we have a 7 x3 concreate hut in our woods, that we would like to extend. i dont want to knock it down and start again as we use it all the time and it seems waistful, when theres nothing wrong with it. we want to extend out the back of the hut into the hill side. we have dug out the area and its been sitting like that all summer. we cant decide on the best meathod to use. bri (my partner) favors a more conventional concreat pad, block walls and lots of damp proof course. surely there must be a better way than that. i was looking at ben laws woodland house and thinking about stones piles then a timber frame off the piles, then to make a new roof over the whole lot, old and new in turf. single stories and using sedum for rthe roof, to keep the weight down.
someone else suggested rammed earth tires as in earthships and a suspened floor off those, iv never worked with tires before though, so am nervous.
we have plenty of trees onsite we could use for a frame, which is why i thought timber but how would it cope with the damp of being semi buried?
if i did use tires what render? and do you render the exterior and then back fill or build right up to the earth and render the interior?
if i left a gap between the earth bank an the timber could i use certain plants to stop the earth collapsing down the bank, if so which ones?
any suggestions gratefully recieved,
Any kind of structure is going to suffer from moisture if damp earth is up against it. Some sort of drainage solution and a french drain is needed on the uphill side of the structure. Surface contouring to drain surface moisture away from structure. A french drain to keep subsurface moisture away. If you are okay with concrete, and a dome doesn't turn you off, look at the Mortarsprayer.com website under thinshell domes. See same site for Lloyd Turner dome patterns for airforms. The guy from Oregon did a good garage out of billboard vinyl for the form, dome shaped. Very strong if you are going to place against the hillside. Minimal material cost. rent a suitable air compressor, buy the Tirolessa sprayer, which also works with papercrete.
I have to agree with bri on this one. It seams to be a small, storage hut so why go through too much time, expense or hassel. CMUs are abundant, cheap and go up very quick. You could probably find salvage for the amount that you need.
Its good to try to use any abundant timber but ground contact and wood is usually not a very long lasting combination.
French drain is a good point but I will go one further and suggest completely backfilling with washed gravel (#57). A 6" to 12" layer up against the drainage layer(dampproofing or drainage fabric) of the block will not allow hydrostatic pressure to build. If you have lots of water or want to be really safe, protect the gravel with silt fabric to prevent it from clogging over time. This method can work for whatever walls you end up using.
"If you want to save the environment, build a city worth living in." - Wendell Berry
If you are building up against the hillside agree with need for drainage and damp-proof membrane.
I wouldn’t leave a gap, as nature will try to fill it over time, and you'll probably get damp.
An ideal solution would be to build up a drainage layer, by lining with a silt-filtering “geomembrane” (otherwise the drainage gravel will silt up over time), porous drain at the bottom, gravel to the top; insulation layer; building your inner wall against that. So, you'd have several layers to build up at the same time, from the outside in:
silt-filtering wrap + gravel
wall (tyres, or other mass structure)
This construction is therefore a multi-barrier approach – trying to intercept and direct water away from the building AND installing a barrier against the damp. A bit of a pain, but if you are using your building much, you really don't want it to be damp.
Damp-proof membrane can be pretty inconvenient as its is usually difficult to work with (big, heavy gauge plastic sheet) and you don't want to damage it while you are building each layer up and gradually unwrapping it. Have tape to fix tears...
Earth-filled tyres are a useful thermal mass building block, and turn a fairly tricky-to-sensibly-dispose of waste product into something useful (a building block).
I find filling them very hard work. Other people have told me its about technique rather than simply strength, but I don't seem to have picked that up.
You could build a mass wall using rammed earth in formers, wacked in layers. Can be quicker (e.g. I think its quicker & less exhausting to use a manual wacker plate, on earth layers, than a sledge hammer in individual tyres – I've personally tried the tyres but not wacking a rammed earth wall, so that's just my guess).
As you probably realise, Ben Law's house is timber frame with straw-bale infill. This is a different principle to the earthship principle: insulated building walls vs: mass walls. I believe Ben's walls are lime rendered; his roof has a large over-hang to keep water off.
What is your building orientation / aspect? - could you be on for an “earthship-type” passive solar heating, heat storage in a massive back wall design? Check:
http://www.groundhouse.com/ (its called “groundhouse as it is not a “Mike Reynolds-approved earthship design)
http://www.lowcarbon.co.uk/earthship-brighton Mike-Reynolds “approved” earthship design (in France): http://web.me.com/gilliantrott/Site/The_Construction.html the earth-ship originator (Mike Reynolds): http://earthship.com/
I don't think the Americans usually use damp-proof membranes, as their original structure were above ground (with an earth bank at the back, in relatively dry climates).
The Brighton and Brittany buildings are both in temperate / wet climates, so both had complete damp-proof membrane wraps, heavy-guage polythene, which completely lies under the floor, up the back wall, to the roof (which is at ground level at the back), all in one sheet.
Daren & Adi have produced a brief book: http://www.groundhouse.com/groundhouse-build-cook-book/ (Yes, there is a review by me, for a permaculture magazine - its a nice, quick, book). There is a lot of detail tucked away on their website though + videos, so tuck in! (I'm credited somewhere for the solar “plumping”, which sounds rather nice, but is supposed to be “plumbing”. I did the underfloor heating too, which we thought would be sensible, since were not sure how the passive nature of the structure would perform in that climate.
The Brighton Earthship & Brittany Groundhouse also have insulative “break” layers at the back, so that you have a mass wall on the inside and are not trying to heat up the whole hillside behind. The material used was rigid sheets made from spun recycled glass, “foamglass”. High compressive strength.
The “render” used on the tyres, all over in fact, is adobe (i.e., mud, sand and binder, such as chopped straw). Check internet for “recipes”. Quite a thick layer, adding to wall mass, useful for sucking up heat in the summer, and releasing it in the winter.
A green roof can be pretty heavy as will soak up a lot of moisture at times.
Both Earthship Brighton & Groundhouse Brittany included their water storage in containers in the hillside in the back – so that rain water from the roof could gravitate to them.
To keep the roof structure light, and ensure less silty water (which is potentially used for drinking), one used steel, the other a membrane over plywood.
The opening sky-lights at the back are sensible (& multifunctional). Obviously allow light in, but also allow air flow (when open). So, on sunnier days, hot air generated by the large sough-facing windows naturally ventilates though the building out through the sky-lights, creating a coiling breeze.
brillant, thanks so much, i have ordered the earthship handbook and i think we are going for tires and some devious drainage. it never even occured to me to sink some water collecting tanks but i will definately do that. because it is in woodland it and it stays quite dark all year we dont benefit much from passive solar, even though it is south facing, but thats fine. our summers get too hot here (charente) our house become unbearable and we decamp down to the woods for a few months. even though its only 7m x3.5 m its very comfy for the four of us and we stick a tipi up as well. we wanted to increase the size so we can continue to live there for longer periods and as our children get bigger they might get sick of everyone bundling into the sleeping chamber together.
thanks so much for all the great input, im off down the garage to beg for some tires in the morning!!