Construction of Holzmiete-Inspired Compost Toilet and Urinal System (Tasmania, Australia)

by Paul Kean, Tiger Hill Permaculture

Last year some trees were cleared for milling on the farm and a by-product of that process was the tree crowns and stumps that can’t be milled. There is estimated to be about 200 ton of stumps and crowns to be cut up for firewood as a result. This ensures that all resources from the project stay on the site and less need to transport firewood in.

I had always loved the look of the traditional German firewood piles and was introduced to these by the late Joe Polaischer of Rainbow Valley Farm in New Zealand. Joe had made these wood piles throughout his property as functional firewood drying systems as well as artsy little structures that looked like houses. These are common place in Austria where Joe was raised.

A holzmiete is translated as an engineered woodpile (a woodpile engineered and stacked in a way that it won’t fall over), and a ‘holzhaufen’ is translated as a wood house (house for firewood).

As the Tiger Hill Farm is in great need of amenities for workshops in the future, I saw an opportunity to combine the woodpile style wall construction into a toilet enclosure. A site within the house envelope was chosen as most people arrive at this location and the energy flow indicated this as a fairly central area. With future courses, most meals will be provided around the house area and the structure is close to the final wood-burning location. In the future this toilet will be the main house toilet in summer, at least to reduce water consumption. There is nothing wrong with returning to the traditional outhouse systems of old. I do plan to remove all the flush toilets from the house and replace with simple box and bucket compost dunnies. I was really awakened a few months ago when I had to purchase water from outside the farm as we had a lot of volunteers coming thru as help. A simple water reduction like this will save so much.

Initial concept drawing. Left side urinal, right side dunny

The site prior to starting

Marking out the footprint. Deciding the final position and entrance.

Surveying the roof structure foot print

Construction underway

Kyle testing the stability. Solid as.

Trusty farm truck unloading split firewood

The doorway structure in place and solid.

Starting to stack the wood

Internal wall and solar chimney exit

Splitting more firewood. A total of 19 cubic meters in total in the entire structure.

Rustic handmade door with latch and bike tube for automatic closing

Holzmiete structure completed in time for volunteers’ departure the next day

Guttering on the back of the holzmiete roof. Catchment into a 900 ltr tank.

Inside the holzmiete, complete with wheelie bin and step.

Water storage and wash station not fully plumbed in yet

The site was surveyed to gauge the height of the roof uprights and the WWOOFers enjoyed learning to use the laser level. We used lime to mark out the footprint and our final design took into account the sun and wind angles for the area. The outside diameter is 4 meters and the internal diameter is 2 meters. All the structural timber used was milled on site in January 2014 and these materials consisted of 4×4 posts and 4×2 roof batons bolted together with coach bolts and notched out for a tight fit. Galvanized straps hold it all down. The posts were secured to the ground in a very unconventional way by lengths of 100mm x 100mm angle iron bashed into the ground about 400mm and then the posts bolted to these. It was a huge saving in time and resources and as the roof has no real weight, it stands very strong.

My concept was to build the firewood wall to fully enclose the roof posts so they were not visible. The doorway frame was also made the same way as the roof structure and pallet timbers nailed to the side of the door frame to retain the firewood pieces around the door frame. The frame was purposely made to simulate a tunnel entrance and to stop the door from over-opening in strong winds.

Rather than filling the centre with wood as all holzmiete are constructed, the centre remains a space to incorporate a toilet. With the dedicated efforts of 5 WWOOFers, this quirky, artistic and functional multiple-use structure is set to be a crowd pleaser. An 80Lt wheelie bin is the compost chamber with a solar chimney plumbed into the rear of the bin to draw air thru and out of the compost toilet to keep odour to a minimum. Half pallets were incorporated into the walls as they were stacked at about shoulder height to allow more light and ventilation and a pallet cut down to size for the solar chimney pipe to extend through within the rear wall.

The finished item has a permanent roof to harvest water for a wash station. There is an electric light with a light shade made from a 4 litre cooking oil can, and a permanent door frame with a hand crafted door. The firewood is stacked with a pitch leaning inwards and the interior of the structure has a lined wall to retain the timber from inside. The wall was made from discarded pallets and old star picket posts.

The timber dries in the pile for up to 3 years, depending on how green the timber is initially. Once dry, the walls are dismantled, stored and consumed. As the roof, door frame and internal wall lining are permanent only the walls need to be refilled for the next drying period. Traditional holzmietes have a wide range of roof finishings including domed stacked wood and shingle type tiles. It is planned to have several of these around the farm workers to use. There are huge piles of material that were pushed up by the dozer then the trees were felled, so we will just make them where the timber is. The initial structure took about 4 weeks to construct and holds 19 cubic meters of firewood.

Next to this holzmiete, we have created another wall up against an existing cabin to create a privacy screen for a gents urinal system. Wheelie bins or barrels are filled with saw dust to soak up the urine, and then the sawdust is composted. This also reduces the use of water in a traditional flush toilet. It’s a creative way to recycle nitrogen. Again we are using wheelie bins as they are easy to relocate to the composting area.

A 900ltr water tank was repurposed from the Tiger Hill Chalet to provide water for a hand wash station and guttering and down pipes were fitted to both the holzmiete and adjacent cabin to harvest approx. 30 square meters of catchment. The over flow from this tank is connected underground to the main house tank which will improve the water harvesting capabilities for domestic consumption.

And yes, the roof is not level, for those of you with a keen eye. This was an engineering flaw, but not drastic enough to compromise the structure. It adds some character.