room is about 5 by 10 in size with a dirt floor. Honestly I would be concerned about radon since it is about 8 feet underground, but since it is sealed from the rest of the house and they don't "live" in the space it should be fine. They say it has been working well staying cool in summer.

>>What is the best way to insulate a root cellar in the basement of a very “tight” new home?<<

A root cellar needs to cool the fruits and vegetables that you put into it. If it is in a heated basement, then it needs to cool any air that leaks in when you open the door and any heat that leaks into the root cellar through the walls that it shares with the heated basement.

If you built with ICFs, and you are mostly below grade, then you have a heated basement by default. Heat loss from the floor above and incidental heat produced by electric lights, hot water heater, washing machine etc. will be plenty to warm the basement nicely. You will not need any dedicated heaters to warm it up.

A root cellar cools by losing heat to the surrounding earth/dirt. Since your foundation walls are ICF, they have R-20 or so insulation value. You probably have R-10 foam insulation under the slab. So there will be no significant cooling of your proposed "root cellar" by the earth. The root cellar might be 2 degrees or so cooler than the heated basement. Not cold enough to preserve food. This discounts the effect of outside ventilation.

If you vent to the outside, the cold winter air would cool the root cellar nicely in December. But when you harvest vegetables in August, the root cellar will be warm.

If you want something like a root cellar in your basement, you will have to build/buy a walk-in cooler/refrigerator. The compressor will throw off heat and you can use that to (partially) heat your house in the winter. So you are getting double benefit from the electricity used. Depending on scale, you might look into commercial food storage solutions.

I recently built a "tight house". It includes a garage. The temperature of the garage fluctuates between 32 and 70 degrees or so. I have two refrigerators in the garage that I use as stable temperature "root cellars". The cool temperature in the garage keeps the electric bill low. Also the doors stay shut most of the time.

If you do the root cellar under the porch recommended by Brock, put in an exhaust fan or even better, a passive chimney-effect vent to create negative air pressure in the root cellar. Otherwise you may have air quality problems in the basement. Root cellars performance depends on local climate and you may need to insulate anything above grade.

No additional insulation is needed in the walls of a an ICF house. And why would you build any other way?