Underground Root Cellar

[OlJarhead]

I've seen a lot of pictures and articles on building root cellars but I haven't found anything that explains things like calculating beam sizes for two feet of dirt roof, or what must be done to support the walls of a root cellar that is ten feet underground.

Perhaps Glenn with his awesome underground cabin could help?

I've dug a hole ten feet deep at the deep end (into a hillside basically) 12-13 feet wide and about 20-30 feet long.  I will have to build a structure that I can then backfill 2-3 feet of dirt on both sides and as much as 5-6 feet at the back and then also at the front leaving a small underground 'porch' to enter the structure with.

I'm not looking to make it too elaborate if I can help it and considered originally using 6x6 beams for the main wall structure and roof beams however now that the hole is dug and much bigger then I planned on I've realized I need to consult some pros.

I can cut plenty of ponderosa pines that could be milled into 8x8's and I was thinking that if I were to make 8x8 posts and beams for the structure I could make it 12x10 instead of the original 10x10 I'd planned and then place a 3rd 'wall' in the center to provide additional support for what I expect would be a massively heavy roof.

I'm looking to bury the cellar under two feet of dirt so anticipate I'll need a pretty strong roof.

The plans I first saw called for heavy beams with 2 layers of 1 1/4" plywood sheeting covered in two layers of 6 mil plastic.  The walls would be posts with 1 1/4" ply sheeting covered in plastic also.  The floor would be dirt.

Anyone have some thoughts on this? 

I also plan to install 60watts of solar power to power lights in the cellar.

Thanks!

[Native_NM]

Bury a conex box.  Add stairs in berm. Instant root cellar. Search YouTube for examples. 

[Turkeyhunter]

and the root celar doubles as a strorm shelter............
i have saw several at different camps in the northeast, worked grea~~~~~ they used poured conc. or block type walls.

[Squirl]

The walls are simpler answer:

http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec004_par001.htm
Table 2 for hollow 8" block with rebar.  12" might be easier with less block infill and rebar.  I know you are in a remote location.  Hauling less weight might be a plus.   I haven't done the research though.
Solid poured:
http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec004_par003.htm

PT wood might be easier to haul, but I think the amount needed to hold back that much soil weight with a PT treatment for burial would be cost prohibitive.  I also don't know how to design the walls for that size.  The best guide I have is PWFs.  They aren't even approved for fill heights taller than 4 ft though.

The roof is more difficult for me.  The average weight of soil is around 3000lbs per cubic yard (online sources).  With 27 cubic feet in a yard that is around 111 lbs per cubic foot. For 2 feet deep that would be 2 cubic feet or 222 lbs per square foot of roof.  Over a 12 ft span that is difficult.  Don_P had some documentation somewhere here about load/span for non 2x lumber from the AWC.  I don't remember where.  For that span I would look into loading capabilities of steel I-beams.  A while ago, I found a lot of information looking up fall out shelters.  I didn't save any of it.  The government put out a lot of information in the 1960's. I believe the minimum safe soil depth was 3 ft.  So they were designed with more of a load. Many had 6-8 inch logs with no space in between.  None of the designs I saw had a large span. IIRC many did have a 6 ft span. So the middle wall idea might work.  I found all this when I was looking up root cellars a while ago.  I didn't save any of it. Sorry.  I was looking for span/load tables for concrete rebar roofs and couldn't find any.  That's as far as I've gotten on the math.

[OlJarhead]

Thanks All. 

I plan to make this entirely out of wood and figure it shouldn't be too difficult as that's how they were done for generations.  And, of course, mines were also shored with wood.

I recently saw a blog on making a root cellar that I thought at least addressed the sidewalls (partially burried logs stood tall and set side by side along the length of the wall).

I'll have to look it up as well as others.

[Native_NM]

All of the old fallout shelter designs are still on the govt website.  I think it's on the FEMA site now.

[rick91351]

My problem comes with the lid, or roof.

I did pour a few fall-out shelters back in the early or mid 70's.  Basically the same thing.  They were shored up with timbers, on top of that was formed a bottom of plywood or heavy roofing metal.  Then they tied a bunch of rebar like #3 on top of that in a 8 or 10 inch grid.  Then we poured it over that.  Usually was about 6 inches thick if I remember right.   All that said, I as well would like to find a way to do the top and not brake the bank.  I want it to last for my grand kids well.  I am thinking of dropping Mr Glen a PM and see what his ideas are when he gets home and decompresses from his current thing.   

I am wanting to do the walls with block, leave the floor decomposed granite.  Then I want to place a water tank inside with a pump and pressure tank for the cabin / house.  Our little low producing well could fill the water tank using a float valve for a shut off.  That way we would not have to drill another well  

http://www.plastic-mart.com/item.aspx?id=2725

Then add racks on the other side for food storage, powder and what not.

[glenn kangiser]

www.undergroundhousing.com

The tables in Mikes book will give you the information you need.  His designs were for 2 feet of dirt and a foot of water though if you are going the full 2 feet I would keep it toward the heavier side on logs if using different species, or reduce loading to 1.5 feet.  Use EPDM and French drains, as well as having proper ventilation  for a root cellar.

