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Foundation for cobwood shed? And other questions.  RSS feed

 
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(Hi guys, I'm new here.)

I live in CNY, about 20mi south of Lake Ontario. It's very windy and wet here, with heavy snowfall, and it seems like a lot of other Earth building resources focus on building in warm, arid regions. My soil has very poor drainage, so I'm thinking I likely have a clay-rich subsoil. I'll do a jar test when it warms up a little.

I'm building the shed mostly for a place to build a forge in to experiment with metalworking (although I'll also be storing the lawnmower in there to get it out from under my porch), so I've been looking at options for low-cost fire-resistant walls and arrived at cobwood, which interested me for two reasons:
1) I intend to sell this property if I can ever afford a better one, so that it can be demolished and buried on-site is good.
2) I'm interested in cobwood specifically because I'd like to start building in the spring, which might make sourcing straw difficult, and also because I have a nature-felled Willow I need something to do with anyway.

My main question is the foundation - it seems like a concrete foundation is just simply my best option given the wetness, poor drainage, etc. Are there any other better options besides stone (there's a gravel pit nearby, but I have no idea where to source larger stone locally. I'm also looking to do this cheaply, and have no clue how much stone costs, but I do know how much concrete costs).

I already have a fairly large pile of waste concrete (I've only kept it around because a neighbor was picking off it to build a retaining wall). I don't think it will be enough to do the entire foundation if I just stack it, though. So can I break this up into small pieces, wet it, and use it to stretch new concrete mix? Or am I best off just pouring all new concrete? Or maybe pouring new concrete to ground level, and stacking this with mortar for a stone-like appearance?
(I can always use this concrete for the floor, so I'm fine with not using it for the foundation, but I'd rather use it there if I can)

Also, what's the best way to affix a wood-framed roof to a cobwood structure? Just set a 2x6 or something in the top to fasten to, and drive some spikes into the wood? Or cob around a frame mounted to the foundation (and does this frame need standard stud spacing, or is a wider spacing acceptable)?
 
pollinator
Posts: 228
Location: Penticton, Canada
35
building rocket stoves woodworking
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Hi William,   Welcome to Permies!

Two books I have read cover to cover many times:
1) The Cob Builders Handbook by Becky Bee
2) The Hand Sculpted Home by Ianto Evans, Micheal Smith and Linda Smiley

Both are an easy read and can be opened anywhere to get exactly what you need.

Off the cuff, I know lots of people use urbanite (concrete chunks) as you stated possibly using for foundations before beginning their cob work.
Bags filled with loose rock have also been used.
Being that you want to have the ability to dismantle it in the future and return it to the earth, I would suggest staying away from using any more cement than you have to.

The books describe using "deadmen" anchored in the wall to secure the roof to if you want to have load bearing cob walls or building a timber frame structure first which would support everything then infill with cob. Lots to ponder I'm sure until you get around to building.... Good luck!
 
William Bailie
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Thanks for the information, Gerry.

I watched some videos demonstrating deadmen and think I have a pretty good idea of what to do there. Most of them mentioned using nails, spikes, or wire to hold into the cob; could I just use fastened perpendicular boards instead?

I'm trying to keep the cost low as possible (I've only saved a few hundred towards this project, and any cost savings means buying blacksmithing tools sooner), so I'm hesitant to buy these books - are there any good online resources you can point me towards?
 
Gerry Parent
pollinator
Posts: 228
Location: Penticton, Canada
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building rocket stoves woodworking
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My idea of a deadman is as you put it: "fastened perpendicular boards "
They are encased in cob several inches to a foot or more depending upon what your trying to hold.



Havn't had the chance to look through this free online book much but it may have some helpful info for you:

Handbook for building homes of earth
 
pollinator
Posts: 279
Location: Stevensville, Montana; Zone 5b
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food preservation forest garden hugelkultur
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I would suggest a rubble trench foundation with a stemwall (footer) that lifts the walls of the ground by 1-2 feet. Use earthbag building for the stemwall, it is super low cost and easy to build.

For the rubble foundation, get a load of gravel from the nearby quarry and fill up your foundation trench with that and your urbanite pile. The urbanite might not be enough for an entire stacked foundation, but it will certainly take up a lot of room in the trench. Since you have a lot of moisture, make sure you run a drain pipe out of the foundation to sunlight--or give it an adequate drainage area if you are not on a slope.

