Wednesday, February 1, 2012

The next stage...

Only a few days after the slab is done, and we’re thinking about the next stage of the job :)

The suspended slab above the garage which forms the floor of the upstairs living area is supported by two walls:

Now, in our building permit and structural spec these are to be constructed of steel reinforced concrete blockwork. That’s fine for the retaining wall against the hillside, as it will only be visible from the utility rooms (power and pump). However, the inner wall borders the garage and stairwell, so I’m not that enthused about using concrete blockwork here as they’re not the prettiest things to look at.

What I’d much rather use here is rammed earth. We saw a house on the mountain a couple of years ago which was predominantly rammed earth construction, and it’s absolutely beautiful - such a warm, natural feel and about the most sustainable building material there is.

As it happens, our soil appears to be pretty well suited to the task too - it’s a sandy / clayey mix which compresses well and holds its shape, so I’m hoping it will make a good base for ramming, with the appropriate cement and water added.

The only problem here is that this internal wall is a very important structural piece of the puzzle. It is designed to bear the load of the upper slab, in addition to the Hebel cladding and roof of the upper storey.. and I have no idea whether a rammed earth wall can be designed to accept such a load, or if it can, whether our soil is up to it.

Sooo, I’ve asked Peter the Architect whether he thinks rammed earth will be up to the task, and he’s getting an opinion from our structural engineer. We both think a 300mm wide wall, possibly with some steel reinforcement, should be capable of doing the job, but we’ll wait for the engineer’s opinion.

However, being the rather impatient bugger that I am I can’t just sit and wait. So, I’m going to go and build some forms anyway and get stuck into a test wall somewhere. Whether or not we can use earth for this particular wall, both Alissa and I love the aesthetic (and the sustainability) of rammed earth too much to build without it in some way, so we’re going to need to a) figure out our soil, and b) practice first :)

Plus, I figure that we’ll use the forms anyway to slip-form rock walls, since we have an absolute abundance of rock on site and we’d have them in our heads if we didn’t use them in the buildings or landscaping!

So, here’s my design so far:

I plan to build them using 2400x1200x18mm form ply sheets cut in half lengthwise, braced using 600mm lengths of 50x50x5mm steel angle, offset to allow the forms to stack on top of each other and lock together. They’ll be spaced using 300x50x50mm hardwood blocks, and clamped using M12 threaded rod which I’ll bend up at one end to form “crank” handles. I reckon they should be strong enough and still lightweight enough for two people to shift around. I guess we’ll find out :)

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