Root cellar - have foundation - need to figure out where to go from here.

Would really appreciate advice on finishing up a root cellar in a fairly cold climate in the mountains of Northeast Oregon.  The photo shows the current situation.  

Planning on finishing the walls with cement blocks.  Would you recommend coating them (and the foundation) with some sort of waterproofing, and if so, what?  I assume it’s recommended to fill all the holes in the blocks with concrete, not just the ones with rebar, eh?  

Was planning on putting in a French drain around the base of the foundation but noticed that a book about root cellars recommends putting a French drain 2-3’ below the post-fill ground level.  Think I should put in both?  

For the floor I was planning on adding gravel up to the level of the top of the footer.  I tried to slope the base of the floor so that it drains to the corner where I dug a hole under the foundation for a drain pipe (the hole is visible in the lower right side of image).  How’s that sound to you?  And would you recommend adding geotextile fabric under the gravel?

One big question is what to do for a roof.  Yes, haven’t planned that out yet.  Would like to avoid the expense of a concrete roof but not sure if there are good alternatives that can hold two feet or so of soil above.  And was thinking that it be good to have rafters running from back to front with an overhang on the front to keep water off of the front wall.  (Can also have the center rafters long enough to make a little porch over the door and support it with posts.)  Would using L-block on the top course of the wall in order to help facilitate roof construction?

Do you recommend the use rigid insulation somewhere in this project?

There’s an intake vent hole already in place (visible to the right of the door opening).  What do you recommend for the out-take vent?

Any advice would be appreciated.  Thanks!

Leon Werdinger wrote:Would really appreciate advice on finishing up a root cellar in a fairly cold climate in the mountains of Northeast Oregon.  The photo shows the current situation.  

It looks great so far!

Planning on finishing the walls with cement blocks.  Would you recommend coating them (and the foundation) with some sort of waterproofing, and if so, what?  I assume it’s recommended to fill all the holes in the blocks with concrete, not just the ones with rebar, eh?  

Was planning on putting in a French drain around the base of the foundation but noticed that a book about root cellars recommends putting a French drain 2-3’ below the post-fill ground level.  Think I should put in both?  

I hope some of our more knowledgeable builders will speak up, but as an amateur who also lives in earthquake country, I'm inclined to say yes to the concrete. Concrete has high embodied energy, but if you're building to last a long time, I expect the payback would be worth it.  I'm in a very wet environment, so to me, more drainage is better than not enough. Much depends on where the water is draining to? Even though you say you are "in the mountains" can this cellar flood if there is an unusually wet period?

Do you recommend the use rigid insulation somewhere in this project?

I don't know the R-value of dirt off the top of my head, or what your expected lows might me. But I would look those up. Some people put an insulated umbrella multiple feet outside the structure, so you've got some dirt helping to moderate temperature. The one spot I would consider using it for sure is on the door and the front wall on the outside to protect the concrete from both heat and cold.

There’s an intake vent hole already in place (visible to the right of the door opening).  What do you recommend for the out-take vent?

The material I've read about venting cold cellars, suggest that it is good to have input and output. I recall a book by Sepp Holzer recommended that the intake air pipe travel through soil so that it gradually cools and dehumidifies so you don't get condensation dripping on food.

This looks like a neat project and I would really like to have a decent cold cellar to extend the harvest.

Thanks much Jay!  

Your suggestions to fill the blocks fully and to add rigid insulation to the front exterior make a lot of sense.  

My question about the outtake vent was too vague.  What I meant was whether it'd be better to have it come out of the roof or an upper wall.  (Either way, I was planning on having it on the opposite corner from the intake vent.)   So glad you mentioned having the intake vent travel through soil for a ways before entering the structure - seems like a great idea and I should be able to do that fairly easily.

BTW - the environment here isn't very wet.  Apx. 18" precip./year.  And fortunately there's still a bit of a downhill slope in front of the cellar for water to be drained to.

Thanks again.  Any other advice would be appreciated.

Building an underground structure is in my not-so-distant future. However, I don't have much experience building except my beehives and a couple projects I helped with. Mike Oehler has some great advice in his books. Also, I've been paying attention to the roundwood timber building they have done at Wheaton Labs. The passive solar greenhouse is well underground and has a roundwood timber roof covered with plastic and soil.

I would protect the concrete from moisture, say with plastic, as I have seen water wear away concrete.

When you mentioned the intake and outtake vents, the rocket mass heaters and earth tubes came to mind. An earthtube is what it sounds like Jay is talking about by burying the pipe to cool the air. The rocket mass heater builds mentioned putting the output pipe on the roof with a cap for better draw. I probably butchered exactly what they said about the rocket mass heater output pipe.