Fill the trench up to about 6" from the top and then do a layer of double bagged drainage bags--i.e. bags of gravel mix. That is your first layer and will drain into the rubble trench. Then do subsequent layers of earthbag with a good earthbag mix--your local quarry will probably have a great roadbase mix which is usually perfect for this application if your own soil has too much clay content.  Build your cordwood wall and then do a nice lime/cement plaster over the exposed bags--they will last multiple lifetimes.

drain.JPG
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Drain for Foundation
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Gravel filled foundation
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road base from local quarry
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earthbags being tamped
 
William Bailie
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Thanks for the link Gerry, I've read a bit of that so far but am not done.

Daniel, some of the Willow logs I have are quite massive - the tree was over a century old and was actually mentioned as denoting the SW corner of my property on the 19th century deed. How will earthbags hold up to having about 200lb dropped right on them? And how big of a drainage area do you recommend for a 2' wide, 4' deep, and 60' long trench (the area I'm planning to build is quite flat near the bottom of a hill, and I was planning to berm the area around the shed). Are those drainage bags essentially just gravel in a sandbag?
 
Daniel Ray
pollinator
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Location: Stevensville, Montana; Zone 5b
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food preservation forest garden hugelkultur
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William, Kelly Hart, author of Essential Earthbag Construction, recommends that posts be placed on full masonry supports. you can place concrete piers within the foundation or elsewhere to support that type of structure. Alternatively, I have seen structures spread the weight of such posts like a top plate on a strawbale wall distributes the roofs weight to the walls. I would recommend following Kelly's advice, he is the expert after all.

The drainage doesn't have to be huge, just enough to let  any moisture migrate out and sink into the ground. The one that I built was on a flat site and I dug a drainage trench 15 feet out from the house and a few feet deeper than the foundation trench, then backfilled with rubble to allow a lot of moisture to drain through.

Drainage bags are just that, gravel in bags. make sure you double bag those as the gravel tends to pierce the bags, this is just that first layer and once they are plastered over, the bags will never degrade.
 
William Bailie
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These aren't long posts, they're logs cut to around 2ft length. I'd say that the biggest is nearly 3' in diameter. I only have a couple near that size, because the tree split into three main branches at about 5ft up. I might just use the biggest log as a foundation for my anvil, and set the second biggest aside for carving a chair. Most of the rest weigh under 80lbs and I should be able to set them down gently. I'd really like to avoid pouring new concrete for a structure that might well only stand for another decade anyway, so I guess I can just hunt down some fallen branches to make up for the loss of those huge space-taking logs.
 
William Bailie
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Hey guys, thanks for all your help so far.

I'm thinking about the roof now. I hate heights but am pretty comfortable on the 4 on 12 slope on my back porch, so I'm thinking I'll do a simple 4 on 12 shed roof. This is a roof I'd be pretty comfortable getting on for installation, maintenance, etc.

But the roofing material is eluding me. Asphalt shingles are the cheap and obvious answer, but as I said I like the idea of just being able to tear the structure down and bury it.

A 4 on 12 is too shallow for straw thatch to work properly.

Cedar shakes aren't hard to find, but expensive. Could try to source logs and split my own, I do believe I've seen some Eastern red cedar around. But I've never done it before, not sure how tricky the technique is. Looked simple enough in a video. Also not sure what that long bladed axe I saw in the video I watched is called, or how much that would cost.

While thinking about this, I realized my porch floor has a mild slope. So do most of the Victorian to Edwardian era houses in the area, including the one I grew up in. Google confirms that this was once a standard practice, to allow draining of rain. The floor boards are just 1x4 tongue and groove pine, finished in oil based paint.
So any reason why cheaply sourced pine or eastern hemlock, brushed with a borax treatment and coated with a good oil based deck stain, couldn't be expected to hold up well as long as I take care to minimize areas that gunk can collect, sweep it off a couple times a year, and restain when the color begins to fade? Besides the solvents, is there anything in common deck stains that's particularly bad?
 
Gerry Parent
pollinator
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Location: Penticton, Canada
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building rocket stoves woodworking
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William,   The tool the person used to make cedar shakes is called a froe. They are pretty straight forward to use and inexpensive to purchase (or if your handy you could even build your own)
I used to go into the woods and find old red cedar stumps leftover from a logging operation, cut to length and then process them right there. I've made thousands of shingles this way until I discovered that I could do it with my 4 ton electric logsplitter. I had to modify the blade (make it longer) by welding on 2 pieces of steel, but now it works like a champ! No more sore hands! Instead of processing them in the woods, I now just make cants (chunks) and haul them out back to the shop for processing.

As for the pine or hemlock, you cold use those too with knowing that they won't naturally last nearly as long as the cedar. I've seen some people use oak as well but have no access to it in our forests so no experience there.  
 
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