[OlJarhead]

www.undergroundhousing.com

The tables in Mikes book will give you the information you need.  His designs were for 2 feet of dirt and a foot of water though if you are going the full 2 feet I would keep it toward the heavier side on logs if using different species, or reduce loading to 1.5 feet.  Use EPDM and French drains, as well as having proper ventilation  for a root cellar.

http://www.bestmaterials.com/savedcart2.aspx?id=test5 found this site and it doesn't sound too expensive.  Thanks!  60 mil sounds better then 6!

Was wondering about using some kind of french drain for excessive water and I've read that root cellars do best with two vents, one high and one low.

I'll have to book mark his site as I think I'd like that book!  One of my sons wants a 'hobbit hole' so perhaps this is a way for him to explore that idea.

[OlJarhead]

http://timberbuttehomestead.com/?m=200812
Bottom of the page (December 2008) are blogs on building a root cellar with old tires.

Very interesting.

[OlJarhead]

The more I search, the more crap I find.

It seemed to me that building a root cellar should be pretty straight forward:  dig a hole, put in strong walls and roof, bury the hole, install a porch and doors, stock the root cellar.

Maybe I'll have to do research, read some books and then blog about it since it appears it's not something others want to share openly.

What amazes me though, is that this isn't rocket science and darn near everyone used to have one....so you'd think the knowledge necessary to build one safely would be easily attainable without coughing up $$$. 

[OlJarhead]

http://www.grit.com/Garden/Root-Cellars-in-the-21st-Century.aspx

This is typical of most articles I find...they tell you what temps to shoot for, humidity, that it should be vented and underground but stop short of saying: dig a ten foot deep hole, build a 'room' out of 6x6's (or whatever) and 2x6's (or whatever) and then bury it.

Oh well.

[UK4X4]

maybe you aught to googling something slight more military !

http://library.enlisted.info/field-manuals/series-1/FM5_34/5344CH.PDF
page 4-15

http://www.survivalprimer.com/NWSS/NWSS%20App%20D%20Expedient%20Blast%20Shelters.pdf

Insures your vegatables are safe from small arms fire  and the odd nuclear explosion;D

[OlJarhead]

http://www.earthbagbuilding.com/history.htm

I may have it

I'm still working out my idea but I think this might kill two birds with one stone so to speak.

First build a room that is 10' by 12' out of wood -- possibly standard 2x4 or 2x6 framing and PT plywood outer shell with no roof.

Then use earth bag construction to build a 2' thick wall around the structure to the height of the walls (8') and finally lag or spike logs on top of the earthbag and wood walls across the 10' span (I'll have to do a little research on the size of these but I'm guessing ~10" ought to be close) on 12" centers.  Then nail to the log framing the 1 1/4" PT plywood sheeting, cover in thick plastic (mentioned 60mil earlier should do nicely) and then backfill.

That's a rough idea anyway but I think it should address the side load issue of the 10' deep hole and the overhead load of 110-220 lbs per square foot of earth.

Then the same method can be used to make the 'porch' entrance as well as the stairway out -- with some mortar on the outside of the bags and some rock enhancements it might just look the part too

[OlJarhead]

http://www.forestryforum.com/members/donp/CalculatorIndex.htm is this from our own DonP?

[OlJarhead]

Posted this in the Forestry Forum where I'm getting quite a few responses   There is a Don P there with calcs and I can't help thinking it's the same DonP we have here!  Must be!  If so DonP, then thanks!

So, at this point I'm thinking 6x6x10 posts (PT's to be safe) buried 2' into the ground below the root cellar floor (if I can get down that far -- might have to settle for less -- with a 2x wall behind them painted with that green copper stain which is supposed to protect from termites and water damage (don't want to buy that many 2x PT's when I can mill my own right), then frame the roof with 8" partially sawn logs (flat top and bottom with round sides) spanning 10 feet but with a load bearing beam (8" log set on 6x6 posts on 5' centers -- maybe less) finished with 2x's painted with the a fore mentioned copper stain and covered in 60 mil (yes sixty mil) plastic.

I'll then be sure to keep lots of diatomaceus earth liberally spread in key places to keep the ants or termites at bay (which we seem to have plenty of in a pine forest).

I can keep the dirt floor (needed, I'm told, to ensure humidity remains high) and should have the strength to hold back the dirt (which is not moving now but the back fill has to put some pressure on the walls.

With an 8 foot ceiling I can put in a prehung steel door to give me some added security (deadbolts etc) and then make my own 2x outer door (there will be a 6x6 ante-chamber to enter before the main cellar to give a buffer zone).

Then I just have to work out the ascent to the ground above which I plan to make fairly steep with storm cellar type doors above (which will have 60 mil plastic inner coatings overlapping to keep water out.

With luck this will work and I'll get many years of use from it Smiley

I've heard wood framed cellars can last 15-20 years or longer.