Passive Solar Composting Toilet Part 1- The Design Process

We will finally (after almost two years waiting for paper work to come through) be starting work on our barn conversion next week!

We decided that we needed a toilet on the land so that the builders who are coming to demolish the inside don’t leave little presents all over the place for us.  I thought that this would be a good opportunity to try out “Light Straw Clay” also known as “Slip Straw” as we want to make the interior walls this way.  We dont have any previous experience with this type of building (or any type of building for that matter) so it will be fun and we can get a feel for technique.

Light Straw Clay is a system that was originally used in Germany.  I really like the sound of it because it looks really easy.  All you have to do is make some “clay slip”(clay mixed with water), toss it over some straw like if you were dressing a salad and then pack it into a form.  Repeat the process until your  wall is finished, leave to dry, remove the forms and presto!  You have a wall that is ready for plastering and is well insulated.

Passive Solar Design

I have been studying passive solar design for a couple of years now and our composting toilepassive solar imaget project is a great excuse to put all of the theory into practise.  It will be an exterior loo, so it could get chilly in the winter and probably not the nicest place to be in if its just a dark and sombre outhouse.  I have designed it so that the sun will shine in and heat it up in the winter, making it a comfortable, warm and bright place to do your duties.

For those of you that are still wondering what Passive Solar Design is; it is basically the use of the heat of the sun shining onto something that will store that heat (mass, normally stone, brick, adobe, etc) to warm  a space.

The Design

I first designed the porta potty in a program called Google Sketchup as it lets me make a scale model and then place it in the exact virtual geographical location to see how the light and shadows react at different times of day and throughout the year.  This is great because it allows you to make changes, try out different configurations until you have something that works.

Our passive solar composting toilet design.

Here it is!

This is the design that I came up with for the shed that will house our composting toilet.  Its form is dictated purely by function.
The roof is slanted at 21.6 degrees which is the angle of the sun at solar noon on the winter solstice (21st of December) in our region.  I have set the roof at that angle so that the sun shines directly inside through the large window at the top giving light and heat which will be captured by the light straw clay and earthen plaster (mass) and then released slowly as night falls.  The light straw clay also acts as insulation which will help to maintain the temperatures fairly constant on the inside.

The overhang is designed so that as the sun gets higher in the sky (closer to summer) it will stop shining straight in and  wont heat the space any more.   If I have done everything correctly the space will be warm and bright in the winter and cool and shady in the summer.

In my next post I will show you my progress with making the frame.

I am hoping that we will be ready for the winter solstice so that I can see if my maths (which is rubbish) is correct and feel the warm sun on my face while depositing a little packet of future fertility for our fruit trees.

The first steps to a dream-come-true

When I went on my first date with Luke on 21st April 2012 I had never heard of Permaculture. By the end of the day I had had quite an intense introduction, as Luke explained the concept to me from the point of view of his dream, while we rock-climbed in Calvià, ate pizza on the dock in Port Andratx, and walked Luna in the forest of Paguera. We said our first goodbye under the lemon tree at his gate, a mere 20 metres from where I sit now, but not before he had bamboozled me with the plans he had drawn for Ca’n Mandala, his permaculture dream-to-come-true.

Already then, we shared a common desire to live in harmony with nature, it’s just that he had already got into much more detail about how that was going to happen! Gradually Ca’n Mandala became a dream that we dream together, a dream that is now becoming a reality. A home built with natural materials (many of which will be reclaimed), which will warm us in the winter and cool us in the summer… where we can re-use all of our waste water on the land, turning our bodily waste into compost to nourish the earth… where we can step outside and collect vegetables from our garden and fruit from our food forest… where animals will help us to farm the land, just by doing what they do best… where we can be happy living a simple life together.

Luna in Kitchen doorway

August 2012

August 2012

We are at the beginning of a very exciting journey, as we build our house and our life together, and we hope you will join us as we share our experiences, the things we learn and the mistakes we make, the joys and the challenges, the triumphs and disappointments. Join us, dear friends, and if you would like to get involved, make some suggestions, lend a hand, please feel free! Welcome one and all.