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You can stretch the odd center to 1,0m where it makes no sense to keep it to 900c/c, but my engineer has advised 900c/c and for heavy clay or concrete tile or planted roofs you will need to reduce to 750mm c/c.

If the timber has been treated with a preservative then there is no reason the timber will rot.

Also if the wall is plastered with clay and lime, then these materials will help keep the timber dry….as long as you do not try and seal these materials ….they need to breathe…so you need a breathing paint.

If you use the lime plaster you then need to protect it with a breathable paint ….like “Breathecoat” paint that acts like a membrane …stopping rainwater entering but allowing moisture vapour out. Otherwise “the Natural Paint company” supply a breathable clear coating…which also breathes and will stop water penetration.

I strongly suggest  staying away from cement plaster and rather using a Breathecoat paint coated lime plaster over a cob / or clay sand undercoat. ….or if you must use cement, then it is imperative you use a separating layer (e.g. plastic ticker tape) to keep the timber out of contact with the cement plaster at all times. Cement plaster is hardly waterproof anyway and will not stop water coming through….and thus is only as good as the paint applied to it to keep the weather out…..and with its higher moisture content is the same a putting the timber in contact with water all the time, whereas the lime plaster is hydroscopic and thus given a chance (with using breathable paints) will actually dry out and if it gets wet will dry out the timber.

If you use cement, the moisture content of cement is higher than timber (unlike lime or clay which has a lower ideal moisture content)….so it will rot the timber. This is the same reason why timber windows should be primed when they are buried in cement mortar and why a timber beam buried in cement is wrapped in plastic to separate the 2 materials.

This Sand Bag Building System that makes use of a timber ladder frame was first developed for new Staff housing at Twinstreams Environmental Centre in Mtunzini on the northern coast of Kwa-Zulu Natal. The project was completed in 2004. This project and it’s innovative building system went on to win the Africa Sustainable Building Best Practice Award for residential projects in 2004. In response to using the only locally available materials at hand, sand and timber, a new building system was developed for the project that could largely involve the local unskilled labour force.

It is not necessary to use brick on the corners…the system uses 2 ladders at 90 degrees to each other at the corners so as to get strength in both directions.

The building system has been designed by a structural engineer without there being any need for brickwork corners.

However if one wants to use bricks one can do that of course… it is just not necessary and the system has been designed without the need for any brickwork columns on the corners …though you will need to put expansion joints between the brickwork and the sandbags if you choose to do this.

If you look at the photos, drawings and stitching patterns you will see they simply work like a pillow case, with all the stitching done on a sewing machine off site. The little flap is simply turned over to hold the sand in.

You use a measure for ensuring equal volumes of sand.....like a cut off 2 liter coke bottle or medium sized tin. Thus once you have established the perfect volume for filling the bags, you mark the level the measure is filled to. For half bags you will need to adjust more on an as need basis and normally we don't worry to make half sized bags one simply folds the extra fabric under.

No the idea is to plaster the bags so that afterwards the walls look like conventional plastered walls. The fabric is not UV proof, so will degrade if left out in the sun for an extended period. Obviously the bags will be fine for months if not years if left unplastered, but it is advisable to plaster once you have the roof up. As an experiment I have a short screen wall made with some bags up on my balcony that have been up for about 6 months and they are still fine.

No....and neither does it matter if the sand is somewhat damp....as it usually is above the top of the pile.....it will dry out once under a roof. Remember that if you are considering using lime cement on to a chicken mesh then you need to protect the timber in contact with the plaster with a strip of bag fabric or plastic ticker tape.

As locally sourced as possible to reduce your carbon footprint and to reduce transport costs, so as to create the least disturbance to existing natural habitat.
You do not need plastering sand.....can be as dead as anything ....we save our good sand for plastering. Just do not use top soil or anything with organic matter as this will break down.