Underground Root Cellar Construction

[OlJarhead]

Hi All,

One of my projects is to get a root cellar constructed at our property (along with the cabin I'm building that's posted elsewhere) and I've run into a bit of a bind -- mainly that I know nothing!

I followed the extras link to: http://www.forestryforum.com/members/donp/CalculatorIndex.htm

And used Southern Pine (and others) to see what Don P's calcs would tell me.  I set the total weight on the log at 2200lbs assuming 220lbs per square foot (2 feet of dirt covering roof of cellar) and the calculator appears to be telling me that a log spanning 10 feet and carrying 2200lbs would need to be about 7" in diameter at the center of the span if I'm reading this correctly.

I then upped the load to 4000lbs to see what change that would make as I am thinking I'll have more on the log if it is set on 16" centers (or more or less depending on what I learn) and it appears that #2 Southern Pine would need to be 7.5" in diameter mid span.

If I am reading this correctly then I should be able to frame the roof of the cellar with 8" diameter logs set 8-12" apart along the span of the roof.   Am I reading this right?

My plan for the roof is to set the logs on the walls (most likely bolted to the walls -- more on that later) and then nail 2x's or thick plywood to the logs and cover with 60 mil plastic draped down the length of the walls.

For walls I'm a little stumped.  Originally I was thinking I'd set the logs into the earth and bury them, but then I realized this might be a bad idea as the earth could cave so I set to searching for a wall design that could hold back the earth walls.  I originally though I'd build a 2x6 wall framed on 16" centers with PT plywood outer walls but then realized that might not nearly be strong enough so I began searching and couldn't find anything definitive (sure there are lots of blogs but nothing clearly stating what is safe).

So, do I build a log framed wall with a ply sheeting or an all log wall?  Is cinder blocks and concrete better for the walls? 

I also considered earth bags but then learned it might not be enough.

I'll post pics of the hole shortly but am hopeful some of you folks will jump in and help me out
Thanks!
Erik

[laffs]

ive never built one , ive seen a fe years ago made from granite, rocks, tohuge fuel tanks.

if your worried about the earth pushing in the walls, why not build a floor and put the walls on the ouside of the floor instead of on top
id consider rolled roofing or heavy tar paper on the roof maybe several layers, and then a liquid tar or driveway sealer on top of that

[Jasperfield]

You might consider a small shipping container. They are available as smal as 10' long and run on up to 40'.

Dig back in the bank, insert it, backfill the sides, and cover the roof.

You could cut holes in the bottom for moisture and heat; and do the same to run a vent out the top.

The walls and roof are strong enough to withstand large loads.

[OlJarhead]

Thanks guys.

At this point I've ruled out the shipping container (couldn't get one there if I wanted to) but it is an interesting idea.

I'm pretty sure log framed walls and roof is all that I need and I have a source for 60 mil plastic which is what the underground house guys use.  So, i just need to make sure I use big enough logs and determine the right way to construct the walls to hold back the dirt.

[SPIKER]

If possible I would go with cinder block walls & a poured floor.   since you are spanning this open room why not build a row of support shelves down the center to help support the roof?   there will be a need for shelves anyway to store food might as well make them heavy to help support the roof as well.

sealing up is important stop water getting in and coolness getting out.  venting is also needed to let the moisture out when it does gets in.

Mark

[OlJarhead]

If possible I would go with cinder block walls & a poured floor.   since you are spanning this open room why not build a row of support shelves down the center to help support the roof?   there will be a need for shelves anyway to store food might as well make them heavy to help support the roof as well.

sealing up is important stop water getting in and coolness getting out.  venting is also needed to let the moisture out when it does gets in.

Mark

I've been giving serious thought to cinder block walls reinforced with rebar and concrete and set on double width footings set 6" below the grade of the floor.  That would probably be more then strong enough, I just didn't want to do THAT much work in the start of this thing! haha

My original idea was a room made of strong wood walls and roof buried in the dirt like root cellars of old -- or so I thought.  However, it's looking like I need a lot more strength to hold the walls back and the 220psf load on the roof.

[Buck]

Invite the Magicman over. He knows about those blocks.

[thecfarm]

I have a root cellar under the sun room.A Lot differant than what you are doing.Mine is just a basement with no floor,just crushed stones.But do not pour a floor. You need the dirt to keep that room at a constant temp.

[chevytaHOE5674]

But do not pour a floor. You need the dirt to keep that room at a constant temp.

My root cellar has a poured cement floor, walls, and arched roof. It stays within a couple of degrees all year long. Been that way for about 80-90 years now.

