Throwing this out there: We need to create something liveable for a family of four for as little cost as possible over the next few months.
The challenging bit: our environment (Taranaki, New Zealand) is harsh. We are at altitude (460m) in a rainforest. Our bit of land is a wide ridge with about 7 degree gradient. There is another 900m in height uphill from us, so lots of little springs. The rainfall is about 3.5metres (say 140 inches) a year, and humidity is 100% a lot of the time. The rain is usually accompanied by enough wind that it is fairly horizontal. In winter the ground surface and the water table quite often coincide. The soil is volcanic ash. Fine silt with zero clay content and free draining. (Edit) The soil has the interesting property of being very strong in-situ but becoming and remaining a slippery muck when disturbed. (/Edit)
Temperature range isn't too bad: max about 27C, min about 3C . It snows lightly once a year on average, and fewer frosts than there used to be. Design wind speed would be at least 160kph - we've had a 3 ton hut on skids get airborne. Oh yeah, we have earthquakes.
I've seen two concrete pads fail in nearby houses, and given the cost of earthworks, geotextiles and concrete around here, I'd say a concrete floor is off the menu.
So we're looking at post and beam with a raised wooden floor, monopitch roof.
I've just disappointed my wife by saying that earth filled tyres are too heavy to support on post and beam.
What ideas do you have for a cladding and insulation combo that will survive?
...and we would probably present this to the council as a shed or workshop that we are going to live in for a couple of years while we plan a permanent house. And that probably means no space heating, because a fully permitted woodburner ends up at about $5000. So insulation will be critical. Oh, we are off grid for power, too.
What has been built in the nearby area, look at them.
Have you thought about stumps, bearers and joists as a flooring system?
Why have concrete slabs failed?
If you have had a 3 tonne shed blow away, maybe this is a bad place to build
John Daley Bendigo, Australia
The Enemy of progress is the hope of a perfect plan
(ln response to a now removed question as to why concrete slabs failed and small buildings got airborne)
Case one, on a more level area, the primary cause was insufficient ground clearance (and grassed soil tends to build up over the years, making it worse). Result was rising damp in the outer walls. Case 2, the house we currently are in, the guy building it in 1981 had two sheets of polythene to go under the concrete. He lapped them by a foot or so and gaffer taped it. Water pressure from the slooe above eventually found a way through resulting in a patch where any floor covering quickly rots. Yes it can be done right, but not on a budget.
The shed was a couple of learning processes. 1) complying with "relocatable" requirement to avoid need for a building permit doesn't mean you can't have any attachment to the ground. And 2) To avoid a monopitched roof acting as a lift-generating wing it needs to be pitched at 18 degrees or greater.
Edit: after sleeping on it, it has occurred to me that the solution for any high-mass earth-based structure (rammed earth, earthbag, earthship etc) is to create a raised platform under it. Roading mix from a quarry about 25km away is $15/m³ plus the cost of trucking it and compacting it. Minimising platform costs would dictate site location - more central on the section than we would otherwise like.
I do not have the solution for you but I think hundreds of thousands of people have lived in those conditions with homemade houses over the millennia. I'd start looking at indigenous building techniques for other windy/monsoon/damp locations like yours and see what the locals do. My guess is that whatever they do would also be affordable.
I've seen climate analog maps where you can see what your climate is and the map shows you other places with similar conditions. That way even if ancestral building techniques for your area don't make the government happy, maybe something from another continent would appease them (or trick them).
I don't really like tires anyway due to personal fears of off-gassing.
When you say "as little cost as possible" are you talking $300, $3,000 or $30,000? Lashing together palm fronds to save $200 on housewrap may or may not be worth it.
The second example given for the concrete floor failure, may not be as you think. The joining process described would normally be ok. perhaps water has ingressed via slab edge?
But if you think the water is coming from the uphill side of the building, a decent cut-off drain may be dug.
But waterproofing retro fix products are available, and that wet patch maybe able to be remedied.
I suggest asking at a good hardware or research 'waterproofing slabs".
John Daley Bendigo, Australia
The Enemy of progress is the hope of a perfect plan
Part of waterproofing under a slab is giving the water an easier path to escape than up through the slab. A few inches of gravel under the membrane, with the ability for the water to drain away from the building on as many sides as possible, would normally work fine.