[Sprucegum]

A row of 6x6 posts 3 or 4 feet apart. Nail 2x6or 8 planks on the outside and backfill; it will hold 

I would use 2x8 rough cut planks for ceiling joists and cover them with 2x whatever planks then plastic

Plywood is for city folks who don't have mills   

[OlJarhead]

A row of 6x6 posts 3 or 4 feet apart. Nail 2x6or 8 planks on the outside and backfill; it will hold 

I would use 2x8 rough cut planks for ceiling joists and cover them with 2x whatever planks then plastic

Plywood is for city folks who don't have mills   

Thanks!  So you think the 2x8 rough cuts will hold the load?  I've read that dirt is roughly 110lbs psf so the load on the beams will be 220lbs (2 feet of backfilled dirt to put the root cellar at optimum depth)?

6x6 posts should be easy enough to do and I was thinking of just milling it all anyway but I've got mostly pine so wanted to be sure before using it.

[Tom]

I'd build the roof out of the heaviest and best timbers I could find, if I were to use wood.  You are'nt figuring the load for just the dirt.  Who could guess what might traverse across the thing.  People will walk over it, lawn mowers maybe, tractors, trucks..? 

How many times have you heard of a truck falling into an old septic tank?

I'd build it like a fortress.

Are termites a problem?  They love Pine sapwood and will eat the heart from all but the very fat-lightered heart.

[Raider Bill]

You might consider a small shipping container. They are available as smal as 10' long and run on up to 40'.

Dig back in the bank, insert it, backfill the sides, and cover the roof.

You could cut holes in the bottom for moisture and heat; and do the same to run a vent out the top.

The walls and roof are strong enough to withstand large loads.

I know a guy that buried a 40' shipping container as described here. in 5 years it caved in due to moisture/rust from the dirt. He thought he had it figured out and coated the outsides with a high dollar membrane to no avail. This was done in SE Tenn and red clay soil.

[Sprucegum]

  I live in an area with no termites and no traffic so I never considered those problems 

The root cellars I have seen have been cut into a steep bank or tucked away behind the house where no one traveled except on foot, looking for a stray cow or goat 

The potato bins and shelves were all constructed of the same posts and planks and may well have given extra support to the roof. The soil was typically sand with some clay and the floor was left natural in most cases; especially in the bins.

[OlJarhead]

Thanks All,

Cows are a problem though I plan to fence that area which 'might' help with that.  Tractors shouldn't be an issue since I own the land and ought to know better (and intend to fence it which will keep ME from walking or driving over it).

However, I like the idea of a center support beam on heavy posts.  That ought to increase the load bearing capacity of the beams/logs used for the ceiling.

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

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

[Jeff]

Root cellars used to be common where I grew up. We had one, and several of the neighbors had them. Every one but one that I was ever in were built of cement plastered concrete blocks with concrete floors and rebar reinforced ceilings. The one that wasn't, was built from wood by my great grandfather. By the time I came along, it was a hill with a hole in the top that everyone said to stay away from because it was a snake den. The concrete one that was on the property I grew up on was built by a previous landowner, probably in the 1920a dad thought. It's still there today.  It's probably on its 3rd set of wooden doors since I was born last I knew.

[Troublermaker]

I know what you talking about Jeff. A man that I use to work for dug a hole out in a hill side big enough for a 10X10 root cellar with 7 foot high walls. We form it up and pour a 4 inch concrete floor with a drain in the middle. Then he use  8 inch cinder block for the walls. We form up a roof out of plywood and cover it with old roofing tin and 2x4. It was brace every way that you think of cause he was going to pour a concrete roof. We nail up some 2x12 so that 4 inches was over the blocks. He went to the junk yard and got some 1 inch rebar that we laid across the roof every 2 feet both ways so that the rebar was sitting on the walls. I had some pieces of concrete that was 2 inches thick that we use to raise the rebar. Then we pour concrete in the wall blocks with 1/2 rebar and pour the roof. He raise the center 4 or 5 inches making like a low A roof. Then 2 or 3 coats of tar on the side and top all cover with plastic. He back fill it slowly and put 2 to 3 feet of dirt on top. I don't know what it would have cost to have some one to build it but I know that it would have been plenty. Except for the 1 inch rebar and concrete he had everything left over from difference jobs and my labor was free. It stays a constant 50 to 55 degrees year-round.

[red]

how many bedrooms will it have electric 

[OlJarhead]

how many bedrooms will it have electric 

Huh?  No bedrooms, it's a root cellar.

Electric provided via solar panel and 12v battery only.

[OlJarhead]

Interesting posts on the concrete structures.  Of course, to do that I'd have to somehow haul up a couple tons of bags of concrete and a mixer and do it all by hand -- not going to happen.

Not sure how the snakes got into the hole but I've read that wood root cellars don't last forever (in damp places anyway)...but I've also heard of some lasting more then two decades if cared for.

Will it last 100 years?  I highly doubt it but then if it last two decades I'm sure a time will come that I can use the trackhoe to clean it out and rebuild it with something longer lasting.  Today, however, it's wood me thinks.