That sounds like a good use case for something, Jeremy Baker mentioned: A dome made of wooden beams (or young trees) that are rammed into the ground and then bend into a pointed dome.
(It doesn't have to be pointed, but that's easier to archive.) The force required to bend it will then resist the wind force. The shape can be adjusted with horizontal tension rings. To pin the structure to the ground, a heavy weight is positioned in the middle and the top of the dome connected to it.
Thanks for the replies so far. With our council, it seems that they are more lenient with future experimental buildings if you first have something comparatively conventional on site. Proviso of living temporarily means slight upgrades to posts, and not allowed a "full" kitchen.
So we're currently getting quotes from farm shed suppliers for a steel-clad post & beam shed (around 50 sq m) - kitset is about $NZ6000 sans floor. I'm thinking along the lines of a poured straw clay or cement-based insulating wall with small plastic bottles built within.
Also looking at underfloor bladder water storage, although that is dearer than a plastic tank.
Your site sounds like a dream come true to me. The slope and soil type are both a challenge and the perfect situation for rammed earth using anywhere from 5% to 10% portland cement depending on the exact needs of the soil. You'll need something to act as the forms x 2 ( if you can get 2x12 by 12ft and good stakes), a roll or two of galvanized wire ( thin single strand is good ), shovels, a place to mix the fill ( a 50 gal drum would be fine), a few tampers ( heavy metal plate that sits flat on the ground with a stick pointing up as a handle ), a strong back, or many strong backs, and a length of clear tubing as long as your longest horizontal dimension plus about 4 ft ( 1m ).
Quick and easy rammed earth:
Dig a trench as deep as convenient running straight down the slope and at least a foot wide (1/3m), setting the dug out material in a neat row/mound beside the trench. Set the forms inline with the sides of the trench, stake them in place and block the ends; don't worry about leveling at this point. At 3ft (1m) intervals, drill two holes about 2inches apart on opposite sides of the form top and bottom ( on the bottom, make the holes about 5 inches from the edge so that they will have enough room for the stub wall below the wire for the second run); run a length of the galvanized wire through both the holes from one side of the form to the other and twist it tight. In your mixing container put in 9 shovels full of soil, one shovel full of portland cement then blend it, repeat until the mixing container is about half full. If your soil isn't the least bit moist you will need to add minimum amounts of water for each group of 10 shovels full, but only enough to make it damp. You are going to need a lot more soil than what you pulled out of the trench so plan on where to excavate (for example, where you are going to put your septic system or your cistern). Place the mix 4 to 6 inches deep into the trench/form and tamp well being careful around the wires. Repeat until the mix is tamped to the top of the form. Set up the second form, remove the blocking from the end between the two form sections and repeat. Remove the first section's form by first clipping the galvanized wires on the outside of the forms. The wall should be quite stiff by now so you can move the form to the other end of the second section. Once you have the first trench done do a second 6ft (2m) to 9ft (3m) to either side and repeat. They don't necessarily need to be parallel but it helps later if everything is square.
Now you have stub walls to attach the forms to for the second row up and the following ( the reason that the holes for the wires are 5" in from the bottom on the bottom side of the form, so the new layer can be attached directly to the wall below). From this second row on, make the form's top level using the clear tubing filled with water except for the last 4 inches on each side as a level, and proceed, stair stepping them if necessary due to the slope. When you have the wall high enough for the foundation block out sections inside the forms at appropriate intervals for floor joists/supports. Side walls inline with the trenches can be continued up, but you don't want the uphill or downhill end walls in contact with the soil so that water can freely move down the hill below the house. The floor must be made water / vapor proof so that moisture does not penetrate from below.
Once you get a platform built on top of your structure, I'd put up a yurt. They are stable even in high winds due to the round shape with little for the wind to push against, weather resistant, and very versatile. If you keep the structure low enough the wind shouldn't be able to lift it. If you decide to take the walls up higher than about 6 feet (2m) you must start to think about footings for the structure as they are what resist lifting due to wind loads. Standard footing tables are available online.
Your volcanic ash soil is the absolute best for rammed earth because of the shape of the particles. They will lock together perfectly and never degrade. With the addition of the portland cement they will last centuries. if you have stones in the area you can use them as fill known as rubble to reduce the amount of soil required.
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